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Abstract:
When both eyes are presented with dissimilar images, human observers report alternating percepts - a phenomenon known as binocular rivalry. Subjects were presented dichoptically with (1) a looming/receding starfield or (2) a looming/receding Shepard Zoom (Berger, Siggraph 2003), the visual equivalent of the Shepard tone illusion. In four psychophysical experiments, we investigated the influence of (1) a real complex tone rising/falling in pitch and (2) rising/falling Shepard tones on the dominance and suppression times of the rivaling visual motion percepts (relative to non-motion sounds or no sounds). First, we observed longer dominance times of looming than receding visual percepts even in the absence of sound. Second, auditory looming signals enhanced this looming bias by lengthening the dominance periods of their congruent visual looming percept. Third, receding auditory motion signals reduced the perceptual looming bias, though this effect was less pronounced and not consistently observed. Collectively,
the results show that the perceptual predominance of looming relative to receding visual motion is amplified by congruent looming/receding auditory signals during binocular rivalry. Auditory looming/receding signals may influence the dominance times of their congruent and incongruent visual percepts via genuine multisensory and higher order attentional mechanisms at multiple levels of the cortical hierarchy.
