Different effects involved in the interaction of saccades and the vestibulo-ocular reflex.

The accuracy of human goal-directed saccades during passive sinusoidal whole-body rotation is the same as that of normal saccades with the head still. Two mechanisms contribute to this accuracy: 1. There is an incomplete summation (70% on the average) of saccade and VOR velocities. 2. The duration of saccades during head rotation is lengthened if VOR and saccade velocities have the same direction, and is shortened if their direction is opposite. The latter finding supports the hypothesis that saccades are controlled by local feedback.