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# Rhythm is alive, though it is not (and never was) the whole story.

Thierry Nazzi

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Thierry Nazzi. Rhythm is alive, though it is not (and never was) the whole story.. Journal of Experimental Psychology. Human Perception and Performance, 2025, 51 (7), pp.827-833. 10.1037/xhp0001258. hal-05266610

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Distributed under a Creative Commons Attribution 4.0 International License
Rhythm is alive, though it is not (and never was) the whole story

Thierry Nazzi

Integrative Neuroscience and Cognition Center, CNRS & Université Paris Cité

Nazzi, T. (2025). Rhythm is alive, though it is not (and never was) the whole story. *Journal of Experimental Psychology: Human Perception and Performance*, 51(7), 827-833.

doi.org/10.1037/xhp0001258

**Address for Correspondence**

Thierry Nazzi. Integrative Neuroscience and Cognition Center (INCC), Language and Cognition
Team. CNRS - Université Paris Cité. Campus Saint-Germain-des-Prés. 45 rue des Saints Pères.

75270 Paris cedex 06. E-mail : thierry.nazzi@parisdescartes.fr

**Keywords:** linguistic rhythm, rhythmic classes, infants, language discrimination
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**Abstract**

Most infants learn their native language, or native languages if they grow up in a multilingual environment, with amazing speed and apparent ease. Developmental research has taught us that many of these acquisitions begin in the first year of life, and has stated to specify early developmental trajectories across various languages. One issue that has caught early attention in the field is the question of when and how infants discriminate languages and start recognizing their native language. The present study reviews the literature on this issue, highlighting the influence of rhythm, pointing towards limitations and raising questions for future research.
Most infants learn their native language, or native languages if they grow up in a multilingual environment, with amazing speed and apparent ease. Fifty years of developmental psycholinguistics have taught us that many of these acquisitions start in the first year of life. They allowed us to better chart early developmental trajectories across various languages, and specify the mechanisms at play behind these acquisitions, whether they are present at birth or emerge later in development, and how they change. One issue that has caught early attention in the field is the question of when and how infants discriminate languages and start recognizing their native language. This question is of importance as it can inform us on the initial perceptual biases infants come to life with, and on the properties of their native language they progressively learn through exposure with surrounding speech input.

About the when, Mehler, Jusczyk, Lambertz, Halsted, Bertoncini and Amiel-Tison (1988) and Moon, Cooper and Fifer (1993), using the high amplitude sucking (HAS) procedure, found that newborns increase their sucking rates when hearing a change between sentences in their native versus a foreign language, and suck more when hearing the sentences in their native language, suggesting language discrimination abilities and native language recognition at birth. Regarding the how, Mehler et al. (1988) had suggested that linguistic rhythm might be implicated in these early discrimination/ preference abilities, as the languages used in these two newborn studies had different types of rhythm (syllable- based French/ stress-based Russian, Mehler et al., 1988; syllable-based Spanish/ stress- based English, Moon et al., 1993). This proposal (see also Mehler, Dupoux, Nazzi & Dehaene- Lambertz, 1996) was directly tested by Nazzi, Bertoncini and Mehler (1998), using low-pass filtered speech removing most segmental (i.e., related to consonants and vowels) information, which established that French-exposed newborns can discriminate sentences from unknown languages of different rhythms (sentences in stress-based English versus
mora-based Japanese; a mix of sentences from stress-based English and Dutch versus a mix
of sentences from syllable-based Italian and Spanish) but fail to discriminate sentences from
unknown languages with the same rhythm (sentences in English versus Dutch; a mix of
sentences from English and Italian versus a mix of sentences from Dutch and Spanish). This
pattern of results was cautiously taken as the first piece of evidence that newborns are
sensitive to the overall rhythm of languages. Indeed, the paper was entitled "Language
discrimination by newborns: toward an understanding of the role of rhythm," and it ended
with a call for more research on this issue. Twenty-five years later, what progress have we
made in understanding the role of rhythm in language discrimination, and what questions
remain pending?

