MotorSpeech

This research leitmotif is the investigation of an overt motor strategy for facilitating speech perception in a noisy environment. Listening to speech activates cortical regions of the sensorimotor system, but their functional role in speech processing, as well as the conditions of their involvement, are strongly debated. Studies on speech perception in adverse listening conditions show that tracking the speech temporal dynamics (the speech rhythm) facilitates speech comprehension. Moreover, this mechanism gains importance with aging. Elderly must indeed rely more on top-down attentional focus, and in particular through the use of temporal cues, to compensate for impaired ascending acoustic information. Connectedly, we recently showed that the motor system is directly involved in the processing of auditory temporal dynamics and that during perception of an auditory rhythmic stream, temporal processing of auditory information is improved when participants produce overt rhythmic movements compared to when they are staying still. In this proposal, we will investigate whether these effects, observed during auditory processing, translate to speech processing. Speech is indeed in essence a temporal signal, structured according to of a hierarchy of timescales (phoneme, syllable, word, phrase). We hypothesize that the main contribution of motor areas to speech processing concerns the analysis of some of these speech timescales, providing a contextual temporal frame to distant auditory and frontal regions that process linguistic information. Moreover, we will characterize the acoustic conditions under which motor activity optimally contributes to speech perception. Hence, we will define whether, when and how the motor system and overt motor activity contributes to speech processing. To explore these issues, we will conduct four complementary state-of-the-art cognitive neurosciences studies on healthy participants. 1. The first study will capitalize on magnetoencephalography (MEG) and human depths stereotactic EEG (sEEG) recordings to investigate the contribution of motor areas to the processing of speech temporal dynamics during natural speech perception. The neural correlates of the phoneme, syllable, word and phrase level rhythms will be investigated. 2. In a behavioral-sEEG-MEG study we will then investigate the conditions under which motor areas optimally contribute to speech perception by manipulating two prime acoustic dimensions hypothesized to modulate motor implication: the speech signal-to-noise ratio and the speech rate. The impact of these acoustic manipulation and of motor activity proper on speech comprehension will also be established. 3. Based on these results, in a subsequent behavioral-sEEG-MEG study, participants will either stay still or overtly move in synchrony with the syllabic, words, or phrasal speech rate during a speech comprehension task. We will thus quantify the impact of an overt motor strategy on speech comprehension and describe its manifestation at the neural level. 4. Finally, in a behavioral-TMS study, we will examine which processes within motor areas are critical to drive such motor modulation of speech perception, by characterizing the relative contribution of the intention to act, the motor action per se, and the somatosensory feedback of the motor act on speech processing. This project both investigates fundamental questions of cognitive neurosciences and the development of a new behavioral strategy to optimise speech comprehension in adverse listening conditions. Overall, we should be able to propose a new motor theory of speech perception, more specified and neurophysiologically grounded. This project’s ultimate goal is to propose a new behavioral motor strategy to help people understand speech in adverse listening conditions. It will thus in particular address the effectiveness of a non-medical intervention designed to enhance speech comprehension.