Abstract
A real or artificial scotoma within a dynamic noise field fills in within a few seconds. When the dynamic noise is replaced with a homogenous field, a twinkling after effect (TwAE) is induced exclusively in the location of the former scotoma. We are employing the appearance of the TwAE to perform rapid perimetry in patients with retinal scotomas. To analyze the loci within the visual system and the mechanisms of filling-in and the TwAE, we examined their orientation tuning, inter-ocular transfer, and threshold versus contrast functions by measuring contrast detection thresholds for stimuli presented in areas that were filled-in or contained the TwAE. For filling-in, detection thresholds were narrowly tuned for orientation, transferred interocularly, and rose monotonically with the contrast of a surround pattern. These results indicate that surround suppression and filling-in involve inhibitory processes originating at cortical stages of visual processing. Threshold versus contrast functions were weakly dipper-shaped for the TwAE, did not transfer inter-ocularly, and were not tuned for orientation. These results indicate that the TwAE involves additive noise that is pre-cortical in origin and that it is distinct from filling-in.