Slow eye movement evoked by sudden appearance of a stationary visual stimulus observed in a step-ramp smooth pursuit task in monkey.

We examined the influence of a peripheral visual stimulus on eye movement while monkeys performed a horizontal step-ramp pursuit task. When an irrelevant visual stimulus was presented before the onset of the target motion, slow eye movement away from the stimulus was observed. When the stimulus appeared during a temporal gap between the offset of the fixation point and the onset of target motion the velocity of the slow eye movement increased. The onset of the movement was time-locked to the onset of the extraneous visual stimulus and its latency was comparable to the latency of smooth pursuit in trials without a peripheral stimulus. The results demonstrate a new form of smooth eye movement, suggesting that the eye movement may be contained in the initial stages of smooth pursuit observed in step-ramp paradigms.