Abstract
Anticipatory smooth pursuit eye movements in the direction of expected target motion can be elicited by symbolic visual or auditory cues (Kowler, 1989). Stimuli in these studies, small targets moving against dark or structured backgrounds, convey the perceptual impression of an object moving across space. Are such interpretations necessary for anticipatory pursuit? We studied random-dot kinematograms (RDKs), composed of dots with very brief lifetimes. RDK's can be pursued (Schütz et al., VSS 2009), but they generate global motion signals, rather than the percept of discrete moving objects. RDKs were composed of dots (4′) moving coherently (2.5 o/s) either up, down, right or left. Dot lifetimes were 52, 104, or 208 ms. The direction of motion was cued by either: (1) the spatial offset of the initial stationary fixation stimulus away from screen center, opposite to the direction of upcoming target motion; or (2) a tone whose frequency indicated whether dots moving downward would change direction to either down-right or down-left. Uncued motion directions, and unlimited lifetime dots, were also tested. Anticipatory smooth eye movements (ASEM) were prominent. Neither their onset time nor velocity depended on dot lifetime. By contrast, both peak eye velocity and steady-state pursuit gain varied with lifetime. Steady-state gains with the longest lifetime approached 1. Gains with the shortest lifetime ranged from 0.1 to 0.7, depending on subject and direction of motion. These results show that anticipatory smooth pursuit eye movements can be elicited with global motion, and do not require representations of an object moving across space. Dot lifetime did not affect anticipatory eye movements, but did affect steady state pursuit. These differential effects of dot lifetime suggest that the study of the pursuit of random-dot kinematograms may be a useful way to dissociate the response to expected and immediate target motion.