Visuomotor Transformation and Directional Bias Characters.
Ghilardi, Maria Felice, James Gordon, and Claude Ghez.
Center for Neurobiology and Behavior, New York State Psychiatric Institute,
and Program in Physical Therapy, College of Physicians and Surgeons, Columbia
University, New York, New York 10032.
APStracts 2:0011N, 1995.
SUMMARY AND CONCLUSIONS
1. The dependence of directional biases in reaching movements on the initial
position of the hand was studied in normal human subjects moving their unseen
hand on a horizontal digitizing tablet to visual targets displayed on a
vertical computer screen. 2. When initial hand positions were to the right of
midline, movements were systematically biased clockwise. Biases were
counterclockwise for starting points to the left. Biases were unaffected by
the screen location of the starting and target positions. 3. Vision of the
hand in relation to the target before movement, as well as practice with
vision of the cursor during the movement, temporarily eliminated these biases.
The spatial organization of the biases suggests that, without vision of the
limb, the nervous system underestimates the distance of the hand from an axis
or plane that includes its most common operating location. 4. To test the
hypothesis that such an underestimate might represent an adaptation, or range
effect, subjects were trained to reach accurately from right or left
positions. After training, movements initiated from other locations, including
ones that were previously error free, showed new biases that again represented
underestimates of the distance of the initial hand position from the new
trained location. 5. We conclude that hand path planning is dependent on
learned representations of the location of the hand in the work space.
Received 17 October 1994; accepted in final form 7 February 1995.
APS Manuscript Number J638-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.