Abstract
We empirically know that visual motion perception deteriorates in mesopic vision, where both rods and cones operate. Visual motion priming is a phenomenon in which the perceived direction of a directionally ambiguous test stimulus is influenced by the moving direction of a preceding priming stimulus. To examine the integration of motion signals at mesopic light levels, where cones operate in the central retina and rods in the peripheral retina (Raphael & MacLeod, 2011), we presented the priming and test stimuli in the central and peripheral retinae, respectively. Subjects judged the perceived direction of the 180° phase-shifted sine-wave grating (rightward or leftward) that was followed by a smoothly drifting priming stimulus at different retinal illuminances (from −1.5 to 2.8 log Td). We found that the strength of motion priming was greatly decreased at mesopic, but not photopic and scotopic, light levels. When the test stimulus was presented before the offset of the priming stimulus, motion priming was prominent irrespective of the retinal illuminance. This finding indicates that the temporal delay in the rod pathway weakens the integration of motion signals in mesopic vision. In a separate experiment, subjects made a saccade after the termination of the priming stimulus and then performed the task involving judging the direction in retinotopic and spatiotopic coordinates (Burr & Morrone, 2012). In the spatiotopic condition, the priming and test stimuli occupied the same position on the display across a saccade. We found that motion priming in the spatiotopic condition was greatly decreased at mesopic, but not photopic and scotopic, light levels. These results suggest that incompleteness in the integration of motion signals due to insufficient build-up of the spatiotopic representation by the temporal delay in the rod pathway causes visual motion perception deterioration in mesopic vision.
Meeting abstract presented at VSS 2014