Bistable perception -- along the processing chain from ambiguous visual input to a stable percept.

The observation of an ambiguous figure leads to spontaneous perceptual reversals while the observed picture stays unchanged. Some ERP studies on ambiguous figures report a P300-like component correlated with perceptual reversals supporting a top-down explanation, while other studies found early visual ERP components supporting a bottom-up explanation. Based on an experimental paradigm that permits a high temporal resolution of the endogenous reversal event, we compared endogenous Necker-cube reversals with exogenously-induced reversals of unambiguous cube variants. For both reversal types, we found a chain of ERP components with the following characteristics: (1) An early occipital ERP component (130 ms) is restricted to endogenous reversals. (2) All subsequent components also appear with exogenously-induced reversals, however 40-90 ms earlier than their endogenous counterparts. (3) The latency difference between reversal types is also reflected in the timing of manual reactions, which occur 100-130 ms after P300-like components. The results suggest that the P300-like component is the same as found in other ERP studies on ambiguous figures. This component does not reflect the reversal per se, but rather its cognitive analysis, 300 ms after a change of the representation in early visual areas. The presented ERP chains integrate the different ERP results and allow to pinpoint the steps where top-down mechanisms begin to exert their influence.

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