# Do developmental dyslexia and congenital amusia share underlying impairments?

Manon Couvignou, Barbara Tillmann, Anne Caclin, Régine Kolinsky

► To cite this version:

Manon Couvignou, Barbara Tillmann, Anne Caclin, Régine Kolinsky. Do developmental dyslexia and congenital amusia share underlying impairments?. Child Neuropsychology, inPress, 10.1080/09297049.2022.2162031. hal-04090421

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Do Developmental Dyslexia and Congenital Amusia Share Underlying Impairments?

Manon Couvignou¹, Barbara Tillmann²,³, Anne Caclin²,³ and Régine Kolinsky¹,⁴

¹Unité de Recherche en Neurosciences Cognitives (Unescog), Center for Research in
Cognition & Neurosciences (CRCN), Université Libre de Bruxelles (ULB), Brussels,

Belgium

²Lyon Neuroscience Research Center, CNRS, UMR 5292, INSERM, U1028, Lyon, France

³University Lyon 1, Lyon, France

⁴Fonds de la Recherche Scientifique-FNRS (FRS-FNRS), Brussels, Belgium

Author Note

Manon Couvignou [https://orcid.org/0000-0002-6652-5286](https://orcid.org/0000-0002-6652-5286)

Barbara Tillmann [https://orcid.org/0000-0001-9676-5822](https://orcid.org/0000-0001-9676-5822)

Anne Caclin [https://orcid.org/0000-0003-1367-5923](https://orcid.org/0000-0003-1367-5923)

Régine Kolinsky [https://orcid.org/0000-0002-2492-2144](https://orcid.org/0000-0002-2492-2144)

Data and material for this study are available at:
[https://osf.io/grua5/?view_only=acf1fc30c6c546bab47bbd44c192cfdc](https://osf.io/grua5/?view_only=acf1fc30c6c546bab47bbd44c192cfdc)

Correspondence concerning this article should be addressed to Manon Couvignou,
Unité de Recherche en Neurosciences Cognitives (Unescog), Center for Research in Cognition
& Neurosciences (CRCN), Faculté des Sciences Psychologiques et de l'Éducation, Université
Libre de Bruxelles (ULB), 50 Avenue F.D. Roosevelt, CP191, B-1050 Brussels, Belgium.

Email: [manon.couvignou@ulb.be](mailto:manon.couvignou@ulb.be)
**Abstract**

Developmental dyslexia and congenital amusia have common characteristics. Yet, their
possible association in some individuals has been addressed only scarcely. Recently, two
converging studies reported a sizeable comorbidity rate between these two neurodevelopmental
disorders (Couvignou et al., *Cognitive Neuropsychology* 2019; Couvignou & Kolinsky,
*Neuropsychologia* 2021). However, the reason for their association remains unclear. Here, we
investigate the hypothesis of shared underlying impairments between dyslexia and amusia.
Fifteen dyslexic children with amusia (DYS+A), 15 dyslexic children without amusia (DYS-
A), and two groups of 25 typically developing children matched on either chronological age
(CA) or reading level (RL) were assessed with a behavioral battery aiming to investigate
phonological and pitch processing capacities at auditory memory, perceptual awareness, and
attentional levels. Overall, our results suggest that poor auditory serial-order memory increases
susceptibility to comorbidity between dyslexia and amusia and may play a role in the
development of the comorbid phenotype. In contrast, the impairments observed in the DYS+A
children for auditory item memory, perceptual awareness, and attention might be a consequence
of their reduced reading experience combined with weaker musical skills. Comparing DYS+A
and DYS-A children suggests that the latter are more resourceful and/or have more effective
compensatory strategies, or that their phenotype results from a different developmental
trajectory. We will discuss the relevance of these findings for delving into the aetiology of these
two developmental disorders and address their implications for future research and practice.

*Keywords:* developmental dyslexia, tone deafness, auditory short-term memory,
auditory perceptual awareness, auditory attention

Word count: 23 593.
Developmental dyslexia is a neurodevelopmental disorder that manifests as a severe and persistent difficulty in acquiring reading despite otherwise normal intellectual functioning, no obvious sensory or neurological damage, and adequate educational opportunities (World Health Organization, 2011). There is strong converging evidence suggesting that developmental dyslexia results from a specific impairment of phonological processes (Ramus, 2003; Vellutino et al., 2004), which impedes efficient mapping of phonemic and graphemic representations. However, the hypothesis that the phonological deficit is the only core impairment in developmental dyslexia has been challenged by the substantial phenotypic variability of the dyslexic population (Valdois et al., 2004), and there is still some debate about the potential role of more primary auditory impairments or temporal processing impairments in the development of this disorder (Goswami, 2015; Habib, 2021; Hornickel & Kraus, 2013; Lallier et al., 2018). More generally, the hypothesis that developmental dyslexia as well as other developmental disorders reflect a core, single underlying cognitive impairment, has been questioned (Pennington, 2006). Rather than reflecting a single underlying cognitive impairment, they may be dimensionalities of comorbid features (e.g., Astle & Fletcher-Watson, 2020; Lervåg, 2021; Pennington, 2006). As for other developmental disorders, dyslexia is frequently comorbid with other disorders such as developmental language disorder, dyspraxia, dyscalculia, or attention deficit / hyperactivity disorders (Germanò et al., 2010; Kaplan et al., 1998; McArthur et al., 2000; Wilson et al., 2015), and it is difficult for a single cognitive deficit model to account for such comorbidity. This is particularly the case with *heterotypic comorbidity*, namely comorbidity between disorders from different diagnostic groupings, such as dyslexia and attention deficit / hyperactivity disorders (Pennington, 2006). In this respect, the extent to which dyslexia might co-occur with congenital amusia is worthy of study but has so far received little attention.
Congenital amusia, or *tone deafness*, refers to a lifelong musical disorder linked to pitch-processing impairments (Peretz, 2013; Tillmann et al., 2015; Williamson & Stewart, 2013), occurring despite intact sensory and intellectual functioning and an adequate musical environment. Individuals with amusia typically fail to recognize familiar tunes without lyrics, to detect false notes, or to judge whether someone is singing out of tune, including themselves (Ayotte et al., 2002; Peretz & Hyde, 2003). Just like dyslexia, amusia is suggested to be genetically influenced (e.g., Fisher & DeFries, 2002 for dyslexia; Peretz et al., 2007; Peretz & Vuvan, 2017 for amusia) and has been proposed to stem from impaired neuronal migration (Galaburda et al., 1985; Galaburda & Kemper, 1979 for dyslexia; Hyde et al., 2007 for amusia).

Other intriguing features shared between amusia and dyslexia is that impaired short-term memory processes and/or impaired conscious access to the relevant representations have been reported for both disorders (Loui et al., 2011; Moreau et al., 2013; Peretz et al., 2009; Ramus & Ahissar, 2012; Ramus & Szenkovits, 2008; Tillmann, Levêque et al., 2016). Whereas the most common interpretation of the specific difficulties observed in dyslexia and amusia proposes that their phonological/pitch representations are degraded in some way (i.e., are less precise, underspecified, less categorical, or noisier; e.g., Adlard & Hazan, 1998; Hornickel & Kraus, 2013; Hyde & Peretz, 2004; Manis et al., 1997; Serniclaes et al., 2004; Ziegler et al., 2009), new theories (e.g., Boets, 2014; Boets et al., 2013; Peretz, 2016; Ramus & Szenkovits, 2008; Tillmann, Levêque et al., 2016) propose alternative hypotheses, according to which their representations would in fact be intact, but more difficult to integrate into memory and/or to access consciously. These memory and awareness impairments have been associated, in both disorders respectively, with a reduced fronto-temporal connectivity between the auditory cortex and inferior frontal regions (Albouy et al., 2015, 2019a; Boets et al., 2013; Hyde et al., 2011; Jasmin et al., 2020; Kovelman et al., 2012; Ramus, 2014). In sum, these various points of similarity call for a comparative examination of the two disorders.
Initial observations in large samples of adult participants reported no particular association betweenamusia and other learning disorders, such as dyslexia (Peretz et al., 2008; Peretz & Vuvan, 2017). Their main limitation, though, is that the presence of dyslexia was estimated based on self-report only (i.e., consulting a speech therapist), namely without an objective measure of literacy performance. This might induce various biases, related in particular to the age of the participants (dyslexia being nowadays more systematically detected by the school system) and lack of diagnostic accuracy. Consistent with this view, Peretz et al. (2008) already noted that younger amusic participants reported learning difficulties (e.g., dyslexia) more frequently than their control participants, in contrast to the older participants in the two groups. Recently, two converging studies using rigorous diagnostic criteria and a large panel of behavioral measures reported a sizeable comorbidity rate between dyslexia and amusia. Although dyslexia and amusia are estimated to occur in 3-7% and 1.5-4% of the general population, respectively (Lindgren et al., 1985; Peretz & Vuvan, 2017), 25-30% of adults with either dyslexia or amusia also met criteria for the other disorder (Couvignou et al., 2019). Further investigations conducted at an earlier stage of development (7-12 years of age) confirmed this observation, with about 34% of the tested dyslexic children diagnosed with congenital amusia (Couvignou & Kolinsky, 2021). These individuals combined the characteristics of both disorders, namely slow and erroneous reading and poor phonological abilities (in particular, poor phonological awareness), as well as difficulties in detecting pitch changes in melodies despite no history of hearing loss, normal nonverbal IQ and regular exposure to music.

Among the potential explanations for this association (together with the hypotheses of a common genetic risk factor and of a causal relationship between musical and phonological impairments, see detailed discussion in Couvignou et al., 2019, 2021), one attractive hypothesis is that dyslexia and amusia would be different manifestations of the same underlying
impairment(s) that may be expressed in either the language or music domain, which would
increase the likelihood that they occur together in the same individual. As argued by Couvignou
et al. (2019), it seems unlikely that one basic auditory impairment underlies this comorbidity,
because the specific types of auditory impairment usually postulated in dyslexia (such as rapid
temporal processing, amplitude rise time processing, or speech perception in noise, e.g., Farmer
& Klein, 1995; Goswami, 2015; Ziegler, Pech-Georgel, George, et al., 2009) are distinct from
the pitch processing impairment postulated in amusia (Tillmann et al., 2015). Rather, the shared
impairment(s) might be situated at higher processing level(s), which will be the focus of the
present investigation.

In addition, as exposed above, it seems hardly plausible that a single common
underlying cognitive impairment accounts for comorbidity. In the present study, we rather
adopted a multifactorial view (e.g., Pennington, 2006) by focusing on three specific cognitive
functions that may be impaired in both dyslexic and amusic individuals: auditory short-term
memory, perceptual awareness, and attention. Without ruling out the importance of other
dimensions that have received increasing interest in recent years in the search for common
underlying impairment(s), such as rhythmic processing, and more generally, the processing of
the temporal structure of sound and/or sequencing (Boll-Avetisyan et al., 2020; Caccia &
Lorusso, 2021; Chang et al., 2019; Fiveash et al., 2021; Lagrois & Peretz, 2019), we will expose
why we think these three cognitive functions deserve further consideration in the aetiology of
both developmental dyslexia and congenital amusia.

First, the comorbidity might reflect an inability to integrate phonological or pitch
information into *short-term memory* (STM). STM allows for the temporary storage of
information and is fundamental to making sense of auditory inputs as they unfold over time. In
this respect, STM might act as a bottleneck for learning: poor STM skills may lead to learning
difficulties, particularly with regard to literacy acquisition (Jeffries & Everatt, 2004; Moll et
al., 2016; Schuchardt et al., 2008). Note, however, that the reverse causal relationship must also be considered as learning likely leads to reciprocal improvements in STM skills (Demoulin & Kolinsky, 2016; Kolinsky et al., 2020). Verbal STM skills, as measured by digit span or pseudoword repetition, are typically impaired in children with phonological dyslexia (e.g., Kramer et al., 2000; Melby-Lervåg & Lervåg, 2012; Plaza et al., 2002). These impairments persist into adulthood and have even been observed in trained musicians with dyslexia in both the verbal and musical modalities (Weiss et al., 2014). In recent years, the memory for serial order or serial positions of items, which is a particular aspect of STM, has gained growing interests. Dissociations between preserved item and impaired serial order memory have been reported in dyslexia (for a review, see Majerus & Cowan, 2016; but see also Staels & Van den Broeck, 2014, 2015), and the serial order impairment appears to occur for the retention of both verbal and nonverbal sequence information (Cowan et al., 2017; Hachmann et al., 2014). In amusia, recent theories have proposed an impairment in pitch STM as the main underlying cognitive cause of the observed musical difficulties (Tillmann, Levêque et al., 2016). Indeed, whereas some amusic individuals have normal pitch discrimination thresholds, all amusic individuals show impaired STM for pitch (Albouy, Mattout, et al., 2013; Albouy, Schulze, et al., 2013; Foxton, 2004; Tillmann et al., 2009). These impairments have been described at each level of processing in STM tasks (i.e., encoding, storage, and retrieval of the pitch information), and have been related to altered brain responses and decreased connectivity within the right fronto-temporal pathway. In contrast, verbal STM skills of adult amusic individuals seem preserved, as evidenced by normal performance on forward/backward span tasks or serial word recognition task (Albouy, Mattout, et al., 2013; Tillmann et al., 2009; Williamson & Stewart, 2010) and brain activations similar to those of controls for the maintenance of words in STM (preserved activation in the left inferior frontal gyrus and left fronto-temporal connectivity; Albouy et al., 2019). Nevertheless, the question of whether auditory STM is a unitary construct
or whether it relies on separate subsystems for musical and verbal information remains debated, both in adults (Caclin & Tillmann, 2018; Gorin et al., 2016, 2018; Hirel et al., 2017) and children (Ginzburg et al., 2022). Taken together, for the aim to search for a common underlying impairment between dyslexia and amusia, these observations lead to propose STM as a potential candidate.

Second, the comorbidity between dyslexia and amusia could be due to a shared disorder of conscious access to existing domain-specific knowledge, namely, difficulties in becoming aware of and explicitly manipulating the constitutive units of speech or music, an hypothesis that has been put forward by Peretz (2016). We here use the term *auditory perceptual awareness* to designate this specific ability. In the language domain, this ability is typically assessed by *phonological awareness* tasks, such as syllable or phoneme counting, deletion, addition or reversal, as well as by the auditory acronym task, in which participants have to isolate the first phonemes of two spoken words and blend them to form a new word. All these tasks require grasping that speech can be analysed into sublexical units, namely syllables and phonemes. Reading in an alphabetic script is specifically contingent on the grasping of the *alphabetic principle*, namely of the intuition that graphemes (letters, alone or in combination such as <ch> in <chat>) stand for phonemes. This is not an easy venture, as, contrary to syllables, phonemes do not correspond to stable physical segments of speech (Liberman et al., 1967). Therefore, *phoneme awareness* (i.e., explicit representations of phonemes) develops hand in hand with the acquisition of the alphabetic principle, namely, with (alphabetic) reading acquisition (e.g., Morais et al., 1987a, b; Wimmer et al., 1991). Consistently, impaired phoneme awareness is one of the major features of the phonological deficit in dyslexia (e.g., Lundberg & Høien, 1989; Snowling, 1998; Swan & Goswami, 1997).

Similar awareness skills applied to the constituent units of music (interval and notes) are likely to underlie music processing. In line with this hypothesis, trained musicians
demonstrate superior analytical listening skills compared to non-musicians, especially in
explicitly analyzing the musical intervals that constitute a melody (Bever & Chiarello, 1974;
Oxenham et al., 2003). To date, very few studies have attempted to compare within the same
children the ability to operate explicitly on speech and music sound units. Two reports (Morais
et al., 2010; Morais et al., 1984) have suggested that dyslexic children are poorer than typical
readers in segmenting speech, but not in segmenting tone sequences. However, unlike the
verbal segmentation task, the musical segmentation task used by Morais et al. (1984) had a
strong visuo-motor component that could have masked potential auditory processing
difficulties, and the small sample size of Morais et al. (2010; 8 dyslexic participants and 12 age-
matched controls) limited potential conclusions. To our knowledge, the performance of amusic
individuals has never been assessed with behavioural tasks specifically targeting auditory
perceptual awareness. Yet, it has been reported that amusic individuals are deficient in
evaluating the direction of a musical interval (Loui et al., 2008), a task that could be considered
akin to an auditory perceptual awareness task, as one strategy is to divide the interval into two
subunits (i.e., two notes), and then compare their respective pitch heights. In some ways, many
of the psychoacoustic tasks in which amusic individuals have been shown to be impaired (e.g.,
Foxton, 2004) require conscious access and some degree of manipulation of musical pitches.
Their lack of conscious access to fine-grained pitch deviances marked by both an inability to
detect them explicitly and abnormal attentive but normal pre-attentive neurophysiological
responses (Moreau et al., 2013; Peretz et al., 2009; Zendel et al., 2015) further suggests that
they may show an impairment in tasks requiring the conscious processing of music sound units.
In a related vein, cases of comorbid dyslexia/amusia described in childhood showed particularly
pronounced impairments in phonological awareness (as assessed by initial syllable or phoneme
deletion tasks, syllable or phoneme inversion tasks, and auditory acronyms) compared to their
peers with pure dyslexia, despite comparable severity of literacy impairments in these two
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subgroups (Couvignou & Kolinsky, 2021). This is consistent with two independent adult
studies reporting severe phonological awareness difficulties (as assessed by syllable or
phoneme deletion tasks, and auditory acronyms) in a subset of amusic individuals (Couvignou
et al., 2019; Sun et al., 2017). More generally, phonological awareness correlates positively
with pitch perception and production skills in school-aged children (Loui et al., 2011). Auditory
perceptual awareness skills thus deserve further investigation in the study of the relationship
between dyslexia and amusia.

