Can the oculomotor control system compensate for initial velocity when making a saccade?

It is generally considered-but unproven-that the oculomotor control system takes initial velocity immediately preceding saccades into account when planning and executing saccadic eye movements. This is probably so that degradation of vision during a saccade can be minimized by achieving an optimal velocity profile which balances conflicting requirements of getting to a target as quickly as possible while not overshooting or ringing once eye has reached its target. Simulations, based on a linear homeomorphic mechanical model of the eyeball and its musculature, showed that the peak velocity of a saccade is strongly dependent on the velocity of the eye just prior to the saccade. An experiment involving 4 normal adult subjects (3M/1F, 20-24 yr) was subsequently undertaken in which each subject was asked to visually track either a stationary or a sinusoidal target. At unexpected times during this smooth oculomotor pursuit, and while the subject´s eyes were stationary or moving at various velocities up to ±40 °/s, the target switched to a step to induce a saccade. The target steps were in both the same and opposite directions to that of the pre-saccade smooth pursuit velocities. Results from this experiment showed that, for both forward and reverse saccades, an increase in initial velocity increases the peak velocity of same-size saccades. For forward saccades, the brain is only able to partially compensate for the initial velocity of the eye. In contrast, for reverse saccades, the brain over-compensates for the initial velocity. This is the first study to demonstrate experimentally that peak velocities during same-size saccades are dependent upon initial eye velocity.