# Articulating while listening: The perception-production link in early infancy

Sónia Frota, Cátia Severino, Jovana Pejovic, Nuno Paulino, Marina Vigário, Aude Noiray

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Sónia Frota, Cátia Severino, Jovana Pejovic, Nuno Paulino, Marina Vigário, et al.. Articulating while listening: The perception-production link in early infancy. 2025. hprints-05367741

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Articulating while listening: The perception-production link in early infancy

Sónia Frota¹ *, Cátia Severino¹, Jovana Pejovic¹, Nuno Paulino¹, Marina Vigário¹ & Aude
Noiray²

¹Center of Linguistics, School of Arts and Humanities, University of Lisbon, Lisbon, Portugal

²Laboratoire de Psychologie et NeuroCognition, Université Grenoble-Alpes, Grenoble, France

*Correspondence concerning this article should be addressed to Sónia Frota

e-mail: sfrota@edu.ulisboa.pt
**Abstract**

There is a growing body of work in infant speech perception proposing that the auditory
analysis of speech is coupled with articulatory information involved in speech production.
These studies show that the link between perception and production emerges early in infancy,
and before infants have some experience with speech production. However, the mechanisms
behind the development of this link are not well understood. Importantly, research has not yet
addressed whether infants produce linguistically-driven articulatory movements when
perceiving speech. To address this question, we employed ultrasound imaging to record the
tongue shapes of 6-month-old infants while listening to vowel-consonant-vowel sequences
that differed in the articulatory configuration of the consonant. If tongue shape varied as a
function of the speech token heard, listening to a dental sound like /t/, and to a velar sound
like /k/, would trigger differences in tongue shape. The results confirmed this prediction,
showing that infants produced articulatory movements by placing the tongue more to the
front or back in the direction of the sounds they heard. Our findings are the first to suggest
that infants engage in speech driven oral-motor responses modulated by the sounds
perceived, advancing our understanding of the mechanisms for the emerging perception-
production link.

**Keywords**

Infant speech perception, perception-production link, sensorimotor information, ultrasound
tongue imaging
**Introduction**

The perceptual foundations of language acquisition are well-established [1-2]. Infants are born
with perception abilities tuned to speech. Newborns prefer natural speech over other complex
sounds, such as acoustically matched nonspeech sounds or backward speech [3-4]. This selective
attention to speech is maintained and further developed during the first year of life [5-6],
showing influences of the language sounds infants are exposed to since the very early stages.
Infants soon display an increased sensitivity for the native language, and quickly develop
perceptual abilities attuned to the specific properties of the native language [7-9].

Importantly, infant speech perception has been argued to involve sensorimotor
constraints, in the sense that the auditory analysis of speech is coupled with articulatory and
motor information from speech production [10-12]. Results from three related domains have
provided converging evidence to this view: brain imaging studies, multimodal audio-visual
speech perception studies, and work on sensorimotor influences in speech discrimination.

Brain imaging studies showed that speech perception activates infants' motor brain areas early in the 1st year of life, before infants start producing speech [13-14]. In addition, at 7 months of age the activation of both auditory and motor brain areas was found in response to all speech sounds, whether they were syllables present in the native language or not [15]. Consequently, the activation of motor brain areas might not reflect infants' experience either with the speech sounds they hear in their natural environment, or with the speech sounds they are already vocalizing.

Studies on multimodal audio-visual speech perception showed that infants integrate
auditory and visual speech cues very early in development [16-17]. Infants have the ability to
match the sounds they hear to images of the visual articulation of the same sounds. As early as 2-
4 months of age, they are sensitive to auditory-visual vowel matches or mismatches. For
example, when listening to the /i/ sound and presented with images of the visual articulation of
/i/ and /a/, they preferred to look at the image that depicts the articulation of /i/ [18-19]. Infants
are also sensitive to auditory-visual consonant matches or mismatches. At 6 months of age, they
were able to match the auditory syllables /ba/ and /va/ with the corresponding silent videos
showing the articulation of each of the syllables, independently of whether the distinction
between /b/ and /v/ is present in the sound system of the native language [20]. Thus, infants'
multisensory speech perception abilities emerge regardless of infants' exposure to the particular
speech sounds perceived, or their ability to already produce those speech sounds.
Research on sensorimotor influences on speech perception demonstrated that experimentally induced inhibitions to articulatory movement selectively affect auditory-only phoneme discrimination between 3 and 6 months of age, both in the case of native and non-native speech perception [12]. English-learning infants were able to successfully discriminate the non-native syllables /dɑ/ and /dɑ/, from Hindi, as well as the native contrast between /ba/ and /da/. However, their discrimination ability was disrupted when a particular teether with a shape that inhibited the articulation involved in the sound distinction was placed in their mouth [21-23]: a flat teether, but not a gummy teether, disrupted the discrimination of the /dɑ/ - /dɑ/ contrast, where the contrasting sounds crucially involve movement of the front and tip of the tongue in their production; a gummy teether, but not a flat teether, disrupted the discrimination of the /ba/ - /da/ contrast, a distinction that uses the lips as an articulator. European Portuguese-learning infants' ability to discriminate the native /da/ and /za/ syllables was also found to be disrupted by the presence of teethers [24]. Again, the sensorimotor influences occur with sounds infants have not had previous experience with in perception, as they are not part of the infants' language environment, or in production, as they are not yet producing those speech sounds.

