Negative afterimages and photopic luminance adaptation in human vision.

Previous studies of the negative afterimage have reported that the process responsible for these aftereffects has a bandpass spatial characteristic. If this finding is correct, then negative afterimages cannot arise from a simple, local, adaptive process. I remeasure the spatial-frequency characteristic of the negative-afterimage process by using an afterimage contrast-matching procedure with retinally stabilized stimuli and find the spatial characteristic to be constant in the low-spatial-frequency region. This finding is consistent with the theory that the negative afterimage results from local luminance adaptation. As a test of the local adaptation explanation of the negative afterimage, the effect of the negative afterimage on the temporal contrast-sensitivity function (CSF) (measured down to 0.062 Hz) is determined. The apparent contrasts of the negative afterimages associated with very slowly (less than 0.5 Hz) flickering, threshold-contrast stimuli are calculated from power-function descriptions of the temporal development of the negative afterimage, and these afterimage contrasts are then subtracted from the temporal CSF's. The resulting curves are constant for temporal frequencies below 1 Hz, indicating that the decline in sensitivity at lower temporal frequencies is due entirely to the negative-afterimage process. Both the spatial and the temporal characteristics of the negative-afterimage process are consistent with its being a component of local luminance adaptation.