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© 2008 Yang and Schwaninger
Circumfluous contours can elicit a length-contrast illusion. Mirror-imaged faces are arranged with the four irises absolutely equidistant. The distance between the middle two irises is perceived as shorter than the distances between the left two or right two irises in an Asian face, whereas it is perceived as longer in a Caucasian face. This illusion remains when the irises are presented together with line drawings of the eye shape, but it disappears when only the isolated irises are presented. The illusion is independent of orientation (no inversion effect) and viewer”s race (no race effect).
Read more about the illusion and possible explanations
Yang’s Iris Illusion,