Gaze, eye, and head movement dynamics during closed- and open-loop gaze pursuit

Horizontal step-ramp stimuli were used to examine gaze, eye, and head movement dynamics during head-unrestrained pursuit with and without imposed retinal velocity errors (RVE; i.e. open- and closed-loop, respectively) in two rhesus monkeys. In the closed-loop experiment , pursuit was elicited by step-ramp stimuli with a constant velocity of 20--80 deg/s. Each monkey used a combination of eye and head motion to initially fixate and then pursue the target. Additionally, we found that initial eye and head acceleration increased as a function of target velocity. In the open-loop experiment, step-ramp stimuli (40 deg/s) were presented and ~125 ms after pursuit onset, a constant RVE was imposed for a duration of 300 ms. In each monkey, when RVE = 0 deg/s, gaze, eye, and head velocity trajectories were maintained at their current or at a damped velocity. Moreover, the head as well as the eyes mediated the observed increase and decrease in gaze velocity when RVE was +10 and -10 deg/s, respectively. Based on our findings we conclude that the pursuit system uses visual and non-visual signals to drive coordinated eye-head pursuit