Research Article

Experimental Brain Research

, Volume 173, Issue 3, pp 425-437

Dissociable effects of the implicit and explicit memory systems on learning control of reaching

  • Eun Jung HwangAffiliated withLaboratory for Computational Motor Control, Department of Biomedical Engineering, Johns Hopkins School of MedicineDivision of Biology 216-76, California Institute of Technology
  • , Maurice A. SmithAffiliated withLaboratory for Computational Motor Control, Department of Biomedical Engineering, Johns Hopkins School of Medicine
  • , Reza ShadmehrAffiliated withLaboratory for Computational Motor Control, Department of Biomedical Engineering, Johns Hopkins School of Medicine Email author 

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

Adaptive control of reaching depends on internal models that associate states in which the limb experienced a force perturbation with motor commands that can compensate for it. Limb state can be sensed via both vision and proprioception. However, adaptation of reaching in novel dynamics results in generalization in the intrinsic coordinates of the limb, suggesting that the proprioceptive states in which the limb was perturbed dominate representation of limb state. To test this hypothesis, we considered a task where position of the hand during a reach was correlated with patterns of force perturbation. This correlation could be sensed via vision, proprioception, or both. As predicted, when the correlations could be sensed only via proprioception, learning was significantly better as compared to when the correlations could only be sensed through vision. We found that learning with visual correlations resulted in subjects who could verbally describe the patterns of perturbations but this awareness was never observed in subjects who learned the task with only proprioceptive correlations. We manipulated the relative values of the visual and proprioceptive parameters and found that the probability of becoming aware strongly depended on the correlations that subjects could visually observe. In all conditions, aware subjects demonstrated a small but significant advantage in their ability to adapt their motor commands. Proprioceptive correlations produced an internal model that strongly influenced reaching performance yet did not lead to awareness. Visual correlations strongly increased the probability of becoming aware, yet had a much smaller but still significant effect on reaching performance. Therefore, practice resulted in acquisition of both implicit and explicit internal models.

Keywords

Reaching Arm movements Awareness Adaptation Force fields Vision Proprioception Computational models Motor control Motor learning