Interactions between apparent motion rivalry in vision and touch

Introduction In multistable perception, the brain alternates between several perceptual explanations of ambiguous sensory signals. Recent studies have demonstrated crossmodal interactions between ambiguous and unambiguous signals. However it is currently unknown whether multiple bistable processes can interact across the senses. [1, 2] Using the apparent motion quartet in vision and touch, this study investigated whether bistable perceptual processes for vision and touch are independent or influence each other when powerful cues of congruency are provided to facilitate visuotactile integration. [3] Methods When two visual flashes and/or tactile vibration pulses are presented alternately along the two diagonals of the rectangle, subjects’ percept vacillates between vertical and horizontal apparent motion in the visual and/or tactile modalities [4]. Observers were presented with unisensory (visual/tactile), visuotactile spatially congruent and incongruent apparent motion quartets and reported their visual or tactile percepts. Results Congruent stimulation induced pronounced visuotactile interactions as indicated by increased dominance times and -bias for the percept already dominant under unisensory stimulation. Yet, the temporal dynamics did not converge for congruent stimulation. It depended also on subjects’ attentional focus and was generally slower for tactile than visual reports. Conclusion Our results support Bayesian approaches to perceptual inference, where the probability of a perceptual interpretation is determined by combining a modality-specific prior with incoming visual and/or tactile evidence. Under congruent stimulation, joint evidence from both senses decelerates the rivalry dynamics by stabilizing the more likely perceptual interpretation. Importantly, the perceptual stabilization was specific to spatiotemporally congruent visuotactile stimulation indicating multisensory rather than cognitive bias mechanisms