Abstract
Whether the retinal process alone or retinal and cortical processes jointly determine afterimage (AI) formation has long been debated. Based on the retinal rebound responses, recent work proposes that afterimage signals are exclusively generated in the retina, although later modified by cortical mechanisms. We tested this notion with the method of “indirect proof”. Each eye was presented with a 2-by-2 checkerboard of horizontal and vertical grating patches. Each corresponding patch of the two checkerboards was perpendicular to each other, which produces binocular rivalry, and can generate percepts ranging from complete interocular grouping to either monocular pattern. The monocular percepts became more frequent with higher contrast. Due to adaptation, the visual system is less sensitive during the AIs than during the inductions with AI-similar contrast. If the retina is the only origin of AIs, comparable contrast appearance would require stronger retinal signals in the AIs than in the inductions, thus leading to more frequent monocular percepts in the AIs than in the inductions. Surprisingly, subjects saw the fully coherent stripes significantly more often in AIs. Our results thus contradict the retinal generation notion, and suggest that in addition to the retina, cortex is directly involved in the generation of AI signals.
Highlights
Whether the retinal process alone or retinal and cortical processes jointly determine afterimage (AI) formation has long been debated
Zaidi and colleagues found that after the removal of the inducing stimuli, the ganglion cells generated rebound responses that could provide after image (AI) signals for later neurons. In their abstract, they conclude that “afterimage signals are generated in the retina, but may be modified like other retinal signals by cortical processes, so that evidence presented for cortical generation of color afterimages is explainable by spatio-temporal factors that apply to all signals”
Each patch of the two checkerboards was rotated 90 degrees with respect to each other, which produces binocular rivalry, and can generate percepts ranging from complete interocular grouping to either monocular pattern
Summary
Whether the retinal process alone or retinal and cortical processes jointly determine afterimage (AI) formation has long been debated. Based on the retinal rebound responses, recent work proposes that afterimage signals are exclusively generated in the retina, later modified by cortical mechanisms. We tested this notion with the method of “indirect proof”. Zaidi and colleagues found that after the removal of the inducing stimuli, the ganglion cells generated rebound responses that could provide AI signals for later neurons In their abstract, they conclude that “afterimage signals are generated in the retina, but may be modified like other retinal signals by cortical processes, so that evidence presented for cortical generation of color afterimages is explainable by spatio-temporal factors that apply to all signals”
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