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Third, the comorbidity may be underpinned by a difficulty in paying attention to
phonological information and pitch information. In this respect, auditory *sustained attention*
and *selective attention*, two fundamental requirements for information processing, as well as
*impulsivity*, are worth exploring. Sustained attention refers to a long-lasting mobilization of
attentional resources. Selective attention, on the other hand, refers to the ability to focus on a
limited array of all available sensory information. Both are closely related to working memory
(Downing, 2000; Gazzaley & Nobre, 2012) and consciousness (De Brigard & Prinz, 2010;
Koch & Tsuchiya, 2007; van Boxtel et al., 2010), and therefore are good candidates in the
search for underlying impairment(s) common to dyslexia and amusia.

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Impulsivity refers to a tendency to act in response to immediate stimuli, without
deliberation or consideration of risks and consequences. Previous research has documented the
frequent occurrence of impulsive behaviors in specific learning disorders (Al-Dababneh & Al-
Zboon, 2018), but their exact role in the aetiology of these disorders is still debated. A variety
of attention impairments has been reported in dyslexia, mainly in the visual domain, but also in
the auditory domain (Facoetti et al., 2010; Lallier et al., 2009, 2010), as well as higher cognitive
impulsivity in dyslexic children (Donfrancesco et al., 2005). To the best of our knowledge,
however, no study has yet investigated attentional abilities comparatively for verbal and
musical materials in the same group of dyslexic participants. In addition, as mentioned above,
1 dyslexia and attention deficit / hyperactivity disorder co-occur frequently, with a comorbidity
2 rate of around 30 % (Germanò et al., 2010). In amusia, sustained attention skills have been
3 studied through electroencephalography, but only in relation to pitch awareness skills (Peretz
4 et al., 2009; Zendel et al., 2015). Interestingly, abnormal neural responses to pitch deviance in
5 a melody emerged in the amusic brain only when an explicit detection of the pitch deviances
6 was required, but not when the task required a judgment on a different dimension (i.e., the
7 detection of unrelated clicks; Zendel et al 2015, see also Tillmann, Lalitte et al., 2016, for
8 converging evidence with behavioral methods). This observation suggests that auditory
9 attention skills of amusic individuals are functional, but interfere with explicit pitch perception
10 judgements. In a related vein, Moreau and collaborators (2013) observed that large pitch
11 changes (but not small ones) were correctly detected and generated normal P300 in amusics,
12 supporting the view that their pitch perception impairment cannot be explained solely by a lack
13 of attentional resources or a general unresponsiveness to pitch variations. Nevertheless, the role
14 of attentional skills remains an important issue and is worthy of further investigation.

15 These three cognitive functions (i.e., auditory short-term memory, perceptual
16 awareness, and attention) have already been investigated in studies on either dyslexia or amusia,
17 but as far as we know, not together. Previous studies examined either the language or the music
18 domain, hence each disorder separately. In addition, they used various dimensions, paradigms,
19 stimuli, and tasks that are not easily comparable across these domains.

20 In the present study, we developed a battery of behavioral tests aiming to characterize
21 the overlap of potential impairments of auditory memory, perceptual awareness, and attention
22 applied to both linguistic and musical materials. These functions were examined in parallel, for
23 each of the domains of specificity of both disorders (syllables and phonemes; musical intervals
24 and notes). As in Tillmann et al. (2009), the generality of the impairments was further assessed
25 with a third auditory control material, namely timbre. Importantly, all the tasks were based on
1 the same set of stimuli, so that any performance difference between tasks would most likely
2 reflect differences at higher processing levels rather than in early/perceptual processing. The
3 battery was administered to four groups of participants: dyslexic children with amusia
4 (henceforth, DYS+A), dyslexic children without amusia (henceforth, DYS-A, of equivalent age
5 and reading level as DYS+A children), and two control groups of typical readers without
6 amusia matched to the two groups of dyslexic participants for either chronological age or
7 reading level (henceforth, CA controls and RL controls, respectively).

8 Comparing these four groups of participants, and in particular DYS+A and DYS-A
9 children to the two control groups, should allow us to identify possible connections and thus
10 pointing to potentially causal underlying impairments. As discussed by Goswami (Goswami,
11 2003, 2015; Goswami & Bryant, 1989) and Huettig et al. (2018), numerous impairments that
12 have been proposed as underlying dyslexia (e.g., poor phonological awareness and low verbal
13 STM, but also sensory impairments such as magnocellular deficit, or impairments in visual
14 attention) might actually result from (rather than cause) the effects of reduced reading
15 experience. This illustrates why the RL control group is critical: "if children with dyslexia
16 perform worse than the younger reading level-matched children, this suggests a causal role for
17 the factor being investigated, as the children with dyslexia have higher chronological and
18 mental ages and better metacognitive skills" (Goswami, 2015 p. 44). Subsequent longitudinal
19 and training studies are then required to properly test the causal hypothesis. In the present study,
20 we thus considered that only a difference between dyslexic children and both control groups
21 would suggest a causal role for the cognitive function at stake.

22 However, not all dyslexic children would necessarily present such impairment(s) in both
23 the language and music domains. Namely, if developmental dyslexia and congenital amusia
24 were sharing common underlying impairment(s) with regards to some specific cognitive
25 function(s), we would expect at least the DYS+A children to differ from both the CA and RL
controls on that or those function(s), whatever the domain investigated. DYS-A children might
also show an impairment in that or those function(s), but to a lesser degree or only in the
language domain. In short, we thus attempted to identify an impairment in one or several of the
three investigated cognitive functions that would manifest itself in both language and music at
least in DYS+A children and potentially, although to a lesser extent, in the DYS-A children.

If dyslexia and amusia shared common underlying impairment(s), the following
predictions should be confirmed. First, dyslexic children should present a marked impairment
for one or several specific function(s), manifesting itself in each of the domains of specificity
of both disorders (phonemes and pitches) and possibly in timbres, whose processing has
sometimes been reported to be deficient in amusia (Marin et al., 2012; Tillmann et al., 2009).
In the verbal domain, the common underlying impairment(s) are expected to be observed in
both the DYS+A and DYS-A children. In the musical domain, they are expected to be
particularly pronounced in the DYS+A children but may be observed in the DYS-A children as
well, although to a lesser extent. In addition, if common cognitive impairment(s) are core
impairments inherent to dyslexia, they should be observed independently of reading experience
and thus be revealed relative to both the CA and the RL control groups (Goswami, 2015;
Huettig et al., 2018). At an individual level, we expect such impairments to affect most cases,
rather than group differences being driven by a small number of poor performers. Finally, we
expect to observe correlational links between participants' performance in the function(s) at
play and their reading/musical skills.

## Methods

### Participants

Eighty-six children were recruited for this study, but six (3 dyslexic and 3 control
candidates) were excluded based on the inclusion phase tests described below. Fifteen DYS+A
children and 15 DYS-A children aged between 7 and 13 years were included, as well as 25 CA
controls and 25 RL controls<fnref n="1" />. All were French native speakers born in Belgium or in France who reported normal hearing and normal or corrected-to-normal vision, and all had nonverbal IQ above percentile 10 (as estimated with the Raven's Colored Progressive Matrices (Raven, 1965), see *inclusion phase* below). They attended school regularly and none of them reported any history of neurological illness or brain damage. The dyslexic children were recruited from either specialist or public elementary schools in Belgium and in France. They previously had received a formal diagnosis of dyslexia by a speech therapist and were receiving or had received speech therapy. The controls were selected from public elementary schools in the same cities as the dyslexic children or through personal networks; none of them had a history of written language impairment. Some of the participants (10 DYS+A, 7 DYS-A, and 9 CA controls) had previously participated in a related study (Couvignou & Kolinsky, 2021). The four groups were matched for sex ratio, music education (as measured by years of extracurricular music instruction), parents' socio-economic status, and nonverbal IQ (Table 1).

Inclusion criteria required children with dyslexia to score at least 1.5 standard deviation (SD) below the grade-appropriate mean in either text or isolated word reading (accuracy or speed; Jacquier-Roux et al., 2005) and CA control participants to score no more than 1 SD below the mean in both tests. In addition to reading abilities, phonological processing was assessed in dyslexic and CA control participants at the inclusion phase. All participants completed the abbreviated version of the *Montreal Battery of Evaluation of Musical Abilities*

<footnote n="1">¹ For our study to have 80% power to detect an effect with a Cohen's *f* of 0.1 and a significance level of .05, 22 participants were required in each group (calculation performed for a mixed ANOVA under G*Power 3; Faul et al., 2007). The final sample satisfied these requirements for CA and RL groups, but not for DYS+A and DYS-A groups, due to the great difficulty in recruiting these children. Note that our sample size still exceeds that of comparable studies conducted with these particular populations (e.g., Graves et al., 2019; Lagrois & Peretz, 2019; Lazzaro et al., 2021; Tao et al., 2019).</footnote>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

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(MBEMA, Peretz et al., 2013), a battery designed to assess melody, rhythm, and music incidental memory skills in school-aged children (see inclusion phase below for a detailed description). Participants were considered amusic when they scored 2 SD below the mean of controls of the same age (i.e., based on CA controls' scores for dyslexic and CA control participants, and based on RL controls' scores for RL control participants) in the melodic task or across the three tasks of the MBEMA<fnref n="2" />. Note that two DYS+A children also had a formal diagnosis of attention deficit disorder (ADD). Therefore, where appropriate, the influence of these children's performance was controlled for in the relevant analyses (see results section). No other comorbidities were reported among the participants.

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The study was conducted with approval of the local Ethics committee of the Université Libre de Bruxelles (agreement number: 034/2017) and was performed in accordance with the principles stated in the Declaration of Helsinki. Written informed consent was obtained from the parents of each child, as well as oral agreement from each participant prior to the study participation. All children received a “diploma” as a reward for their time and participation. In the context of the COVID-19 pandemic, necessary precautions have been taken to avoid contaminations including appropriate protection sanitary measures (remote body temperature measurement, hand and material disinfection, safety interpersonal distance, mask wearing, and regular ventilation). Also, parents signed an additional consent form in which they explicitly

<footnote n="2">² Using the cutoffs of Peretz et al. (2013), the categorization remained the same for all participants except three DYS+A children (S038, S040, and S054), who performed above the threshold of -2 SD for both global and melodic scores by these norms and would therefore be considered non-amusic. Following previous studies defining the diagnostic criterion for amusia based on a matched control group (see Vuvan et al., 2018, for a review of methods for identifying amusia using the MBEA), we kept them in the DYS+A group. Indeed, this method has the advantage of controlling for the effects of several cognitive and demographic variables that may influence musical performance such as IQ, SES, or level of musical education.</footnote>
1

consented to their name being communicated to the accredited federal service if needed in case

2

of a known positive contact or infection.

3

- *Insert Table 1 here* -

4

**Materials and Procedure**

5

Children were tested individually in a quiet room of their school or home, over three sessions

6

of about one hour each (or six sessions of 30 minutes each, for the youngest ones), with a few

7

days between sessions. The inclusion tests were administered in the first session, and the

8

experimental tests were distributed over the other sessions. The 26 children who participated in

9

a previous study (Couvignou & Kolinsky, 2021) were not presented with the inclusion tests

10

again if their data had been acquired less than one year before the present testing phase, with

11

the exception of the *Mécanisme d'Identification des Mots* (MIM, “Word Identification

12

Mechanism”) reading subtest (see inclusion phase below for more details), which was not part

13

of the previous battery. All tasks were programmed under *PsychoPy2* (Peirce et al., 2019),

14

except for nonverbal intelligence, reading, and rapid naming tests, which were administered in

15

paper form. Stimuli were presented through *Sennheiser HD206* headphones at a comfortable

16

subjective loudness level.

17

The evaluations were conducted by the first author or by one of the four Master students

18

involved in the project. To minimize inter-experimenter variability and to agree on how to

19

interact with the children, precise written instructions were provided in advance and the first

20

week of evaluation was conducted under the direct supervision of the first author. All

21

experimenters tested participants of all groups, to eliminate the potential source confounding

22

between group and experimenter differences.

23

**Inclusion Phase**

24

The *inclusion phase* consisted of a set of tasks aimed at assessing nonverbal intelligence,

25

reading accuracy and speed, phonology, and musical skills.
Nonverbal intelligence was assessed using the Raven's Colored Progressive Matrices (Raven, 1965). In this test, children were presented with an incomplete picture and six alternatives among which they must choose the one that best completes the picture. The test consisted of 36 visual patterns of increasing difficulty. French norms (Raven, 1998) were used to convert raw scores to age-standardized scores and to ensure that all children performed above percentile 10.

Reading accuracy and speed were assessed in all participants using the MIM subtest of the *Batterie d'Évaluation du Langage Écrit* (BELEC, Written Language Assessment Battery; Mousty et al., 1994), which evaluates reading of lists of 72 isolated words and pseudowords varying in length, frequency, and complexity. In addition, dyslexic and CA control participants took two complementary standardized reading tests from the French Battery *Outil de Dépistage des Dyslexies* (ODEDYS, Dyslexia Screening Tool; Jacquier-Roux et al., 2005). In the *text reading* test, children were asked to read aloud the text "Monsieur Petit" for one minute. The number of words read without error was scored. In the *word/pseudoword reading* test, children were administered three lists of 20 items each: irregular words, regular words and pseudowords. They were asked to read them aloud as quickly and as accurately as possible. Both accuracy and speed were scored.

Phonological skills were investigated with tests of phonological memory, phonological awareness, and rapid access to phonological information in dyslexic and CA control participants. Phonological memory was estimated with the *pseudoword repetition* tests of the BELEC (Mousty et al., 1994), even though this task cannot be considered a pure measure of phonological memory, as it also involves phonological discrimination, phonological programming, and articulation skills. Children were instructed to repeat recorded pseudowords of increasing length (1 to 5 syllables) as accurately as possible. Five series of four items each were presented under two conditions: the pseudowords' syllables had either a simple structure
1 (consonant-vowel, CV condition) or a complex one (consonant-consonant-vowel, CCV
2 condition). The number of pseudowords repeated without error was scored. In the initial
3 syllable deletion and initial phoneme deletion tests of the BELEC (Mousty et al., 1994),
4 children were required to repeat CVCV pseudowords without the initial syllable (16 items) as
5 well as to repeat CVC (16 items) and CCV (10 items) monosyllables without the initial
6 phoneme. Four practice trials were given before each condition. The score was the total number
7 of correct answers. Rapid access to phonological and lexical information was evaluated through
8 a Rapid Automatized Naming (RAN) task, in which children named as fast as possible two
9 series of 50 objects each. The score was the sum of total naming time for both series.

10 Musical skills were assessed using the abbreviated version of the *Montreal Battery of
11 Evaluation of Musical Abilities* (MBEMA, Peretz et al., 2013), which involves two tests
12 evaluating melody and rhythm processing, as well as one test examining incidental memory of
13 unfamiliar tonal melodies. Each test comprised two practice trials with feedback followed by
14 20 experimental trials and used the same pool of 20 unfamiliar melodies that were written
15 according to the rules of the Western tonal system. The *Melody* and *Rhythm* tests involved pairs
16 of melodies and consisted of a same-different judgement. The *Memory* test required children to
17 recognize a melody as having been presented earlier during the session or not. The score was
18 the total number of correct answers. Note that the 26 children from our previous study had taken
19 the full version of this battery, which involves three tests of melody processing instead of one
20 (see Peretz et al., 2013 for a detailed description). For the *Melody* test, their results were
21 converted so that only the trials present in the abbreviated version were included in the score
22 calculation. For the *Rhythm* and *Memory* tests, the original score was kept.

23 Average performance on the tests used in the inclusion phase are presented in Table 1.
24
**Experimental Phase**
The experimental phase was presented in the form of three computer games: “Spot the difference”, “The missing wagon”, and “The sound hunter”, which respectively aimed to assess auditory STM, perceptual awareness, and attention skills in a comparative way for the three materials: words, tones, and timbres. The tasks were based on the same set of stimuli, a detailed description of which can be found in Schulze and Tillmann (2013). For the word tasks, six monosyllabic meaningful French words were used (CV combination, using the vowel /u/; that is: /bu/, /gu/, /lu/, /mu/, /pu/, and /tu/), all spoken by a female voice and adjusted to the pitch of 230 Hz. For the pitch tasks, six tones differing in pitch height were used, namely C4 (262 Hz), D4 (294 Hz), E4 (330 Hz), F4 (349 Hz), G4 (392 Hz), and A4 (440 Hz), all generated with a piano timbre. For the timbre tasks, we used six timbres (cello, flute, guitar, piano, trumpet, and vibes), all played at 330 Hz (E4). The stimuli of each material had a duration of 500 ms each and were subjectively equalized in loudness. Children were sensitized to the stimuli before starting the tests, with a short *minimal pair discrimination* task involving the least salient contrasts (i.e., linguistic pairs differing only by a single phonetic feature: /bu/ - /gu/, /pu/ - /bu/, /tu/ - /pu/; pitch pairs separated by one tone or semitone: C4 - D4, E4 - F4, G4 - A4; and the (subjectively) more similar timbres: cello - flute, guitar - piano, vibes - guitar). The task included 18 trials presented in a fixed order: 6 pairs for each material (word, pitch, timbre), with half of them being “same” trials and the other half being “different” trials. Feedback was given after each trial, together with the option to listen to the trial again in case of failure. A 6-point discrimination score was calculated for each material.

