Hues being framed and the nulling of the afterimage [Abstract]

A common technique to study afterimage intensity is to null them by addition of physical stimuli. But does this mean that real chromatic stimuli would null colour afterimages at every stage of visual processing? It is known that discrimination of both is enhanced by luminance contours and this process is thought to occur at early cortical levels. We hypothesised that if adaptation occurs mainly at the retinal level, contours would modulate the signal resulting from the sum of the physical stimulus and afterimage. Therefore, the same afterimage would be always be nulled by the same faint stimuli, with or without a contour. In contrast, we observed that luminance contours specifically increased the intensity of afterimages. This result suggests that chromatic adaptation is not solely a retinal phenomenon but occurs at various levels, and these levels are differently modulated by the presence of a contour. Furthermore, although you can determine conditions that null the conscious perception of an afterimage, it is unlikely that this afterimage will be nulled at every single loci of adaptation. These findings may also relate to why we are sometimes conscious of afterimages and other times not, despite no differences in retinal adaptation