Abstract
Introduction. The visual system displays memory for perception of ambiguous figures: Perceptual dominance following an interruption depends on the last dominant percept before the interruption. A common interpretation of this phenomenon is that the last preceding percept leaves some form of memory trace, which in turn determines perceptual choice following the interruption. Here we show that, on the contrary, the last preceding percept has no special importance in determining the content of memory. Rather, perceptual choice is determined by a minute-scale history of prior perception, which includes, but is not limited to, the last preceding percept.
Methods. We establish the content of memory by intermittently presenting an ambiguous stimulus until a subject consistently perceives the same percept for eight presentations in a row: Robust perceptual memory. Then we leave the stimulus on continuously, causing spontaneous perceptual alternations. Finally, we probe the content of memory following spontaneous alternations by assessing dominance during a renewed period of intermittent presentation.
Results. Perceptual choice following spontaneous alternations is influenced by the last percept during the alternations, but more strongly by the content of memory prior to the alternations. This long-lasting memory trace survives up to about one minute, or more than four perceptual alternations. This is evidence of unexpectedly complex memory behavior in ambiguous perception, indicating information integration over prolonged periods of time rather than straightforward storage of a single percept.