**Auditory STM** was assessed using a recognition paradigm based on Schulze and Tillmann (2013; Figures 1A, 2A), but the task was adapted to children in terms of length by reducing the numbers of trials and the number of items per sequence. In addition, we investigated item memory separately from order memory, because phonological representations are thought to be involved differently in these two types of tasks (Majerus & Cowan, 2016).
The child listened to pairs of auditory sequences separated by a 2-second silent interval and had to judge by pressing one of the two response keys (on the left or right side of the keyboard) whether the pairs were the same or different. The next trial automatically started 2 seconds after the child had given his/her answer. Throughout the test, the child was asked to keep his/her index fingers on the response keys in order to avoid any delay due to reaching the key. Two experimental conditions were contrasted without the child's knowledge. In the *item condition*, the incorrect trials were constructed by exchanging a single item of the second sequence (e.g., A B C - A *D* C). In the *order condition*, the incorrect trials were constructed by switching the position of two adjacent items in the sequence (e.g., A B C - A *C* B). Each of these two conditions were tested separately in three randomized blocks (one for each material), each of the blocks themselves being divided into three levels of memory load, depending on the length of the to-be-remembered sequence (3, 4, and 5 items of 500 ms each per sequence respectively, with an inter-stimulus interval of 20 ms). In line with previous studies reporting sequence length effects for both verbal and musical materials (Gorin et al., 2018; Schulze & Tillmann, 2013), we expected performance to decrease with increased memory load (i.e., increased sequence length). Two sets of trials were used, which were counterbalanced over participants and conditions (i.e., half of the participants were tested with set 1 in the item condition and set 2 in the order condition, the other half of participants with set 2 in the item condition and set 1 in the order condition). Both sets respected the following constraints: (i) an item was never used twice within the same sequence, (ii) the occurrence of item by position was balanced, so that each item was presented once in each position of the sequence, and (iii) the first item of the second sequence was never changed for different trials to prevent participants from solving the task by comparing only the first item of the two sequences. Pitch material implied additional constraints in terms of melodic contour: (iv) the melodic contour of the initial sequences was balanced between the two sets and the two conditions (i.e., the same alternating descending and
ascending patterns were used for the construction of the initial sequences of both sets and both conditions), and (v) "different" trials systematically induced at least one contour change in the sequence. Post-hoc analyses conducted on the mean size of the interval change and the mean number of contour changes showed that overall, for the pitch material, the changes were not comparable across conditions and lengths (see detailed results in Supplementary Material S1).

The pattern of sequence pairs of the pitch material served as a template to generate the sequence pairs for the word and timbre materials. The task was presented to participants with two three-item sequence trials (one same, one different) at the beginning of each block. Feedback was given for these practice trials only, together with the option to listen to the trials again. In total, the task included 216 experimental trials: 12 pairs for each condition (item, order), material (word, pitch, timbre), and length (3, 4, 5), with half of them being same trials and the other half being different trials. A pseudo-randomized presentation was used so that: (i) a given sequence could not be presented on consecutive trials and (ii) the type of pair (same, different) changed after at most three trials (i.e., no more than three consecutive "same" or "different" trials). To avoid fatigue, the two conditions (item, order) were not tested within the same experimental session but spread over two different sessions a few days apart. Each session lasted about 30 minutes.

**Auditory Perceptual Awareness** was assessed using a recognition paradigm inspired by Morais et al. (2010; Figures 1B, 2B, 2C). Based on that study, we decided to use a correctness judgment task to minimize memory load. The child listened to pairs of auditory sequences separated by a 2-second silent interval and had to judge by pressing one of the two response keys (on the left or right side of the keyboard) whether or not the second sequence was correctly repeated without the first element. The next trial automatically started 2 seconds after the child had given his/her answer. Throughout the test, the child was asked to keep his/her index fingers on the response keys in order to avoid any delay due to reaching the key. For the
word and the pitch tasks, the sequences were composed of two large perceptual units (e.g., 2 syllables or 2 musical intervals), each of which could be divided into two smaller subunits (e.g., 2 phonemes or 2 notes). The task had to be performed at the level of either large or small perceptual units, which was illustrated to the child using drawings of train wagons of varying lengths (Figures 2B, 2C). We also used a control condition involving timbre processing, in which the sequences were composed of two timbres. Each syllable, note, and timbre lasted 500 ms: consequently, the duration of the sequences was unequal across materials (i.e., each sequence lasted 1000 ms for word and timbre materials but 2000 ms for pitch material). This choice was made to privilege the matching of the materials in terms of number of perceptual units. As in the STM task, two experimental conditions (item and order) were contrasted without the child's knowledge, depending on how the incorrect trials were built, namely on the basis of a manipulation of either item identity or presentation order (see Figure 1B for an example for each material and condition). These two conditions were tested separately in five blocks (syllable, phoneme, interval, note, timbre) using a pseudo-randomized order so that the syllable material always preceded the phoneme one and the interval material always preceded the note one. In this way, the condition involving the largest perceptual units (assumed to be easier to achieve) was always presented first. Again, two sets of trials were used, which were counterbalanced over participants and conditions. Both sets respected the following constraints: (i) an item was never used twice within the same sequence, (ii) the occurrence of item by position was balanced, so that each item was presented once in each position of the sequence. For a closer match between word and pitch materials, (iii) the same initial sequences were used for syllable and phoneme, as well as for interval and note, and (iv) incorrect propositions were always created by a change located on the third subunit of the initial sequence (i.e., third phoneme or third note). In addition, for pitch material, (v) the melodic contour of the initial sequences was balanced between the two sets and the two conditions (i.e., the same alternating
descending and ascending patterns were used for the construction of the initial sequences of both sets and both conditions). Given all these constraints and the limited number of items, the “different” trials did not always induce a contour change in the sequence. Control analyses showed that the mean size of the interval change was significantly lower for the interval than for the note material (see detailed results in Supplementary Material S2). Hence, any difference in performance between these two materials should be interpreted with caution, as better performance might be linked to bigger changes in note material. The task was demonstrated with four trials (two correct, two incorrect) at the beginning of each block. Feedback was given for these practice trials only, together with the option to listen to the trial again. In total, the task included 120 experimental trials: 12 pairs for each condition (item, order), and material (syllable, phoneme, interval, note, timbre), with half of them being correct and the other half being incorrect. A pseudo-randomized presentation was used so that: (i) a given sequence could not be presented on consecutive trials and (ii) the type of pair (correct, incorrect) changed after at most three trials (i.e., no more than three consecutive “correct” or “incorrect” trials). Again, to avoid fatigue, the two conditions (item, order) were not tested within the same experimental session but spread over two different sessions a few days apart. Each one lasted about 20 minutes.

**Auditory Attention** was assessed using a go/no-go paradigm (Figures 1C, 2D). The child listened to a series of sounds presented at regular time intervals (items of 500 ms each, with an inter-stimulus interval of 1 s) and had to press a response key as soon as he/she heard a target sound. Throughout the test, the children were asked to keep their index finger on the response key so that they could press it as soon as they heard the target. The task consisted of three randomized blocks (one for each material), each divided into two levels of difficulty. At level 1, the target had to be distinguished from a single distractor (i.e., /lu/ among /pu/; A4 among E4; flute among vibes). At level 2, the same target had to be identified among three
different distractors (i.e., /lu/ among /pu/, /gu/, and /tu/; A4 among E4, D4, and C4; flute among
vibes, cello, and guitar), making the identification of the stimuli more demanding on the
memory level and involving selective attentional skills to a greater extent. To minimize the role
of discrimination abilities in task performance, distractors were chosen to be as distinct as
possible from the target, in terms of phonetic features, pitch height or family of musical
instruments (woodwind, percussion, bowed strings, or plucked strings). Before each level of
each block, the target was presented to the child in isolation, followed by 15 practice trials (3
targets to be found among 12 distractors at level 1, or among 3 different distractors presented 4
times each at level 2) for which feedback was given. In total, the task included 720 experimental
trials: 120 for each material (word, pitch, timbre) and level (1, 2) including 24 targets and 96
distractors (or 3 distractors presented 32 times each at level 2), so that the target/distractor ratio
was kept constant. Note that the target/distractor ratio (1/4) was intentionally kept low, in order
to more specifically assess vigilance and sustained attention rather than inhibition. The
experimental trials were carried out without feedback. The whole task lasted about 30 minutes.

15

- Insert Figure 1 here -

16

- Insert Figure 2 here -

17

**Data Analysis**

Auditory STM and perceptual awareness, as well as attention performance were
assessed using Signal Detection Theory (Macmillan & Creelman, 2004). We calculated d'
sensitivity index as d' = z (H) - z (FA) for each participant as a function of each condition,
material, sequence length, and/or level. Hits and false alarms (FAs) were defined as follows:
for the auditory STM tasks, H = p (response = different | stimulus = different) and FA = p
(response = different | stimulus = same); for the auditory perceptual awareness tasks, H = p
(response = incorrect | stimulus = incorrect) and FA = p (response = incorrect | stimulus =
correct); and for the auditory attention tasks, H = p (response = target | stimulus = target) and

18

19

20

21

22

23

24

25
# SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

1

$FA = p$ (response = target | stimulus = distractor). To avoid infinite $d'$ values, proportions of 0 and 1 were adjusted to $1/(2N)$ and $1 - 1/(2N)$, respectively, where $N$ is the number of trials on which the proportion is calculated. One RL control was excluded from the STM analyses and one RL control from the auditory perceptual awareness analyses because they probably did not understand the task<fnref n="3" />.

2

3

4

5

6

## Results

7

### Group Comparisons

8

#### Minimal Pair Discrimination

9

10

11

12

13

This task refers to the short discrimination test designed to make children aware of the different contrasts between the stimuli before starting the other tests. DYS+A children performed significantly worse than both DYS-A children and CA controls but not significantly different from RL controls for pitch material (Table 2). No other group difference was significant.

14

- Insert Table 2 here -

15

#### Auditory STM

16

17

18

To explore the potential role of auditory STM in the comorbidity between dyslexia andamusia, a 2 (Condition: item, order) x 3 (Material: word, pitch, timbre) x 3 (Sequence length, henceforth Length: 3, 4, or 5 items per sequence) x 4 (Group: DYS+A children, DYS-A

<footnote n="3">³ Both presented a mean $d'$ of zero in the easiest conditions (i.e., for the STM tests: in the item condition for length 3 across materials, and for the auditory perceptual awareness tests: in the item condition across materials), while all other participants were quite able to perform the task with mean $d'$ scores in the easiest STM tests of 2.2 (SD = 0.8), 2.6 (SD = 0.5), 2.8 (SD = 0.6), and 2.0 (SD = 0.8) for DYS+A children, DYS-A children, CA controls, and RL controls respectively, and mean $d'$ scores in the easiest auditory perceptual awareness tests of 1.3 (SD = 0.6), 2.2 (SD = 0.5), 2.4 (SD = 0.5), 2.4 (SD = 0.6), and 1.8 (SD = 0.7) for DYS+A children, DYS-A children, CA controls, and RL controls, respectively.</footnote>
1 children, CA controls, RL controls) mixed-design analysis of variance (ANOVA) was
2 computed on the *d'* sensitivity index, with condition, material, and length as within-participant
3 factors and group as between-participants factor. Table 3 summarizes the outcomes of this
4 analysis and Figure 3 presents the average *d'* values.

5 - *Insert Figure 3 here* -

6 The ANOVA revealed significant main effects of condition, *F*(1, 75) = 23.05, *p* < .001,
7 η²p = .235, material, *F*(2, 150) = 57.00, *p* < .001, η²p = .432, length, *F*(2, 150) = 222.16, *p* <
8 .001, η²p = .748, and group, *F*(3, 75) = 8.39, *p* < .001, η²p = .251, as well as significant
9 interactions between condition and length, *F*(2, 150) = 7.45, *p* < .001, η²p = .090, material and
10 length, *F*(4, 300) = 3.34, *p* = .011, η²p = .043, length and group, *F*(6, 150) = 2.52, *p* = .024, η²p
11 = .091, and material and group, *F*(6, 150) = 2.54, *p* = .023, η²p = .092. In addition, significant
12 3-way interactions were observed between condition, material, and length, *F*(4, 300) = 3.34, *p*
13 = .011, η²p = .043, and between condition, length, and group, *F*(6, 150) = 4.15, *p* < .001, η²p =
14 .142. No other interaction was significant (all *Fs* < 1 except for Condition x Group: *F*(3,75) =
15 1.88, *p* = .141, and Condition x Material x Length x Group: *F*(12, 300) = 1.56, *p* = .103).
16 Additional analyses, presented in Supplementary Material S3.1, showed that the lower pitch
17 discrimination performance of DYS+A children (Table 2) did not influence this pattern of
18 results.

19 The absence of the Condition x Material x Length x Group interaction was further
20 investigated by performing Bayesian analyses. Indeed, a key advantage of the Bayes factor over
21 the *p*-value is that, unlike the *p*-value, the Bayes factor can lead to support for the null
22 hypothesis as well as the alternative hypothesis. A 2 (Condition) x 3 (Material) x 3 (Length) x
23 4 (Group) Bayesian mixed-design ANOVA was conducted on *d'*, with condition, material, and
24 length as within-participant factors and group as between-participants factor. An analysis of
25 specific effects showed a medium *BF*<sub>exclusion</sub> score for the interaction between condition,
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

material, length, and group ($BF_{exclusion}$ = 8.53), providing positive (Raftery, 1995) or even substantial (Jeffreys, 1961) evidence in favor of the absence of such interaction.

Regarding the interaction between material and group, post-hoc comparisons indicated that DYS+A children showed impaired STM for both words and pitches compared to typical readers of the same age, without differing from typical readers of the same reading level. For pitches, this impairment was also observed in comparison with their DYS-A peers. However, it did not extend to timbres. In contrast, DYS-A children showed no impairment in auditory STM compared to the other groups. In addition, an age effect<fnref n="4" /> was observed for pitches, with CA controls performing better than RL controls on this material, but not for words or timbre. These analyses are presented in detail in Supplementary Material S3.2.

Regarding the 3-way interaction between condition, material, and length, the performance difference between the item and order conditions was length dependent for words and timbres, but not for pitches (see detailed results in Supplementary Material S3.3). This interaction will not be detailed here because it does not involve group differences.

The 3-way interaction between condition, length, and group was further investigated by performing two separate 3 (Length) x 4 (Group) mixed-design ANOVAs on the item and order conditions, averaging across materials.

In the item condition, the ANOVA revealed main effects of length, $F(2, 150) = 179.26$, $p < .001$, $\eta_p^2 = .705$, and group, $F(3, 75) = 7.38$, $p < .001$, $\eta_p^2 = .228$, but the interaction failed to reach significance, $F(6, 150) = 2.09$, $p = .058$. Post-hoc comparisons indicated that DYS+A children showed a general item STM impairment compared to typical readers of the same age but not to typical readers of the same reading level. In contrast, DYS-A showed no item STM impairment across materials. In addition, an age effect was observed, with CA controls

<footnote n="4">⁴ Note that for sake of simplicity throughout the paper we report the difference between CA and RL controls as an age effect although it may actually be linked to school acquisitions, including literacy acquisition.</footnote>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

performing better than RL controls. These analyses are presented in detail in Supplementary
Material S3.4.

In the order condition, the ANOVA revealed main effects of length, *F*(2, 150) = 88.64,
*p* < .001, η²_p_ = .542, group, *F*(3, 75) = 6.97, *p* < .001, η²_p_ = .218, and a significant interaction
between length and group, *F*(6, 150) = 4.23, *p* < .001, η²_p_ = .145. Post-hoc comparisons revealed
that DYS+A children showed a general auditory serial-order STM impairment for length 3
compared to their DYS-A peers and typical readers of both the same age and the same reading
level, and for length 4 compared to typical readers of both the same age and the same reading
level. In contrast, DYS-A children showed no serial-order STM impairment across materials.
No age effect was observed, CA controls performing not significantly different from RL
controls for all sequence lengths. These analyses are presented in detail in Supplementary
Material S3.5.

13 *Auditory Perceptual Awareness*

To explore the potential role of auditory perceptual awareness in the comorbidity
between dyslexia and amusia, a 2 (Condition: item, order) x 5 (Material: syllable, phoneme,
interval, note, timbre) x 4 (Group: DYS+A children, DYS-A children, CA controls, RL
controls) mixed-design ANOVA was computed on the *d'* sensitivity index, with condition and
material as within-participant factors and group as between-participants factor. The outcomes
of this analysis are summarized in Table 3 and average *d'* values are shown in Figure 4.

