Influence of superimposed optokinetic stimulus on smooth pursuit eye movements elicited by sinusoidal spot target oscillation.

In 6 healthy subjects, smooth pursuit eye movements (SPEMs), elicited by sinusoidal spot target oscillation, were measured against three different backgrounds: dark, stationary texture (texture), and texture background movement in-phase with the spot target (coupled). Spot-target oscillation frequencies ranging between 0.2 to 1.6 Hz and peak velocities ranging between 19 to 75 degrees/s were employed. SPEM gain did not differ significantly among the three backgrounds below 0.8 Hz. However when at 1.6 Hz it responded to a peak velocity of 75 degrees/s, the gain for the "coupled" background condition was greater than that for the "dark" condition, which in turn was greater than the gain for "texture". However, SPEM phase delays were found to be similar for the three background conditions. Since the responses during "coupled" and "texture" backgrounds are most likely elicited by rapid-rise optokinetic reflex (OKR) interaction it can be concluded that SPEMs and the rapid-rise OKR system have the same latency (response) time.