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

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.

Basal ganglia network mediates the control of movement amplitude

“…Changes in RT can re¯ect the time required for discrete aspects of motor planning independent of feedback control processes. Relevant here, precues for movement extent and direction can reduce RTs additively, implying thereby that movement direction and amplitude are planned separately (Rosenbaum, 1980;Lepine et al, 1989;Bock & Arnold, 1992). This idea is also supported by disparate additional observations: speci®cation of extent and direction follows different timecourses (Ghez et al, 1997); visuomotor gains are learnt more readily and generalize more widely than directional rotations (Krakauer et al, 2000;Vindras & Viviani, 2002); learning of rotations and gains activates different cortical and subcortical networks (Krakauer et al, 2004); and, direction and extent errors vary independently (Gordon et al, 1994;Desmurget et al, 1997;Vindras & Viviani, 1998;Desmurget et al, 1999).…”

“…By contrast, an amplitude precue should be useless if the motor program to be scaled is not de®ned. Further arguments supporting these claims can be in found in behavioural results showing that the in¯uences of amplitude and direction precues on RT are independent and additive (Rosenbaum, 1980;Lepine et al, 1989).…”

Effects of motor preparation and spatial attention on corticospinal excitability in a delayed-response paradigm

“…Humans and other primates are able to use prior information to prepare their motor system for a later response (Rosenbaum 1980). This motor preparation is evident in a shorter reaction time and is reXected in preparatory neural activity.…”

Planning and Representing Intentional Action

“…Third, the time it takes to begin with an action often reflects the action's complexity [30,31,32] or the number of steps it consists of [33,34,35], as well as the number of action features that could not be planned in advance of the reaction stimulus [36,37,38,39]. Thus, the amount of planning required seems to determine when people can begin to carry out an action.…”