Effects of smooth pursuit eye movement on ocular responses to sudden background motion in humans

We studied the effects of horizontal smooth pursuit on the ocular tracking responses to brief perturbations of a textured background in humans. When t he subject was fixating a stationary spot, a brief perturbation (60 degrees /s, 40 ms) of the background in any one of four directions (right, left, up , down) elicited a small tracking response. When the subject was pursuing a target moving against the stationary background, the same background pertu rbation elicited a larger response when in the same direction as the pursui t, but a smaller response when its direction was opposite to the pursuit; t he response to vertical background perturbations was also enhanced during p ursuit. When the subject was pursuing while the target and background were moving together, the same background perturbations elicited the larger resp onses regardless of their direction. These results indicate that the sensit ivity to background motion is increased during smooth pursuit. However, whe n pursuit is executed against a stationary background - the usual situation in everyday life - the system is selectively insensitive to the reafferent visual input associated with pursuit, thereby reducing the potentially adv erse effect of the background on pursuit performance. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.