Figure 1.

Characteristics of smooth pursuit. (a) (i): example of smooth pursuit in the Rhesus monkey. The target (dashed line) was initially stationary, then stepped to a 3° eccentric position and started to move at a constant velocity (15 deg s⁻¹). This particular stimulus is referred to as a Rashbass step-ramp target motion [2]. Adapted from [3]. (ii): target and eye velocity for the same trajectory. After a delay period of approximately 120 ms, eye velocity rapidly increased and overshot the target velocity (initiation period). Afterwards, during sustained pursuit, oscillations of eye velocity around the target velocity were also observed but with a decaying amplitude. A saccade was triggered to reduce the accumulated error in position. Adapted from [3]. (b) Smooth pursuit in humans shows the same oscillations as observed in monkeys. At the end of the pursuit response, eye velocity rapidly decayed with an approximately exponential time course. Note the absence of overshoot and oscillations at the end of pursuit. Modified from Robinson et al. [1].