This set of findings strongly suggests that the link between perception and production emerges very early in infancy, before infants have had some experience with speech production. Adult speech perception has long been seen as intertwined with speech production, and a large body of work offers clear evidence that motor brain areas are involved in perceptual analysis [25-27, 12 and 15 for reviews]. The motor theory of speech perception contends that what the listener auditorily perceives are the articulatory gestures, or production motor plans, of the speaker [28-29]. Within ‘Analysis by Synthesis’ approaches, the listener reconstructs the articulatory gestures of the speaker, resulting in an abstract representation of a motor program, or even an actuated motor program [30-31]. While adult listeners’ representations might be fed by their experience producing speech, as suggested in most of this work, the development of the link between perception and production and its foundations in infancy are currently under debate.

Vocal imitation studies have shown that after continued exposure to specific speech sounds infants are able to adjust their speech production and alter their vocalizations to exhibit similar phonetic properties to the speech sounds they were exposed to [32-33, 11]. Moreover, between 6 and 8 months of age, infants show a preference for speech sounds with infant-like vocal track resonances. The strength of the preference is positively correlated with age, indicating that it develops with infants’ emerging vocal production skills [34]. These findings
seem to suggest that the perception-production link emerges with infants' speech production abilities, namely with their developing vocalizations of canonical syllables as sequences of consonants and vowels.

However, the sensorimotor constraints to speech perception demonstrated in the infant brain imaging studies, multimodal audio-visual speech perception studies, and studies on sensorimotor influences in speech discrimination described above, crucially emerged independently of infants' auditory exposure to the speech sounds (i.e., in response to sounds they had never heard), or their ability to actually produce them. This raises the fundamental question of the mechanisms behind the early development of the perception-production link. A current view suggests that the early developing auditory-articulatory mappings are rooted in spontaneous non-speech movements in utero and in the first months of life [12]. Yet, a crucial piece is still missing in the developmental account of the perception-production link, as research has not addressed whether infants produce linguistically-driven articulatory movements when perceiving speech. Such covert articulatory movements, not connected to real vocalizations, would be the manifestation of actuated movements triggered by speech perception that could play a critical role in establishing auditory-articulatory mappings.

The present study addressed this key question by employing ultrasound imaging, a noninvasive method commonly used to capture tongue movement in young children [e.g., 35-36]. We recorded the tongue shapes of 6-month-old infants while listening to vowel-consonant-vowel sequences that differed only in the articulatory configuration of the consonant, to determine whether infants produced articulatory movements that approximated to the articulatory gestures of the speech sounds they perceived. To the best of our knowledge, there are no studies on speech driven tongue movements in children younger than 12 months.

## Methods

### Ethics

The study was conducted in accordance with the recommendations of the European Union Agency for Fundamental Rights and the Declaration of Helsinki. Ethical approval was obtained by the Ethics Committee for Research of the School of Arts and Humanities of the University of Lisbon (P2LINK project, 19_CEI2021). Infants' parents gave written informed consent before participation in the study.
## Participants

Data from thirteen infants were included in the study (eight girls, mean age 6 months and 18 days, age range from 5 months and 25 days to 7 months and 13 days). The infants were raised in monolingual European Portuguese-speaking homes and were recruited from the wider Lisbon area. They were born full term, had no familial risks for language impairment, and no known language-related or hearing-related issues according to parental report. The employment and educational status of the infants' parents or guardians was balanced, with 55% classified as moderately to highly qualified and 45% as low to moderately qualified (according to the Portuguese Classification of Occupations, Instituto Nacional de Estatística, 2011 [37]). Another nine infants were tested but excluded due to bad data quality and missing data (as detailed in the data processing section). Eight infants were tested but did not complete the experiment due to moving (1), fussiness (6), and equipment failure (1). Overall, the attrition rate was high, but similar to that usually reported for experiments with infants, such as those using the high amplitude sucking procedure, or the electrophysiological method (e.g., [38-39]).

