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Thomas G.G. Wegner, Jan Grenzebach, Alexandra Bendixen, Wolfgang Einhäuser; Parameter dependence of first and subsequent percepts in visual tri-stability. Journal of Vision 2019;19(10):62c. doi: https://doi.org/10.1167/19.10.62c.
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Multistability refers to alternations in perception caused by a physically constant stimulus. It has been a matter of debate whether the first perceptual interpretation after stimulus onset is fundamentally different from subsequent perceptual interpretations. Here we study this question by systematically varying stimulus parameters and by assessing the resulting proportion of different percepts at onset and during continuous viewing. We used two overlaid colored drifting gratings, which can be perceived as individual gratings passing in front of each other (“segregated percept”) or as an integrated plaid (“integrated percept”). In this configuration of the plaid stimulus, either grating can be perceived as dominant during segregated perception, resulting in tri-stability (one integrated, two segregated percepts). We asked 18 participants to view ten versions of the plaid stimulus that differed in the enclosed angle between the gratings. Each version was presented ten times for 30s each. To mimic a real onset (rather than just a blank interval), observers performed a fixation task on three points between presentations of different stimulus versions. Unlike most previous studies that used two response options, we asked observers to report either of the three percepts by holding one of three buttons. To verify the responses, we measured the direction of the optokinetic nystagmus induced by the stimulus. We compared predominance of the integrated percept during prolonged viewing to the probability to perceive the integrated percept after stimulus onset. In both measures, integration dominated for shallow angles, segregation for acute angles. For medium angles, the integrated percept still dominated at onset, but segregation became more dominant during subsequent viewing phases. Our results underline the distinct role of the first percept, which shows a different dependence on stimulus parameters than percepts during prolonged viewing.
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