## Definitions of linguistic rhythm

Let's start this reflection by some considerations regarding what is meant by linguistic
rhythm in the literature. Three rhythmic classes have been considered, the stress-, syllable-
and mora-based classes, and initial definitions of these classes referred to isochrony in the
duration of the specific rhythmic units underlying the rhythm of each class: the stress unit
(i.e., the foot) for stress-based languages (as attested by the regular occurrence of stressed
syllables), the syllabic unit for syllable-based languages, and the moraic unit (i.e., a
subsyllabic unit, which in Japanese can be a (C)V, or the post-vocalic portion of a syllable due
to lengthening of a vowel, gemination (i.e., doubling) of a consonant, or a nasal consonant)
for mora-based languages (Abercrombie, 1967; Ladefoged, 1975; Pike, 1945).

However, this definition turned out not be supported by acoustic analyses leading to
more complex definitions based on phonetics/phonology (e.g., Dauer, 1983). For example, it
was proposed that the type of syllabic structure, the presence/absence of vocalic reduction
(i.e., weakening) and the placement/realization of stress strongly determine linguistic
rhythm (Dauer, 1983). More recently, several proposals have offered acoustic metrics to
capture the rhythmic classes. In Ramus, Nespor and Mehler (1999) metrics, the best
parameters proposed were vocalic interval durations as percentage of utterance duration
(%V) and variability in consonant interval durations (ΔC). In Grabe and Low (2002) metrics,
the best parameters were normalized Pairwise Variability Index for vowels (nPVI-V) and raw
Pairwise Variability Index for consonants (rPVI-C). In White and Mattys (2007) metrics, the
best parameters were standard deviation of vocalic interval durations (VarcoV) and %V.
Although these metrics differ, all the proposed parameters relate to duration of consonantal
and vocalic parts of the signal, variability in their duration (overall or consecutive), and
relative durational proportion of both types of segments. As such, they might all reflect the
phonetic/phonological factors proposed by Dauer (1983).

One way to look at this literature is to consider that there are acoustic, phonetic and
phonological factors that allow to categorize languages into the three rhythmic classes.
However, three points of cautions should be kept in mind. The first is that most of the
languages that have been considered are Indo-European languages, and there is a need to
extend this work to more numerous languages, from more linguistic families. The second
point is that these analyses can also be taken as suggesting a more continuous,
multidimensional conceptualization of linguistic rhythm, in which the rhythm of a specific
language would be more syllable-based than stress- or mora-based for example, with some
languages having more mixed properties. This leads to the last point, that the three rhythmic
units have a hierarchical link, in the sense that stress units are made up of syllables that are
made up of morae. Accordingly, what might be at stake here is which of these three units
are relevant for a given language, and what is the relative weight given to them in that
language. With these cautions in mind, let us now turn to the evidence of the role of
linguistic rhythm in early language discrimination.

Rhythm in infant language discrimination

Following Nazzi et al. (1998), many behavioral and brain-related (Electroencephalography – EEG- or Functional Near Infrared Spectroscopy –fNIRS-) studies have been conducted to assess the role of linguistic rhythm on language discrimination and preference.

At birth, French-exposed newborns were found to discriminate stress-based Dutch
from mora-based Japanese when presented with sentences played forward but not
backward, an ability also found in tamarins (Ramus, Hauser, Miller, Morris & Mehler, 2000).
Moreover, newborns from mothers speaking both stress-based English and syllable-based
Tagalog discriminated these two languages and recognized both of them as familiar (Byers-
Heinlein, Burns & Werker, 2010). Further studies using fNIRS showed differences in the
processing of sentences in the native language versus a non-native language of a different
rhythm at birth, when the sentences were played forward (English-Tagalog: May, Byers-
Heinlein, Gervain & Werker, 2011; Japanese-English: Sato, Hirabayashi, Tsubokura, Kanai,
Ashida, Konishi, Uchida-Ota, Konishi & Maki, 2012). Lastly, newborns' EEG responses in the
delta (1-3 Hz) and theta (4-8 Hz) bands did not differ when presented with sentences in
native syllable-based French versus same class Spanish. However, responses to the
sentences in these two languages differed from responses to the sentences in stress-based
English. This confirms between-class discrimination and within-class lack of discrimination
(Ortiz-Barajas, Guevara & Gervain, 2023).