Infants' emerging speech production abilities were assessed with the European Portuguese version of the Communication and Symbolic Behavior Scales Developmental Profile (CSBS DP) Infant-Toddler checklist [40], as well as the Language and Communication Subscale of the Griffiths Mental Developmental Scales [41]. The CSBS DP checklist is a parental report that includes an item specifically targeting the ability to produce sound sequences combining consonants and vowels. The Language and Communication Subscale of the Griffiths includes an observational item responded by the professional administering the scale indicating whether the infant has produced repeated sequences of canonical syllables. Based on the CSBS DP, only two of the infants were reported to produce consonant-vowel sound combinations. According to the Griffiths observational measure, the same two infants and one other infant were able to produce sequences of two repeated syllables that included a consonant different from the labials /m/ and /b/. All the other infants were reported as not producing sound combinations (8 infants), or using only labial consonants in their syllabic vocalizations (2 infants).

## Stimuli

The stimuli consisted of naturally produced vowel-consonant-vowel (VCV) sequences. The vowel used was the low back vowel /a/ that was kept the same, whereas the consonant varied. Three consonants with distinct articulatory targets were used: the labial voiceless stop /p/, the
dental voiceless stop /t/, and the velar voiceless stop /k/. While /p/ is articulated with both lips only, the articulation of /t/ and /k/ involves the tongue. Crucially, different parts of the tongue are involved in the production of the two consonants: /t/ is produced with the tip and blade of the tongue moving towards and touching the back of the upper front teeth; /k/ is produced with the back of the tongue moving towards and touching the soft palate. Thus, /t/ is produced with a tongue shape towards the front of the mouth cavity, whereas /k/ is produced with a tongue shape towards the back of the mouth cavity. Ultrasound images illustrating the articulation of /t/ and /k/ by an adult European Portuguese speaker are provided in the Supplementary materials (Figure S1).

We focused on consonants given that in prior work sensorimotor influences in infant speech perception were demonstrated with consonants [21-24]. Voiceless stops were chosen because they are among the most frequent consonants in the native language, and overall more frequent than voiced stops [42]. Based on the criterion of accurate production 80% of the time a target with the consonantal sound is attempted by the infant, the age of acquisition of these consonants by European Portuguese-learning infants has been reported to be after 12 months, in the following order [43]: /p/ (Mean age, 18 months), /t/ (Mean age 22 months), /k/ (Mean age 25 months). Emerging target-like productions occur earlier and were reported to follow the same order: /p/ (Mean age 14 months), /t/ (Mean age 15 months), /k/ (Mean age 19 months). These patterns of acquisition reflect general tendencies reported across languages [44], with stop consonants (together with nasals) being acquired before other consonants, and labials (like /p/) and coronal consonants (like the dental /t/) being acquired before dorsal consonants (like the velar /k/).

A female native speaker of European Portuguese uttered the three types of VCV sequences – /apa/, /ata/, and /aka/ – in child-directed speech, as if each VCV sequence constituted one utterance with statement intonation (see Figure S2 in the Supplementary materials). A Philips SBC ME400 microphone connected to the SpeechStation21 Software (Sensimetrics Corporation) via a Toshiba laptop computer was used and the speech recordings took place in a sound treated room at the Lisbon Baby Lab at the University of Lisbon. Four tokens of each type of VCV sequence were selected and included in the stimuli sound files. Three stimuli sound files were constructed, each consisting of four tokens of one type (e.g., /ata/), separated by an interval of one second. Each sound file had nine seconds in length.
## Procedure

Infants were tested at the Lisbon Baby Lab. They were all recorded with the Micro Speech Research ultrasound system (Articulate Instruments Ltd), with a microconvex short 10mm radius probe with large field of view, and a sampling rate of 132 Hz (the interval between ultrasound frames was around 8 ms). The probe was positioned with the probe mark visible to the researcher, determining the direction of the tongue tip to the left in the ultrasound tongue image.

