Auditory influences on the temporal dynamics of binocular rivalry

Introduction When the two eyes are presented with dissimilar images, human observers report alternating percepts – a phenomenon coined binocular rivalry. These perceptual fluctuations reflect competition between the two visual inputs both at lower, monocular and at binocular, higher-level processing stages. Even though perceptual transitions occur stochastically over time, their temporal dynamics can be modulated by changes in stimulus strength, context and attention. While increases in stimulus strength (such as contrast) primarily abbreviate suppression phases of a percept, attentional and contextual factors predominantly lengthen its dominance periods. Goals This project investigates the influence of concurrent auditory stimulation on the temporal dynamics of binocular rivalry. In two psychophysics studies, we investigated whether sounds that provide directionally congruent, incongruent or no motion information modulate the dominance periods of rivaling visual motion percepts. Methods In the first psychophysics study, observers dichoptically viewed random-dot kinematograms (RDK) at 0 motion coherence in one eye and 50 in the other in a stereoscope, while being concurrently presented with directionally congruent auditory motion, noise and no sound. In the second psychophysics study, they viewed two RDKs of opposite motion directions at 100 coherence, with the auditory motion stimulus being directionally congruent with one of the two rivaling motion percepts. In both experiments, congruent auditory motion was temporally synchronized with visual motion to facilitate audio-visual integration into a coherent percept. Initial results Both experiments consistently revealed a statistically significant influence of sound on perceptual dominance times. In the first experiment, directionally congruent auditory motion but not noise increased the duration of the dominance phases of the RDK at 50 motion coherence. In the second experiment, auditory motion lengthened the dominance periods of the directionally congruent 100 RDK and abbreviated those of the directionally incongruent 100 RDK. Initial conclusions The results demonstrate that auditory stimuli influence the temporal dynamics of binocular rivalry. Auditory motion lengthened the dominance periods of a visual motion percept when it was directionally congruent, but shortened them when it was directionally incongruent. Thus, the (in)congruency of auditory motion primarily influences the duration of the dominance periods similar to purely visual contextual effects, even though a small effect was also observed on the suppression periods. In conclusion, the human brain draws on information from multiple senses to arbitrate between multiple rivaling perceptual interpretations