RETINAL ADAPTATION OF VISUAL PROCESSING TIME DELAYS

A significant proportion of the processing delays within the visual sy stem are luminance dependent. Thus placing an attenuating filter over one eye causes a temporal delay between the eyes and thus an illusion of motion in depth for objects moving in the fronto-parallel plane, kn own as the Pulfrich effect. We have used this effect to study adaptati on to such an interocular delay in two normal subjects wearing 75% att enuating neutral density filters over one eye. In two separate experim ental periods both subjects showed about 60% adaptation over 9 days. R eciprocal effects were seen on removal of the filters. To isolate the site of adaptation we also measured the subjects' flicker fusion frequ encies (FFFs) and contrast sensitivity functions (CSFs). Both subjects showed significant adaptation in their FFFs. An attempt to model the Pulfrich and FFF adaptation curves with a change in a single parameter in Kelly's [(1971) Journal of the Optical Society of America, 71, 537 -546] retinal model was only partially successful. Although we have de monstrated adaptation in normal subjects to induced time delays in the visual system we postulate that this may at least partly represent re tinal adaptation to the change in mean luminance.