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Updated: Jul 26, 2026

Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition
Published on: July 21, 2020
The spoke brightness illusion originates at an early motion processing stage
A O Holcombe1, J Intriligator, P U Tse
1Department of Psychology, Harvard University, 33 Kirkland St., Cambridge, MA 02138, USA. holcombe@wjh.harvard.edu
Abstract:
When a bright white disk revolves around a fixation point on a gray background, observers perceive a "spoke": a dark gray region that connects the disk with the fixation point. Our first experiment suggests that motion across the retina is both necessary and sufficient for spokes: The illusion occurs when a disk moves across the retina even though it is perceived to be stationary, but the illusion does not occur when the disk appears to move while remaining stationary on the retina. A second experiment shows that the strength of the illusion decreases with decreasing luminance contrast until subjective equiluminance, where little or no spoke is perceived. These results suggest that spokes originate at an early, predominantly luminance-based stage of motion processing, before the visual system discounts retinal motion caused by smooth pursuit.
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