The spatial spread of filling-in for afterimages produced from orthogonal pairs of stimuli

Abstract

Sequential viewing of two orthogonally related patterns produces an afterimage related to the first pattern (Vidyasagar, et al, 1999). Thus, viewing a horizontal grating and then a vertical grating produces an afterimage of a horizontal grating. Francis & Rothmayer (2003) interpreted this finding in terms of Grossberg's BCS-FCS theory. In this theory the afterimage percept is the result of color-complement after responses in the FCS system interacting with orientation after responses in the BCS system. The two types of after responses interact at a stage of neural filling-in to produce the afterimage percept. In the current experiments we introduced a gap running vertically through the horizontal grating. Observers were asked to report whether the afterimage had a visible gap between the left and right sides. When the gap was small (16 minutes of visual arc) observers reported seeing a gap in the afterimage only 22% of the time. As the gap increased in size observers were more likely to report seeing a gap in the afterimage (64% of the time for a gap of 45 minutes). We used these findings to parameterize a mechanism of filling-in that interpolates brightness information across the gap. The findings help identify the spatial range of the filling-in mechanism in this context.