The two circles seem to move when the viewer’s head is moving forwards and backwards while looking at the black dot.
The cognitive processes hypothesis claims that visual illusions occur because the neural circuitry in our visual system evolves, by neural learning, to a system that makes very efficient interpretations of usual 3D scenes based in the emergence of simplified models in our brain that speed up the interpretation process but give rise to optical illusions in unusual situations.
According to Richard Gregory (British psychologist and Emeritus Professor of Neuropsychology) there are three main classes of optical illusions: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions.
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