Taken together, these studies support the idea that language discrimination can be
found at birth, but only when the languages presented differ in rhythm. Only two
experiments from the original Mehler et al. (1988) study do not fit with this interpretation: the non-discrimination of French and Russian by newborns born in France of families in which the primary language was not French, and the lack of discrimination of syllable-based Italian and stress-based English by French-exposed newborns. The first failure might be due to a smaller sample size, and the mix of primary languages involved. The second failure is surprising, first, given the results presented in the figures, and might be due to statistical issues (analyses performed on groups separated according to the language presented in the first phase of the experiment rather than on the entire group of infants). It is also surprising given the later findings by Nazzi et al. (1998), although it might suggest that the presence of segmental information in the unfiltered stimuli of Mehler et al. (1988), which was removed with low-pass filtering in Nazzi et al. (1998), made the discrimination more difficult when the non-native language was not presented. Lastly, note that a corollary of this rhythm-based interpretation is that the recognition of the native language suggested by Mehler et al. (1988) and Moon et al. (1993) might be better understood as a preference for the rhythm of the native language, rather than the native language per se.

At 2 months of age, language discrimination results follow a pattern similar to the one found in newborns, although some changes in discrimination abilities seem to emerge. American English-learning 2-month-olds discriminated sentences in English versus Italian (even when the stimuli were low-pass filtered), but not sentences in Russian versus French, although the results presented in the figure suggested a trend towards discrimination (Mehler et al., 1988). Moreover, British English-learning 2-month-olds discriminated stress-based English from mora-based Japanese, but failed to discriminate syllable-based French and Japanese, again pointing to the possibility of harder non-native discrimination when presenting clear speech. When it comes to another stress-based language, Dutch, they
showed intermediate performance, marginally discriminating it from either English or Japanese; the authors suggested that some of these 2-month-olds were still processing Dutch as English, while others could now discriminate the two languages (Christophe & Morton, 1998). This interpretation of a transitional period in which discrimination within rhythmic classes seems to emerge is in line with the finding that French-learning 2-month-olds can discriminate French from another syllable-based language, Turkish (Christophe, Nespor, Guasti & van Oojien, 2003).

This developmental shift is further supported by results from infants aged 4 months onward, which clearly establish discrimination abilities between languages of the same class. At that age, Spanish-Catalan bilingual 4-month-olds discriminated these two syllable-based languages (Bosch & Sebastian-Galles, 1997, 2001), US-English-learning 5-month-olds discriminated stress-based English and Dutch (Nazzi, Johnson & Jusczyk, 2000), Basque-Spanish monolingual and bilingual 3.5-month-olds discriminated these two syllable-based languages (Molnar, Gervain & Carreiras, 2014). At the brain level, using EEG and measuring induced gamma-band responses, a similar shift was observed in Spanish-learning infants: at 3 months, differences in processing were found between syllable-based Spanish and mora-based Japanese, but not between Spanish and syllable-based Italian, while at 6 months, responses to Spanish differed from responses to the other two languages (Peña, Pittaluga & Mehler, 2010). At 5 months, within-class discrimination seems more difficult when the native language is not presented, as attested by US-English-learning infants' failure to discriminate stress-based Dutch and German (Nazzi et al., 2000). At this age, it also seems more difficult to discriminate languages that belong to a rhythmic class other than the native class, as attested by US-English-learning infants' failure to discriminate syllable-based Italian and Spanish (Nazzi et al., 2000), or British-English-learning infants' failure at discriminating
syllable-based French and Finnish, or syllable-based Spanish and Finnish, although they could
discriminate French and Spanish (White, Delle Luche & Floccia, 2016).

