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Chen Song, D. Samuel Schwarzkopf, Geraint Rees; Does size matter more in the same eye?. Journal of Vision 2010;10(7):1389. doi: 10.1167/10.7.1389.
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© ARVO (1962-2015); The Authors (2016-present)
Our perception of objects depends not only on their physical characteristics but also on the context in which they appear. In the Ebbinghaus illusion, two physically identical circles, one surrounded by large circles and one by small circles, appear perceptually different in size. This illusion has long been used as a means to study the neural pathways involved in perception and action. However, the neural mechanisms of this illusion remain largely unexplored. Here we compared monocular, binocular and dichoptic versions of the Ebbinghaus illusion to begin investigating the cortical stages at which it arises. Two circles (targets) and two groups of surrounding circles (inducers) were separately presented to the two eyes. The inducers were presented to one eye, and the targets were presented to either the same eye (monocular), or the opposite eye (dichoptic), or to both eyes simultaneously (binocular). We found that the illusion was strongest when inducers and targets were both presented to the same eye (monocular). The illusion also persisted when inducers and targets were presented to different eyes (dichoptic or binocular). The strength of the illusion for fully monocular presentation, coupled with incomplete interocular transfer, may be consistent with the Ebbinghaus illusion being at least partially mediated by monocular neurons in the primary visual cortex.
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