20 - *Insert Figure 4 here -*

The ANOVA revealed significant main effects of condition, *F*(1,75) = 9.88, *p* = .002,
*η*²_p_ = .116, material, *F*(4, 300) = 56.21, *p* < .001, *η*²_p_ = .428, and group, *F*(3, 75) = 10.56, *p* <
.001, *η*²_p_ = .297, as well as a significant interaction between condition and material, *F*(4, 300)
= 23.27, *p* < .001, *η*²_p_ = .237, and a 3-way interaction between condition, material, and group,
*F*(12, 300) = 1.81, *p* = .047, *η*²_p_ = .067. No other interaction was significant (all *Fs* < 1 except
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

1 for Material x Group: $F(12, 300) = 1.13, p = .338$). Similarly to the STM task, additional
2 analyses showed that the lower pitch discrimination performance of DYS+A children did not
3 influence this pattern of results (Supplementary Material S4.1). The 3-way interaction was
4 further investigated by performing five separate 2 (Condition) x 4 (Group) mixed-design
5 ANOVAs on each material.

6 For syllables, the ANOVA revealed main effects of condition, $F(1,75) = 8.42, p = .005$, 
7 $\eta^2_p = .101$, and group, $F(3,75) = 7.59, p < .001$, $\eta^2_p = .233$, but no significant interaction ($F <$ 
8 1). Post-hoc comparisons indicated impaired syllable awareness in DYS+A children compared 
9 to typical readers of the same age, but not to children with the same reading level. In contrast, 
10 DYS-A children showed no impairment in syllable awareness compared to the controls. In 
11 addition, it can be noted that syllable awareness performance was age sensitive, with CA 
12 controls performing better than RL controls. These analyses are presented in detail in 
13 Supplementary Material S4.2.

14 For phonemes, the ANOVA revealed main effects of condition, $F(1,75) = 27.20, p <$ 
15 .001, $\eta^2_p = .266$, and group, $F(3,75) = 3.51, p = .019$, $\eta^2_p = .123$, but no significant interaction 
16 ($F = 2.39, p = .076$). Post-hoc comparisons indicated impaired phoneme awareness in DYS+A 
17 children compared to typical readers of the same age, but not of the same reading level. In 
18 contrast, DYS-A children showed no impairment in phoneme awareness compared to the 
19 controls. In addition, phoneme awareness performance was not age sensitive, with CA controls 
20 performing not significantly different from RL controls. These analyses are presented in detail 
21 in Supplementary Material S4.3.

22 For intervals, the ANOVA revealed main effects of condition, $F(1,75) = 36.56, p < .001$, 
23 $\eta^2_p = .328$, and group, $F(3,75) = 9.22, p < .001$, $\eta^2_p = .269$, but no significant interaction ($F =$ 
24 1.98, $p = .124$). Post-hoc comparisons indicated impaired interval awareness in DYS+A 
25 children compared to both their DYS-A peers and typical readers of the same age, but not to
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

1

typical readers of the same reading level. In contrast, DYS-A children showed no impairment
in interval awareness compared to the controls. In addition, interval awareness performance
was age sensitive, with CA controls performing better than RL controls. These analyses are
presented in detail in Supplementary Material S4.4.

2

3

4

5

For notes, the ANOVA revealed a main effect of group, *F*(3,75) = 3.58, *p* = .018, η²_p_ = .125, but no significant main effect of condition (*F* < 1) or interaction (*F* = 1.52, *p* = .216). Post-hoc analyses indicated impaired note awareness in DYS+A children compared to typical readers of the same age, but not to their DYS-A peers nor to typical readers of the same reading level. In contrast, DYS-A children showed no impairment in note awareness compared to the controls. In addition, note awareness performance was not age sensitive, with CA controls performing not significantly different from RL controls. These analyses are presented in detail in Supplementary Material S4.5.

6

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8

9

10

11

12

13

For timbres, the ANOVA revealed main effects of condition, *F*(1,75) = 27.10, *p* < .001, η²_p_ = .265, and group, *F*(3,75) = 4.42, *p* = .003, η²_p_ = .172, but no significant interaction (*F* = 1.12, *p* = .345). Post-hoc comparisons indicated impaired timbre processing in DYS+A children compared to both their DYS-A peers and typical readers of the same age, but not to typical readers of the same reading level. In contrast, DYS-A children showed no impairment in timbre processing compared to the controls. In addition, it can be noted that timbre performance was not age sensitive, with CA controls performing not significantly different from RL controls. These analyses are presented in detail in Supplementary Material S4.6.

14

15

16

17

18

19

20

21

Auditory Attention

22

To explore the potential role of auditory attention in the comorbidity between dyslexia
and amusia, a 3 (Material: word, pitch, timbre) x 2 (Level of difficulty, henceforth Level: target
to be identified among 1 vs. 3 types of distractors) x 4 (Group: DYS+A children, DYS-A
children, CA controls, RL controls) mixed-design ANOVA was computed on the *d'* sensitivity

23

24

25
index, with material and level as within-participant factors and group as between-participants factor. The outcomes of this analysis are summarized in Table 3 and average *d'* values are shown in Figure 5.

- *Insert Figure 5 here -*

The ANOVA revealed significant main effects of level, *F*(1, 76) = 234.07, *p* < .001, η²_p = .755, and group, *F*(3, 76) = 11.81, *p* < .001, η²_p = .318, and a significant interaction between material and level, *F*(2, 152) = 21.51, *p* < .001, η²_p = .221, but no other significant main effect or interaction (all *Fs* < 1 except for Material x Level x Group: *F*(6, 152) = 1.67, *p* = .133)<fnref n="5" />.
Importantly, the interaction between material and group was not significant, nor was the higher-order interaction including these two factors. This was confirmed by a 3 (Material) x 2 (Level) x 4 (Group) Bayesian mixed-design ANOVA on *d'*. An analysis of specific effects showed a high *BF*<sub>exclusion</sub> score for the interaction between material and group (*BF*<sub>exclusion</sub> = 36.6), providing strong (Raftery, 1995) or very strong (Jeffreys, 1961) evidence in favor of the absence of such interaction.

Regarding the interaction between material and level, it was mainly due to a particularly
strong difference in salience for timbres between levels 1 and 2, compared to the other materials
(see detailed results in Supplementary Material S5.1). Regarding the main effect of group, post-
hoc comparisons indicated impaired auditory attention in DYS+A children compared to both
their DYS-A peers and typical readers of the same age, but not to typical readers of the same
reading level. In contrast, DYS-A children showed no impairment in auditory attention
compared to the other groups. In addition, auditory attention performance was age sensitive,

<footnote n="5">⁵ When the two DYS+A children with ADD were removed from the analyses, the results remained similar, with significant main effects of level, *F*(1, 74) = 231.76, *p* < .001, *η*²_p = .758, and group, *F*(3, 74) = 10.91, *p* < .001, *η*²_p = .307, and a significant interaction between material and level, *F*(2, 148) = 23.55, *p* < .001, *η*²_p = .241, but no other significant main effect or interaction (all *Fs* < 1).</footnote>
1 with CA controls performing better than RL controls. These analyses are presented in detail in

2 Supplementary Material S5.2.

3 **Summary of Key Group Differences across Tasks**

4 Table 3 summarizes the significant main effects and interactions involving the group

5 factor in the ANOVAs and corresponding post-hoc analyses for each task of the experimental

6 battery. Of the three investigated functions (auditory STM, perceptual awareness, and

7 attention), only auditory serial-order STM revealed the pattern of group differences that might

8 indicate a core impairment common to dyslexia and amusia: namely, for short- and medium-

9 length auditory sequences, DYS+A children performed significantly worse than both CA and

10 RL controls. This impairment was expressed independently of material and regardless of the

11 lower pitch discrimination skills of DYS+A children. The auditory item STM, perceptual

12 awareness, and attention tasks also revealed impairments in the DYS+A children, but only in

13 comparison to CA controls. In contrast, DYS-A children did not show impairment in any of the

14 tasks.

15 - *Insert Table 3 here* -

16 **Individual Profiles**

17 Beyond the group effects reported above, the purpose of the following analyses was to

18 examine individual profiles to determine whether children with dyslexia were consistently

19 impaired across all tests. Of particular interest was the case of the 15 DYS+A children. To limit

20 the number of comparisons, for each task, *d'* sensitivity indexes were first averaged across

21 conditions, materials, lengths, and/or levels based on the results of the ANOVAs presented in

22 Table 3. We selected only those factors for which group differences emerged significantly in

23 the post-hoc comparisons, resulting in a total of 11 composite variables (i.e., for the auditory

24 STM tasks: word, pitch, item, order length 3, and order length 4 performance; for the auditory

25 perceptual awareness tasks: phoneme, syllable, interval, note, and timbre performance; for the
1

2

3

4

5

6

7

8

auditory attention tasks: overall performance; see Table 3 for an overview). For each composite variable, participants' performance was transformed into two standardized z-scores: one was calculated by reference to the mean and standard deviation of the CA controls, the other by reference to the mean and standard deviation of the RL controls<fnref n="6" />. We then examined the proportion of participants scoring significantly below the norm in each group and for each variable. Any z-score falling below a threshold of -1.65 (i.e., below the 5th percentile of a normal distribution) relative to both CA and RL controls was considered as reflecting deviant performance.

9

10

11

12

13

Table 4 summarizes the number of participants showing deviant performance for each variable. As indicated by chi-square tests, a higher proportion of DYS+A children had deviant performance for pitch STM compared to CA controls, for order length 3 STM compared to DYS-A children, CA controls, and RL controls, and for order level 2 STM compared to CA and RL controls. No other significant group difference was observed.

14

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17

18

19

20

21

Table 5 shows the individual performance profiles of the dyslexic children. Among the 15 DYS+A children, two did not show any deviant score, three showed a specific impairment for one variable (one for order length 3 STM, one for order length 4 STM, and one for note awareness), and all others showed deviant scores for multiple variables. Among the 15 DYS-A children, two showed a specific impairment for one variable (one for order length 3 STM and one for order length 4 STM), two showed deviant scores for multiple variables (one for pitch STM and order length 4 STM, and one for word STM and syllable awareness), and all others did not show any deviant score. Overall, despite considerable heterogeneity in individual

<footnote n="6">⁶ Note that the mean and SD used for z-score calculation was computed after removing the CA and RL participants with extreme performance (i.e., *z* > 1.65 and *z* < -1.65, relative to the distribution of their respective groups), but that these extreme performers were still included in the following analyses.</footnote>
1 profiles, auditory serial-order STM stood out as the most convincing candidate to explain the
2 comorbidity between dyslexia and amusia.

3 - *Insert Table 4 here* -

4 - *Insert Table 5 here* -

5 **Relationships Between Reading Level, Music Perception Skills and Tasks Performance**

6 We computed correlations between the *MIM index* (calculated by dividing the MIM
7 reading score by the MIM reading time), MBEMA global score, and participants' performance
8 as represented by our 11 composite variables. Several positive correlations, both within and
9 between domains, were significant across the four groups of participants after partialing out
10 potential confounding factors such as age, parents' SES, music education, and nonverbal
11 intelligence. In particular, we observed moderate to strong positive correlations between
12 participants' order STM performance, reading level, and music perception skills. However,
13 almost none of them reached significance when carried out by group (see Supplementary
14 Material S6 for detailed results). Given the number of participants in each group, it is difficult
15 to determine whether the absence of significant within-group correlations was due to a lack of
16 statistical power, or whether the correlations observed across all participants merely reflected
17 group differences, without a general relationship.

18 Discussion

19 The present experiment aimed at testing the hypothesis that developmental dyslexia and
20 congenital amusia might share common underlying cognitive impairment(s), which may
21 explain the observation of substantial comorbidity between these two developmental disorders
22 (Couvignou et al., 2019; Couvignou & Kolinsky, 2021). For this purpose, we designed a set of
23 auditory behavioural tasks assessing short-term memory (STM), perceptual awareness, and
24 attention skills for words, pitches, and timbres. These tasks were administered to dyslexic
25 children with amusia (DYS+A), dyslexic children without amusia (DYS-A), as well as to two
1 groups of typically developing children matched to the dyslexic children on either
2 chronological age (CA) or reading level (RL).

3 Overall, our results suggest that, of the underlying functions considered in the present
4 work, only poor auditory serial-order STM increases susceptibility for comorbidity between
5 dyslexia and amusia and may play a causal role in the development of the comorbid phenotype.
6 The impairments in auditory item STM, auditory perceptual awareness, and auditory attention
7 observed in the DYS+A children, in contrast, may be a consequence of their reduced reading
8 experience combined with weaker musical skills, rather than a core impairment inherent to both
9 disorders. Comparisons of performance between the DYS+A and DYS-A children suggest that
10 the latter are more resourceful and/or have more effective compensatory strategies, or that their
11 phenotype results from a different developmental trajectory.

12 We will first review the evidence our data provide for and against the hypothesis of
13 common underlying impairment(s) between dyslexia and amusia. We will then discuss how
14 these findings are of interest for delving into the aetiology of these two developmental disorders
15 and for theoretical models of STM. Finally, after discussing some of the limitations of this
16 study, we will address its implication for future research and practices.

17 Are Dyslexia and Amusia Different Manifestations of Similar Underlying Impairment(s)?

18 Assuming that dyslexia and amusia share common underlying impairment(s), we
19 expected that (1) children with dyslexia would show a marked impairment in one or several of
20 the specific functions examined, manifesting itself in both the DYS+A and DYS-A children in
21 the verbal domain and being more pronounced in DYS+A children in the musical domain, (2)
22 this impairment would be observed independently of reading experience and thus be revealed
23 relative to both the CA and the RL control groups, (3) this impairment would affect most
24 individual cases, and (4) participants' performance in the impaired function(s) would be
25 positively correlated with their reading/musical performance.
1 We will examine, for each of the three functions investigated here, how consistent our
2 data are with these predictions. Regarding auditory STM, an important issue was the distinction
3 between item-based and serial order-based retention processes. On item memory, the DYS+A
4 children performed significantly worse than the CA controls but not significantly different from
5 the RL controls, regardless of the material and length of the to-be-remembered sequence. The
6 reasoning that this result pattern reflects the single effect of reduced reading experience does
7 not seem valid in this case, because DYS-A have comparable reading experience (approximated
8 by equivalent reading level) as DYS+A but do not show the same item memory impairment.

9 Rather, we suggest that the DYS+A children’s item memory impairment is a consequence of
10 their reduced reading experience combined with other characteristics that are specific to their
11 condition, such as weaker musical skills. On serial order memory, in contrast, the DYS+A
12 children performed significantly below both the CA and RL controls for short and medium
13 sequences, regardless of the material. This suggests that serial-order STM impairment may play
14 a causal role in the development of the comorbidity. Analysis of individual profiles were
15 consistent with this hypothesis, with a large majority of DYS+A children (12 of 15) showing
16 serial-order STM deviant performance relative to both the CA and RL controls, whereas such
17 an impairment was poorly represented in the other groups. In line with these observations, we
18 also observed moderate to strong positive correlations between participants’ order STM
19 performance, reading level, and music perception skills after partialing out potential
20 confounding factors such as age, parents’ SES, music education, and nonverbal intelligence.
21 However, almost none of these correlations reached significance when carried out by group,
22 which may either be due to insufficient sample size or suggest the absence of a general
23 relationship.

24 Regarding auditory perceptual awareness and auditory attention, the DYS+A children
25 performed worse than the CA controls, but not significantly different from the RL controls,
regardless of the material. Again, as the DYS-A children did not exhibit the same impairments, these probably result from the combined effects of DYS+A children's reduced reading experience and weaker musical skills. Analyses of individual profiles confirmed that the proportion of participants with deviant performance on these tasks relative to both the CA and RL controls was not significantly different between the DYS+A children and the other groups.

Finally, music perceptual awareness performance (i.e., awareness of intervals, notes, and timbres, but not of syllables or phonemes) correlated moderately with music perception performance, but not with reading performance. Auditory attention performance correlated moderately with both reading and music perception performance.

Overall, of the cognitive functions investigated in the present study, auditory serial-order STM verified almost all our predictions and appears to be the strongest candidate to explain the comorbidity between dyslexia and amusia. As we shall see, however, the absence of a clear impairment in the DYS-A children and the lack of a group of children with pure amusia do not allow us to conclude decisively about the role of this function in the aetiology of dyslexia and amusia separately. Therefore, our data do not provide a complete answer to the search for common underlying impairments between the two disorders. Impairments in auditory item STM, auditory perceptual awareness, and auditory attention were also associated with the comorbid phenotype, but they may merely be a consequence of the reduced reading experience inherent to dyslexia combined with weaker musical skills and are less likely to play a causal role in its development.

