Poor synchronization to the beat may result from deficient auditory-motor mapping.

Moving to the beat of music is natural and spontaneous for humans. Yet some individuals, so-called 'beat deaf', may differ from the majority by being unable to synchronize their movements to musical beat. This condition was recently described in Mathieu (Phillips-Silver et al. (2011). Neuropsychologia, 49, 961-969), a beat-deaf individual, showing inaccurate motor synchronization to the beat accompanied by poor beat perception, with spared pitch processing. It has been suggested that beat deafness is the outcome of impoverished beat perception. Deficient synchronization to the beat, however, may also result from inaccurate mapping of the perceived beat to movement. To test this possibility, we asked 99 non-musicians to synchronize with musical and non-musical stimuli via hand tapping. Ten among them who revealed particularly poor synchronization were submitted to a thorough assessment of motor synchronization to various pacing stimuli and of beat perception. Four participants showed poor synchronization in absence of poor pitch perception; moreover, among them, two individuals were unable to synchronize to music, in spite of unimpaired detection of small durational deviations in musical and non-musical sequences, and normal rhythm discrimination. This mismatch of perception and action points toward disrupted auditory-motor mapping as the key impairment accounting for poor synchronization to the beat.