Optical illusions: caused by eye or brain?
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Date posted: 12/11/2008
Posted by: Site Administration
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The Brain

For the past 200 years, researchers have debated whether the illusion of motion in a static image is caused by mechanisms in the eye, in the brain, or by a combination of both. Because measuring these kinds of physiological responses is difficult, no study has successfully measured direct and tightly timed correlations between a kinetic illusion and a physiological precursor.

But recently, a team of researchers from the Barrow Neurological Institute in Phoenix, Arizona, and the University of Vigo in Vigo, Spain, has found a direct correlation between illusory motion and microsaccades, which are tiny eye movements that involuntarily occur several times per second during visual fixation. Although the team hasn?t determined the neural mechanism behind the correlation, the finding rules out the hypothesis that the origin of the kinetic optical illusion is purely cortical.

?These results revealed a direct link between the eye motions and the perception of illusory motion, and ruled out the hypothesis that the Enigma illusion originates solely in the brain,? Susana Martinez-Conde, Director of the Laboratory of Visual Neuroscience at the Barrow Neurological Institute, told PhysOrg.com. ?Our study provides a possible explanation for an entire family of visual illusions central to the fields of visual art and visual science. It would be quite unexpected if Enigma turned out to be the only motion illusion affected by eye movements.?

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