With regards to the potential underlying neural substrates, a set of neuroimaging studies conducted in adults and typically developing children have identified a right frontoparietal network centered on the intraparietal sulcus specifically associated with serial-order STM performance (Attout et al., 2019; Henson et al., 2000; Majerus et al., 2010; Marshuetz et al., 2006). Consistently, serial-order STM impairments in dyslexia have been associated with
abnormal activation in a network encompassing the right intraparietal sulcus and superior frontal gyrus, in both the verbal and the visual domains. In amusia, the neural correlates of serial-order STM processes have rarely been studied to date, with the majority of imaging studies using paradigms that maximize item STM (Albouy, Mattout, et al., 2013; Albouy et al., 2015, 2019a). Only a transcranial alternating current stimulation study showed that modulation of the right dorsolateral prefrontal cortex selectively enhanced pitch serial-order STM in amusia, suggesting a causal involvement of this region for this ability (Schaal et al., 2015). These findings, combined with our observation of a serial-order STM impairment in DYS+A children, calls for an investigation of the neural correlate of the comorbidity between dyslexia and amusia, with the hypothesis that it might be related to the presence of dysfunctional networks in the right intraparietal sulcus or in the right dorsolateral prefrontal regions.

## 12 Variability in Individual Profiles

Although our data converge towards a role of auditory serial-order STM in explaining the substantial comorbidity rate between dyslexia and amusia, we also observed strong variability in the expression of this impairment across dyslexic participants. In particular, as a group, the DYS-A children did not show significant impairments in any of the experimental tasks. Although average results suggest that DYS-A children slightly underperform both the CA and RL controls in serial-order STM tasks for medium word sequences, at the individual level only a minor proportion of DYS-A children (3 of 15) showed deviant performance on the auditory serial-order STM task relative to both the CA and RL controls. One might wonder why they do not show such an impairment more clearly, at least for the verbal material, whilst the severity of their reading impairments is equivalent to those of the DYS+A children.

Several hypotheses can be considered in this regard. First, it could be that the DYS-A children do have such an auditory serial-order STM impairment, but that it is masked by the fact that they are more resourceful and/or have more effective compensatory strategies. In
agreement with this hypothesis, the DYS-A group showed a slightly (although not significantly) higher nonverbal IQ and better auditory attentional skills than the DYS+A children. These differences, however, should be viewed with caution, as working memory capacity is also a strong predictor of fluid intelligence (Conway et al., 2002; Gray et al., 2017; Jaeggi et al., 2008) and has been shown to mediate the relationship between attention and intelligence scores (Cochrane et al., 2019). Thus, another potential interpretation of these group differences in nonverbal IQ and attention is that they are driven by the DYS+A children's STM impairment.

Conversely, one might think that the DYS+A children's pitch processing impairment exacerbates their phonological deficit, so that their impairments are more salient than those of DYS-A children and only these are detected by the battery. Indeed, very fine spectral and temporal differences (in particular, formants frequencies for vowels, and either voice onset time (VOT) or the frequencies of formant transitions for stop consonants) can lead to the perception of different phonemes. As Sun et al. (2017) argued, an impairment in the early stage of auditory processing may have a cascading effect on later stages, regardless of domain, and affect both musical and phonological processing. Our own data are not consistent with this hypothesis, because, overall, the reading and phonological performances of the DYS+A children were not statistically different from those of the DYS-A children despite their weaker pitch discrimination abilities. In fact, among the set of reading and phonological tasks, the DYS+A children performed slightly lower than the DYS-A in the pseudoword repetition task only, which probably reflects their auditory STM impairment.

Finally, it may be that the DYS+A and DYS-A children belong to two subtypes of dyslexia resulting from two different developmental trajectories, or at least that the reading difficulties of a significant number of children in the DYS-A group are primarily due to factors other than an auditory serial-order STM impairment. In particular, a number of children in the DYS-A group may have a reduced visual attention span, which has been suggested as an
alternative core impairment in developmental dyslexia (Bosse et al., 2007; Valdois et al., 2004).

This hypothesis seems quite unlikely, however, given the moderate prevalence of such disorder
in the dyslexic population and its limited power to explain reading difficulties beyond the
phonological deficit (Saksida et al., 2016). In this regard, it should be noted that the DYS-A
children did show a phonological deficit compared to the CA controls, as assessed by standard
phonological tests (i.e., pseudoword repetition, initial syllable/phoneme deletion, and RAN).

Poor Serial-Order STM as a Common Risk Factor for Learning Disorders?

More broadly, and despite these individual disparities, our results are consistent with
the hypothesis that auditory serial-order STM is a common risk factor for learning disorders,
rather than a causally unrelated associated impairment. Note that by “risk factor” we do not
mean that a serial-order STM impairment is a unique causal factor for all learning disorder
profiles, but rather that its presence is likely to increase the probability of developing one or
more of these disorders and to lead to comorbid phenotypes. In recent years, this hypothesis
has received increasing support, with several studies pointing to serial-order STM impairments
in dyslexia (Cowan et al., 2017; Majerus & Cowan, 2016; but see also Staels & Van den Broeck,
2014, 2015) and dyscalculia (Attout & Majerus, 2015; De Visscher et al., 2015; Morsanyi et
al., 2018) while highlighting the likely heterogeneity of these populations with respect to the
presence and severity of these impairments. Yet, only a small number of studies addressed this
issue in children (Attout & Majerus, 2015; Cowan et al., 2017; Morsanyi et al., 2018; Perez et
al., 2012; Staels & Van den Broeck, 2014, 2015) and even fewer of these included a reading-
level matched control group (but see e.g., Perez et al., 2012, for an exception), leaving the
interpretation of most group differences ambiguous. In addition, the available evidence comes
exclusively from the study of pure cases, leaving unanswered the question of the role of serial-
order STM in the development of comorbid profiles.
Here, we extend previous findings (Cowan et al., 2017; Majerus & Cowan, 2016) by showing that such an impairment can be observed in dyslexia independently of reading experience, but predominantly in cases with comorbid amusia, pointing to this impairment as a potential origin of the frequent co-occurrence of these two disorders. As exposed in the Introduction, auditory STM impairments have been extensively investigated in amusic adults over the past decade (for reviews, see: Caclin & Tillmann, 2018; Tillmann, Levêque et al., 2016). Yet, little attention has been paid to the potential distinction between item and serial-order STM processing in this population. In fact, while the gold standard battery for diagnosing amusia (Peretz et al., 2003) and its child-friendly versions (Peretz et al., 2013, 2021) involve mostly item STM (at least in the melodic subtests), subsequent paradigms used to characterize the auditory STM impairment of amusic individuals were sometimes item-based (Albouy et al., 2015, 2016, 2019b; Albouy, Mattout, et al., 2013; Foxton, 2004) and sometimes serial order-based (Albouy, Schulze, et al., 2013; Gosselin et al., 2009; Marin et al., 2012; Schaal et al., 2015; Tillmann et al., 2009; Williamson & Stewart, 2010), with no clear rationale for choosing one or the other memory process (note however that item-based and serial order-based STM tasks lead to rather similar performance in non-amusic adults, Talamini et al., 2022). Taken together, these studies point to both item and serial-order auditory STM impairments in congenital amusia, but the fact that these two aspects have never been studied comparatively and only in adults leaves several questions open. Do the two types of impairments co-exist with equivalent prevalence? Does one causes/exacerbates the other? How do these two processes interact during development?

Our study is one of the few to investigate the cognitive characteristics of congenital amusia in children (Couvignou & Kolinsky, 2021; Lebrun et al., 2012; Mignault Goulet et al., 2012) and the first to suggest that the dissociation between item and serial-order STM processes might be relevant to the aetiology of this disorder. However, because the amusic children we
tested had comorbid dyslexia, it is difficult to draw specific conclusions. It would be worthwhile to investigate this issue in pure cases of amusia, using tasks that allow for a systematic comparison of item and serial-order STM processes such as those we have developed here. The investigation of potential specific brain networks involved, as has been done in dyslexia for verbal and visual material (Martinez Perez et al., 2015), may shed further light on the status of item and serial order STM in amusia.

Implications for Theoretical Models of STM

Beyond considerations related to the aetiology of learning disorders, our results further support that the distinction between item-based STM processes and serial-order STM processes is relevant in several auditory domains. Gorin et al. (2016) provided direct evidence for this hypothesis in healthy adults, by comparing the differential effects of time-based interfering tasks on item and serial-order processing in verbal and musical STM. Here, we show that the item/order dissociation might be already relevant in both language and music at an earlier stage of development, as impaired serial-order STM appears to alter the processing of both domains in children. As reviewed by Ordonez-Magro et al. (2020) in the verbal domain, such distinction is critical to understanding the relationships between STM and reading acquisition insofar as item and serial order information interact with linguistic representations in different ways. Specifically, whereas recall of item information appears to be directly influenced by existing linguistic knowledge (i.e., the quality of the phonological, lexical, and semantic representations), the recall of serial order information seems to be relatively independent of it (Binamé & Poncelet, 2016; Poirier et al., 2015; Poirier & Saint-Aubin, 1995; Saint-Aubin et al., 2005). On the same basis, one might speculate that music perception relies on distinct involvement of item and order processes, with item information more strongly determined by the quality of pitch representations than serial order information. The hypothesis of impaired access to relatively intact auditory representations in dyslexia and amusia (Boets, 2014; Boets
et al., 2013; Moreau et al., 2013; Peretz et al., 2009; Ramus & Szenkovits, 2008; Tillmann, 2016; Levêque et al., 2016), combined with the observation of a stronger impairment in order STM compared to item STM in DYS+A children in our sample, may be consistent with these considerations. Overall, whereas the relevance of the item/order dissociation is relatively well documented in the verbal domain, our data further strengthens the need for musical STM models to take this distinction into account.

Another related debate that our data could help to inform is that of the domain specificity of STM processes. With respect to the auditory modality, and in particular the issue of the relationship between language and music, the body of evidence from healthy subjects, brain-injured patients, and subjects with congenital amusia suggests a partial dichotomy of verbal and musical STM processes, which tend to be affected together but not in a systematic way (Caclin & Tillmann, 2018). Recent data point to similar developmental trajectories between these two processes during childhood (Ginzburg et al., 2022). In the present study, the impaired serial-order STM of DYS+A children was expressed independently of material (i.e., for words, pitches, and timbre), as revealed by the absence of interaction with this variable. This may support the argument that serial-order STM is governed by common processes in the verbal and musical domains, in line with previous studies that have shown similar hallmarks of serial-order effects in verbal and musical STM (Gorin, 2021; Gorin et al., 2018; see also Williamson et al., 2010). One proposal is that music and language serial-order processing possibly rely on common sequential processes. Indeed, a number of theoretical models of serial-order STM suggest that serial order information is encoded using time-based processes (Brown et al., 2000; Burgess & Hitch, 1999, 2006). More generally, it would be worthwhile to test whether the processes engaged in auditory modality can cover other sensory modalities, such as vision. This proposition has received some support (Bigelow & Poremba, 2012; Pillai & Yathiraj, 2017; Visscher et al., 2007) but deserves to be further investigated, especially in children.
Our results hold potential implications for clinical practice. First, the dissociation between item and order STM processes, observed in our sample as well as in a growing number of studies (e.g., Attout et al., 2019; Cowan et al., 2017; Majerus & Cowan, 2016), should prompt practitioners to assess these two abilities separately in children with learning disorders. Accordingly, while the use of a standard digit span task may be useful in providing insight into the general functioning of working memory, it does not accurately characterize the impairments at play in case of failure. Our data suggest that additional measures of item and order STM would provide a more specific picture of the child's difficulty profile, and thus allow for more targeted and effective care.

Furthermore, our results may be useful for the construction of early detection batteries for children at risk for learning disorders. Given the negative impact of these disorders on schooling and daily life (e.g., Aro et al., 2019; Livingston et al., 2018), early detection of children likely to develop such difficulties constitutes a major public health issue. Specifically, our data encourage the inclusion in these batteries of tasks assessing serial-order STM, which, as discussed above, appears to be a common risk factor for several learning disorders. They further suggest the interest of extending this type of task to several materials (not only to the verbal domain, but also to the musical domain) for a better detection of children at risk of comorbidity. One advantage of the tasks we have developed here is that they are not only easily understandable and potentially administrable before reading acquisition, but also highly comparable across materials and conditions, allowing for an accurate profile of children's strengths and weaknesses. The paradigm adopted here (same/different judgment tasks) also allows to bypass production, which is problematic in the musical domain.

The next step would be to design intervention programs to address the learning difficulties of these children, potentially including exercises focused on training serial-order
1 STM. However, longitudinal and training studies are first needed to properly test the causality
2 hypothesis. Several longitudinal studies suggest an involvement of verbal STM in reading
3 acquisition (Bogaerts et al., 2016; Martinez Perez et al., 2012; Ordonez Magro et al., 2020) and
4 in numerical development (Attout et al., 2014) but, to our knowledge, none has directly
5 investigated the potential benefits of serial memory training on these skills. In the musical
6 domain, an attractive proposal could be to offer training programs centered around rhythmic
7 perception and production, which solicit sequential processing and would thus potentially train
8 serial-order STM. Several theoretical models support such far transfer effects between rhythm
9 and speech (e.g., Fiveash et al., 2021; Goswami, 2011; Tierney & Kraus, 2014), or more
10 generally, between music and speech (Besson et al., 2011; Moreno & Bidelman, 2014; Patel,
11 2011, 2014), and some studies have suggested potential benefits of music practice on various
12 phonological abilities in dyslexia, including phonological sensitivity and awareness, categorical
13 perception, and pre-attentive perception of VOT (Flaugnacco et al., 2015; Frey et al., 2019;
14 Habib et al., 2016; Zuk et al., 2018). Yet, the experimental evidence for a causal effect of music
15 training on reading skills remains debatable, with the latest meta-analyses showing weak to
16 moderate effects (Bigand & Tillmann, 2022; Gordon et al., 2015). We suggest that future
17 training studies in this field would benefit from incorporating more sequencing-focused
18 exercises into the proposed remediation program, which is often very general and does not
19 allow for specific conclusions to be drawn about the cause of any observed improvement.

## Potential Limitations

20 Our study presents several shortcomings, potentially limiting some of the conclusions
21 that can be drawn from our data set. First, as the sample size might be considered as relatively
22 small compared to the number of tests and comparisons performed, generalization of our results
23 to the dyslexic population requires replication in larger cohorts. Second, we did not constitute
24 a group of children with pure amusia, which is difficult as they are not detected by the school
25
system and hence are hard to identify. The absence of this group constrains us to conjecture
about congenitalamusia from the DYS+A cases, which amounts to conceptualizing
comorbidity as the simple addition of the two disorders without considering their probable
interaction. Yet, comorbid individuals often differ in important ways from those with an
isolated disorder, including greater symptom severity, more extensive and severe functional
impairment, and poorer long-term outcomes (Willcutt et al., 2019). Future studies wishing to
draw specific conclusions about the absence/presence of any of the disorders should benefit
from the comparison of the three diagnostic categories (children with pure dyslexia, pure
amusia, or presenting the comorbidity), although without neglecting the role of continuous
measures of traits (e.g., *d'* performance) in informing the effect of the degree of severity of the
impairment on the development of these different cognitive profiles.

Third, it would have been desirable for the different groups to be matched on any social
or cognitive characteristic (other than those inherent to dyslexia and amusia) that might
influence their ability to perform the tasks. For example, we did not have precise information
on the nature and duration of speech therapy received by the dyslexic participants, although it
would have been relevant to match the DYS+A and DYS-A groups on these variables to avoid
potential confounding influences. In a future study, these data should be collected and related
to participants' performance or to the severity of their STM impairment. As discussed above,
DYS+A children had slightly lower (though not significantly) non-verbal IQ than the other
groups. Their pitch discrimination skills were also lower than those of the other children (Table
2), which is consistent with the characteristics of impaired pitch processing in congenital
amusia (Hyde & Peretz, 2004; Peretz et al., 2002). These differences may have influenced the
performance pattern observed in the experimental tests, particularly for the pitch STM tasks
(Jiang et al., 2013). We tried to control for this possibility by removing the trials involving
musical intervals below the pitch discrimination threshold of each participant (which did not
change the pattern of results), but we cannot completely rule it out. It should be noted, however, that the serial-order STM impairment of the DYS+A children was observed independently of material and therefore our main conclusion remains valid despite this limitation.

Several other weaknesses related to the construction of our experimental battery can be discussed, as well as its validity for measuring some of the cognitive functions studied. Notably, in the STM task, the item and order conditions were not perfectly matched in terms of difficulty for the pitch material, as the item condition involved larger interval changes than the order condition (Supplementary Material S1). These mismatches may have influenced our results for the pitch material, but do not alter the overall conclusion of the study relative to the serial-order STM of the DYS+A children, which was observed independently of material. Likewise, the verbal counterpart of the perceptual awareness task (syllable and phoneme perceptual awareness) did not correlate with reading measure, which is in contradiction with a large body of literature linking phonological awareness and reading performance (Swanson et al., 2003), and suggests that we might not have fully measured the intended skill. This is in line with the result showing that the DYS-A children did not present a clear impairment with phonemes in this task, even though phoneme awareness is considered one of the most consistent features of dyslexia. A notable difference between our experimental task and classical syllable/phoneme deletion tasks that have consistently shown deficits in dyslexia is that our task requires a simple identification of the correct answer without oral production. This choice was made to avoid singing production in the musical version of the task, because singing abilities are often impaired in children with comorbid dyslexia and amusia (Couvignou & Kolinsky, 2021) and difficult to apply to timbres, which we used as a control material. A consequence of this design, however, is that our task may have required less effort to access phonological information than classical deletion tasks. Specifically, it may be that such access is more accurately estimated in a “remember” rather than in a “know” paradigm, which requires the recall of items instead of
1

their recognition. Thus, the absence of group differences is not sufficient to rule out a role for
perceptual awareness in the comorbidity between dyslexia and amusia.

