Efferent and Afferent Control of Fast and Slow Arm Movements

Abstract

The "outflow" hypothesis suggests that subjects can monitor the efferent activity effecting movements and can be aware of the course of movements independent of proprioception. To test the outflow hypothesis eight subjects were trained to make a simple arm movement and to subjectively estimate its extent. Following training, the extent of the movement was experimentally manipulated by introducing or omitting a small unperceived mechanical resistance, and subjective estimates of movement extent were evaluated. The presence of a shift in subjective movement extent would suggest a proprioceptive dependency, while the absense of a shift would suggest efference monitoring. Clear evidence for efference monitoring was not found, although subjective movement extent was found not to vary as would be expected from purely proprioceptive feedback monitoring suggesting other (possibly feedforward) mechanisms.