Human movement initiation: Specification of arm, direction, and extent.

TLDR

Reaction time is assumed to reflect the time needed to specify movement values that were not precued. The study introduces a method to discover how the defining values of forthcoming body movements are specified. Using a movement precuing technique, the authors varied the amount of information given about arm, direction, and extent of aimed hand movements, and inferred value‑specification processes from reaction‑time differences across precue conditions. Results showed that arm specification takes longest, followed by direction and extent, with serial but non‑invariant ordering; precuing effects were not due to stimulus identification or selection from prepared sets, supporting a distinctive‑feature rather than hierarchical motor‑programming model.

Abstract

This article presents a method for discovering how the defining values of forthcoming body movements are specified. In experiments using this movement precuing technique, information is given about some, none, or all of the defining values of a movement that will be required when a reaction signal is presented. It is assumed that the reaction time (RT) reflects the time to specify those values that were not precued. With RTs for the same movements in different precue conditions, it is possible to make detailed inferences about the value specification process for each of the movements under study. The present experiments were concerned with the specification of the arm, direction, and extent (or distance) of aimed hand movements. In Experiment 1 it appeared that (a) specification times during RTs were longest for arm, shorter for direction, and shortest for extent, and (b) these values were specified serially but not in an invariant order. Experiment 2 suggested that the precuing effects obtained in Experiment 1 were not attributable to stimulus identification. Experiment 3 suggested that subjects in Experiment 1 did not use precues to prepare sets of possible movements from which the required movement was later selected. The model of value specification supported by the data is consistant with a distinctive-feature view, rather than a hierarchical view, of motor programming.