Behavioral/Cognitive Implicit Perceptual Memory Modulates Early Visual Processing of Ambiguous Images

Thewayweperceive thepresent visual environment is influencedbypast visual experiences.Herewe investigated theneural basis of such experiencedependency.We repeatedly presentedhumanobserverswith anambiguous visual stimulus (structure-from-motion) that can give rise to two distinct perceptual interpretations. Past visual experience is known to influence the perception of such stimuli. We recorded fast dynamics of neural activity shortly after stimulus onset using event-related electroencephalography. The number of previous occurrences of a certain percept modulated early posterior brain activity starting as early as 50 ms after stimulus onset. This modulation developed across hundreds of percept repetitions, reflecting severalminutes of accumulating perceptual experience. Impor-tantly, there was no such modulation when the mere number of previous stimulus presentations was considered regardless of how they were perceived. This indicates that the effect depended on previous perception rather than previous visual input. The short latency and posterior scalp location of the effect suggest that perceptual history modified bottom-up stimulus processing in early visual cortex. We propose that bottom-upneural responses to a given visual presentation are shaped, in part, by feedbackmodulation that occurredduring previous presentations, thus allowing these responses to be biased in light of previous perceptual decisions. Key words: ambiguous figures; EEG; perceptual memory; perceptual rivalry; vision; visual corte