Motor psychophysics.

Motor psychophysics, a field pioneered by Woodworth, is concerned with rules governing motor performance and with interactions of central and peripheral factors during movement. One unresolved issue in motor psychophysics is the role of proprioceptive inputs and the present article reviews evidence relevant to this issue. In normal subjects, accuracy of small movements is disrupted by perturbations causing unexpected proprioceptive inputs but accuracy of large movements is relatively unaffected. In patients with proprioceptive loss secondary to selective large fiber sensory neuropathy, small movements are grossly inaccurate and there are deficits in maintenance of stable postures and steady force outputs. These results support the notion that proprioceptors play a critical role in postural stability and precise changes of motor output.