Cortical mechanisms for afterimage formation: evidence from interocular grouping

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.

Contrast-modulated stimuli produce more superimposition and predominate perception when competing with comparable luminance-modulated stimuli during interocular grouping

“…is the process that mediates interocular grouping related to that which generates superimposition? One recent study showed that when decreasing stimulus strength bilaterally for both split-gratings, IOG increases 59 , which we also found when lowering the contrast bilaterally for L and LM gratings ( Fig. 2A).…”

Image-based and eye-based influences on binocular rivalry have similar spatial profiles

“…For instance, distinct proposals that incorporate the idea of multiple levels being involved differ regarding whether different levels would be engaged by different stimuli (Alais & Parker, 2006;Wilson, 2003) or whether a given stimulus would engage several levels at the same time (Tong et al, 2006). Nevertheless, our present results add to a body of studies (Dong, Holm, & Bao, 2017;Holten et al, 2016;Stuit et al, 2011Stuit et al, , 2014 that have separately assessed grouping based on eye-based cues and grouping based on cues that go beyond eye of origin (in these cases, image-based cues) and that all point to monocular information as critical (also see Quinn & Arnold, 2010). Perhaps, then, the multiple levels at which binocular rivalry grouping and, potentially, binocular rivalry competition more generally, can occur, are restricted to areas at which monocular information is available.…”

The Mechanisms Underlying Colour Afterimages

“…Still others, claimed that afterimages occur through adaptation of cortical mechanisms that involve shape and object recognition 19-22,35 , binocular integration 23,24 and/or colour constancy 25 , contradicting classical evidence for a retinal origin 26,27 . Top-down effects on colour perception are well known 36,37 .…”