Mirror mechanisms and predictive sensorimotor coding during vowel perception and production: a sparse-sampling adaptation fMRI study

International audienceRecent studies on mirror mechanisms and motor control have provided evidence for sensorimotor interactions in both speech production and perception. During speech production, decrease neural responses observed within the auditory and somatosensory cortices are thought to reflect feedback control mechanisms in which sensory consequence of the speech-motor act are evaluated with actual sensory input in order to further control production. Conversely, motor system activity observed during speech perception has been proposed to partly constrain phonetic interpretation of the sensory inputs through the internal generation of candidate articulatory categorizations. To identify possible sensory-to-motor and motor-to-sensory loops involved in predictive coding during both speech perception and production, we used a repetition suppression paradigm while measuring neural activity with functional magnetic resonance imaging. This adaptation paradigm refers to decreased activity in specific neural population due to either repeated motor acts or perceptual stimuli and has been proposed to reflect reduced prediction errors by means of top-down projections. In a first task, participants passively listened to 9 vowels (/i/, /y/, /u/, /e/, /ø/, /o/, /ɛ/, /œ/ and /ɔ/) previously recorded from their own voice. In a subsequent task, they produced the same vowels according to visual instructions. To determine adaption effects, each vowel occurred six times in a row in both tasks. In order to minimize scanner noise and movement-related imaging artifacts, a sparse sampling acquisition technique was used where vowel perception or production occurred during a silent interval between successive image acquisitions. To minimize possible covert motor simulation, the passive perception task was first performed in separate functional runs with the participants just being instructed to pay attention to the auditory stimuli. In line with a previous fMRI study (Grabski et al., 2010), a conjunction analysis on perception and production performed at the group-level showed common activations in the superior temporal gyrus and around the posterior part of the superior temporal sulcus (pSTS) bilaterally. Crucially, neural responses in the IFG, bilaterally, the left pSTS and the left inferior parietal lobule (IPL) were suppressed during both repeated vowel production and perception. Compared to the perception task, the suppressed responses observed during vowel production however differed in terms of magnitude and response curves and therefore cannot only be attributed to auditory feedback. The observed common brain areas sensitive to phoneme repetition during both perception and production provide evidence for mirror perceptuo-motor mechanisms involved in predictive coding and further highlight the sensorimotor nature of speech representations