2

3

Accordingly, it would be worth investigating further the issue of conscious access to
auditory representations, including at the neurophysiological level, looking at the early and late
components of auditory brain evoked potentials for both speech and music. In particular, if a
delayed conscious access to fine auditory changes underlies comorbidity between the two
disorders (Moreau et al., 2013; Neuhoff et al., 2012), the P3b component (associated with the
conscious discrimination of targets in a sequence of repeated distractors; van Dinteren et al.,
2014) but not the MMN (which reflects unattentive processing to changes in a continuous
stream of identical sounds; Näätänen et al., 2007) should be impaired for both materials in
comorbid individuals. Alternatively, if unattentive processing was affected, the MMN should
also be affected. Although our experimental measures did not show any behavioral impairment
in the DYS-A children, this type of neurophysiological investigation could help reveal a more
subtle impairment in these individuals.

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Finally, the conclusions that can be drawn from the current study are limited to the
cognitive functions we have investigated. For feasibility concerns (the experimental battery
being already demanding to administer to young children), we focused on the target domains
of the two disorders (phonemes and pitch). However, it is quite possible that other dimensions
play a role in the increased comorbidity. In particular, the role of the time dimension of music
would be worth exploring (Fiveash et al., 2021). Impaired temporal processing has been
reported in both dyslexia (e.g., Casini et al., 2018; Farmer & Klein, 1995; Goswami, 2011) and
tone deafness amusia (Lagrois & Peretz, 2019), and a sizeable proportion of individuals with
the comorbidity demonstrate difficulties in the *Rhythm* subtest of the MBEA/MBEMA,
although difficulties with pitch processing prevail (Couvignou et al., 2019; Couvignou &
1

Kolinsky, 2021<sup>7</sup>). More generally, self-reported developmental disorders appear to be

2

preferentially associated with time-based rather than pitch-based musical impairments (Peretz & Vuvan, 2017), and recent theoretical reviews have proposed rhythm difficulties as a common

3

risk factor for developmental disorders, including developmental speech and language

4

5

disorders (Ladányi et al., 2020; Lense et al., 2021). Temporal processing as in rhythm
processing or even beat and meter, requires sequential capabilities. The auditory serial-order

7

STM impairment revealed by the present study is likely based on such processes as well.

8

Together, these considerations call for further exploration of rhythm processing in future studies
aimed at unraveling the links between dyslexia and amusia.

9

10

**Concluding Remarks**

11

Overall, our results point to auditory serial-order STM as a plausible candidate to
explain the shared variance and comorbidity between reading and music disorders. Despite its
limitations, our study sheds new light on the currently underexplored relationship between
dyslexia and amusia, and also on understanding the broader issue of comorbidities between
learning disabilities. In addition, it contributes to a better theoretical understanding of auditory
STM. Further research (in particular, longitudinal and training studies) will be needed to assert
the potential causal role of this function in the aetiology of developmental disorders.

12

13

14

15

16

17

18

Acknowledgements

19

MC is supported by a PhD Grant from The Belgian Kids' Fund for Pediatric Research ("Bourse en mémoire du Professeur André Kahn"), by the David and Alice Van Buuren Fund, and by the Jaumotte-Demoulin Foundation and was supported by the ULB Neuroscience Institute (UNI).

20

21

22

RK is Research Director of the Fonds de la Recherche Scientifique-FNRS (FRS-FNRS),
Belgium. BT and AC are supported by a grant from the Auvergne-Rhône-Alpes Region

23

<footnote n="7"><sup>7</sup> See also data from the present study, available under OSF: 10 of 15 DYS+A children performed below -2 SD on this subtest.</footnote>
1

(COGAUDYS project). This work was conducted in the framework of the LabEx CeLyA

2

("Centre Lyonnais d'Acoustique", ANR-10-LABX-0060) of Université de Lyon, within the

3

program "Investissements d'avenir" (ANR-11-IDEX-0007) operated by the French National

4

Research Agency (ANR). The teams CAP (Barbara Tillmann) and PAM (Anne Caclin) of the

5

Lyon Neuroscience Research Center are part of the GIS "Autisme et Troubles du Neuro-

6

Développement" research network. We thank all the children, schools and families that

7

collaborated in this study and thank Sevana Boyadjian, Augustin Dumont, Louise Vizier, and

8

Justine Wéry for their help in data collection. We thank Katrin Schulze for providing the

9

auditory stimuli that were used in the experimental tasks. We also want to thank Franck Ramus

10

for helpful discussions and Hichem Slama for his feedback on the auditory attention tasks.

11

**Disclosure statement**

12

The authors report no conflict of interest.

13

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16
Tables with caption

<caption>**Table 1**</caption>

*Demographic and Cognitive Characteristics of Participants as a Function of Group*

<table><thead><tr><th rowspan="2"></th><th colspan="4">Groups</th><th colspan="6">Between-groups comparisons</th></tr><tr><th>DYS+A<br>n = 15</th><th>DYS-A<br>n = 15</th><th>CA<br>n = 25</th><th>RL<br>n = 25</th><th>DYS+A<br>vs. DYS-A</th><th>DYS+A<br>vs. CA</th><th>DYS+A<br>vs. RL</th><th>DYS-A<br>vs. CA</th><th>DYS-A<br>vs. RL</th><th>CA<br>vs. RL</th></tr></thead><tbody><tr><td>Age (years)</td><td>10.6<br>(1.7)</td><td>10.4<br>(1.6)</td><td>10.7<br>(1.6)</td><td>8.3<br>(1.5)</td><td>0.18</td><td>-0.06</td><td>1.56***</td><td>-0.24</td><td>1.39***</td><td>1.64***</td></tr><tr><td>Sex<sup>a</sup></td><td>8 F / 7 M</td><td>8 F / 7 M</td><td>14 F / 11 M</td><td>14 F / 11 M</td><td>.00</td><td>.03</td><td>.03</td><td>.03</td><td>.03</td><td>.00</td></tr><tr><td>Grade<sup>b</sup></td><td>4.7<br>(1.7)</td><td>4.7<br>(1.5)</td><td>5.0<br>(1.7)</td><td>2.4<br>(1.5)</td><td>-0.04</td><td>-0.17</td><td>1.39***</td><td>-0.14</td><td>1.52***</td><td>1.56***</td></tr><tr><td>Music education<br>(years)</td><td>0.7<br>(1.0)</td><td>0.6<br>(1.3)</td><td>0.7<br>(1.2)</td><td>0.6<br>(1.3)</td><td>0.01</td><td>-0.03</td><td>0.03</td><td>-0.04</td><td>0.01</td><td>0.05</td></tr><tr><td>Parents' SES<sup>c</sup></td><td>65.3<br>(13.4)</td><td>69.9<br>(13.0)</td><td>73.6<br>(13.0)</td><td>66.8<br>(13.6)</td><td>-0.35</td><td>-0.63</td><td>-0.11</td><td>-0.28</td><td>0.23</td><td>0.51</td></tr><tr><td>Nonverbal IQ<sup>d</sup></td><td>94.2<br>(10.3)</td><td>101.7<br>(15.1)</td><td>100.7<br>(12.8)</td><td>97.2<br>(12.9)</td><td>-0.58</td><td>-0.55</td><td>-0.25</td><td>0.07</td><td>0.32</td><td>0.28</td></tr><tr><td>Reading<br>MIM score (/72)<sup>e</sup></td><td>49.3<br>(11.0)</td><td>49.5<br>(16.7)</td><td>64.9<br>(3.5)</td><td>50.8<br>(15.3)</td><td>-0.01</td><td>-2.15***</td><td>-0.11</td><td>-1.46***</td><td>-0.08</td><td>1.27***</td></tr><tr><td>MIM time (s)</td><td>159.5<br>(89.3)</td><td>203.2<br>(168.5)</td><td>62.1<br>(11.8)</td><td>220.9<br>(196.3)</td><td>-0.32</td><td>1.77***</td><td>-0.37</td><td>1.37***</td><td>-0.10</td><td>-1.14***</td></tr><tr><td>Phonology<br>Pseudoword<br>repetition (/40)</td><td>24.1<br>(3.0)</td><td>26.7<br>(2.7)</td><td>29.5<br>(2.9)</td><td></td><td>-0.90*</td><td>-1.82***</td><td></td><td>-1.00**</td><td></td><td></td></tr><tr><td>Initial S/P<br>deletion (/42)</td><td>36.7<br>(3.8)</td><td>38.4<br>(3.8)</td><td>41.6<br>(0.7)</td><td></td><td>-0.46</td><td>-2.08***</td><td></td><td>-1.34***</td><td></td><td></td></tr><tr><td>RAN (s)<sup>f</sup></td><td>126.7<br>(23.7)</td><td>116.2<br>(27.3)</td><td>92.2<br>(19.1)</td><td></td><td>0.41</td><td>1.65***</td><td></td><td>1.07**</td><td></td><td></td></tr><tr><td>MBEMA (/60)<sup>g</sup></td><td>40.1</td><td>53.3</td><td>52.8</td><td>48.6</td><td>-2.56***</td><td>-2.98***</td><td>-1.66***</td><td>0.01</td><td>1.08**</td><td>1.14***</td></tr></tbody></table>
(6.0)

(4.0)

(2.8)

(4.5)

*Note.* Group means are shown (standard deviations in parentheses). The last six columns present the results of group comparisons ($\chi^2$ tests for sex ratio, *t*-tests showing Cohen's *d* for all other variables). DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls.

<sup>a</sup> Sex ratio (F: Female, M: Male). <sup>b</sup> Mean grade was calculated using the following scale: 1<sup>st</sup> G (G: Grade) = 1, 2<sup>nd</sup> G = 2, 3<sup>rd</sup> G = 3, 4<sup>th</sup> G = 4, 5<sup>th</sup> G = 5, 6<sup>th</sup> Grade = 6, 7<sup>th</sup> G = 7, 8<sup>th</sup> G = 8. <sup>c</sup> Parents' socio-economic status (SES) was estimated by averaging their Index for Individual Socioeconomic Level (Genoud, 2011), calculated as follows: age – 6 x level of school completed – 4 x employment category + 55. An index of 55-67 corresponds to the middle class. An index of 68-80 corresponds to the upper middle class. <sup>d</sup> Nonverbal IQ is expressed as standardized score. <sup>e</sup> MIM = *Mécanisme d'Identification des Mots* subtest from the *Batterie d'Évaluation du Langage Écrit* (BELEC, Mousty et al., 1994). S/P = Syllable/Phoneme. <sup>f</sup> RAN = Rapid Automatized Naming. <sup>g</sup> MBEMA = *Montreal Battery of Evaluation of Musical Abilities* (Peretz et al., 2013).

* p < .05. ** p < .01. *** p < .001.
# SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

<table><caption>## Table 2</caption><thead><tr><th rowspan="2"></th><th colspan="4">Groups</th><th colspan="6">Between-groups comparisons</th></tr><tr><th>DYS+A</th><th>DYS-A</th><th>CA</th><th>RL</th><th>DYS+A<br>vs. DYS-A</th><th>DYS+A<br>vs. CA</th><th>DYS+A<br>vs. RL</th><th>DYS-A<br>vs. CA</th><th>DYS-A<br>vs. RL</th><th>CA<br>vs. RL</th></tr></thead><tbody><tr><td>Word (/6)</td><td>5.6<br>(0.6)</td><td>5.9<br>(0.4)</td><td>5.7<br>(0.5)</td><td>5.4<br>(0.8)</td><td>-0.21</td><td>-0.10</td><td>0.08</td><td>0.11</td><td>0.28</td><td>0.17</td></tr><tr><td>Pitch (/6)</td><td>4.2<br>(1.2)</td><td>5.1<br>(1.1)</td><td>5.2<br>(1.1)</td><td>4.8<br>(1.1)</td><td>-0.44*</td><td>-0.48**</td><td>-0.31</td><td>-0.02</td><td>0.16</td><td>0.20</td></tr><tr><td>Timbre (/6)</td><td>5.9<br>(0.3)</td><td>5.9<br>(0.4)</td><td>5.8<br>(0.5)</td><td>5.6<br>(0.6)</td><td>0.07</td><td>0.10</td><td>0.22</td><td>0.03</td><td>0.16</td><td>0.12</td></tr></tbody></table>

*Note.* Group means are shown (standard deviations in parentheses). The last six columns present the results of group comparisons (Mann-Whitney U tests showing Rank-Biserial correlation). DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls.

<footnote>\* *p* < .05. \*\* *p* < .01. \*\*\* *p* < .001.</footnote>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

<caption>**Table 3**</caption>

*Summary of the Significant Effects and Interactions Involving the Group Factor in the Main ANOVAs and Corresponding Post-hoc Tests Conducted on the d' Sensitivity Index for Each Task of the Experimental Battery*

<table><thead><tr><th>Task</th><th>Significant effects of or interactions with group</th><th>Group differences on</th><th>Post-hoc tests</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td rowspan="3">Material x Group</td><td>Word</td><td>DYS+A &lt; CA<br>RL &lt; CA</td></tr><tr><td>Pitch</td><td>DYS+A &lt; DYS-A<br>DYS+A &lt; CA<br>RL &lt; CA</td></tr><tr><td>Timbre</td><td>n.s.</td></tr><tr><td rowspan="3">Condition x Length x Group<sup>a</sup></td><td>Item</td><td>DYS+A &lt; CA<br>RL &lt; CA</td></tr><tr><td>Order length 3</td><td>DYS+A &lt; DYS-A<br><b>DYS+A &lt; CA</b><br><b>DYS+A &lt; RL</b></td></tr><tr><td>Order length 4</td><td><b>DYS+A &lt; CA</b><br><b>DYS+A &lt; RL</b></td></tr><tr><td rowspan="3">Auditory perceptual awareness</td><td rowspan="3">Condition x Material x Group<sup>b</sup></td><td>Item</td><td>n.s.</td></tr><tr><td>Syllable</td><td>DYS+A &lt; CA<br>RL &lt; CA</td></tr><tr><td>Phoneme</td><td>DYS+A &lt; CA</td></tr><tr><td rowspan="4">Auditory attention</td><td rowspan="4">Group</td><td>Interval</td><td>DYS+A &lt; DYS-A<br>DYS+A &lt; CA<br>RL &lt; CA</td></tr><tr><td>Note</td><td>DYS+A &lt; CA</td></tr><tr><td>Timbre</td><td>DYS+A &lt; DYS-A<br>DYS+A &lt; CA</td></tr><tr><td></td><td>DYS+A &lt; DYS-A<br>DYS+A &lt; CA<br>DYS-A &gt; RL<br>RL &lt; CA</td></tr></tbody></table>

*Note.* DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls. In bold: expected pattern if there was a causal underlying impairment. n.s. = no significant group difference.

<footnote><sup>a</sup> The Condition x Length x Group interaction is not decomposed by length for item condition, because the Length x Group interaction was not significant in this condition. <sup>b</sup> The Condition x</footnote>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

Material x Group interaction is not decomposed by condition, because the Condition x Group
interaction was not significant for any of the materials.
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

<caption>**Table 4**</caption>

*Number of Individuals Performing Below the Threshold of -1.65 Standard Deviation Relative to both CA and RL Controls, for Each Composite Variable and Group*

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th colspan="4">Groups</th><th colspan="6">χ<sup>2</sup></th></tr><tr><th>DYS+A<br>n = 15</th><th>DYS-A<br>n = 15</th><th>CA<br>n = 25</th><th>RL<br>n = 24<br>or 25<sup>a</sup></th><th>DYS+A<br>vs. DYS-A</th><th>DYS+A<br>vs. CA</th><th>DYS+A<br>vs. RL</th><th>DYS-A<br>vs. CA</th><th>DYS-A<br>vs. RL</th><th>CA<br>vs. RL</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term<br>memory</td><td>Word</td><td>3</td><td>1</td><td>2</td><td>1</td><td>0.29</td><td>0.38</td><td>1.09</td><td>0.22</td><td>0.16</td><td>0.00</td></tr><tr><td>Pitch</td><td>4</td><td>1</td><td>0</td><td>2</td><td>0.96</td><td><strong>4.74*</strong></td><td>1.18</td><td>0.07</td><td>0.18</td><td>0.52</td></tr><tr><td>Item</td><td>2</td><td>0</td><td>1</td><td>1</td><td>0.54</td><td>0.23</td><td>0.18</td><td>0.07</td><td>0.06</td><td>0.00</td></tr><tr><td>Order length 3</td><td>11</td><td>1</td><td>1</td><td>4</td><td><strong>13.89***</strong></td><td><strong>18.29***</strong></td><td><strong>12.52***</strong></td><td>0.14</td><td>0.17</td><td>0.89</td></tr><tr><td>Order length 4</td><td>7</td><td>2</td><td>2</td><td>1</td><td>2.54</td><td><strong>5.98*</strong></td><td><strong>7.79**</strong></td><td>0.00</td><td>0.18</td><td>0.00</td></tr><tr><td rowspan="5">Auditory perceptual<br>awareness</td><td>Syllable</td><td>3</td><td>1</td><td>0</td><td>2</td><td>0.59</td><td>2.91</td><td>0.32</td><td>0.07</td><td>0.18</td><td>0.52</td></tr><tr><td>Phoneme</td><td>0</td><td>0</td><td>0</td><td>1</td><td>0.00</td><td>0.03</td><td>0.08</td><td>0.00</td><td>0.06</td><td>0.00</td></tr><tr><td>Interval</td><td>0</td><td>0</td><td>0</td><td>2</td><td>0.00</td><td>0.03</td><td>0.16</td><td>0.00</td><td>0.16</td><td>0.52</td></tr><tr><td>Note</td><td>3</td><td>0</td><td>1</td><td>2</td><td>1.48</td><td>1.19</td><td>0.32</td><td>0.07</td><td>0.25</td><td>0.00</td></tr><tr><td>Timbre</td><td>3</td><td>0</td><td>0</td><td>5</td><td>3.33</td><td>2.91</td><td>0.73</td><td>0.00</td><td>0.16</td><td>3.57</td></tr><tr><td>Auditory attention</td><td>Global</td><td>3</td><td>0</td><td>0</td><td>4</td><td>3.33</td><td>2.91</td><td>0.01</td><td>0.00</td><td>0.28</td><td>2.45</td></tr></tbody></table>

*Note.* DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls. Yates' correction was applied if any frequency was less than 1, or if at least 20% of frequencies were less than 5. In bold: significant between-group differences.