Lastly, infants were found to distinguish not only different languages, but also
different dialects of the same language. Indeed, US-English-learning 5-month-olds were
found to discriminate two dialects of their native language, US and British English, further
attesting of increased language discrimination abilities by that age (Nazzi et al., 2000).

However, extensions of this finding brought mixed results of discrimination or failure to do
so depending on the dialects tested (Butler, Floccia, Goslin & Panneton, 2011).

Infant language discrimination beyond rhythm

What could be the cues other than linguistic rhythm that infants use to succeed at
these more fine-grained, within-class discriminations, starting around 4 months of age? At
present, very few studies have started to address this issue. An acoustic analysis of the
British and US English sentences used to establish dialect discrimination revealed a greater
proportion of higher sentence-initial pitches and terminal rises, and greater variability in the
production of syllable durations in British than US English sentences, leading the authors to
suggest that these additional prosodic cues could support the dialect discrimination they had
found (Nazzi et al., 2000). Moreover, regression analyses of discrimination performance of
British-English-learning 5- and 7-month-olds, based on acoustic analyses of the stimuli
presented, found that discrimination across Plymouth-, Welsh- and Scottish-accented
English was related to utterance-final lengthening, a more local durational variation than
(utterance-level) rhythm (White, Floccia, Goslin & Butler, 2014). More directly, a study
showing that US-English-learning 5-7-month-olds discriminated US English and German
when natural intonation was present in the stimuli, but not when it was replaced by a
monotone, establishes the role of intonational properties for explaining the discrimination between these two specific languages (Chong, Vicenik & Sundara, 2018).

Lastly, a recent meta-analysis of all language discrimination/ preference studies investigated whether the rhythmic classes and the acoustic parameters proposed in the durational metrics discussed earlier (Ramus et al., 1999; Grabe & Low, 2002; White & Mattys, 2007) can account for the discriminations/ preferences observed (Gasparini, Langus, Tsuji & Boll-Avetisyan, 2021). Models testing for the role of rhythmic classes only found it to be a significant predictor in discrimination tasks. Models testing for the role of durational metrics found that better language discrimination was linked to smaller differences in ΔV (an effect opposite to the authors' predictions, which might be linked to sensitivity to speech rate) and larger differences in rPVI-C. Note however that in the Gasparini et al. (2012) analyses, the acoustic values were not always those of the stimuli used in the experiments, but those reported in the literature. As the authors remark, given between-speaker variability in durational metrics, the values used may or may not have corresponded to those in the stimuli actually used in the experiments, which constitutes an important limitation to these analyses (and highlights the need to do acoustic measurements on sets of speakers as large as possible). When both rhythmic class and acoustic parameters were entered in the same model, there was still a role of rhythmic class although its effect was only found in preference experiments.

Taken together, these findings suggest that as infants gain more experience with their native language(s), they start using more cues to discriminate between languages. Rhythm appears to remain a cue, but other prosodic cues (lengthening, intonation) have started to be identified. Future work will have to continue exploring other potential prosodic cues. It would be of particular interest to test whether the presence versus absence of lexical
tones in a language allows language discrimination, even when the two languages have the
same rhythm (for example, within the syllable-based class, non-tonal French versus tonal
Mandarin Chinese), and from what age (already at birth? only by 4 months?). Moreover, it is
also likely that as infants start acquiring the inventory of the consonants and vowels of their
native language (English: Werker & Tees, 1984; Kuhl, Williams, Lacerda, Stevens & Lindblom,
1992; French: Hoonhorst, Colin, Markessis, Radeau, Deltenre & Serniclaes, 2009), or its
phonotactic properties (i.e., the regularities regarding the order in which they can be
combined; English: Jusczyk, Luce& Charles-Luce, 1994; French: Gonzalez-Gomez & Nazzi,
2012), they will use knowledge of these language-specific properties to discriminate
between speech input from different languages or dialects. While such effects have been
found at the lexical level (at 6 months for prosodic differences, at 9 months for phonotactic
difference, Jusczyk et al., 1993), this has not been directly tested at this point at the
sentence level in younger infants.

