Effect of stimulus position and velocity upon the maintenance of smooth pursuit eye velocity.

The relative contributions of retinal slip velocity and position errors to the generation of smooth pursuit eye movements were examined in three rhesus monkeys. Recognizing the unlikelihood of producing a pure retinal slip velocity or position error signal, these two stimulus parameters were combined under open-loop conditions. Both slip velocity and position error were used by the monkey to maintain an established eye velocity. Both parameters had the greatest effects upon eye velocity when they were in the same direction, enabling the monkey to maintain an established pursuit velocity. When slip velocity and position error were in the direction opposite to the initial pursuit, eye velocity reversed direction and moved very quickly towards zero. When the two parameters were in opposite directions, their effect upon eye velocity was minimized.