A-03 Velocity discrimination in scotopic vision

Abstract

To characterize scotopic motion mechanisms, we examined how variation in average luminance affects the ability to discriminate velocity. Stimuli were drifting horizontal sine-wave gratings. Velocity discrimination performance was most acute at a temporal frequency of about 5.0Hz, and fell off at both higher and lower temporal frequencies under photopic conditions. With decreasing adapting level, discrimination of high temporal frequencies became increasingly worse, while discrimination of low temporal frequencies remained largely unaltered. Discrimination performance was best at about 2.0Hz. These results can be explained by a motion mechanism comprising both low-pass and band-pass temporal filters under scotopic conditions.