Effect of light level on the postdictive perception of visual motion
56.4013, Tuesday, 19-May, 2:45 pm - 6:45 pm, Pavilion
Sanae Yoshimoto1,2, Tatsuto Takeuchi1; 1Japan Women's University, 2Japan Society for the Promotion of Science
Visual motion perception is affected by the subsequent visual input. This is a type of postdictive modulation induced by the spatiotemporal integration of motion signals. The aim of this study was to clarify the effect of light level on the postdictive modulation of visual motion, because motion perception can be varied with the light level (Yoshimoto & Takeuchi, J. Vis., 2013). For this purpose, we investigated how the perceived direction of a directionally ambiguous test stimulus is changed by the unidirectional drifting of a subsequent stimulus under various light conditions. The test stimulus was generated by shifting the phase of a sine-wave grating by 180°. Because the postdictive modulation of visual appearance occurs within a limited time range (Eagleman & Sejnowski, J. Vis., 2007), the stimulus-onset asynchrony (SOA) between the test and the subsequent stimulus was set to 250 ms. The eccentricity of stimulus presentation was varied from 0.0° to 10.0°. Observers judged the perceived direction of the test stimulus (rightward or leftward), which preceded a subsequent stimulus at different light levels ranging from photopic to scotopic levels (42–0.0024 cd/m2). We found that postdictive modulation, in which the test stimulus was perceived to move in the same direction as the subsequent stimulus, was stronger under mesopic conditions than under photopic or scotopic conditions. The strongest postdictive modulation was observed when the stimuli were presented at an eccentricity of 3.3°–6.7°, where the relative contributions of the cones and rods are almost equal under mesopic conditions (Raphael & MacLeod, J. Vis., 2011). These results suggest that motion integration is facilitated as a form of postdictive perception of motion to deal with the incoming spatiotemporally different signals from cones and rods.