Abstract
We compare how three different systems – saccades, pursuit, and perception – determine the direction of the same moving target. Recent studies suggest that this motion information, although it affects all three systems (saccades, Gellman & Carl, 1991; pursuit, Lisberger, 2010; perceived position, De Valois & De Valois, 1991), might be processed differently depending on the purpose of the process (Simoncini, et al., 2012). We take advantage of a perceptual illusion (Tse & Hsieh, 2006) in which motion signals within a moving aperture viewed in the periphery dramatically affect the perceived direction of the aperture itself. We presented moving apertures filled with noise that either drifted orthogonal to the aperture’s direction, or varied dynamically with no net motion. The targets appeared in the periphery and moved (12°/s) either toward or away from fixation. Participants were asked to saccade to these targets as soon as they appeared, and then track them with their gaze. Following the trial, participants reported the target direction using a directional arrow. In the trials with internal motion, however, the target disappeared at saccade onset. In these trials, early post-saccadic pursuit (open loop) still occurred so that the effect of the presaccadic illusory direction was seen in the postsaccadic pursuit. We also estimated the direction of target motion taken into account by the saccadic system from the saccade landing errors. Results show that motion signals from the internal drift strongly affect the perceived aperture direction (average direction shift of 25°), and also affect the direction seen in postsaccadic pursuit (average deviation from physical direction of 23°). In contrast, the effect on saccade landing was much smaller (equivalent to about 10° deviation), revealing that the saccade system integrates the internal and external motions of the target differently from the perception and pursuit systems.
Meeting abstract presented at VSS 2015