The Journal of Neurophysiology Vol. 85 No. 5 May 2001, pp. 2298-2302
Copyright ©2001 by the American Physiological Society

RAPID COMMUNICATION

Throwing Accuracy in the Vertical Direction During Prism Adaptation: Not Simply Timing of Ball Release

 ¹Department of Anatomy and Neurobiology and  ²Department of Neurology and Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri 63110; and  ³Division of Biology, California Institute of Technology, Pasadena, California 91125

Martin, Tod A., Bradley E. Greger, Scott A. Norris, and W. Thomas Thach. Throwing Accuracy in the Vertical Direction During Prism Adaptation: Not Simply Timing of Ball Release. J. Neurophysiol. 85: 2298-2302, 2001. In a previous study, others have hypothesized that the variance in vertical errors that occurs while throwing at visual targets is caused by changes in any of three throw parameters: hand location in space, hand translational velocity, and hand orientation. From an analysis of skilled throwers, those authors concluded that vertical error is best correlated with variance in hand orientation, which in turn is related to the timing of ball release. We used a vertical prism adaptation paradigm to investigate which of these throwing parameters subjects use when adapting to external perturbation. Our subjects showed no correlation between hand position or hand translational velocity and ball impact height in normal, over-practiced throwing. However, video-based motion analysis showed that modifications both of position and speed of the hand play an important role when subjects are forced to compensate for a vertically shifting prism perturbation during a dart-like throw (these factors contribute ~30% of the adaptation). We concluded that, during adaptation, more degrees of freedom and more sources of potential error are modified to achieve the gaze-throw recalibration required to hit the target than are employed in this type of throw during normal conditions.