Involuntary eye movements in response to first- and second-order motion.

We trained monkeys to maintain fixation while first- and second-order motion stimuli were displayed centrally in the visual field. Stimulus velocity, spatial frequency and contrast were varied to determine differences in patterns of involuntary eye movements elicited by random onset of stimulus motion. We observed different patterns of eye movement latency and velocity suggesting very early (< or = 100 ms) components of oculomotor activity are used to initiate smooth pursuit of object trajectory. Eye movement latency was insensitive to the complexity of stimulus motion, whereas second-order motion elicited faster eye movements than first-order motion. Instantaneous eye movement velocity might be related to the earliest stages of visual processing of component motion.