THE ROLE OF SENSORY INFORMATION IN THE GUIDANCE OF VOLUNTARY MOVEMENT- REFLECTIONS ON A SYMPOSIUM HELD AT THE 22ND ANNUAL-MEETING OF THE SOCIETY FOR NEUROSCIENCE

This article reviews a symposium on the sensory control of movement he ld at the 22nd annual meeting of the Society for Neuroscience. Four sp eakers addressed a large audience on the proposition that ''one can on ly control what one senses.'' Charles Vierck supported the notion with a description of the severe motor deficits caused by lesions of the s pinal dorsal columns (DCs) in monkeys. In the discussion of Vierck's p resentation, Robert Forget described the difficulties experienced by d eafferented patients in tasks of daily life. Next, John Brooke showed that sensorimotor transformations vary greatly with task, anticipation , and uncertainty. In light of this, he questioned the simplifications inherent in servo and equilibrium-point theories of motor control. Pa ul Cordo then showed that in a rapid throwing task, proprioceptive inf ormation is used to control the moment of release (contradicting the i dea that sensory feedback is too delayed for ballistic movements). Dic k Burgess, like Brooke, criticized equilibrium-point models; he argued that a subject's sense of effort is a measure of the internal motor c ommand, which should correspond to specific equilibrium points. Howeve r, his experimental data were inconsistent with this interpretation. H e suggested instead that motor output is adjusted by comparing incomin g afferent information to an expected ''afferent template.'' Anatol Fe ldman and Mark Latash disagreed, saying that a constant sense of effor t does not imply a constant equilibrium-point command. The equilibrium -point debate was not resolved, but the symposium ended with a consens us that in most motor tasks, one can control only what one senses.