Abstract
When listening to auditory rhythms, such as in music, most people spontaneously and easily perceive an underlying periodic beat. Visual rhythms, in contrast, do not generally produce as strong a sense of the beat (i.e., spontaneous toe-tapping to visual rhythms is rare). Here we show that previous auditory experience changes how visually presented rhythms are perceived, increasing the likelihood of an implied beat being perceived in the visual stimulus.
Functional magnetic resonance imaging was used to characterize brain activity during perception of simple auditory and visual rhythms. In separate fMRI sessions, participants heard auditory rhythms or watched visual rhythms with the order of auditory and visual rhythm presentation counterbalanced across participants. Auditory and visual rhythms were delineated by sequences of tones or black squares, respectively, and participants judged whether sequences were ‘speeding up’ or ‘slowing down’. Two types of sequences were used. ‘Control’ sequences elicited similar behavioral judgments across all subjects. However, behavioral judgments for ‘test’ sequences were diagnostic of the strength/ease with which individuals perceived the underlying implicit beat.
As expected, participants perceived the implied beat much less in visual rhythms than in auditory rhythms. However, behavioral and brain responses to visual rhythms depended on prior exposure to the auditory rhythms. Behaviorally, visual rhythms produced a stronger sense of beat when they were preceded by exposure to the auditory rhythms than when they were presented first. Moreover, fMRI results revealed that visual rhythms with prior auditory exposure produced greater brain activity in the basal ganglia, right inferior operculum, supramarginal gyrus, and cerebellum compared to visual rhythms without prior auditory exposure. No such behavioral or neural order-dependent differences were found for the auditory rhythms.
