Role of threshold in afterimage visibility.

The negative afterimage from grating can be considered equivalent to a renal grating, the contrast of which decreases over time. The interval between the onset of the afterimage and the time at which the effective contrast of the afterimage falls below threshold defines afterimage duration. In a series of experiments with several predictions based on this formulation were confirmed. Square-wave gratings yielded longer afterimage durations than sinusoidal gratings, a difference that is attributable to the difference in threshold between these two types of grating. Also, grating adaptation before afterimage induction was found to abbreviate afterimage duration because of threshold elevation. Finally, it was found that, even after fading to invisibility, an afterimage could interact with a real grafting to influence threshold performance on a forced-choice detection task.