Multistable perceptual phenomena are a rare form of visual perception phenomena which is characterized by an unpredictable sequence of spontaneous subjective changes.
Perceptual multistability can be evoked by visual patterns that are too ambiguous for the human visual system to recognise with one unique interpretation. Famous examples include the Necker cube, structure from motion, monocular rivalry and binocular rivalry, but many more visually ambiguous patterns are known. Since most of these images lead to an alternation between two mutually exclusive perceptual states, they are sometimes also referred to as bistable perception .
Transitions from one percept to its alternative are called perceptual reversals. They are spontaneous and stochastic events which cannot be eliminated by intentional efforts (although some control over the alternation process is learnable). Reversal rates vary drastically between stimuli and observers, and has been found to be slower for people with Bipolar disorder ("sticky" interhemispheric switch in bipolar disorder) .
Human interest in these phenomena can be traced back to antiquity. The fascination of multistable perception probably comes from the active nature of endogenous perceptual changes or from the dissociation of dynamic perception from constant sensory stimulation. Multistable perception was a common feature in the artwork of the Dutch lithographer M. C. Escher, who was strongly influenced by mathematical physicists such as Roger Penrose.
A pop culture example can be found in Crow T. Robot, a puppet character on Mystery Science Theater 3000. At times, the puppet appears to be speaking to the audience instead of facing the screen due to the way his head curves.