Infants sat in a baby lounge chair, fixed and slightly reclined, while a researcher gently and firmly held the ultrasound probe below the infant's chin (see Figure 1). Two well-trained experimenters were involved in data collection. One held the probe and controlled for infant head movement by placing the left hand gently on the infant's nape. The other monitored the ultrasound equipment. During data collection, the infant's caregiver held a toy in front of the infant. This helped to reassure the infant and keep them calm and still. Caregivers were instructed not to talk or interact with the infant in any way. The audio stimuli were delivered at a constant and comfortable hearing level through a loudspeaker positioned behind the chair.

<figure><img src="image_2.png" /><figcaption>Figure 1. Setup of the infant ultrasound experiment.</figcaption></figure>

The experiment followed a block design beginning with stretch of silence followed by four repetitions of one type of VCV token per block, corresponding to a 9 second sound file (see Figure 2). Overall, infants listened to eight VCV tokens of each type in two blocks, with a one second silent interval between tokens and a 9 second interval between a sequence of three
blocks. The nine second interval consisted of a non-speech sound of running water, to introduce
a clear break into the speech auditory mode. The experiment lasted less than 1,5 minutes.

<figure><img src="image_3.png" /><figcaption>Figure 2. Experimental design.</figcaption></figure>

Prior to testing, several pilots were run with different groups of infants to fine-tune the
experimental design and procedure. Aspects like the position of the infant, the use of caregiver
collaboration, toy use as a fixation point, and the number of token repetitions were modified to
face the challenges of articulatory data collection with infants and optimize the experimental
design and procedure. Nevertheless, despite our efforts, the attrition rate was high and several
infants did not provide enough good quality datapoints for analysis (as detailed below) and had
to be excluded.

Data processing and analysis

Tongue image analysis was performed with Articulate Assistant Advanced (AAA) software (Articulate Instruments Ltd, [45]). Following a common procedure in studies with young children (e.g., [36]), qualitative examinations of the video data post recording were conducted and bad tokens were marked and excluded from analysis (e.g., those without a clear tongue contour image, or with signs of infant/probe movement). For all the other tokens, automatic detection of the tongue contour within the one second interval after the auditory presentation of a VCV sequence was hand-checked and corrected.

With the goal of quantifying the position of the tongue contour relative to the front/back
dimension, the curve position (CP) measure was used. This measure quantifies the extent of
maximal excursion within a single tongue shape and determines where on the tongue curve the
excursion is [46] (see Figure 3): lower CP values indicate that the tongue has moved towards the
back, and higher CP values denote that the tongue has moved towards the front. Ménard et al.
(2012) [46] showed that the CP measure is robust to ultrasound probe movements. The CP
measured was extracted in sixteen equally spaced intervals within the one second interval after
the presentation of a VCV sequence. Therefore, a measure of the front-back position of the
tongue was taken roughly every 60 ms within the one second window after an auditory stimulus
was presented. Consequently, 128 datapoints were obtained for each of the three VCV token
types per participant (16 x 8). Participants included in the analysis had a minimum of 50% of all
the possible datapoints per token type (i.e., 64 out of 128). Overall, 4752 datapoints were
considered for analysis: 1568 for /apa/, 1584 for /ata/, and /1600/ for /aka/.

<figure><img src="image_4.png" /><figcaption>Figure 3. Curve position measure: the ratio of the distance AD over DB. Tongue shape with the tongue positioned towards the front of the vocal tract (in blue), versus the tongue positioned towards the back of the vocal tract (in red).</figcaption></figure>

To test for differences in CP across the three token types /apa/, /ata/ and /aka/, we
employed a linear mixed-models analysis performed in SPSS (version 29, IBM SPSS Statistics).
The fixed effects were token type (/apa/, /ata/, /aka/) and token number (token position within a
block, i.e., 1, 2, 3, 4), with interaction term, and we controlled for participants in the random
effect structure. The reference was set to /ata/ for token type and to ‘4’ for token number. Token
number was included in the model to test whether infants systematically differed in CP across
token type regardless of token type position, or whether differences in CP only emerged after a
number of repetitions of the same token type. A Type III Analysis of Variance with Satterhwaite
method was used to account for differences across groups. If infant tongue shape varied as a
function of the speech token they heard, we expect to find evidence of some kind of tongue to
sound correspondence, with lower CP values triggered by listening to /aka/ as opposed to higher
values for /ata/. Given that the articulation of /p/ does not involve the tongue, we expect that the
tongue shape after listening to /apa/ reflected the articulation of the back vowel, with CP values
closer to /aka/ than to /ata/. By contrast, an overall arousal response to speech would be
unconstrained, displaying no systematic articulatory to sound correspondences.
## Results