<sup>a</sup> The performance of the two RL controls who probably did not understand some of the tasks was removed from the relevant analysis (i.e., *n* = 24 RL in the auditory short-term memory task; *n* = 24 RL in the auditory perceptual awareness tasks; *n* = 25 RL in the auditory attention task).

* *p* < .05. ** *p* < .01. *** *p* < .001
# SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

<caption>## Table 5</caption>

*Individual Performance Profiles of Dyslexic Children With and Without Amusia for each Composite Variable*

(a)

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th colspan="15">DYS+A<sup>a</sup></th></tr><tr><th>S038</th><th>S040</th><th>S054</th><th>S055</th><th>S075</th><th>S077</th><th>S079</th><th>S081</th><th>S083<sup>c</sup></th><th>S090</th><th>S095</th><th>S096</th><th>S110<sup>c</sup></th><th>S119</th><th>S130</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td>Word</td><td>✓</td><td>X</td><td>~</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>X</td><td>✓</td><td>✓</td></tr><tr><td>Pitch</td><td>~</td><td>~</td><td>✓</td><td>X</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>X</td><td>X</td><td>X</td><td>✓</td></tr><tr><td>Item</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>✓</td><td>~</td><td>X</td><td>X</td><td>~</td><td>✓</td></tr><tr><td>Order length 3</td><td>✓</td><td>X</td><td>✓</td><td>X</td><td>X</td><td>X</td><td>✓</td><td>X</td><td>X</td><td>X</td><td>X</td><td>X</td><td>X</td><td>X</td><td>✓</td></tr><tr><td>Order length 4</td><td>X</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>X</td><td>X</td><td>✓</td><td>✓</td><td>X</td><td>X</td><td>X</td><td>✓</td></tr><tr><td rowspan="5">Auditory perceptual awareness</td><td>Syllable</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>✓</td><td>X</td><td>X</td><td>✓</td><td>~</td><td>X</td><td>✓</td><td>✓</td></tr><tr><td>Phoneme</td><td>~</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>~</td><td>✓</td><td>✓</td></tr><tr><td>Interval</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>✓</td><td>~</td></tr><tr><td>Note</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>X</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td></tr><tr><td>Timbre</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>X</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>~</td><td>X</td><td>X</td><td>✓</td></tr><tr><td>Auditory attention</td><td>Global</td><td>✓</td><td>~</td><td>✓</td><td>~</td><td>X</td><td>~</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>X</td><td>X</td><td>~</td><td>~</td></tr></tbody></table>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

(b)

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th colspan="15">DYS-A<sup>b</sup></th></tr><tr><th>S039</th><th>S047</th><th>S048</th><th>S052</th><th>S053</th><th>S060</th><th>S070</th><th>S076</th><th>S078</th><th>S080</th><th>S109</th><th>S132</th><th>S134</th><th>S136</th><th>S137</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td>Word</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>X</td></tr><tr><td>Pitch</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>~</td></tr><tr><td>Item</td><td>~</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>~</td></tr><tr><td>Order length 3</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td></tr><tr><td>Order length 4</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>X</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td></tr><tr><td rowspan="5">Auditory perceptual awareness</td><td>Syllable</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>X</td><td></td></tr><tr><td>Phoneme</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>X</td></tr><tr><td>Interval</td><td>✓</td><td>~</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td></tr><tr><td>Note</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td></tr><tr><td>Timbre</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>~</td></tr><tr><td>Auditory attention</td><td>Global</td><td>✓</td><td>✓</td><td>~</td><td>~</td><td>✓</td><td>~</td><td>~</td><td>~</td><td>~</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td>✓</td><td></td></tr></tbody></table>

*Note.* Individual performance profiles are shown (a) for DYS+A children, and (b) for DYS-A children. X: score below the threshold of -1.65 SD relative to both CA and RL controls, considered deviant. ~: score below -1.65 SD relative to CA controls only. ✓: score above -1.65 SD relative to both CA and RL controls. DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls.

<sup>a</sup> Among the DYS+A children, S054 and S130 did not show any deviant score, S038, S077, and S079 showed a specific impairment for one variable, and all others showed deviant scores for multiple variables. <sup>b</sup> Among the DYS-A children, S048 and S109 showed a specific impairment for one variable, S060 and S137 showed deviant scores for multiple variables and all others did not show any deviant score. <sup>c</sup> S083 and S110 presented the triple comorbidity dyslexia, amusia, and ADD. As can be seen, S083 performance profile is not fundamentally different from those of his DYS+A
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

peers without ADD. S110 shows the most numerous and severe impairments, but his profile is comparable to S096, who nevertheless has no additional ADD diagnosis. We therefore included S083 and S110 in the analyses despite their additional diagnosis of ADD, thereby maximizing the sample size.
Figures

<figure><img src="image_2.png" /><figcaption>Figure 1</figcaption></figure>

Note. (A) Short-term memory test (same/different judgment, here illustrated for length 3, with 3 items per sequence), (B) perceptual awareness test (correct/incorrect judgment), (C) attention test (go/no-go). The examples can be heard in Supplementary Material S7.
<figure><img src="image_3.png" /><figcaption>Figure 2</figcaption></figure>

*Note.* (A) Short-term memory test, (B) syllable, interval, and timbre perceptual awareness tests, (C) phoneme and note perceptual awareness tests, (D) attention test. In tasks A-C, the children had to wait until the end of the stimuli presentation (illustrated on the screen by headphones) to give their answer, response choices being then illustrated on the screen. In task D, the target was first presented in isolation and then the test began after a visual countdown.
<figure><img src="image_4.png" /><figcaption>Figure 3</figcaption></figure>

*Note.* Average *d'* values are shown. Error bars represent standard errors. DYS+A: dyslexic children with amusia, DYS-A: dyslexic children without amusia, CA: chronological-age matched controls, RL: reading-level matched controls.
<figure><img src="image_5.png" /><figcaption>Figure 4</figcaption></figure>

*Note.* Average *d'* values are shown. Error bars represent standard errors. DYS+A: dyslexic children withamusia, DYS-A: dyslexic children withoutamusia, CA: chronological-age matched controls, RL: reading-level matched controls.
<figure><img src="image_6.png" /><figcaption>Figure 5</figcaption></figure>

*Note.* Average *d'* values are shown. Error bars represent standard errors. DYS+A: dyslexic children withamusia, DYS-A: dyslexic children withoutamusia, CA: chronological-age matched controls, RL: reading-level matched controls.
**Figure captions**

**Figure 1**

*Schematic Illustration of the Materials and Tasks*

**Figure 2**

*Schematic Illustration of the Trials*

**Figure 3**

*Performance in the Auditory Short-term Memory Task as a Function of Group, Condition (Item, Order), Material, and Sequence Length (3, 4, or 5 Items per Sequence)*

**Figure 4**

*Performance in the Auditory Perceptual Awareness Task as a Function of Group, Condition (Item, Order), and Material*

**Figure 5**

*Performance in the Auditory Attention Task as a Function of Group and Level of Difficulty (Target to be Identified Among 1 vs. 3 Types of Distractors)*
**Supplementary Material S1**

**Control ANOVA on the Material used in the Auditory Short-term Memory Task**

In order to test whether changes in pitch were comparable between conditions and sequence length, two 2 (Condition: item, order) x 3 (Sequence length, henceforth Length: 3, 4, or 5 items per sequence), ANOVAs were conducted on the mean size of the interval change (in cents) and the mean number of contour changes, respectively. For the size of the interval change, the ANOVA revealed significant main effects of condition, $F(1, 66) = 16.96, p < .001$, $\eta^2_p = .204$, and length, $F(2, 66) = 5.11, p = .009$, $\eta^2_p = .134$, but no significant interaction ($F < 1$). Regarding the main effect of condition, post-hoc comparisons using Bonferroni correction indicated that the mean size of the interval change was significantly larger in the item condition ($M = 616.7$ cents, $SD = 220.2$) than in the order condition ($M = 419.4, SD = 220.2$), $t(70) = 4.12, p < .001$, $d = 0.92$, 95% CI [101.6, 292.8]. Regarding the main effect of length, post-hoc comparisons using Bonferroni correction indicated that the mean size of the interval change was significantly larger for length 3 ($M = 612.5, SD = 223.2$) than for length 4 ($M = 425.0, SD = 206.9$), $t(46) = 3.2, p = .006$, $d = 0.87$, 95% CI [46.9, 328.1], but not significantly different from that for length 5 ($M = 516.7, SD = 242.6$), $t(46) = 1.63, p = .321$, the latter being also not significantly different from that for length 4, $t(46) = -1.56, p = .369$. For the number of contour changes, the ANOVA revealed a significant main effect of length, $F(2, 66) = 3.32, p = .042$, $\eta^2_p = .091$, but no other significant main effect or interaction (all $Fs < 1$ except for condition: $F(1, 66) = 1.78, p = .186$). Post-hoc comparisons using Bonferroni correction indicated that the mean number of contour changes for length 3 ($M = 1.5, SD = 0.5$) was not significantly different from that for length 4 and 5 (respectively: $M = 1.2, SD = 0.5, t(46) = 1.91, p = .182$; $M = 1.5, SD = 0.6, t < 1$), but that the mean number of contour changes for length 4 tended to be significantly lower than that for length 5, $t(46) = -2.45, p = .05, d = -0.70$, 95% CI [-0.7, 0.0].
## Supplementary Material S2

### Control ANOVA on the Material Used in the Auditory Perceptual Awareness Task

In order to test whether changes in pitch were comparable between conditions and interval/note materials, two 2 (Condition: item, order) x 2 (Material: interval, note) ANOVAs were conducted on the mean size of the interval change (in cents) and the mean number of contour changes, respectively. For the size of the interval change, the ANOVA revealed a significant main effect of material, $F(1, 44) = 15.97, p < .001$, $\eta_p^2 = .266$, but no other significant main effect or interaction (all *Fs* < 1). Post-hoc comparisons using Bonferroni correction indicated that the mean size of the interval change was significantly lower for the interval (*M* = 216.7, *SD* = 149.4) than for the note material (*M* = 450.0, *SD* = 237.7), *t*(46) = -4.00, *p* < .001, *d* = -1.18, 95% CI [-351.0, -115.7]. For the mean number of contour changes, however, the ANOVA revealed no significant main effect or interaction (all *Fs* < 1 except for Condition x Material, $F(1,44) = 3.43, p = .071$).
**Supplementary Material S3**

**Details of the ANOVA on *d'* for the Short-term Memory Task**

**Supplementary Material S3.1**

*Control Analysis for DYS+A Children's Lower Pitch Discrimination Skills*

To ensure that the lower pitch discrimination performance of DYS+A children (Table 2) did not influence the results, the analyses were repeated by removing, individually for each participant, trials involving pitch changes below their discrimination threshold. This threshold was estimated based on the results of the discrimination test, considering a threshold of 100 cents in case of failure on the trial involving a semitone difference, and a threshold of 200 cents in case of failure on both trials involving a one-tone difference. 2 DYS+A children, 1 DYS-A child, 2 CA controls, and 4 RL controls were considered to have a 100-cents threshold; 4 DYS+A children, 2 CA controls, and 2 RL controls were considered to have a 200-cents threshold. After removing the relevant trials (for a 100-cents threshold, 1 or 2 trials out of 216 depending on the set; for a 200-cents threshold, 5 or 6 trials out of 216 depending on the set), the pattern of results remained the same, with significant main effects of condition, *F*(1, 75) = 29.60, *p* < .001, η²_p = .237, material, *F*(2, 150) = 55.32, *p* < .001, η²_p = .424, length, *F*(2, 150) = 222.25, *p* < .001, η²_p = .748, and group, *F*(3, 75) = 8.46, *p* < .001, η²_p = .253, as well as significant interactions between condition and length, *F*(2, 150) = 7.25, *p* < .001, η²_p = .088, material and length, *F*(4, 300) = 3.90, *p* = .004, η²_p = .049, length and group, *F*(6, 150) = 2.60, *p* = .020, η²_p = .094, and material and group, *F*(6, 150) = 2.57, *p* = .021, η²_p = .093, and significant 3-way interactions between condition, material, and length, *F*(4, 300) = 3.41, *p* = .009, η²_p = .044, and between condition, length, and group, *F*(6, 150) = 4.43, *p* < .001, η²_p = .151. No other interaction was significant (all *Fs* < 1 except for Condition x Group: *F*(3,75) = 1.79, *p* = .155, and Condition x Material x Length x Group: *F*(12, 300) = 1.52, *p* = .115).
**Supplementary Material S3.2**

*Details of the Post-hoc Analyses for the Material\*Group Interaction*

Regarding the interaction between material and group, post-hoc comparisons using Bonferroni correction indicated that, for words, DYS+A children (M = 1.1, SD = 1.1) performed significantly worse than CA controls (M = 1.9, SD = 1.3), t(38) = -3.81, p = .004, d = -0.43, 95% confidence interval (CI) [0.1, 1.6], but not significantly different from both DYS-A children (M = 1.4, SD = 1.2), t(28) = -1.49, p = .273, and RL controls (M = 1.4, SD = 1.2), t(37) = -1.54, p = .273. No other group difference was significant (all ps > .191). For pitches, DYS+A children (M = 1.3, SD = 1.1) performed significantly worse than both DYS-A children (M = 2.2, SD = 1.2), t(28) = -3.67, p = .006, d = -0.41, 95% CI [-1.7, -0.1], and CA controls (M = 2.5, SD = 1.1), t(38) = -5.53, p < .001, d = -0.62, 95% CI [-2.0, -0.5], but not significantly different from RL controls (M = 1.7, SD = 1.2), t(37) = -2.07, p = .273, the latter also performing significantly worse than CA controls, t(47) = -3.94, p = .002, d = -0.44, 95% CI [-1.4, -0.1]. No other group difference was significant (all ps > .273). For timbres, no significant group-difference was observed (all ps < .273).