Going back to the meta-analysis (Gasparini et al., 2021), it revealed that both
rhythmic class and durational parameters partly account for the language discrimination/
preference results. Since these durational parameters have been linked to rhythmic classes,
this finding again raises the question of whether linguistic rhythm is better accounted for in
terms of classes/categories, or in terms of a continuous distinction along multiple acoustic
dimensions. Yet because, as said earlier, the rhythmic units are discrete units, placed in a
hierarchy, it might be that both a categorical and a continuous definition have psychological
reality, depending on the tasks used and the levels of processing they tap into, and on the
ages of the infants tested.
Rhythm beyond language discrimination

In this section, we discuss three other lines of research that investigated the potential role of
rhythmic classes at processing levels other than language discrimination. First, Nazzi et al.
(1998) referred, in their general discussion, to some studies having shown that, depending
on the rhythmic class of their native language, adults use different procedures to segment
speech and access words in their lexicons, with evidence that English-speaking adults use the
trochaic stress unit, French-speaking adults use the syllabic unit, and Japanese-speaking
adults use the moraic unit (Cutler, Mehler, Norris & Segui, 1986; Mehler, Dommergues,
Frauenfelder & Segui, 1981; Otake, Hatano, Cutler & Mehler, 1993). They reasoned that
these processing differences might originate from newborns' sensitivity to linguistic rhythm,
which would allow these procedures to emerge early in development. Support for this idea
came from subsequent studies exploring early wordform segmentation abilities in infants
learning stress- and syllable-based languages. For stress-based languages, an advantage at
segmenting trochaic over iambic wordforms was found at 7.5 months in US English-learning
infants (Juszyck, Houston & Newsome, 1999) and at 10 months in Dutch-learning infants
(Kooijman, Hagoort & Cutler, 2005, 2009). Both findings are consistent with the hypothesis
that infants learning a stress-based language use the stress unit to segment fluent speech.

In contrast, for syllable-based languages, behavioral studies reveal an advantage of
the syllabic unit over disyllabic wordforms in Parisian French during the first year of life
(Nazzi, lakimova, Bertoncini, Frédonie & Alcantara, 2006; Nishibayashi, Goyet & Nazzi, 2015).
A slightly different pattern was found in another French variant, as a behavioral study
revealed that Canadian French-learning infants use both syllables and disyllabic wordforms
at 8 months. However, the fact that a familiarity effect was found for the disyllabic
wordforms while a novelty effect was for the syllables suggest different mechanisms, and is
compatible with easier segmentation of the syllables (Polka & Sundara, 2012; for a similar argument for Parisian French, see the EEG study of Goyet, de Schonen & Nazzi, 2010). This earlier or easier use of syllables to segment is consistent with the hypothesis that infants learning a syllable-based language use the syllabic unit to segment fluent speech.

Taken together, these crosslinguistic findings support the proposal that early segmentation of fluent speech into potential wordforms relies (at least in part) on the rhythmic unit of the native language. However, no data so far has been able to establish mora-based segmentation abilities in a mora-based language, with many experiments conducted on Japanese-learning infants failing to find early segmentation abilities (Hayashi & Mazuka, 2008). Moreover, as the short list of languages tested makes apparent, much work is needed to extend these studies to more languages, in order to provide better bases for generalizability (or not) of the findings so far. It should also be noted that the differences in results found within each of the rhythmic classes tested (in terms of timing for the stress-based languages; in terms of units segmented for the syllable-based languages) point to the fact that rhythm alone cannot be the sole type of information behind wordform segmentation. This is in line with many segmentation studies showing early effects of, for example, distributional properties (English: Saffran et al., 1996; French: Mersad & Nazzi, 2012) or phonotactic cues (English: Mattys & Jusczyk, 2001; French: Gonzalez-Gomez & Nazzi, 2013).

