Motor-output variability: A theory for the accuracy of rapid motor acts.

TLDR

Current theories of rapid movement emphasize error correction while ignoring how motor‑output variability scales with movement amplitude and time, a limitation noted since early studies of limb movement laws. The study proposes a theory linking movement amplitude, movement time, mass, and resulting error to explain motor‑output variability. The theory derives predictions from physical principles and tests them across single‑aiming, reciprocal, and rapid‑timing tasks. Empirical data from these paradigms confirm the predictions, supporting the theory’s explanatory power.

Abstract

Theoretical accounts of the speed-accuracy trade-off in rapid movement have usually focused on within-moveme nt error detection and correction, and have consistently ignored the possibility that motor-output variability might be predictably related to movement amplitude and movement time. This article presents a theory of motor-output variability that accounts for the relationship among the movement amplitude, movement time, the mass to be moved, and the resulting movement error. Predictions are derived from physical principles; empirical evidence supporting the principles is presented for three movement paradigms (single-aiming responses, reciprocal movements, and rapid-timing tasks); and the theory and data are discussed in terms of past theoretical accounts and future research directions. Examining the current level of understanding about the production and control of motor responses, many would no doubt be tempted to say that we have not come very far since the early writings of Woodworth (1899) and Hollingworth (1909). These writers were concerned with the basic laws of limb movements (analogous, perhaps to the basic laws of motion that were the cornerstone of physics) that denned the relationship between the simplest aspects of motor