Perceptual memory influences perception of a changing and a stable visual environment in opposite ways

In every day life sensory information is inherently incomplete and ambiguous, forcing the brain to make inferences regarding the properties of the outside world. Ambiguity in sensory input results in competition between multiple, mutually exclusive, perceptual interpretations. Because of this, observers experience ongoing perceptual changes without any change in the outside world. The time course of these ongoing changes is thought to be stochastic, i.e. memory-less. However, recent findings showed that previous encounters with similar sensory input influence the very first percept at appearance of an ambiguous stimulus. In other words, the interpretation of new visual information inclines toward memorized interpretations from the past. In the present study we investigated whether perceptual memory also influences the interpretation of stable visual input. We presented an ambiguous stimulus intermittently to stabilize perception and build-up perceptual memory for one particular perceptual interpretation. Subsequently, we tested the effect of this memory during sustained viewing of the same ambiguous stimulus. If perceptual memory favors the memorized percept, we would expect this percept to predominate during a period of stable visual input. Surprisingly, our results indicate the opposite. Instead of being predominant, the percept that dominated during intermittent viewing is suppressed during sustained viewing. This suggests that the visual system searches for alternative, not previously encountered, interpretations for the perception of sustained ambiguous information. This effect remains for several minutes, and only gradually wanes away. We conclude that new information is initially judged on its resemblance to familiar objects and is re-evaluated later on to allow for alternative interpretations of the outside world.