Perceptual memory influences both continuous and intermittent ambiguous perception, but in opposite ways

When observers view an ambiguous stimulus that is continuously presented their percept changes without any change in the stimulus itself. These perceptual alternations appear to occur in a stochastic, i.e. memory-less, manner. However, when short presentations of an ambiguous stimulus are interleaved with blank periods observers tend to see the same percept for many consecutive presentations. This suggests that perceptual memory influences intermittent ambiguous perception but not continuous ambiguous perception. We investigated this apparent inconsistency. We tested whether perceptual memory, built up during intermittent viewing of ambiguous stimuli, influences subsequent continuous viewing of those stimuli. Interestingly, we find that during continuous viewing the durations of the memorized percept are much shorter than the durations of the opposite percept. This reveals a direct link between continuous and intermittent ambiguous perception: the percept that dominated during intermittent viewing is inhibited during continuous viewing. We conclude that continuous viewing of ambiguous stimuli is not a memory-less process.