Awareness of Central Luminance Edge is Crucial for the Craik-O?Brien-Cornsweet Effect

Abstract

The Craik-O’Brien-Cornsweet (COC) effect demonstrates that perceived lightness depends not only on the retinal input at corresponding visual areas but also on distal retinal inputs. In the COC effect, the central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. To investigate the underlying mechanisms of the effect, we examined whether the subjective awareness of the COC edge is necessary for the generation of the effect. We manipulated the visibility of the COC edge using visual backward masking and continuous flash suppression while monitoring subjective reports regarding online percepts and aftereffects of adaptation. Psychophysical results showed that the online percept of the COC effect nearly vanishes in conditions where the COC edge is rendered invisible. On the other hand, the results of adaptation experiments showed that the COC edge is still processed at the early stage even under the perceptual suppression. These results suggest that processing of the COC edge at the early stage is not sufficient for generating the COC effect, and that subjective awareness of the COC edge is necessary.

Size Aftereffects Are Eliminated When Adaptor Stimuli Are Prevented from Reaching Awareness by Continuous Flash Suppression

“…For the current purposes, the results from Masuda et al (2011) indicate that on the one hand early visual regions can process Cornsweet circles even when suppressed from awareness. On the other hand, the experiments reported by Masuda et al (2011) reinforce the suggestion that top–down signals associated with conscious awareness appear to be necessary for higher-order processing of Cornsweet circles as required for aftereffects.…”

“…It is possible that although retinal inputs from the suppressed eye reached at least as far as V1, the current results may reflect the inability of the Cornsweet illusion to be detected without awareness rather than an absence of size aftereffects per se . Indeed, Masuda et al (2011) presented the edge of a Cornsweet illusion to participants under backward masking and CFS conditions and revealed that one must have a conscious awareness of the edge to experience a real-time illusion of differing luminance either side of the edge. More critically, in a separate adaptation experiment, the authors briefly applied CFS to the edge of the illusion and then had participants view a gray background.…”

“…These results indicate that although the perception of the Cornsweet illusion disappears without awareness of the edge, suggesting the necessity of higher-order processing, the edge is nonetheless still processed at monocular stages of processing. Masuda et al (2011) proposed two mechanisms to be involved in the Cornsweet illusion: a feedback mechanism associated with the subjective awareness of the edge followed by a mechanism for surface lightness, which may rely on lateral connectivity being activated by the feedback signal. For the current purposes, the results from Masuda et al (2011) indicate that on the one hand early visual regions can process Cornsweet circles even when suppressed from awareness.…”

“… Masuda et al (2011) proposed two mechanisms to be involved in the Cornsweet illusion: a feedback mechanism associated with the subjective awareness of the edge followed by a mechanism for surface lightness, which may rely on lateral connectivity being activated by the feedback signal. For the current purposes, the results from Masuda et al (2011) indicate that on the one hand early visual regions can process Cornsweet circles even when suppressed from awareness. On the other hand, the experiments reported by Masuda et al (2011) reinforce the suggestion that top–down signals associated with conscious awareness appear to be necessary for higher-order processing of Cornsweet circles as required for aftereffects.…”

Visual evoked potentials to an illusory change in brightness

“…Except for the gradients near the border, the two rectangles are equiluminant. If one covers the border between the rectangles, say with a pencil, the illusion disappears, indicating the importance of the luminance contrast-defined border 5 .…”