Child-directed speech (CDS) differs from adult-directed speech (ADS) in several respects whose possible facilitating effects for language acquisition are still being studied. One such difference concerns articulation rate --- the number of linguistic units by the number of time units, excluding pauses --- which has been shown to be generally lower than in ADS. However, while it is well-established that ADS exhibits an inverse relation between articulation rate and information-theoretic surprisal --- the amount of information encoded in a linguistic unit --- this measure has been conspicuously absent in the study of articulation rate in CDS. Another issue is if the lower articulation rate in CDS is stable across utterances or an effect of local variation, such as final lengthening. The aim of this work is to arrive at a more comprehensive model of articulation rate in CDS by including surprisal and final lengthening. In particular, one-word utterances were studied, also in relation to word-length effects (the phenomenon that longer words generally have a higher articulation rate). To this end, a methodology for large-scale automatic phoneme-alignment was developed, which was applied to two longitudinal corpora of Swedish CDS. It was investigated i) how articulation rate in CDS varied with respect to child age, ii) whether there was a negative relation between articulation rate and surprisal in CDS, and iii) to what extent articulation rate was lower in CDS than in ADS. The results showed i) a weak positive effectof child age on articulation rate, ii) a negative relation between articulation rate and surprisal, and iii) that there was a lower articulation rate in CDS but that the difference could almost exclusively be attributed to one-word utterances and final lengthening. In other words, adults seem to adapt how fast they speak to their children's age, speaking faster to children is correlated with a reduced amount of information, and the difference in articulation rate between CDS and ADS is most prominent in isolated words and final lengthening. More generally, the results suggest that CDS is well-suited for word segmentation, since lower articulation rate in one-word utterances provides an additional cue.

Ce travail a trois objectifs principaux. Tout d’abord, contribuer à l’étude du système rythmique des langues et des variétés dialectales à travers l’analyse du rythme de l’anglais parlé au pays de Galles et de la langue galloise en utilisant comme point de comparaison l’anglais dit standard. Puis, démontrer qu’il existe un allongement final bien plus marqué en gallois et en anglais gallois (bilingues & monolingues) qu’en anglais standard. Et enfin, prouver que les résultats obtenus lors de cette étude sont étroitement liés à l’influence majoritaire de la langue galloise sur celle des autres variétés d’anglais présentes dans ce pays. Dans cette optique, nous avons, dans un premier temps, élargi la base de données Eurom I et nous avons ensuite mené différents tests de perception et études statistiques. Il en ressort que la langue galloise est effectivement le substrat principal de l’anglais parlé au pays de Galles, que ce soit chez les gallois bilingues ou monolingues (personnes résidant au pays de Galles ne parlant qu’anglais). En effet, la longueur de l’allongement en syllabe finale inaccentuée va en décroissant du gallois à l’anglais standard. Cependant, étant donné l’impossibilité de catégoriser de façon précise le rythme du gallois et de l’anglais gallois en tenant compte de tous les paramètres métriques, il est plus difficile d’affirmer de façon catégorique que la langue galloise joue un rôle prépondérant sur ces derniers. / This thesis has three main objectives. First of all, to contribute to the study of the rhythmical system of languages and dialectal varieties through the analysis of rhythms in Welsh English and Welsh, using Standard English as a focal comparative element; then, to demonstrate that the final lengthening is much more notable in Welsh and in Welsh English (bilinguals and monolinguals) than in standard English; finally, to prove that this study’s results are tightly intertwined with the influence of the Welsh language, which is greater than that other English accents present in this country. For that purpose, we have first widened the Eurom 1 database and then carried out various perception tests and statistical analysis. The results show that the Welsh language is the substratum of the English spoken in Wales, as much for bilinguals as for monolinguals (residents of the country speaking only English). Indeed, the length of the final unstressed syllable decreases from Welsh to Standard English. However, as it is impossible to classify with precision the rhythm of Welsh and Welsh English taking into account all the metrics, it is more difficult to establish with certainty whether the Welsh language has a major influence on the latter.