Abstract
Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern (Vidyasagar, et al, 1999; Francis & Rothmayer, 2003). We investigated how the timing between the first stimulus (a vertical bar grating) and the second stimulus (a horizontal bar grating) affected the visibility of the afterimage (a perceived vertical grating), when observers were forced to report on what was seen one second after offset of the second stimulus. We found that the afterimage was perceived 75% of the time if the second stimulus followed the first by three seconds. However, reports of the afterimage percept monotonically decreased to 20% of the time as the duration between the first and second stimulus increased to twelve seconds. We interpret 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. As the duration between the stimuli increases, the color after responses weaken so that visible filling-in is less likely to occur. The time course of the afterimage is used to parameterize the parts of the model that produce the after responses.