The CP values across token types for all infants are shown in Figure 4. The analysis revealed a statistically significant effect of Token Type (F(2,4728) = 81.95, p < 0.001), Token number (F(3,4728) = 4.79, p = 0.002), and their interaction (F(6,4728) = 3.42, p = 0.002). Further inspection of the model showed that /aka/ and /apa/ were significantly different from /ata/ (Intercept = 1.031; β[aka] = -0.07, SE = 0.016, t = -4.56, p < 0.001, CI 95 [-0.10, 0.04]; β[apa] = -0.05, SE = 0.016, t = -3.44, p = 0.001, CI 95 [-0.08, -0.02]). Pairwise comparisons (Bonferroni adjusted) demonstrated that the CP values for /ata/ (M = 1.054) were higher than for /aka/ (M = .976), t = 10.08, p < .001) and /apa/ (M = .962, t = 11.89, p < 0.001). By contrast, /aka/ and /apa/ did not differ (t = 1.87, p = 0.146). An illustration of infants’ tongue shapes showing the tongue positioned more towards the front of the vocal tract (higher CP value) after listening to /ata/, and more towards the back of the vocal tract (lower CP value) after listening to /aka/ is provided in Figure 5.

<figure><img src="image_5.png" /><figcaption>Figure 4. Violin plots of curve position values across token types. The central dot indicates the median, the box the interquartile range, and tails the range from minimum to maximum value.</figcaption></figure>
<figure><img src="image_6.png" /></figure>

Figure 5. Ultrasound tongue images of an infant participant after listening to /ata/ (top panel) and /aka/ (bottom panel). ‘M’ indicates the mandible. The AAA tracking of the tongue contour is shown in red, and the white line above it corresponds to the hard and soft palate structures. The arrow signals the location of the point of maximal excursion on the tongue contour.

Furthermore, the main effect of Token number was driven by values for token 3 (M = 1.01) being generally higher than for token 4 (M = 0.99, t = 2.68, p = 0.036), and token 1 (M = 0.98), t = 3.45, p = 0.03). No other comparisons reached significance (ts < 2.3, ps > .09). Finally, the model revealed a significant interaction between Token type and Token number. Pairwise comparisons showed that /ata/ was significantly higher than /aka/ (ts > 2.8, ps < .01), and apa (ts > 3.4, ps < .001) in all token numbers. /aka/ and /apa/ were different in token numbers 1 and 2 (ts > 2.2, ps < 0.024, /aka/ being higher than /apa/) and similar in token numbers 3 and 4 (ts < 1.08, ps > 0.28).

## Discussion

The present study investigated a key question not yet addressed in studies on the emerging perception-production in early development: whether infants produce covert, linguistically-driven articulatory movements when perceiving speech. To that end, we employed ultrasound imaging and recorded the tongue shapes of 6-month-old infants while listening to vowel-consonant-vowel sequences that contrasted only in the articulatory configuration of the
consonant: /apa/, /ata/, and /aka/. Using a block design, infants were exposed to four repetitions of each token type per block. Infants' tongue shapes were measured within the one second silent interval between the auditory tokens, by computing the curve position (CP) measure, a quantitative measure of the position of the tongue contour relative to the front/back dimension [45-46]. We hypothesized that, if infant tongue shape varied as a function of the speech token heard, higher CP values would be triggered by listening to /ata/, as the /t/ consonant is articulated towards the front of the vocal tract, and lower CP values by listening to /aka/, as /k/ is articulated towards the back of the vocal tract. In addition, and given that the consonant /p/ does not involve the tongue as an articulator, we expected that CP values after listening to /apa/ would approximate those for /aka/ and differ from /ata/, possibly reflecting the articulation of the back vowel /a/. These hypotheses, if borne out, would provide evidence for the presence of a tongue to sound correspondence. On the contrary, any overall arousal response to speech should display no systematic articulatory to sound correspondence.

Our findings revealed a crucial difference in infants' tongue shape between the /ata/ and /aka/ conditions, with higher CP values for /ata/ than /aka/ in line with our hypothesis. Moreover, CP values for /ata/ were also higher than for /apa/, whereas those for /apa/ and /aka/ did not differ. Importantly, the CP values for /ata/ were higher than those for /aka/ and /apa/ after each of the four repetitions of each token type. These results indicate that differences in CP triggered by the auditory token started to emerge immediately after the first token was heard, and were robustly maintained during the four repetitions of the auditory token. In other words, the effect unfolded quickly in time, without requiring continued exposure to a specific speech sound sequence. Overall, the results demonstrate that infants produced articulatory movements by placing the tongue more to the front or back in the direction of the sounds they heard.

