Étude de la modularité de la synchronisation à la pulsation musicale : synchronisation sensorimotrice dans l’amusie congénitale

Music naturally compels most individuals to engage in rhythmic behaviors. We can think of someone tapping his foot or nodding his head to the beat of music. Synchronizing a movement to the beat may seem simple at first, but it is a complex behavior. At least, someone needs to be able to extract the beat and predict the timing of upcoming beats. This ability to couple movement and music could be achieved through entrainment. The specificity of beat-based entrainment to music is, however, debated. This thesis aimed to assess sensorimotor synchronization to music, singing, and speech in congenital amusia, in order to test the specificity of entrainment mechanism to musical beat. Congenital amusia refers to a neurodevelopmental disorder that can affect, depending on cases, pitch perception (pitch-based amusia) or beat perception (beat-based amusia). In the first study, individuals with pitch-based amusia were tested on their ability to perceive and to produce musical beat. The results indicated that about fifty percent of pitch-based amusic participants had associated deficits in beat production and beat perception. Still, cases of dissociation, with spared ability to synchronize to and perceive musical beat, were also identified. Therefore, findings highlight a connection between melody and rhythm processing in most cases of pitchbased amusia, although it is possible for these domains to be selectively impaired. Concurrently, cases of beat-based amusia, included in Study 2 and Study 3, had a specific impairment in their ability to synchronize a simple movement with musical beat, while performing within the normal range on a standardized measure of pitch perception. Study 2 and Study 3 had the objective to test hypotheses regarding the domain specificity of beat-based entrainment. In Study 2, entrainment to speech and music was compared in participants with beat-based amusia. Participants had to align taps to the perceived regularity in the rhythm of naturally spoken, regularly spoken (similar to rap music), and sung sentences. It was found that the amusic participants synchronized less accurately in all conditions. This result suggests that a general entrainment mechanism could maybe drive sensorimotor synchronisation to speech and music. In Study 3, we assessed the hypothesis according to which vocal imitation and beatbased synchronisation could share a common sensorimotor coupling mechanism. Here, participants had to sing a familiar song from memory, after hearing a model, with the model, and with a metronome. First, results from this study indicate that vocal-pitch abilities are similar to the general population in beat-based amusia, when singing from memory. Cases of poor-pitch singing could still be identified among amusic participants. However, no clear association between synchronization to beat and vocal-pitch abilities was found. Nonetheless, results from synchronous singing and singing with a metronome mirrored results from tapping tasks, indicating a lowered ability to synchronize with the beat across contexts in beat-based amusia. Overall, by investigating sensorimotor synchronization to music and singing in congenital amusia, this thesis work provides new evidence that sensorimotor synchronization to musical beat may be built on a domain-general entrainment mechanism that could be involved with auditory stimuli that are not beat-based, like speech.

Keyphrases: congenital amusia, beat, sensorimotor synchronization, music, singing, speech