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Jan W. Brascamp, Andre J. Noest, Albert V. van den Berg; The third percept in bistable perception. Journal of Vision 2005;5(8):1050. doi: 10.1167/5.8.1050.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction. ‘Bistable perception is the phenomenon that when faced with ambiguous visual input, one experiences a percept alternating between two interpretations.’ Sentences like this form the starting point of myriad papers on the subject, but bistable perception as a two-state process is a simplification: between dominance phases of percept A and B there are phases during which neither prevails. This has been noted before1 but is routinely ignored. We try to clarify how this is possible and study the features of the transition stage in a binocular grating paradigm.
Methods. Due to the transition stage's short duration we cannot rely on subjects' key presses to report it, but use a novel method based on synchronisation and cueing. Synchronisation means that we force the onset at t0 of a dominance phase, using the flash suppression effect. Then after a chosen time lag, by replacing the gratings by a mask, we cue subjects to report what they saw the instant before mask appearance. By repeating this at various lags, we get probability distributions of percepts as a function of time after t0. Subjects were tested twice: first we instructed them to report the percept to be either A or B; the second time we added the option of reporting a transition percept.
Results. Subjects easily executed the two-alternative choice experiment. Still, with the option of reporting a third phase, its mean duration was 300–1100 ms: 0.2–0.7 times that of a dominance phase (the duration of an entire cycle was unaffected). Concluding, reports of putative bistable perception do not prove the absence of a transition percept; merely that subjects were not asked to report it. Instead, the transition stage is a substantial part of the alternation cycle, that models of bistable perception should incorporate. We are presently studying its characteristics, e.g. its duration distribution, its dependence on stimulus features and associated detection thresholds.
Ref. 1: Blake Mueller. Biol. Cybern. 61, 1989.
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