The purpose of the research presented here was to systematically investigate the role of speech perception on speech production in speakers of different ages and those with PD and hypokinetic dysarthria. For this, the experimental designs of auditory perturbation and mimicry were chosen. The initial research phase established that the magnitude of compensation to auditory vowel perturbation was reduced in 54 speakers of New Zealand English (NZE) when compared to previous studies conducted with speakers of American (AE) and Canadian English (CE). A number of factors were studied to determine possible predictors of compensation and distinguish between potential changes associated with ageing. However, no predictors of compensation were found for the overall group. Post-hoc analyses established an increased variability in response patterns in NZE when compared to previous studies of AE and CE. Subsequent follow-up analyses focused on the response-dependent categories of (1) big compensators, (2) compensators, (3) big followers, and (4) followers. Linear mixed-effect modelling revealed that in big compensators, the magnitude of compensation was greater in speakers who exhibited larger F1 baseline standard deviation and greater F1 vowel distances of HEAD relative to HEED and HAD. F1 baseline standard deviation was found to have a similar predictive value for the group of compensators. No predictors of compensation were found for the other two subgroups. Phase two was set up as a continuation of phase one and examined whether a subset of 16 speakers classified as big compensators adapted to auditory vowel perturbation. Linear mixed-effect modelling revealed that in the absence of auditory feedback alterations, big compensators maintained their revised speech motor commands for a short period of time until a process of de-adaptation was initiated. No predictors of adaptation were found for the group. Due to the unexpected results from the first two research phases indicating a dominant weighting of somatosensory feedback in NZE compared to auditory-perceptual influences, a different experimental paradigm was selected for phase three - mimicry. The purpose of this study was to determine whether eight speakers with PD and dysarthria and eight age-matched healthy controls (HC) are able to effectively integrate speech perception and speech production when attempting to match an acoustic target. Results revealed that all speakers were able to modify their speech production to approximate the model speaker but the acoustic dimensions of their speech did not move significantly closer to the target over the three mimicry attempts. Although speakers with moderate levels of dysarthria exhibited greater acoustic distances (except for the dimension of pitch variation), neither the perceptual nor the acoustic analyses found significant differences in mimicry behaviour across the two groups. Overall, these findings were considered preliminary evidence that speech perception and speech production can at least to some extent be effectively integrated to induce error-correction mechanisms and subsequent speech motor learning in these speakers with PD and dysarthria.

Le contrôle moteur a traditionnellement été étudié séparément des autres processus cognitifs qui sous-tendent la parole, dans la lignée de théories de la cognition présentant le cerveau comme un ensemble de modules relativement indépendants (Fodor & Pylyshyn, 2007). Cependant les recherches autour de la cognition incarnée (Varela, Thompson, & Rosch, 1991) et située (Barsalou, 2008), ainsi que des systèmes dynamiques (Smith & Thelen, 2003), menées ces trois dernières décennies soulignent que la cognition ne peut pas être considérée séparément d’un corps et de son environnement. Ce cadre constitue une source d’inspiration pour cette thèse et une motivation pour étudier les processus sensorimoteurs de la parole en lien avec les autres processus cognitifs.La parole peut-être décomposée en séquence d’unités linguistiques structurées sous forme d’une hiérarchie. Nous soutenons que ces unités sont ancrées dans des représentations sensorimotrices, associant une structure linguistique avec des informations perceptives et motrices. Ces unités correspondent-elles à des mots ? Des syllabes ? Des phonèmes ? Pour sonder les représentations assurant l’articulation de la parole, nous proposons d’utiliser un paradigme d’apprentissage auditorimoteur basé sur la perturbation du retour auditif (Caudrelier & Rochet-Capellan, accepté). Ce paradigme permet de modifier chez un locuteur des représentations sensorimotrices spécifiques, les représentations qui sous-tendent la production d’un item d’entrainement, par exemple un mot. Nous faisons ainsi l’hypothèse que si cette modification affecte la prononciation d’un autre mot, cela veut dire que la production de ce mot s’appuie sur une partie de ces représentations. Ainsi, l’observation du transfert d’apprentissage