The rhythmic organization of speech into regular intervals (i.e. isochrony), is a strong perceptual phenomenon. However, Investigators have been unable to demonstrate the existence of isochrony in production data. It is hypothesized in this study that the intended rhythm of a speaker is in fact isochronous, but that this is obscured by several distorting influences which introduce durational irregularity at the syllable level, e.g. intrinsic duration, stress, position of the syllable in a phrase and number of syllables in a phrase. It is proposed that removing the predictable durational irregularities will yield a more regular signal, reflecting the (hypothesized) Intended Isochronous rhythm of the speaker. The latter two sources of distortion introduce progressive durational irregularity or "warping" which can be readily incorporated into an automated "dewarplng" procedure. A computer program was devised to compensate, at the syllable level for these two sources of distortion. The former two sources are not amenable to such an automated procedure, and were therefore not included. The "dewarping" program was run on the speech amplitude envelopes of two speakers, one French and one English. The results indicate that, for the French speaker, dewarping does remove some of the durational Irregularity, yielding a more regular amplitude envelope. For the English speaker, no such Improvement in regularity is obtained. This indicates that the dewarping used, which presumes the syllable as "unit" of dewarping, is appropriate for syllable-timed languages such as French, but inappropriate for stress-timed languages such as English. It therefore provides some support for isochrony in French at the syllable level. Finally, the results also give support to the hypothesis that the degree of warping perceived as regular in speech perception studies corresponds to the degree of dewarping which, conversely, yields the most regular speech amplitude envelope; however, further experimentation is necessary to determine the optimum values of the parameters of the dewarping function. / Medicine, Faculty of / Audiology and Speech Sciences, School of / Graduate

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Motor response selection is the process by which an intention to act is transformed into an action; this multifaceted process occurs at the interface between cognitive and motor systems. Despite the importance of response selection, the nature and neural implementation of this process is still a subject of debate (Thompson-Schill et al, 1997; Botvinick et al., 2001; Rushworth et al., 2004; Nachev et al., 2007). While previous research has demonstrated that the selection of finger movements relies on a distributed network involving premotor and prefrontal areas, the specific contribution of these regions, however, remains unclear. It is also unclear if the selection of words engages similar processes as the selection of finger movements, that is, if response selection is a domain-general or a domain-specific process. In order to address these issues, a set of four complementary studies using functional magnetic resonance imaging (fMRI) and repetitive transcranial magnetic stimulation (rTMS) was developed in which different factors affecting response selection were examined: selection mode, response type (words vs. oral movements), attention and response competition (conflict). / The results of these studies provide new insights into the neural architecture of response selection by uncovering the respective contribution of premotor areas (pre-SMA and PMA) and prefrontal areas (DLPFC and IFG). A preliminary two-stage model of response selection is proposed, in which the PMA is generating a set of response alternatives from which the pre-SMA performs selection using one of two different mechanisms (response facilitation and response inhibition). In general, these findings do not support the hypothesis of a medio-lateral gradient of control (Goldberg, 1985) but confirm the fundamental role of the lateral (PMA) and medial (pre-SMA) premotor areas in the process of selecting motor responses. / Importantly, the results also demonstrate that selection is a domain-general (response-independent) process. Uncovering the general, multifaceted nature of brain mechanisms is essential to reveal the basic units of control in the central nervous system; this knowledge is fundamental to broaden current understanding of the basic brain operations that are used to produce language. Theoretical and clinical implications of these findings are discussed.

This study was designed to clarify some of the issues surrounding the nature of hemispheric contributions to the processing of emotional and linguistic prosody, as well as to examine the relative contribution of different sensory modalities in processing prosodic structures. Ten healthy young participants were presented with semantically neutral sentences expressing affective or linguistic prosody solely through the use of non-verbal cues (intonation, facial expressions) while undergoing tMRI. The sentences were presented under auditory, visual, as well as audio-visual conditions. The emotional prosody task required participants to identify the emotion of the utterance (happy or angry) and the linguistic prosody task required participants to identify the type of utterance (question or statement). Core peri-sylvian, frontal and occipital areas were activated bilaterally in all conditions suggesting that processing of affective and linguistic prosodic structures is supported by overlapping networks. The strength of these activations may, in part, be modulated by task and modality of presentation.

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