Visuomotor Adaptation: How Forgetting Keeps Us Conservative

Abstract

Even when provided with feedback after every movement, adaptation levels off before biases are completely removed. Incomplete adaptation has recently been attributed to forgetting: the adaptation is already partially forgotten by the time the next movement is made. Here we test whether this idea is correct. If so, the final level of adaptation is determined by a balance between learning and forgetting. Because we learn from perceived errors, scaling these errors by a magnification factor has the same effect as subjects increasing the amount by which they learn from each error. In contrast, there is no reason to expect scaling the errors to affect forgetting. The magnification factor should therefore influence the balance between learning and forgetting, and thereby the final level of adaptation. We found that adaptation was indeed more complete for larger magnification factors. This supports the idea that incomplete adaptation is caused by part of what has been learnt quickly being forgotten.

The Decay of Motor Memories Is Independent of Context Change Detection

“…Since the motor system seems to be attempting to eliminate these asymptotic errors, stable but incomplete asymptotic adaptation can only be achieved as an equilibrium between the new learning on each trial (usually 5–20% of the remaining error [ 2 , 19 , 29 ]) and the same amount of decay on each trial. This idea is further supported by a recent study from van der Kooij et al [ 30 ], who manipulated the balance between new learning and decay by magnifying or shrinking endpoint feedback during learning, which should affect the learning on each trial but not the decay. They demonstrated that when the error signal was magnified, thereby increasing the drive for error-dependent learning, asymptotic adaptation increased compared to veridical error display because the stronger learning required less true error to balance the decay.…”

A Bayesian Account of Vocal Adaptation to Pitch-Shifted Auditory Feedback

“…Computationally, our model can be seen as a generalization of forgetting models of incomplete adaptation [ 24 ]: Namely, by replacing the term in Eq (4) by a constant term α , we find that the level of adaptation is set by two terms among which the target pitch μ * has the role of driving a forgetting term. Our nonlinear model is more general than simple forgetting-retention models in the sense that it correctly explains zero adaptation for highly magnified errors ( Fig 2a ) and that adaptation time constants are not fixed but depend on posterior evidence.…”

Formation of a long-term memory for visuomotor adaptation following only a few trials of practice

“…Why would one remember an action or aiming direction that was ultimately unsuccessful (i.e., led to a target miss), as is often the case given the bias toward baseline often exhibited at asymptote (Kitago et al 2013;van der Kooij et al 2015;Vaswani et al 2015)? It is plausible that a memory for action could be formed because of strong positive reward prediction errors experienced by subjects during the initial course of adaptation.…”