Second, a recent study on adults tested whether cortical tracking of speech is modulated cross-linguistically, and whether linguistic rhythm plays a role in this modulation (Peter, Ommen, Kalashnikova, Mazuka, Nazzi & Burnham, 2022). Adult native speakers of three languages of different rhythmic classes were tested: stress-based English, syllable-based French and mora-based Japanese. They were presented with streams of 200ms-long
CVN (Consonant Vowel Nasal) syllables, to test whether their brain responses entrain at the stress unit level (2.5 Hz), the syllable level (5 Hz) or the mora level (10 Hz), with more entrainment in each language group for the rhythmic unit of their native language. Although this prediction was not confirmed, the results first established cortical tracking only at the syllabic and moraic levels, with more tracking at the syllabic level for all groups. Since acoustic analyses showed that this level was the most prominent in the stimuli used, this suggests that cortical tracking is partly determined by bottom-up factors. This might also explain why no tracking was found at the level of the stress unit, since these units were not marked acoustically in any way (all syllables used were equally stressed). Second, because more tracking was found for the French-speaking adults compared to the other two groups, and because this effect was more marked at the syllabic level, the results further establish some crosslinguistic modulation and top-down determinants of cortical tracking. Third, the results of more tracking at the syllable level in all language groups might be taken as initial evidence that the syllabic rhythm is the default, language-general rhythm (in link with the syllable being the basis of mandibular articulation; see acoustic data by Ding et al., 2017; Varnet, Ortiz-Barajas, Erra, Gervain & Lorenzi, 2017). Moreover, the fact that this effect is stronger in French suggests that sensitivity to this level might increase with the learning of a syllable-based language. This work will have to be continued in the future, for example to determine whether, when stress is acoustically marked in the signal, stress-based entrainment can be obtained, at least in adult speakers of a stress-based language. If such effects of rhythm on adult neural entrainment were confirmed, it would be important to test infants at different ages to determine when entrainment to different levels emerges, when it starts to be modulated cross-linguistically, and whether it plays a role in language acquisition.
Third, one line of research provides initial evidence that rhythm might have implications beyond speech processing itself, and impact cognition. This is suggested by studies exploring the impact of language input on object categorization, which have started investigating the potential role of rhythm in this process. They first established that hearing sentences in their native language while seeing different exemplars of unfamiliar object categories helps US English-learning infants to form new categories (Ferry, Hespos & Waxman, 2010). To define the specificity of this link, further experiments tested whether US English-learning 4-month-olds also form new object categories when hearing sentences in a foreign language. Success was found when presenting sentences in stress-based German but not in syllable-based Cantonese (Perszyk & Waxman, 2019). This pattern of results is consistent with the idea that rhythmic proximity might play a role in infants' ability to use language to form object categories, although other factors might play a role (see evidence from machine learning by Lau, Fyshe & Waxman, 2022), such as the absence of lexical tones in both English and German versus the presence of lexical tones in Cantonese. Evidently, further work will be needed to confirm or disconfirm the role of rhythm in those tasks.

**Rhythm or not rhythm? Directions for future research**

In conclusion, following the initial proposal by Nazzi et al. (1998), some evidence of an impact of linguistic rhythm on young infants' abilities to discriminate languages has been found. However, the studies on language discrimination also clearly showed that, except maybe in the first days or weeks following birth, rhythm is not the only cue infants can use, and that they do use other cues to discriminate languages or dialects from the same rhythmic class. The importance of these cues should not be neglected. Yet, if rhythm is the first cue used to discriminate languages (which remains to be further tested, given that
only), it might differentially impact other processes during language acquisition. Future research will have to address several pending questions. For example, only two studies (Nazzi et al., 1998; Ortiz-Barajas et al., 2023) explored within-class discrimination in newborns, both in newborns from French-speaking families. More evidence should be gathered on this issue, to consolidate the current evidence. By testing different language pairs, chosen to contrast on specific cues, this would allow to identify further cues, and to better understand how the different cues that can support language discrimination are used at different points in development, how their relative weight changes developmentally, and whether this depends on the properties of the native languages(s).

