Plan-based generalization shapes local implicit adaptation to opposing visuomotor transformations

Abstract

The human ability to use different tools demonstrates our capability of forming and maintaining multiple, context specific motor memories. Experimentally, this has been investigated in dual adaptation, where participants adjust their reaching movements to opposing visuomotor transformations. Adaptation in these paradigms occurs by distinct processes, such as strategies for each transformation or the implicit acquisition of distinct visuomotor mappings. While distinct, transformation-dependent aftereffects have been interpreted as support for the latter, they could reflect adaptation of a single visuomotor map, which is locally adjusted in different regions of the workspace. Indeed, recent studies suggest that explicit aiming strategies direct where in the workspace implicit adaptation occurs, thus potentially serving as a cue to enable dual adaptation. Disentangling these possibilities is critical to understanding how humans acquire and maintain motor memories for different skills and tools. We therefore investigated generalization of explicit and implicit adaptation to untrained movement directions after participants practiced two opposing cursor rotations, which were associated with the visual display being presented in the left or right half of the screen. Whereas participants learned to compensate for opposing rotations by explicit strategies specific to this visual workspace cue, aftereffects were not cue-sensitive. Instead, aftereffects displayed bimodal generalization patterns that appeared to reflect locally limited learning of both transformations. By varying target arrangements and instructions, we show that these patterns are consistent with implicit adaptation that generalizes locally around movement plans associated with opposing visuomotor transformations. Our findings show that strategies can shape implicit adaptation in a complex manner.

Differential contributions of implicit and explicit learning mechanisms to various contextual cues in dual adaptation

“…We saw that those in the Instruction Experiment were able to immediately compensate by implementing the aiming strategy, but they failed to improve, only retaining a small portion of the aiming strategy by the end of the training session, and later reflected in the lack of implicit reach aftereffects. In contrast, using a strongly predictive cue of target workspace separation, Schween et al (2018) nicely demonstrated significant implicit reach aftereffects in their group that received verbal instructions about how to counter their blocked 60° CW and CCW rotations (Schween et al, 2018) that were otherwise shown to interfere. Indeed, we found a similar effect whereby dual adaptation as cued by separated target sets were able to elicit reach aftereffects that decreased in size as a function of the distance between workspaces (Baldeo et al, 2013).…”

“…(2) an implicit process which is thought to function without awareness, reflect adaptation of internal models in the cerebellum, and largely produce reach aftereffects (Heuer & Hegele, 2008;Taylor, Klemfuss, & Ivry, 2010). Explicit and implicit contributions can also be elicited when adapting to opposing visuomotor rotations for some contextual cues, such as when targets are displayed in different workplaces (a cue that usually leads to dual adaptation rates similar to that for single-rotation adaptation (Baldeo & Henriques, 2013;Woolley, Tresilian, Carson, & Riek, 2007)), and when the perturbations are large and blocked, as demonstrated by Schween and colleagues (Schween, Taylor, & Hegele, 2018). In one of their dual adaptation experiments, Schween and colleagues showed that overlapping strategies led to interference, but when provided with compensatory strategies, participants showed overall learning and reach aftereffects (Schween et al, 2018).…”

“…Previous work on dual adaptation has largely demonstrated that motor-based or "intrinsic" cues tend to be more successful at reducing interference and facilitating learning (Ayala et al, 2015;Ayala & Henriques, 2018;Baldeo & Henriques, 2013;Galea & Miall, 2006;Schween et al, 2018;Wang & Musseler, 2014;Woolley, de Rugy, Carson, & Riek, 2011). We further explored this idea by investigating whether self-generated movement sequence cues, which are motor-based by nature, can facilitate dual adaptation.…”

“…Thus, when reaching without visual feedback of the cursor, regardless of whether or not they are asked to, participants tend to disregard any strategies by default. Still, it's possible that this applies only for moderately effective cues, while stronger, more predictive cues such as workspace location (Baldeo & Henriques, 2013;Schween et al, 2018) are able to recruit not only implicit, but also explicit mechanisms.…”

“…Explicit and implicit contributions can also be elicited when adapting to opposing visuomotor rotations for some contextual cues, such as when targets are displayed in different workplaces (a cue that usually leads to dual adaptation rates similar to that for single-rotation adaptation (Baldeo & Henriques, 2013;Woolley, Tresilian, Carson, & Riek, 2007)), and when the perturbations are large and blocked, as demonstrated by Schween and colleagues (Schween, Taylor, & Hegele, 2018). In one of their dual adaptation experiments, Schween and colleagues showed that overlapping strategies led to interference, but when provided with compensatory strategies, participants showed overall learning and reach aftereffects (Schween et al, 2018). Still, it's unclear to what extent these underlying processes are engaged, so here we break down the explicit and implicit contributions to dual adaptation across a diverse set of contextual cues.…”