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Alexandra List, Marcia Grabowecky, Satoru Suzuki; Characterizing mixed percepts during binocular rivalry. Journal of Vision 2011;11(11):302. doi: 10.1167/11.11.302.
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© ARVO (1962-2015); The Authors (2016-present)
When two distinct images are presented to each eye at the same position, alternations or mixtures of those images are perceived: binocular rivalry. The properties and dynamics of unitary percepts during binocular rivalry have been well-characterized. Here, we instead focus on characterizing the properties and dynamics of mixed percepts. To do so, we presented rivaling face and house images that were large in order to promote mixed percepts. To allow for an analysis of memory effects, we used brief 5-second trials separated by 1-second inter-trial intervals. To measure spontaneous changes in mixed percepts, as well as unitary percepts, we asked participants to separately track dominant percepts within each visual quadrant by pressing or releasing four spatially-compatible buttons. Mixed percepts comprised 14 possible combinations of face-dominant and house-dominant quadrants. The results revealed two notable phenomena. First, the 14 possible mixed percepts were not reported with equal probability. Specifically, right/left half-and-half percepts were more frequent than chance level, whereas top/bottom half-and-half (and all other mixed) percepts were reliably less frequent than chance level. This result suggests that even for mixed percepts, perception is not stochastic. Second, we found a memory effect for mixed percepts. In previous binocular rivalry studies using similarly brief rivalry trials, there was a tendency for initial unitary percepts to repeat across trials. Here, participants reported systematic sequences of mixed percepts that tended to repeat across trials, demonstrating that the previously-reported memory effect continues beyond the initial percept, extending through the 3rd-6th percepts depending on the individual. This result suggests that a unitary and meaningful percept (e.g., house or face) is not necessary for a memory effect to occur in binocular rivalry. Furthermore, memory influences not only the mechanisms controlling the initial rivalry competition, but also those mechanisms underlying the subsequent spatio-temporal perceptual cascade experienced during binocular rivalry.
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