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Xoana Troncoso, Stephen Macknik, Jorge Otero-Millan, Susana Martinez-Conde; Microsaccades drive illusory motion in “Enigma”. Journal of Vision 2008;8(6):638. doi: 10.1167/8.6.638.
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© ARVO (1962-2015); The Authors (2016-present)
Visual images consisting of repetitive patterns can elicit striking illusory motion percepts. For almost 200 years, artists, psychologists and neuroscientists have debated whether this type of illusion originates in the eye or in the brain. For more than a decade, the controversy has centered on the powerful illusory motion perceived in the painting “The Enigma”, created by op-artist Isia Leviant. However, no previous study has directly correlated the Enigma illusion to any specific physiological mechanism, and so the debate rages on. Here we show that microsaccades, a type of miniature eye movement produced during visual fixation, drive illusory motion in Enigma. We asked subjects to indicate when illusory motion sped up or slowed down during the observation of Enigma, while we simultaneously recorded their eye movements with high precision. Before “faster motion” periods, the probability and magnitude of microsaccades increased. Before “slower/no motion” periods, the probability and magnitude of microsaccades decreased. These results reveal a direct link between microsaccade production and the perception of illusory motion in Enigma, and rule out the hypothesis that the origin of the illusion is purely cortical. They also have important implications for other types of illusory motion effects arising from static images.
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