Abstract
Psychophysical studies of spatial localization have demonstrated that motion can influence the perceived location of a stationary stimulus. For example, drifting sinusoidal gratings within a static Gaussian envelope produce systematic errors in perceptual localization such that the envelope appears shifted in the direction of motion (De Valois & De Valois, 1991; Ramachandran & Anstis, 1990). However, the relationship between errors in the perceptual and visuomotor systems is poorly understood. In a series of experiments, we examined whether illusory position shifts induced by drifting Gabors could influence saccade landing position. Subjects were presented with Gabor targets that could appear at random locations in the left or the right visual field and drifted either rightward or leftward. Subjects made reactive saccades to the Gabor following its onset. Subjects’ saccade landing positions were biased in the direction of the Gabor’s drift, and this effect was present with stimulus durations as short as 60 ms. The effect persisted for volitional saccades in which subjects were cued to saccade to the Gabor following a variable delay. Comparison with a control condition in which subjects were presented with drifting gratings within a hard aperture demonstrated that this effect was based on a shift in perceived location, rather than induced by motion signals alone. Finally, we provide evidence for saccadic adaptation based on error signals from the perceived (illusory), rather than physical, location of the target. We induced saccadic adaptation by presenting a static Gabor target on each trial and replacing it with an inward drifting Gabor upon the initiation of the saccade. This resulted in a decrease in saccade amplitude over the course of 200 trials. Together, our results provide evidence for a rapid, adaptive mechanism by which the visual system updates moving target positions to improve the accuracy of saccadic eye movements to moving objects.
Meeting abstract presented at VSS 2012