Figure 3.

The diagrams show a simple model for prediction of colored afterimages based on cellular receptor adaptation (18, 19). A shows in green and red the stimulus input to the M-cone (middle wavelength-sensitive), and L-cone (long wavelength-sensitive) receptors, respectively. The signal generated in M-cones is increased and that in L-cones is decreased, as imposed by the d-isoluminant constraints. The model is based on the predicted changes in mean response level of M- and L-cone receptors during modulation: an increase in mean signal response for L-cones and a corresponding decrease in M-cone responses, as shown in B. The output of a red-green chromatic channel based on the difference between L- and M-cone signals is shown in C. The assumptions made are sufficient to predict the observed afterimages and the half-cycle increase in afterimage response latency (as shown in C). When the modulation terminates and the stimulus returns to background level, the normal response properties are restored with a time constant characteristic of build-up and decay of afterimages. The model also predicts that the signal level in the luminance channel that is based on summation of L- and M-signals remains unaffected during the modulation. This explains the absence of perceived achromatic afterimages when adapting to isoluminant stimuli (27).