Stimulus modality affects the accuracy of rhythm production in rats

Vocal learning species such as humans and parrots show auditory dominance when they synchronize their actions to an external rhythm. However, whether non-vocal-learners show a specific modality dominance in a rhythmic task has scarcely been examined. We predicted that rats, who are nocturnal and known to rely on acoustic communication, would exhibit higher sensitivity to auditory rhythm compared to visual rhythm. We investigated whether performance of a synchronization task by rats differs based on stimulus modality. We trained five rats to press a lever in time to auditory-visual, isochronous stimuli presented at three different tempos. Rats showed a lower correct response rate when auditory stimuli were presented than when visual or auditory-visual stimuli were presented in the 0.5-s inter-onset interval condition. Neither the asynchrony with the stimulus onset, nor the variability of interval production differed significantly based on the stimulus modality. Therefore, contrary to the prediction, they did not show auditory dominance; rather, rats showed poor performance on the task when a visual stimulus was not present. These results are consistent with the gradual audio-motor evolution hypothesis, and suggest that rats share ability for rhythm production, but this might not necessarily depend on auditory modality.