Abstract
Sequential viewing of two orthogonally related patterns produces an afterimage the same shape as 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 generated in the BCS system. The two types of after responses interact at a stage of neural filling-in to produce the afterimage percept. Implicit in this explanation is that the color complement after responses are the “opposite” color of the first stimulus. Thus, a black and red bar horizontal grating followed by a black and white vertical grating should produce an afterimage of a white (light-gray) and green horizontal grating. However, when we queried observers about the colors of the afterimage, they reported that it appeared to contain green and red bars. We report on experiments that quantify these observations and discuss how the model must be elaborated to account for this new finding.