Eye movements of rhesus monkeys directed towards imaginary targets

Is the presence of foveal stimulation a necessary prerequisite for rhesus m onkeys to perform visually guided eye movements? To answer this question, w e trained two rhesus monkeys to direct their eyes towards imaginary targets defined by extrafoveal cues. Independent of the type of target, real or im aginary, the trajectory of target movement determined the type of eye movem ent produced: steps in target position resulted in saccades and ramps in ta rget position resulted in smooth pursuit eye movements. There was a tendenc y for the latency of saccades as well as pursuit onset latency to be delaye d in the case of an imaginary target in comparison to the real target. The initial eye acceleration during smooth pursuit initiation elicited by an im aginary target decreased in comparison to the acceleration elicited by a re al target. The steady-state pursuit gain was quite similar during pursuit o f an imaginary or a real target. Our results strengthen the notion that pur suit is not exclusively a foveal function. (C) 1999 Elsevier Science Ltd. A ll rights reserved.