permet de révéler la structure de représentations qui assurent la production de parole.Une première étude chez l’adulte montre que le transfert d’apprentissage auditorimoteur a lieu à la fois aux niveaux du phonème, de la syllabe et du mot (Caudrelier, Schwartz, Perrier, Gerber, & Rochet-Capellan, 2018). Ces observations suggèrent que ces unités co-contribuent à l’articulation de la parole chez l’adulte. Les résultats sont mis en perspective par rapport aux théories et modèles de production de parole. Une 2ème expérience suggère que la modalité de présentation du stimulus (un mot à lire ou une image à dénommer) peut influencer le transfert d’apprentissage auditorimoteur (Caudrelier, Perrier, Schwartz, & Rochet-Capellan, 2018). Une 3ème étude chez des enfants de 4-5 ans et de 7-8 ans montre que les représentations du phonème émergent avant l’acquisition de la lecture (Caudrelier et al., en révision). De plus, un lien entre adaptation à la perturbation auditive et conscience phonologique est mis en évidence dans les deux groupes d’âge. Le potentiel caractère prédictif ou causal de ce lien est discuté.En conclusion, cette thèse exploite un outil original et productif pour explorer les représentations de la parole et étudier leur développement. Ce travail pourrait avoir des implications cliniques, pour la rééducation de la parole, et pour la dyslexie développementale. Il met en évidence des liens entre les niveaux sensorimoteurs, linguistiques et contextuels qui questionnent la nature des représentations qui sous-tendent la parole. / Speech motor control has traditionally been studied apart from other cognitive processes underlying speech production, since first cognitive theories presented the brain as a set of relatively independent modules (Fodor & Pylyshyn, 2007), taken apart from the body. However developments in embodied cognition (Varela, Thompson, & Rosch, 1991), grounded cognition (Barsalou, 2008) and dynamic systems (Smith & Thelen, 2003) occurred in the last three decades underline that cognition cannot be considered separately from a body and its environment. These frameworks constitute an inspiration for this thesis and a motivation to study motor control and sensorimotor processes in relation to other cognitive processes. Whether linguistic structures are grounded in sensorimotor processes will be an underlying question.A spoken message can be decomposed into sequences of linguistic units hierarchically structured. We argue that these speech units are grounded in sensorimotor representations, associating linguistic structures with auditory and motor information. Do these units correspond to words? Syllables? Phonemes? To probe the building blocks of speech production, we propose to use a paradigm of auditory-motor learning based on auditory feedback perturbation (Caudrelier & Rochet-Capellan, in press). This paradigm actually enables to change specific internal sensorimotor representations in speakers. Adaptation induces updating sensorimotor representations underlying the production of the training item. We assume that if this change affects the pronunciation of another word, it means that this word uses some of these updated representations. Thus, transfer patterns may reveal the structure of representations at stake.A first study in adults shows that transfer of auditory-motor learning occurs at word, syllable, and phoneme levels in parallel (Caudrelier, Schwartz, Perrier, Gerber, & Rochet-Capellan, 2018). These observations suggest that all these units may co-contribute to the organization of speech articulation in adult speakers. Experimental results are discussed in the light of existing theories and models of speech production. A second experiment suggests that whether a speaker reads a word aloud or names a picture may have an influence on the transfer of auditory-motor learning (Caudrelier, Perrier, Schwartz, & Rochet-Capellan, 2018). A third study in 4- to 5-year-old and 7- to 8 year-old children investigates whether phoneme sensorimotor representations may emerge during reading acquisition, or prior to it (Caudrelier et al., in revision). The observed transfer patterns suggest that phoneme representations emerge before reading acquisition, as a consequence of speech experience. Moreover, we found a relationship between adaptation to auditory perturbation and phonological awareness scores in both age groups. This suggests a link between sensorimotor representations and more explicit phonological representations. The potential causal or predictive nature of this link is discussed.Overall, this work exploits an original and fruitful tool to probe speech representations and study their development. It may have clinical implications with regards to speech rehabilitation, as well as developmental dyslexia. It also highlights connections between speech sensorimotor level and higher linguistic and contextual levels that further question the nature of speech representations.