Positive and negative afterimages from brief target gratings

Threshold luminance levels for the production of negative afterimages from brief target gratings were determined as a function of background luminance and grating frequency. The obtained thresholds were extremely low--typically below the values that would maintain constant space-average luminance between target and background. The implications of these results for other studies that may have inadvertently produced negative afterimages with their stimulus conditions were noted. As a demonstration, visual persistence estimates from these gratings were determined under conditions that carefully excluded negative afterimages, and clear differences from previously published work were obtained.