Where's my hand? Updating proprioception and prediction for motor learning


Knowing the position of one's limbs is essential for moving them, and hence it makes sense that several signals provide information on limb position. These include vision and proprioception, as well as predictive estimates based on efference copies of the movement. And since both proprioceptive and predictive estimates of hand position have been shown to change when we adapt our movements to altered visual feedback of the hand (i.e., a visuomotor rotation), it is unclear how much each contributes to post-adaptation changes in where we localize our hand. By having participants localize their hand with and without efference signals, we can tease the two contributions apart. In summary, we find that 1) visuomotor training leads to changes in both predicted, efferent-based and proprioceptive estimates of the hand, but that the change in prediction is smaller than that of perception, 2) these changes do not vary with awareness nor the size of the visual perturbation, but do differ in older adults, and 3) proprioception-based changes occur very rapidly, while efference-based contributions come about less rapidly, at about the same rate as motor changes. These findings imply that both these sources for estimating limb position are updated during learning and in turn contribute to changes in motor performance. This means that the plasticity in our estimates of limb position depends on multiple sources of feedback, and our brains likely take into account the peculiarities of the separate signals to arrive at a robust limb position signal.