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Hauke S. Meyerhoff, Brian Scholl; Auditory-induced bouncing is a visual (rather than a cognitive) phenomenon: Evidence from illusory crescents. Journal of Vision 2014;14(10):426. doi: https://doi.org/10.1167/14.10.426.
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© ARVO (1962-2015); The Authors (2016-present)
When two discs move toward each other, superimpose, and continue moving afterwards, observers typically perceive them as streaming past each other. If a brief tone occurs at the moment of overlap, however, then the discs are perceived as bouncing off each other. Recent research has attributed this effect to decisional (rather than perceptual) processes by showing that auditory tones alter response biases but not the underlying sensitivity for detecting objective bounces. Here we explore the nature of this phenomenon using 'illusory causal crescents': if observers view disc A move until fully overlapped with disc B, after which A stops and B moves, they may perceive either streaming or launching — but when perceiving launching, they also see B move before being fully overlapped with A (i.e. leaving an uncovered crescent). In several experiments, we measure illusory crescents in bouncing/streaming displays with auditory tones. Participants adjusted two probe discs until they matched the perceived overlap of an ongoing streaming/bouncing event. We first show that an illusory crescent emerges when the onset of a brief tone is synchronized with the moment of overlap between the two discs. We then show that the timing of this tone matters: illusory crescents still arise for tones occurring slightly earlier than the moment of maximal visual overlap, but when the tone follows the moment of maximal overlap, the crescents disappear. Moreover, the perceived "coincidence" of the tone timing is critical: illusory crescents also disappear when a perfectly-synchronized tone is heard as part of a larger repeating perceptual group of sounds. The presence of illusory crescents at all in such displays explains why observers have difficulty distinguishing objective streaming vs. bouncing. And collectively, these experiments suggest that sound-induced bouncing is a perceptual (rather than a cognitive) phenomenon, resulting from changes in visual (rather than decisional) processing.
Meeting abstract presented at VSS 2014
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