Preprogrammed and feedback-guided movements of monkeys

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Evidence is presented for preprogramming of a certain type of arm movement made by chronic Cebus monkeys in execution of a self-paced step tracking task. Accuracy of guiding a handle into mechanically undetectable target areas depended on adequate auditory or visual target cues or on consistent practice without cues. “Continuous” movements made in one step retained their original learned amplitudes, revealing their preprogrammed mode of execution. In contrast, “discontinuous” movements, made in successive small steps, over- or undershot for many trials, until residual cues were used by the animals. Monkeys that were well trained to the use of continuous movements retained their use during cue deprivation, while others substituted discontinuous movements.