Skip to main content
Log in

Differential effect of task conditions on errors of direction and extent of reaching movements

Experimental Brain Research Aims and scope Submit manuscript

Abstract

 Invariant patterns in the distribution of the endpoints of reaching movements have been used to suggest that two important movement parameters of reaching movements, direction and extent, are planned by two independent processing channels. This study examined this hypothesis by testing the effect of task conditions on variable errors of direction and extent of reaching movements. Subjects made reaching movements to 25 target locations in a horizontal workspace, in two main task conditions. In task 1, subjects looked directly at the target location on the horizontal workspace before closing their eyes and pointing to it. In task 2, arm movements were made to the same target locations in the same horizontal workspace, but target location was displayed on a vertical screen in front of the subjects. For both tasks, variable errors of movement extent (on-axis error) were greater than for movement direction (off-axis error). As a result, the spatial distributions of endpoints about a given target usually formed an ellipse, with the principal axis oriented in the mean movement direction. Also, both on- and off-axis errors increased with movement amplitude. However, the magnitude of errors, especially on-axis errors, scaled differently with movement amplitude in the two task conditions. This suggests that variable errors of direction and extent can be modified independently by changing the nature of the sensorimotor transformations required to plan the movements. This finding is further evidence that the direction and extent of reaching movements appear to be controlled independently by the motor system.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Author information

Authors and Affiliations

Authors

Additional information

Received: 8 October 1996 / Accepted: 14 January 1997

Rights and permissions

Reprints and permissions

About this article

Cite this article

Messier, J., Kalaska, J. Differential effect of task conditions on errors of direction and extent of reaching movements. Exp Brain Res 115, 469–478 (1997). https://doi.org/10.1007/PL00005716

Download citation

  • Issue Date:

  • DOI: https://doi.org/10.1007/PL00005716

Navigation