Saccades to remembered targets exhibit enhanced orbital position effects in monkeys

Abstract

Remembered saccades of rhesus monkeys are markedly influenced by starting eye position. Altering the initial position systematically affects the direction or amplitude of the movements to a striking degree. In general, changes in the horizontal or vertical starting position primarily produce changes in the horizontal or vertical component, respectively, regardless of whether the target displacement occurs in the horizontal or vertical direction. For some monkeys, a similar pattern of initial position influence on movement direction can be seen in the curvature of visually guided saccades. Starting position also modulates the upward offset in fixation, which monkeys display in the dark.