We have also highlighted the debate regarding whether linguistic rhythm should be better understood in terms of classes or continua. We have suggested that both types of representations might be relevant, though possibly at different processing or representational levels, or at different developmental times. At present, a categorical approach might better explain language discrimination at birth, or early wordform segmentation, while a continuous approach might better account for later language discrimination. To shed light on these issues, future acoustic studies will be needed to characterize the rhythmic properties of a larger range of languages (also measuring productions from a larger number of speakers per languages), to test whether the three classes and/or the rhythmic parameters that have been proposed generalize beyond the relatively few languages investigated so far. Recent preliminary findings on three languages spoken in Ghana suggest that some of the acoustic parameters proposed to characterize rhythmic classes might not allow to classify all languages (Boll-Avetisyan, Omane & Kügler, 2020). Extending this research to further languages spoken in Africa and Asia, that host the largest diversity of human languages, and include many tonal languages, will be crucial to
test the relevance of the current rhythmic classes, beyond the most studied related Indo-
European languages.

Other studies will also be needed to increase both the linguistic diversity of the
languages used in language discrimination studies, and the languages of the infants tested
on this question, as we have underlined the fact that the data on which the current
proposals are based remain scarce even after 25 years of research. As in other areas of
developmental psychology (Singh, Cristia, Karasik, Rajendra & Oakes, 2023) and of language
acquisition in particular (Singh, Rajendra & Mazuka, 2022), it appears critical to continue to
widen the range of languages investigated to probe the developmental theories we are
building. Note that Nazzi (1997) conducted some pilot language discrimination studies with
adults, using stimuli from 10 different languages (6 Indo-European languages: French, Italian,
Spanish, English, Dutch and Swedish; 4 non-Indo-European languages: Arabic, Turkish, Wolof
and Japanese). However, for lack of time, the newborn could only be tested on a limited
number of language contrasts. Through these extensions, the role of rhythm in early
language discrimination will again be questioned, and it will end up strengthened or
weakened. But in both cases, our language acquisition theories will end up strengthened.

We have also presented some evidence that rhythm could affect other areas of
speech processing and language acquisition, such as wordform segmentation, neural
entrainment to speech, or object categorization. Future research will have to investigate
whether other domains might also be impacted. For example, Johnson et al. (2011)
established that Dutch-learning 7.5-month-olds better discriminate voices in their native
language than in two foreign languages (either Italian or Japanese). However, in that study,
the rhythm of both foreign languages differed from the rhythm of the native language.
Whether this effect would extend to a foreign language of the same rhythm remains
untested. Moreover, rhythm might also affect voice recognition, and one could imagine that
it would be easier in a foreign language with the same kind of rhythm than in a foreign
language with another rhythm. Rhythm might also modulate infants' ability to associate
voices with individual faces, which was found to be better in the native language than in a
foreign language with a different rhythm (Spanish) in monolingual English-learning 9-month-
olds (Fecher & Johnson, 2019, 2022). Additional studies could explore how infants fare in
this task in a foreign language sharing the rhythm of the native language.

## Acknowledgments

The author would like to thank Ranka Bijeljac-Babic, Barbara Höhle and Caroline Floccia for comments on a previous draft of this paper, coauthors, collaborators and colleagues who worked on the issues discussed in this commentary, parents for bringing their infants to the lab, and the infants for accepting to answer queries, even in ways that do not confirm our predictions. Writing of this paper was made possible by funding from an ANR-DFG grant (ANR-16-FRAL-0007 to T Nazzi), and a LABEX Empirical Foundations of Language grant (ANR-10-LABX-0083).

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