Auditory and tactile signals combine to influence vision during binocular rivalry

Resolution of perceptual ambiguity is a major function of cross-modal interactions, making the study of bistable perception in multisensory contexts a powerful and revealing tool. We previously used binocular rivalry, a visual bistable phenomenon, to show that touch can specifically interact with vision to resolve spatial conflict between the eyes (Lunghi, Binda and Morrone, 2010). Here we investigate whether auditory and tactile stimuli can influence binocular rivalry generated by interocular temporal conflict. Using visual stimuli of different temporal frequencies (spatio-temporal noise filtered at 3.75 or at 15 Hz) to produce visual perceptual alternations, we added an amplitude modulated sound or a vibration that was congruent with one or the other visual temporal frequencies. We found that auditory and tactile stimulation interacted with binocular rivalry by promoting dominance of the congruent visual stimulus. This effect depended on the strength of the auditory/tactile stimulus, and was absent when a modulation depth declined to 33%. However, when auditory and tactile stimuli that were too weak on their own to bias binocular rivalry were combined, their influence over vision was very strong, suggesting the auditory and tactile temporal signals were summated. When auditory and tactile stimuli were presented at maximum strength, but temporally in anti-phase, they had no influence over vision, a null effect that again suggests audio-tactile summation in the temporal domain. These results indicate a functional link between auditory and tactile low temporal frequency channels, suggesting the existence of common neural substrates for the two sensory modalities.