In perceptual rivalry an observer is presented with an ambiguous stimulus that can generate two mutually exclusive, alternating perceptions. The bistable apparent motion quartet, where two stimuli from diagonally opposite corners of a square are presented at the same time in alternation with the other diagonals of the square, has been shown to induce perceptual rivalry in both the visual and tactile domains. We explored the cross-modal effects of a stable, unambiguous tactile apparent motion stimulus on a bistable visual apparent motion quartet during both an event-related and a continuous report task, using spatially coinciding visual and tactile stimuli attached to the 2nd and 4th digit of subjects’ hand. In the event related task, subjects were presented with a sequence of two 500ms visual motion quartets at 600ms inter-stimulus interval and were asked to report the perceived sequence of the two possible percepts (horizontal or vertical motion). In the continuous report task, subjects were presented with 3 minute visual motion quartets (no ISI) and asked to continuously press a response button corresponding to their current percept. During both tasks, subjects were also presented with unambiguous tactile motion stimuli, either simultaneously or preceding the visual stimulus by 40 ms, in order to test potential cross-sensory biasing effects
No significant cross-modal influence of the tactile stimulus was observed in the event-related task. However, in the continuous report task, tactile stimulation in the horizontal direction significantly increased the total time subjects spent perceiving the ambiguous visual stimulus as a horizontal motion stimulus. Furthermore, results showed a significant bias in the perceptual reversal rate of the bistable visual stimulus towards the horizontal direction of the unambiguous tactile motion stimulus. These data show that the perception of a bistable motion stimulus in one modality (visual) can be positively biased by concurrent cross-sensory input (tactile), demonstrating multisensory links during perceptual rivalry.