Methods matter: Your measures of explicit and implicit processes in visuomotor adaptation affect your results

Abstract

Visuomotor rotations are frequently used to study the different processes underlying motor adaptation. Explicit aiming strategies and implicit recalibration are two of these processes. Various methods, which differ in their underlying assumptions, have been used to dissociate the two processes. Direct methods, such as verbal reports, assume explicit knowledge to be verbalizable, where indirect methods, such as the exclusion, assume that explicit knowledge is controllable. The goal of this study was thus to directly compare verbal reporting with exclusion in two different conditions: during consistent reporting and during intermittent reporting. Our results show that our two conditions lead to a dissociation between the measures. In the consistent reporting group, all measures showed similar results. However, in the intermittent reporting group, verbal reporting showed more explicit re‐aiming and less implicit adaptation than exclusion. Curiously, when exclusion was measured again, after the end of learning, the differences were no longer apparent. We suspect this may reflect selective decay in implicit adaptation, as has been reported previously. All told, our results clearly indicate that methods of measurement can affect the amount of explicit re‐aiming and implicit adaptation that is measured. Since it has been previously shown that both explicit re‐aiming and implicit adaptation have multiple components, discrepancies between these different methods may arise because different measures reflect different components.

External error attribution dampens efferent-based predictions but not proprioceptive changes in hand localization

“…Here, participants make open-loop reaches with (implicit and explicit) or without (implicit) the strategy they learned. This process dissociation procedure (PDP 16 ) is consistent with similar tasks 53 , 55 , has been used in previous studies 17 , 18 , 43 , 56 , and doesn’t seem to evoke additional explicit learning unlike other methods 56 – 58 . While explicit learning does not necessarily correspond to external error attribution, it is likely that external error attribution is accompanied by more explicit adaptation.…”

Implicit motor learning within three trials

“…In the first approach, subtracting a measure of explicit adaptation from training reach deviations relies on a largely untested assumption that implicit and explicit adaptation linearly add to produce behavior 13,30 . Aside from the effect the aiming task may have on adaptation 38,39 , this is not a biologically plausible mechanism, and it should not be surprising that an actual measure of implicit adaptation, as we use here, shows a different time course. Our results set the nature of the mechanism by which implicit and explicit adaptation are combined as a topic for future study.…”

The explicit/implicit distinction in studies of visuomotor learning: Conceptual and methodological pitfalls

“…The important findings reported by Maresch and colleagues (Maresch et al., 2020) illustrate that there is no gold standard for decomposing adaptation into implicit and explicit components. It is to be hoped that their results will lead to more caution when interpreting and comparing the results of future studies that use different methodologies to identify implicit and explicit components of adaptation.…”

“…This unsatisfactory state of affairs underscores the need for a single study that carefully and directly compares these two measurement approaches. Here, Maresch and colleagues (Maresch et al., 2020) sought to do exactly this. In a series of experiments, they used both verbal report and exclusion methods to assess implicit and explicit adaptation both during and immediately following VMR training.…”

“…In addition, variation in measurement methodology may inadvertently favor one component of the measured quantity over another, leading to different results even though the measured quantity has not changed-for example, both gross domestic product and gross national product assess the economic activity of a country, but focus on different components. A recent paper by Maresch, Werner, and Donchin in this issue of the European Journal of Neuroscience (Maresch et al, 2020) brings these issues to bear on one of the most widely studied motor learning paradigms -visuomotor adaptation (Krakauer et al, 2000;Martin et al, 1996).…”