The effects of awareness of the perturbation during motor adaptation on hand localization

Abstract

Awareness of task demands is often used during rehabilitation and sports training by providing instructions which appears to accelerate learning and improve performance through explicit motor learning. However, the effects of awareness of perturbations on the changes in estimates of hand position resulting from motor learning are not well understood. In this study, people adapted their reaches to a visuomotor rotation while either receiving instructions on the nature of the perturbation, experiencing a large rotation, or both to generate awareness of the perturbation and increase the contribution of explicit learning. We found that instructions and/or larger rotations allowed people to activate or deactivate part of the learned strategy at will and elicited explicit changes in open-loop reaches, while a small rotation without instructions did not. However, these differences in awareness, and even manipulations of awareness and perturbation size, did not appear to affect learning-induced changes in hand-localization estimates. This was true when estimates of the adapted hand location reflected changes in proprioception, produced when the hand was displaced by a robot, and also when hand location estimates were based on efferent-based predictions of self-generated hand movements. In other words, visuomotor adaptation led to significant shifts in predicted and perceived hand location that were not modulated by either instruction or perturbation size. Our results indicate that not all outcomes of motor learning benefit from an explicit awareness of the task. Particularly, proprioceptive recalibration and the updating of predicted sensory consequences appear to be largely implicit.

The effect of age on visuomotor learning processes

“…The procedure and set up are similar to our previous study [18]. It includes two experimental sessions ( Figure 2), and each session had several repetitions of the same four tasks (described in detail below) The first session (illustrated on the top row of Figure 2) measured baseline results where the cursor was aligned with the hand during reach training.…”

“…Further, the persistent shifts in hand localization in these patients suggest that perhaps the part of these learning-induced changes that may be due to proprioceptive recalibration could occur outside the cerebellum [44]. The contributions of the afferent and efferent sources of these changes in hand localization have been recently investigated in young adults [18,33,35,50]. However, it is not clear how predicted estimates of hand location change with healthy aging.…”

“…Adaptation requires both a cognitive, or explicit, component which tends to contribute to early stages of learning, as well as implicit processes that predominate in the later stages. The explicit component has been assessed by having participants indicate their aiming strategy either in a trial-by-trial basis [4,16], or indicate their developed strategy post-adaptation when reaching without a perturbation [4,5,[17][18][19][20]. In addition, explicit instruction about how to compensate for a visual perturbation have been used to facilitate initial learning [16,[19][20][21].…”

“…In turn, this visually-induced change in hand proprioception appears to contribute to changes in motor performance, particularly reach aftereffects [13, [42][43][44][45]. These changes in proprioception seem to be largely implicit, in that they are not affected by instructions [18], are similar following both abrupt and gradual introduction to the perturbation [46], and do not change with age when using the usual perceptual reports [15,44]. Thus, if the implicit contributions to learning remain largely intact across age, we predict that, like reach aftereffects, proprioceptive recalibration should not differ between older and younger adults.…”

“…In fact, many computational models of motor learning specify that the forward model, used to generate predicted sensory consequences based on efferent signals, must be updated for implicit motor learning to occur [47]). The amount of change in these state estimates has been quantified by measuring changes in hand localization following visuomotor adaptation [18,33,35,48,49]. Synofzik et al [48] and Izawa et al [49] found that cerebellar patients show significant but smaller learning-induced changes in hand estimates, compared to healthy controls and concluded that the reduction reflects the critical role that the cerebellum plays in updating predicted sensory consequences for learning.…”