**Supplementary Material S3.3**

*Details of the Post-hoc Analyses for the Condition\*Material\*Length Interaction*

The 3-way interaction between condition, material, and length was further investigated by performing three separate 2 (Condition: item, order) x 3 (Length: 3, 4, or 5 items per sequence) repeated measures ANOVAs on words, pitches, and timbres, averaging across groups. For words, the ANOVA revealed main effects of condition, F(1,78) = 6.09, p = .016, η²p = .072, and length, F(2,156) = 138.13, p < .001, η²p = .639, and a significant interaction

<footnote n="1">¹ All *t*-tests reported in the present study are two-sided tests.</footnote>
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

between condition and length, *F*(2,156) = 4.80, *p* = .009, *η*²_p_ = .058. Post-hoc comparisons
using Bonferroni correction revealed that, for length 3, item performance (*M* = 2.5, *SD* = 0.9)
was not significantly different from order performance (*M* = 2.2, *SD* = 1.0), *t*(78) = 2.20, *p* =
.086. In contrast, for length 4, item performance (*M* = 1.5, *SD* = 1.1) was significantly better
than order performance (*M* = 1.1, *SD* = 1.2), *t*(78) = 3.24, *p* = .004, *d* = 0.37, 95% CI [0.0, 0.8].
For length 5, item performance (*M* = 0.8, *SD* = 1.0) was not significantly different from order
performance (*M* = 0.9, *SD* = 1.0), *t*(78) < 1. For pitches, the ANOVA revealed main effects of
condition, *F*(1,78) = 13.76, *p* < .001, *η*²_p_ = .150, and length, *F*(2,156) = 56.82, *p* < .001, *η*²_p_ =
.421, but no significant interaction between condition and length (*F* < 1). Regarding the main
effect of condition, post-hoc comparisons using Bonferroni correction indicated that item
performance (*M* = 2.1, *SD* = 1.1) was significantly better than order performance (*M* = 1.8, *SD*
= 1.3), *t*(78) = 3.71, *p* < .001, *d* = 0.42, 95% CI [0.2, 0.5]. Regarding the main effect of length,
post-hoc comparisons using Bonferroni correction indicated that performance at for length 3
(*M* = 2.5, *SD* = 1.1) was significantly better than performance for lengths 4 (*M* = 2.0, *SD* = 1.1),
*t*(78) = 4.94, *p* < .001, *d* = 0.56, 95% CI [0.3, 0.8], and 5 (*M* = 1.4, *SD* = 1.2), *t*(78) = 9.30, *p* <
.001, *d* = 1.05, 95% CI [0.8, 1.4] and that performance for length 4 was better than performance
for length 5, *t*(78) = 7.08, *p* < .001, *d* = 0.80, 95% CI [0.4, 0.8]. For timbres, the ANOVA
revealed main effects of condition, *F*(1,78) = 13.57, *p* < .001, *η*²_p_ = .166, and length, *F*(2,156)
= 50.47, *p* < .001, *η*²_p_ = .427, and a significant interaction between condition and length,
*F*(2,156) = 6.32, *p* = .002, *η*²_p_ = .075. Post-hoc comparisons using Bonferroni correction
revealed that, for length 3, item performance (*M* = 2.1, *SD* = 1.0) was significantly better than
order performance (*M* = 1.4, *SD* = 1.0), *t*(78) = 5.13, *p* < .001, *d* = 0.58, 95% CI [0.3, 1.1]. In
contrast, for length 4, item performance (*M* = 1.0, *SD* = 1.0) was not significantly different from
order performance (*M* = 0.9, *SD* = 1.2), *t*(78) < 1. For length 5, item performance (*M* = 0.7, *SD*
= 1.0) was not significantly different from order performance (*M* = 0.6, *SD* = 0.9), *t*(78) < 1.
# SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

Overall, the difference in performance between item and order conditions was length dependent for words and timbres, but not for pitches (for which item performance was better than order performance for each length).

## Supplementary Material S3.4

### *Details of the Post-hoc Analyses for the Main Effects of Length and Group in the Item Condition*

Regarding the main effect of length, post-hoc comparisons using Bonferroni correction indicated that performance for length 3 (M = 2.4, SD = 0.7) was significantly better than performances for lengths 4 (M = 1.6, SD = 0.8), t(78) = 12.67, p < .001, d = 1.43, 95% CI [0.7, 1.0], and 5 (M = 1.0, SD = 0.7), t(78) = 18.18, p < .001, d = 2.05, 95% CI [1.2, 1.6], and that performance for length 4 was significantly better than performance for length 5, t(78) = 6.80, p < .001, d = 0.77, 95% CI [0.4, 0.7]. Regarding the main effect of group, post-hoc comparisons using Bonferroni correction revealed that DYS+A children (M = 1.0, SD = 0.7) performed significantly worse than CA controls (M = 1.3, SD = 0.6), t(38) = -4.16, p < .001, d = -0.47, 95% CI [-1.3, -0.3], but not significantly different from both DYS-A children (M = 1.8, SD = 0.5), t(28) = -2.31, p = .142, and RL controls (M = 1.5, SD = 0.6), t(37) = -.93, p = 1.000, the latter also performing significantly worse than CA controls, t(47) = -3.68, p = .003, d = -0.41, 95% CI [-1.0, 0.2]. No other group difference was significant (all ps > .645).

## Supplementary Material S3.5

### *Details of the Post-hoc Analyses for the Length\*Group Interaction in the Order Condition*

Post-hoc comparisons using Bonferroni correction revealed that, for length 3, DYS+A children (M = 1.2, SD = 0.7) performed significantly worse than DYS-A (M = 2.3, SD = 0.6), t(28) = -4.09, p = .001, d = -0.46, 95% CI [-2.1, -0.2], CA controls (M = 2.3, SD = 0.7), t(38) =
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

-4.37, *p* = .001, *d* = -0.49, 95% CI [-2.0, -0.2], and RL controls (*M* = 2.0, *SD* = 0.8), *t*(37) = -3.27, *p* = .025, *d* = -0.37, 95% CI [-1.7, 0.1], no other group difference being significant (all *ps* > .273). For length 4, DYS+A children (*M* = 0.5, *SD* = 0.7) performed significantly worse than both CA controls (*M* = 1.7, *SD* = 1.0), *t*(38) = -4.82, *p* < .001, *d* = -0.54, 95% CI [-2.1, -0.3], and RL controls (*M* = 1.4, *SD* = 0.8), *t*(37) = -3.46, *p* = .013, *d* = -0.39, 95% CI [-1.7, -0.0], no other group difference being significant (all *ps* > .273). In contrast, no group difference was significant for length 5 (all *ps* > .193).
## Supplementary Material S4

### Details of the ANOVA on *d'* for the Auditory Perceptual Awareness Task

#### Supplementary Material S4.1

*Control Analysis for DYS+A Children's Lower Pitch Discrimination Skills*

Similarly to the STM task, the pattern of results remained the same after removing trials involving pitch changes below each participant's discrimination threshold (for a 100-cents threshold, 8 or 13 trials out of 120 depending on the set; for a 200-cents threshold, 4 or 5 trials out of 120 depending on the set), with significant main effects of condition, $F(1,75) = 8.49, p = .002$, $\eta_p^2 = .120$, material, $F(4, 300) = 55.30, p < .001$, $\eta_p^2 = .424$, and group, $F(3, 75) = 10.47, p < .001$, $\eta_p^2 = .295$, as well as a significant interaction between condition and material, $F(4, 300) = 21.91, p < .001$, $\eta_p^2 = .226$, and a 3-way interaction between condition, material, and group, $F(12, 300) = 1.86, p = .039$, $\eta_p^2 = .069$. No other interaction was significant (all $F$s < 1 except for material x group: $F(12, 300) = 1.15, p = .318$).

#### Supplementary Material S4.2

*Details of the Post-hoc Analyses for the Main Effects of Condition and Group for Syllables*

Regarding the main effect of condition, post-hoc comparisons using Bonferroni correction indicated that item performance ($M = 2.8, SD = 0.8$) was significantly better than order performance ($M = 2.3, SD = 1.1$), $t(78) = 3.31, p < .001$, $d = 0.37$, 95% CI [0.2, 0.7]. Regarding the main effect of group, post-hoc comparisons using Bonferroni correction indicated that DYS+A children ($M = 2.13, SD = 1.13$) performed significantly worse than CA controls ($M = 3.0, SD = 0.8$), $t(38) = -3.87, p < .001$, $d = -0.44$, 95% CI [-1.6, -0.3], but not significantly different from both DYS-A children ($M = 2.7, SD = 0.7$), $t(28) = -2.02, p = .282$, and RL controls ($M = 2.2, SD = 1.1$), $t < 1$, the latter also performing significantly worse than
## SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

CA controls, *t*(47) = -4.09, *p* < .001, *d* = -0.46, 95% CI [-1.4, -0.3]. No other group difference was significant (all *ps* > .328).

## Supplementary Material S4.3

### Details of the Post-hoc Analyses for the Main Effects of Condition and Group for Phonemes

Regarding the main effect of condition, post-hoc comparisons using Bonferroni correction indicated that item performance (*M* = 2.0, *SD* = 1.2) was significantly better than order performance (*M* = 1.4, *SD* = 1.2), *t*(78) = 5.06, *p* < .001, *d* = 0.57, 95% CI [0.4, 0.9]. Regarding the main effect of group, post-hoc comparisons using Bonferroni correction indicated that DYS+A children (*M* = 1.3, *SD* = 0.9) performed significantly worse than CA controls (*M* = 2.2, *SD* = 1.3), *t*(38) = -2.89, *p* = .030, *d* = -0.33, 95% CI [-1.8, -0.1], but not significantly different from both DYS-A children (*M* = 1.7, *SD* = 1.3), *t*(28) = -1.17, *p* = 1.000, and RL controls (*M* = 1.5, *SD* = 1.2), *t*(37) = -.65, *p* = 1.000, the latter performing also not significantly different from CA controls, *t*(47) = -2.56, *p* = .074. No other group difference was significant (all *ps* > .699).

## Supplementary Material S4.4

### Details of the Post-hoc Analyses for the Main Effects of Condition and Group for Intervals

Regarding the main effect of condition, post-hoc comparisons using Bonferroni correction indicated that item performance (*M* = 1.0, *SD* = 1.1) was significantly worse than order performance (*M* = 1.7, *SD* = 1.4), *t*(78) = -6.03, *p* < .001, *d* = -0.68, 95% CI [-1.1, -0.5]. Regarding the main effect of group, post-hoc comparisons using Bonferroni correction indicated that DYS+A children (*M* = 0.4, *SD* = 0.9) performed significantly worse than both DYS-A children (*M* = 1.6, *SD* = 1.1), *t*(28) = -3.43, *p* = .006, *d* = -0.39, 95% CI [-2.2, -0.3], and CA controls (*M* = 2.0, *SD* = 1.9), *t*(38) = -4.96, *p* < .001, *d* = -0.56, 95% CI [-2.4, -0.7], but not
# SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

significantly different from RL controls (M = 1.1, SD = 1.4), t(37) = -2.11, p = .227, the latter also performing significantly worse than CA controls, t(47) = -3.23, p = .011, d = -0.36, 95% CI [-1.6, -0.1]. No other group difference was significant (all ps > .564).

## Supplementary Material S4.5

### *Details of the Post-hoc Analyses for the Main Effects of Group for Notes*

Regarding the main effect of group, post-hoc analyses using Bonferroni correction indicated that DYS+A children (M = 0.3, SD = 0.9) performed significantly worse than CA controls (M = 1.4, SD = 1.2), t(38) = -3.23, p = .011, d = -0.36, 95% CI [-1.9, -0.2], no other group difference being significant (all ps > .235).

## Supplementary Material S4.6

### *Details of the Post-hoc Analyses for the Main Effects of Condition and Group for Timbres*

Regarding the main effect of condition, post-hoc comparisons using Bonferroni correction indicated that item performance (M = 2.3, SD = 0.9) was significantly better than order performance (M = 1.6, SD = 1.0), t(78) = 5.70, p < .001, d = 0.64, 95% CI [0.5, 1.1]. Regarding the main effect of group, post-hoc comparisons using Bonferroni correction indicated that DYS+A children (M = 1.5, SD = 1.0) performed significantly worse than both DYS-A children (M = 2.2, SD = 0.9), t(28) = -2.88, p = .031, d = -0.32, 95% CI [-1.3, 0.0], and CA controls (M = 2.2, SD = 0.9), t(38) = -3.24, p = .011, d = -0.37, 95% CI [-1.3, -0.1], but not significantly different from RL controls (M = 1.7, SD = 1.0), t < 1, the latter also performing not significantly different from CA controls, t(47) = -2.61, p = .066. No other group difference was significant (all ps > .170).
**Supplementary Material S5**

**Details of the ANOVA on *d'* for the Auditory Attention Task**

**Supplementary Material S5.1**

*Details of the Post-hoc Analyses for the Material*\*Level Interaction

Regarding the interaction between material and level, post-hoc comparisons using Bonferroni correction indicated that, at level 1, word performance (M = 4.0, SD = 1.2) was not significantly different from pitch performance (M = 3.7, SD = 1.2), t(79) = 2.43, p = .096, and not significantly different from timbre performance (M = 4.4, SD = 0.9), t(79) = -2.62, p = .056, and pitch performance was significantly worse than timbre performance, t(79) = -5.04, p < .001, *d* = -0.56, 95% CI [-1.0, -0.3]. In contrast, at level 2, word performance (M = 3.0, SD = 1.1) was not significantly different from pitch performance (M = 3.1, SD = 1.4), t(79) = -.59, p = .400, and not significantly different from timbre performance (M = 2.7, SD = 1.2), t(79) = 2.62, p = .055, but pitch performance was significantly better than timbre performance t(79) = 3.21, p = .009, *d* = 0.36, 95% CI [0.0, 0.8]. This pattern of results was mainly due to greater salience between distractors and targets for timbres at level 1 than at level 2. Indeed, whereas the vibes timbre (distractor) was highly distinct from the flute timbre (target) at level 1, the cello timbre (distractor) was often mistaken for the flute timbre at level 2, which led to a higher rate of false alarms and a decrease in performance.

**Supplementary Material S5.2**

*Details of the Post-hoc Analyses for the Main Effect of Group*

Regarding the main effect of group, post-hoc comparisons using Bonferroni correction indicated that DYS+A children (M = 2.9, SD = 1.3) performed significantly worse than both DYS-A children (M = 3.7, SD = 1.2), t(28) = -2.85, p = .034, *d* = -0.32, 95% CI [-1.6, 0.0], and CA controls (M = 4.1, SD = 1.1), t(38) = -4.74, p < .001, *d* = -0.53, 95% CI [-1.87, -0.51], but
SHARED IMPAIRMENTS IN DYSLEXIA AND AMUSIA?

not significantly different from RL controls ($M = 3.0, SD = 1.3$), *t* <1, the latter also performing
significantly worse than both DYS-A children, *t*(48) = -2.82, *p* = .037, *d* = -0.32, 95% CI [-1.4,
0.0], and CA controls, *t*(48) = -5.05, *p* < .001, *d* = -0.56, 95% CI [-1.7, -0.5]. No other group
difference was significant (all *ps* > .745).
Supplementary Material S6

Correlation Analysis

**Table S6.1**

*Partial Correlations Between MIM Index, MBEMA Score, and Performance for Each Composite Variable as a Function of Group*

(a) All

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th rowspan="2">df</th><th colspan="2">r</th></tr><tr><th>MIM index</th><th>MBEMA score</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td>Word</td><td>72</td><td><strong>.37*</strong></td><td><strong>.37*</strong></td></tr><tr><td>Pitch</td><td>72</td><td><strong>.36*</strong></td><td><strong>.58***</strong></td></tr><tr><td>Item</td><td>72</td><td><strong>.35*</strong></td><td><strong>.52***</strong></td></tr><tr><td>Order length 3</td><td>72</td><td>.24</td><td><strong>.54***</strong></td></tr><tr><td>Order length 4</td><td>72</td><td><strong>.40*</strong></td><td><strong>.44**</strong></td></tr><tr><td rowspan="5">Auditory perceptual awareness</td><td>Syllable</td><td>72</td><td>.26</td><td>.33</td></tr><tr><td>Phoneme</td><td>72</td><td>.33</td><td>.24</td></tr><tr><td>Interval</td><td>72</td><td>.30</td><td><strong>.56***</strong></td></tr><tr><td>Note</td><td>72</td><td>.24</td><td><strong>.39*</strong></td></tr><tr><td>Timbre</td><td>72</td><td>.18</td><td><strong>.40**</strong></td></tr><tr><td>Auditory attention</td><td>Global</td><td>72</td><td><strong>.37*</strong></td><td><strong>.44**</strong></td></tr></tbody></table>

(b) DYS+A

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th rowspan="2">df</th><th colspan="2">r</th></tr><tr><th>MIM index</th><th>MBEMA score</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td>Word</td><td>9</td><td>-.13</td><td>.29</td></tr><tr><td>Pitch</td><td>9</td><td>.18</td><td>-.49</td></tr><tr><td>Item</td><td>9</td><td>-.30</td><td>.11</td></tr><tr><td>Order length 3</td><td>9</td><td>.25</td><td>.01</td></tr><tr><td>Order length 4</td><td>9</td><td>.04</td><td>-.35</td></tr><tr><td rowspan="5">Auditory perceptual awareness</td><td>Syllable</td><td>9</td><td>.08</td><td>.02</td></tr><tr><td>Phoneme</td><td>9</td><td>.13</td><td>-.08</td></tr><tr><td>Interval</td><td>9</td><td>-.08</td><td>.01</td></tr><tr><td>Note</td><td>9</td><td>-.31</td><td>.31</td></tr><tr><td>Timbre</td><td>9</td><td>.21</td><td>.37</td></tr><tr><td>Auditory attention</td><td>Global</td><td>9</td><td>-.32</td><td>.24</td></tr></tbody></table>

(c) DYS-A

<table><thead><tr><th rowspan="2">Task</th><th rowspan="2">Composite variable</th><th rowspan="2">df</th><th colspan="2">r</th></tr><tr><th>MIM index</th><th>MBEMA score</th></tr></thead><tbody><tr><td rowspan="5">Auditory short-term memory</td><td>Word</td><td>9</td><td>.05</td><td>.57</td></tr><tr><td>Pitch</td><td>9</td><td>.17</td><td>.57</td></tr><tr><td>Item</td><td>9</td><td>.24</td><td>.65</td></tr><tr><td>Order length 3</td><td>9</td><td>.54</td><td>.28</td></tr><tr><td>Order length 4</td><td>9</td><td>-.27</td><td>.59</td></tr><tr><td></td><td>Syllable</td><td>9</td><td>.11</td><td>.13</td></tr></tbody></table>