It has been argued that infant speech perception involves articulatory and motor information from speech production [10-12]. Evidence from brain imaging [13-15], multimodal audio-visual speech perception [16-20], and sensorimotor constraints on speech discrimination [21-24] clearly supports the view that the perception-production link emerges very early in infancy. In adult speech perception, the long documented link between perception and production might rely on adult listeners' experience producing speech [28-31]. However, in infants evidence for the perception-production link has been found before infants have had some experience with speech production, and critically before they have developed the ability to actually produce the sounds they are perceiving. Moreover, the link between speech perception
and articulatory-motor information from production has also been found in response to speech
sounds infants' had never heard before because they were not present in the infants' language
environment. This has raised fundamental questions about the foundations and development of
the perception-production link.

Our findings that infants produce linguistically-driven articulatory movements when perceiving speech add an important piece to the current understanding of the developing auditory-articulatory mappings in early infancy. The presence of such covert articulatory movements triggered by speech perception, but independent from real vocalizations, contributes to explain why speech perception activates infants’ motor brain areas before infants produce speech. It also offers a new angle to the understanding of infants’ multisensory speech perception abilities to integrate auditory and articulatory-visual information relative to speech sounds they are not (yet) able to produce and/or have not been exposed to. Furthermore, it provides a straightforward explanation for sensorimotor influences on infant speech perception: given that speech perception triggers a specific actuated articulatory response, infants’ discrimination abilities are disrupted when that specific articulatory response is inhibited due to the presence of some sort of oral-motor manipulation (e.g., a teething toy).

Early developing auditory-articulatory mappings have been suggested to be rooted in
spontaneous non-speech movements in utero and in the first months of life [12]. Our findings
suggest that 6-month-old infants produce speech driven actuated movements, adding a crucial
piece to the developmental account of the perception-production link. These spontaneous
auditory driven articulatory responses while listening to speech might further support the early
developing auditory-articulatory mappings, which will be later strengthened with infants’
upcoming experience with speech production.

In conclusion, our findings are the first to suggest that infants engage in speech driven
oral-motor responses modulated by the sounds perceived, advancing our understanding of the
mechanisms for the emerging perception-production link. Future research needs to replicate the
present findings in larger samples of infants and in infants exposed to different languages to
assess the robustness and generalizability of the articulating while listening effect. It should also
address the emergence of the articulating while listening effect by studying younger infants (e.g.,
between 3 to 5 months of age). Additionally, other ultrasound tongue imaging measures should
be explored to examine other possible dimensions of tongue to sound correspondences, such as
tongue bunching (contrasting articulations with a more bunched/elevated tongue versus a flatter
tongue). Last but not least, the presence or absence of linguistically driven articulatory responses when perceiving speech should be studied across diverse populations of infants, including those with atypical development, to further our understanding of the role emergent auditory-articulatory mappings might play in language development.

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Acknowledgments

The authors would like to thank all infants and parents who participated in this study, and Gabriela Silva for help with data collection. This research was funded by The Foundation for Science and Technology (FCT) through the project P2Link—The Perception-Production Link in Early Infancy: A language acquisition oral-motor intervention study, grant number PTDC/LLT-LIN/1115/2021, https://doi.org/10.54499/PTDC/LLT-LIN/1115/2021.

Author contributions

S.F. and M.V. conceived, designed and coordinated the study. A.N. contributed to the study design. C.S. collected the data. Data analysis was conducted by C.S and N.P., and S.F., M.V. and A.N. contributed to the interpretation of the findings. Statistical analysis was performed by C.S. with the contribution of J.P.. S.F. drafted the manuscript, and M.V. and A.N. critically revised it.

Data availability statement

The dataset generated by this study is available from the corresponding author on reasonable request.

Competing interests statement

The authors declare no conflicts of interest
Supplementary materials

<figure><img src="image_7.png" /><figcaption>Figure S1. Ultrasound image of a female adult speaker showing the tongue shape during the articulation of /t/ (top panel) and /k/ (bottom panel), before the release of the stop consonant. ‘M’ indicates the mandible. The tongue contour is highlighted in red.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure S2. A sequence of four tokens of the /ata/ (top panel) and /aka/ (bottom panel) type. The black line represents the falling pitch contour characteristic of statement intonation.</figcaption></figure>