The 24-h savings of adaptation to novel movement dynamics initially reflects the recall of previous performance

Abstract

Humans rapidly adapt reaching movements in response to perturbations (e.g., manipulations of movement dynamics or visual feedback). Following a break, when reexposed to the same perturbation, subjects demonstrate savings, a faster learning rate compared with the time course of initial training. Although this has been well studied, there are open questions on the extent early savings reflects the rapid recall of previous performance. To address this question, we examined how the properties of initial training (duration and final adaptive state) influence initial single-trial adaptation to force-field perturbations when training sessions were separated by 24 h. There were two main groups that were distinct based on the presence or absence of a washout period at the end of day 1 (with washout vs. without washout). We also varied the training duration on day 1 (15, 30, 90, or 160 training trials), resulting in 8 subgroups of subjects. We show that single-trial adaptation on day 2 scaled with training duration, even for similar asymptotic levels of learning on day 1 of training. Interestingly, the temporal force profile following the first perturbation on day 2 matched that at the end of day 1 for the longest training duration group that did not complete the washout. This correspondence persisted but was significantly lower for shorter training durations and the washout subject groups. Collectively, the results suggest that the adaptation observed very early in reexposure results from the rapid recall of the previously learned motor recalibration but is highly dependent on the initial training duration and final adaptive state. NEW & NOTEWORTHY The extent initial readaptation reflects the recall of previous motor performance is largely unknown. We examined early single-trial force-field adaptation on the second day of training and distinguished initial retention from recall. We found that the single-trial adaptation following the 24-h break matched that at the end of the first day, but this recall was modified by the training duration and final level of learning on the first day of training.

A Very Fast Time Scale of Human Motor Adaptation: Within Movement Adjustments of Internal Representations during Reaching

“…6C, left), that is the online adjustments were smaller in the first trials than in the last trials. This idea is consistent with the presence of savings, characterizing a faster re-learning on exposure to a previously experienced environment (Smith et al, 2006;Gonzalez Castro et al, 2014;Shadmehr and Brashers-Krug, 1997;Caithness et al, 2004;Overduin et al, 2006;Coltman et al, 2019;Nguyen et al, 2019). This assumption was captured here by an increase in online learning rate across simulations (␥ parameter, note that ␥ was fixed within each trial).…”

“…This assumption was based in part on the observation that the learning rate can change dependent on the context (Gonzalez Castro et al, 2014), and on the hypothesis of savings characterized by the ability to re-learn faster. This hypothesis has been documented in many tasks including adaptation to FFs (Shadmehr and Brashers-Krug, 1997;Caithness et al, 2004;Overduin et al, 2006;Coltman et al, 2019;Nguyen et al, 2019). Here, we used the same concept applied to the online learning rate.…”

Can we improve slow learning in cerebellar patients?

“…We addressed this limitation in different ways. First, we used washout at the end of each session to reduce transfer (Caithness et al, 2004; Krakauer et al, 2005; Nguyen et al, 2019; but see also Kitago et al, 2013; Villalta et al, 2015). Second, order of the tasks and perturbation direction was counterbalanced between subjects and we tested for order effects (see supplementary materials).…”

Slowing the body slows down time perception

“…Both experiments utilized a robotic arm manipulandum (KINARM End-Point Lab, BKIN Technologies; Nguyen et al, 2019 ; Hosseini et al, 2017 ). Here, the participants manipulated the right arm on a planar workspace to perform the tasks and were blocked from viewing their arm directly by a horizontal screen display.…”