MOTOR AND PERCEPTUAL MECHANISMS INVOLVED IN THE CONTROL OF SMOOTH PURSUIT EYE MOVEMENT
The smooth pursuit system allows a person to visually follow a target moving at slow to moderate velocity (5 - 50 deg/sec). Much of the research in our laboratory has been concerned with defining the quantitative features of the mechanisms for control of smooth pursuit. Our work has concentrated on four broad issues: (1) the stimuli for pursuit; (2) the internal dynamics of the pursuit system; (3) control of initiation and termination of pursuit; and (4) the perception of motion and location during pursuit. We have shown that the stimuli for smooth pursuit includes, besides target velocity, target offset from the fovea (target position) and the perception of target velocity. Some of our work suggests that the pursuit system involves an internal neural feedback loop with a response time-constant of about 0.5 sec. Recently, we have investigated the exponential decrease in eye velocity that occurs during pursuit termination. Results from this study suggest that the exponential decrease comes from a reduction in the potency of target velocity, as stimulus, relative to target position. Our current research is concerned with the perception of target location at the time of pursuit movement. In these experiments, subjects make a psychophysical judgment about the location of a target flash presented at various times before, during or after pursuit. The data from such studies can be used to infer the characteristics of a pursuit system signal concerned with perceptual localization. However, there are problems with the target flash as a stimulus: e.g., does the flash have a significant influence on perceived location and thus on the assumed characteristics of the pursuit system signal? To explore this, we are developing theoretical models to study the interaction of visual signals with pursuit signals.