Multistable perceptual phenomena are a form of perceptual phenomena in which there are unpredictable sequences of spontaneous subjective changes. While usually associated with visual perception, such phenomena can be found for auditory and olfactory percepts.
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 have been found to be slower for people with bipolar disorder,
Cultural history 
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.
Real world examples 
Photographs of craters, from either the moon or other planets including our own, can exhibit this phenomenon. Craters, in stereo imaging, such as our eyes, should appear to be pit-like structures. However in mono-vision, such as that of photographs, the elimination of our depth perception causes multistable perception to take over, and this can cause the craters to inverse their depth values and instead look like plateaus rather than pits. Sometimes rotating the image so that the photographic direction of the source of light matches a light source in the room can cause the correct perception to suddenly switch.
A pop culture example can be found in Crow T. Robot, a puppet character on Mystery Science Theater 3000. The premise of the show involves three characters (including Crow) making fun of bad movies, and as such they appear superimposed in silhouette at the bottom of the screen. Due to the design of Crow's head, it can appear that he is looking at the audience rather than at the screen.
See also 
- Optical illusion
- Experimental psychology
- Gestalt psychology
- Cognitive neuroscience
- M. C. Escher
- Salvador Dalí
- Op art
- The Spinning Dancer
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- VisualFunHouse Optical Illusions Multistable perception Optical Illusions
- A collection of visually ambiguous patterns
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- Ambiguous figures Ambiguity of spatial perception (fr)