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 held at the 22nd annual meeting of the Society for Neuroscience. Four speakers addressed a large audience on the proposition that "one can only control what one senses". Charles Vierck supported the notion with a description of the severe motor deficits caused by lesions of the spinal dorsal columns (DCs) in monkeys. In the discussion of Vierck's presentation, Robert Forget described the difficulties experienced by deafferented 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. Paul Cordo then showed that in a rapid throwing task, proprioceptive information is used to control the moment of release (contradicting the idea that sensory feedback is too delayed for ballistic movements). Dick Burgess, like Brooke, criticized equilibrium-point models; he argued that a subject's sense of effort is a measure of the internal motor command, which should correspond to specific equilibrium points. However, his experimental data were inconsistent with this interpretation. He suggested instead that motor output is adjusted by comparing incoming afferent information to an expected "afferent template". Anatol Feldman and Mark Latash disagreed, saying that a constant sense of effort does not imply a constant equilibrium-point command. The equilibrium-point debate was not resolved, but the symposium ended with a consensus that in most motor tasks, one can control only what one senses.