Behavioral Reference Frames for Planning Human Reaching Movements

• Published in: Journal of neurophysiology 2006-07, Vol.96 (1), p.352-362
• Main Authors: Beurze, Sabine M, Van Pelt, Stan, Medendorp, W. Pieter
• Format: Article
• Language: English
• Subjects: Adult; Arm - innervation; Arm - physiology; Eye Movements - physiology; Hand - innervation; Hand - physiology; Humans; Motor Cortex - physiology; Movement - physiology; Psychomotor Performance - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.01362.2005

1 Nijmegen Institute for Cognition and Information, 2 FC Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, Nijmegen, The Netherlands Submitted 27 December 2005; accepted in final form 25 March 2006 At some stage in the process of a sensorimotor transformation for a reaching movement, information about the current position of the hand and information about the location of the target must be encoded in the same frame of reference to compute the hand-to-target difference vector. Two main hypotheses have been proposed regarding this reference frame: an eye-centered and a body-centered frame. Here we evaluated these hypotheses using the pointing errors that subjects made when planning and executing arm movements to memorized targets starting from various initial hand positions while keeping gaze fixed in various directions. One group of subjects ( n = 10) was tested without visual information about hand position during movement planning (unseen-hand condition); another group ( n = 8) was tested with hand and target position simultaneously visible before movement onset (seen-hand condition). We found that both initial hand position and gaze fixation direction had a significant effect on the magnitude and direction of the pointing error. Errors were significantly smaller in the seen-hand condition. For both conditions, though, a reference frame analysis showed that the errors arose at an eye- or hand-centered stage or both, but not at a body-centered stage. As a common reference frame is required to specify a movement vector, these results suggest that an eye-centered mechanism is involved in integrating target and hand position in programming reaching movements. We discuss how simple gain elements modulating the eye-centered target and hand-position signals can account for these results. Address for reprint requests and other correspondence: S. M. Beurze, Nijmegen Institute for Cognition and Information, University of Nijmegen, P.O. Box 9104, NL-6500 HE, Nijmegen, The Netherlands (E-mail: s.beurze{at}0040nici.ru.nl )