Choosing which hand to use for an action is one of the most frequent decisions people make in everyday behavior. We developed a simple reaching task in which we vary the lateral position of a target and the participant is free to reach to it with either the right or left hand. While people exhibit a strong preference to use the hand ipsilateral to the target, there is a region of uncertainty within which hand choice varies across trials. We manipulated the reinforcement rates for the two hands, either by increasing the likelihood that a reach with the non-dominant hand would successfully intersect the target or decreasing the likelihood that a reach with the dominant hand would be successful. While participants had minimal awareness of these manipulations, we observed an increase in the use of the non-dominant hand for targets presented in the region of uncertainty. We modeled the shift in hand use using a Q-learning model of reinforcement learning. The results provided a good fit of the data and indicate that the effects of increasing and decreasing the rate of positive reinforcement are additive. These experiments emphasize the role of decision processes for effector selection, and may point to a novel approach for physical rehabilitation based on intrinsic reinforcement.
Keywords: motor control, decision making, action selection, reinforcement learning, reaching
Citation: Stoloff RH, Taylor JA, Xu J, Ridderikhoff A and Ivry RB (2011) Effect of reinforcement history on hand choice in an unconstrained reaching task. Front. Neurosci. 5:41. doi: 10.3389/fnins.2011.00041
Received: 15 January 2011;
Accepted: 14 March 2011;
Published online: 23 March 2011.
Edited by:Julia Trommershaeuser, New York University, USA
Reviewed by:Stefan Pollmann, Otto-von-Guericke University, Germany
Copyright: © 2011 Stoloff, Taylor, Xu, Ridderikhoff and Ivry. This is an open-access article subject to an exclusive license agreement between the authors and Frontiers Media SA, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.
*Correspondence: Richard B. Ivry, University of California Berkeley, 3210 Tolman Hall, Berkeley, CA 94720-1650, USA. e-mail: email@example.com