LINKING DIFFERENCES IN PHONOLOGICAL REPRESENTATIONS
AND COARTICULATION DEGREE: A MODELLING APPROACH

Dzhuma Abakarova<fnref n="1" />,<fnref n="2" />, Susanne Fuchs<fnref n="2" />, Aude Noiray<fnref n="3" />,<fnref n="4" />

There is converging evidence across languages that children show greater coarticulation degrees (CD) i.e., greater spatial overlap between consecutive segments than adults (e.g., Noiray et al., 2013; Noiray et al., 2019a; Nittrouer, 1989; Zharkova et al., 2011). Previous research has suggested that CD reflects the nature of phonological representations, and so related developmental differences in CD to the emergent awareness of phonemes (Nittrouer et al., 1989). Recent findings of a negative correlation between CD and phonological awareness (Noiray et al., 2019b) provide support for this view. However, phonological awareness develops in parallel to motor control, vocabulary and various other cognitive abilities, making it difficult to experimentally control for the independent contribution of each of these factors into CD differences. That is why the present study employs dynamic modelling to address the question of whether developmental differences in coarticulation degree and phonological representations are causally related.

In our understanding, phonological representations are sensorimotor in nature. They are associations between sensory cues and motor plans. Children's initial motor representations are more variable than adults' with less clearly defined boundaries between categories and they lack an abstract level of categorization. With the growing vocabulary and practice, children's motor representations for various segments become more delimited. Over time, the optimal trajectories are selected and the ones that lead to overlap and compromise intelligibility or take more effort are discarded. Therefore, in children, the space of motor realizations for a segment is larger than in adults. We hypothesize that greater variability in phonological representations allows for greater spatial overlap between co-produced segments and results in the observed age differences in CD. To test this hypothesis, we conducted a series of simulations with the Task Dynamics Application (TaDA, Nam et al., 2004). To enable comparison with experimental findings, we simulated the utterances from Noiray et al. (2019) dataset. The dataset consisted in ultrasound tongue imaging data collected in 3- to -7-year-old children and adults producing CV syllables ( /b/, /d/, or /g/ in six vowel contexts), and preceded by a carrier word /amə/.

The age differences in variability of representations were simulated by manipulating the variability of the gestural targets in TADA. Gestural targets determine constriction locations within the vocal tract (i.e., further front or back). In the default TADA settings, they are point targets, but here they are modeled as target regions of varying size to simulate the difference between smaller and bigger space of motor realizations for a segment. Preliminary results suggest that the simulations with higher variability in gestural targets result in higher CD, as was observed for children in the experimental data (Figure 1). The effect is rather marginal for /b/, which does not involve a tongue gesture, while variability of /d/ and /g/ has a more pronounced effect on CD. This work contributes to an improved understanding of phonological representations and their development. It also helps dissect the relative role of developing phonological representations with respect to the experimentally observed age-related changes in coarticulation patterns.

<footnote n="1">¹University of Potsdam, Potsdam, Germany</footnote>

<footnote n="2">²Leibniz-Centre General Linguistics (ZAS), Berlin, Germany</footnote>

<footnote n="3">³Laboratoire Dynamique du Langage, CNRS UMR 5596, Lyon, France</footnote>

<footnote n="4">⁴Haskins Laboratories, New Haven, CT, United States of America</footnote>
<figure><img src="image_1.png" /></figure>

The linear regression of the horizontal position of the tongue body at the acoustically determined temporal midpoint of the consonant (consx) on the position of tongue body at acoustically determined temporal midpoint of the subsequent vowel (vowx). The regressions were fit for three consonants (/b, d, g/), each followed by one of the six vowels (/i:, y; u: a; e; o:/), for three simulated variability values (labelled "var"). A steeper slope of the line corresponds to a higher coarticulation degree.

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