Abstract
The way the brain interprets visual input is strongly dependent on visual experience. This becomes strikingly evident when the same ambiguous visual input is seen repeatedly: Whereas continuous viewing of an ambiguous stimulus leads to ongoing abrupt changes in visual awareness, intermittent viewing results in the same perceptual interpretation over and over again. Memory for a certain perceptual interpretation thus boosts this interpretation during later encounters with the stimulus. This is contrary to the effect of adaptation, which inhibits previously seen percepts. As yet there is very limited evidence regarding the neural mechanisms underlying perceptual memory. To investigate these neural mechanisms we measured fMRI when subjects viewed an ambiguously rotating globe with intervening blank periods. As expected the intermittent presentation paradigm resulted in long sequences of reoccurrence of the same percept (either clockwise or counter-clockwise rotation). The build-up of perceptual memory during a sequence of stabilized perception was accompanied by an increase in the amplitude of the BOLD response in motion sensitive brain regions. This increase in amplitude cannot be explained as adaptation to the stimulus, because it is well established that adaptation results in a decreased amplitude of the BOLD response. We thus conclude that perceptual memory is represented by an increase in the amplitude of response in those brain regions that represent the memorized percept.