We present a multidimensional acoustic report describing variation in speech productions on data collected from 500 francophone adult speakers (20 to 93 y.o.a.) as a function of age. In this cross-sectional study, chronological age is considered as a continuous variable while oral productions, in reading and speech-like tasks, are characterized via 22 descriptors related to voice quality, pitch, vowel articulation and vocalic system organization, time-related measures and temporal organization, as well as maximal performances in speech-like tasks. In a first analysis, we detail how each descriptor varies according to the age of the speaker, for male and female speakers separately. In a second analysis, we explore how chronological age is, in turn, predicted by the combination of all descriptors. Overall, results confirm that with increasing age, speakers show more voice instability, sex-dependent pitch changes, slower speech and articulation rates, slower repetition rates and less complexity effects in maximal performance tasks. A notable finding of this study is that some of these changes are continuous throughout adulthood while other appear either at old age or in early adulthood. Chronological age appears only moderately indexed in speech, mainly through speech rate parameters. We discuss these results in relation with the notion of attrition and with other possible factors at play, in an attempt to better capture the multidimensional nature of the notion of “age”.
Past results have suggested that initial strengthening (IS) effects target the contrastive phonetic properties of segments, with a maximization of acoustic contrasts in initial position of strong prosodic domains. Here, we investigate whether IS effects translate into a better acoustic discriminability within the French oral vowels system. Discriminability is assessed on the basis of classification results of two types of classifiers: a linear discriminant analysis (LDA) based on the four formants frequencies, and a deep convolutional neural network (CNN) based on spectrograms. The test set includes 720 exemplars of /i, y, e, ɛ, a, x, u, o, ɔ/ (with /x/=/ø, oe/) produced in a labial context, either in intonational phrase initial (IPi) or word initial (Wi) position. Classifiers were trained using a set of 4500 vowels extracted from a large read speech corpus. Results show a better discriminability of vowels (overall better classification rate) in IPi than in Wi with the two methods. Less confusion in IPi is found between rounded and unrounded, and between back and front vowels, but not between the vowels along the four-way height contrast. Less confusion between peripheral and central vowels also expresses a maximization of contrasts within the acoustic space in IPi position.
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