Abstract
We have shown that when subjects reach with continuous, misaligned visual feedback of their hand, their reaches are adapted and proprioceptive sense of hand position is recalibrated to partially match the visual feedback (Salomonczyk et al., 2011). It is unclear if similar changes arise after reaching with visual feedback that is provided only at the end of the reach (i.e., terminal feedback), when there are shorter temporal intervals for subjects to experience concurrent visual and proprioceptive feedback. Subjects reached to targets with an aligned hand-cursor that provided visual feedback at the end of each reach movement across a 99-trial training block, and with a rotated cursor over three successive blocks of 99 trials each. After each block, no cursor reaches, to measure aftereffects, and felt hand positions were measured. Felt hand position was determined by having subjects indicate the position of their unseen hand relative to a reference marker. We found that subjects adapted their reaches following training with rotated terminal visual feedback, yet slightly less (i.e., reach aftereffects were smaller), than subjects from a previous study who experienced continuous visual feedback. Nonetheless, current subjects recalibrated their sense of felt hand position in the direction of the altered visual feedback, but this proprioceptive change increased incrementally over the three rotated training blocks. Final proprioceptive recalibration levels were comparable to our previous studies in which subjects performed the same task with continuous visual feedback. Thus, compared to reach training with continuous, but altered visual feedback, subjects who received terminal altered visual feedback of the hand produced significant but smaller reach aftereffects and similar changes in hand proprioception when given extra training. Taken together, results suggest that terminal feedback of the hand is sufficient to drive motor adaptation, and also proprioceptive recalibration.
Highlights
Numerous studies have shown that people can rapidly adapt their reaches when provided with altered visual feedback of their hand, such as a misaligned hand cursor
We have shown that it is the discrepancy between vision and proprioception that drives this change in felt hand position, or what we refer to as proprioceptive recalibration (Henriques and Cressman, 2012)
When we compared the terminal feedback aftereffects made soon after reach training with the aftereffects completed after proprioceptive estimates, we found no significant difference across the three blocks, F(1,10) = 1.67, p = 0.22
Summary
Numerous studies have shown that people can rapidly adapt their reaches when provided with altered visual feedback of their hand, such as a misaligned hand cursor. We have shown that it is the discrepancy between vision and proprioception (rather than motor error signals) that drives this change in felt hand position, or what we refer to as proprioceptive recalibration (Henriques and Cressman, 2012). Our aim in this study was to test whether reducing the duration of this discrepancy to only the very end of the reaching movement is sufficient to lead to changes in felt hand position. We asked whether adapting reaches to terminal feedback of the hand (i.e., to a hand-cursor that appears only at the end of the reach), and limiting subjects exposure to a visual-proprioceptive discrepancy, would lead to proprioceptive recalibration
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