Making the incredible credible: Afterimages are modulated by contextual edges more than real stimuli

Abstract

We explored whether color afterimages and faint physical chromatic stimuli are processed equivalently by the visual system. Afterimage visibility in classic illusions appears to be particularly influenced by consistent contexts, while real stimulus versions of these illusions are absent in the literature. Using both a matching and a nulling paradigm, we present converging evidence that luminance edges enhance the perceived saturation of afterimages more than they do physical stimuli of similar appearance. We suggest that afterimages violate the response norms associated with real stimuli. This leads to the afterimage signal being ambiguous for the visual system, and thus more susceptible to modulation by contexts that increase or decrease the probability of the signal representing a real object. This could explain why afterimages are rarely experienced in everyday life, where they will be overruled by inconsistent context.