Synchronization to auditory and visual rhythms in hearing and deaf individuals.

A striking asymmetry in human sensorimotor processing is that humans synchronize movements to rhythmic sound with far greater precision than to temporally equivalent visual stimuli (e.g., to an auditory vs. a flashing visual metronome). Traditionally, this finding is thought to reflect a fundamental difference in auditory vs. visual processing, i.e., superior temporal processing by the auditory system and/or privileged coupling between the auditory and motor systems. It is unclear whether this asymmetry is an inevitable consequence of brain organization or whether it can be modified (or even eliminated) by stimulus characteristics or by experience. With respect to stimulus characteristics, we found that a moving, colliding visual stimulus (a silent image of a bouncing ball with a distinct collision point on the floor) was able to drive synchronization nearly as accurately as sound in hearing participants. To study the role of experience, we compared synchronization to flashing metronomes in hearing and profoundly deaf individuals. Deaf individuals performed better than hearing individuals when synchronizing with visual flashes, suggesting that cross-modal plasticity enhances the ability to synchronize with temporally discrete visual stimuli. Furthermore, when deaf (but not hearing) individuals synchronized with the bouncing ball, their tapping patterns suggest that visual timing may access higher-order beat perception mechanisms for deaf individuals. These results indicate that the auditory advantage in rhythmic synchronization is more experience- and stimulus-dependent than has been previously reported.