The Contribution of Cross-Sensory Error Signals to Reach Aftereffects and Proprioceptive Recalibration

Reaching with altered visual feedback leads to adaptation of internal motor plans, which result in aftereffects, deviated reaching without visual feedback and proprioceptive recalibration, a shift in perceived hand location (Cressman & Henriques, 2010). Zbib, Henriques, and Cressman (2016) found motor changes arise more quickly than proprioceptive changes, which required prolonged training to become significantly shifted. But their methodology may not have captured the finer incremental changes in aftereffects and proprioception. Our lab also investigated the time course of these changes using a much quicker method of proprioceptive assessment. Results suggest that both motor and proprioceptive recalibration occurred in as few as 6 rotated-cursor training trials (7.6 and 3.9 respectively). Our current study focuses on the specific contribution of cross-sensory error signals on reach aftereffects and proprioceptive recalibration. Participants moved their hand to a remembered target while they were constrained to a force channel. The cursor always moved straight to the target site, while the hand was abruptly deviated 30 CCW of the intended target (making the cursor rotation CW as per the previous study). This passive training resulted in significant aftereffects and change in felt hand position within 6 training trials. Reach aftereffects were even larger by the end of passive-training (10.6), which were expectedly smaller than those produced during volitional reaches (15.7). In addition, all participants recalibrated their sense of felt hand position equally (11.3), which was larger than the shift seen with volitional reaching (5.09). The time course of these sensory and motor changes differed slightly across experiments but more across the different measures (motor vs. sensory). Our results suggest that proprioception is much more important for motor learning, with even the mere discrepancy between felt and seen hand location being enough to drive robust motor adaptation.