Abstract
Previous research on motion perception has found that static luminance texture produces an increase in the perceived speed of moving stimuli. The experiments discussed here study the influence of texture on another aspect of motion perception: the motion aftereffect (MAE). In Experiment 1, we measured static MAE duration in three conditions: 1- luminance modulated gratings to which no texture was added 2- luminance modulated gratings to which static texture (static luminance noise) was added 3- contrast modulated noise. Our results demonstrate that adding static luminance texture to a drifting luminance-modulated sinewave grating greatly diminishes static MAE duration and can even completely eliminate the static MAE. Our results also show that no difference in static MAE duration occurred between luminance-modulated gratings to which static luminance texture was added and contrast-modulated noise. This suggests that the failure of contrast-modulated texture to elicit a static MAE may not come from a fundamental difference in the processing of first- and second-order motion, but from the luminance texture inherently present in these second-order stimuli. Our results and the static MAE are discussed in a Bayesian context in which adaptation creates a shift in the prior's center in the direction opposite to the direction of adaptation and texture is used as a landmark. This is consistent with a recalibration and error-correcting account of the MAE. In Experiment 2, we studied the effects of texture characteristics on the MAE by notch-filtering the luminance noise in Fourier space. Preliminary data show that filtering out high pass information along the axis of motion produces longer MAE durations, but that filtering out high-pass information along an axis orthogonal to the axis of motion does not. This is consistent with the proposal that the visual system uses luminance texture in the assessment of motion.