Timing of skilled motor performance: Tests of the proportional duration model.

Historically, theories of motor control have been based on either central or peripheral mechanisms. This article examines a current, expfieit, central theory accounting for the observed flexibility in motor performance: the generafized motor program with a multiplicative rate parameter. Reanalysis of data from a variety of motor skills reported in the literature and a detailed study of skilled typewriting show that a generalized motor program with a multiplicative rate parameter generally does not fit observed performance. Instead, the data support a composite model of motor control in which performance is determined by both central and peripheral mechanisms.