Invariant errors reveal limitations in motor correction rather than constraints on error sensitivity

Abstract

Implicit sensorimotor adaptation is traditionally described as a process of error reduction, whereby a fraction of the error is corrected for with each movement. Here, in our study of healthy human participants, we characterize two constraints on this learning process: the size of adaptive corrections is only related to error size when errors are smaller than 6°, and learning functions converge to a similar level of asymptotic learning over a wide range of error sizes. These findings are problematic for current models of sensorimotor adaptation, and point to a new theoretical perspective in which learning is constrained by the size of the error correction, rather than sensitivity to error.

Exploring Contextual Interference in Implicit and Explicit Motor Learning

“…During training, we observed similar rates of adaptation between error-clamp groups, which shows that implicit adaptation really is an invariant process Morehead et al, 2017;Kim et al, 2018). It is not affected by switching between targets or rotations and, therefore, contextual interference.…”

“…From previous studies, we would have predicted no difference in adaptation since it is traditionally thought of as a robust process that would not be influenced by factors such as cursor rotation or target arrangement (Morehead et al, 2017;Kim et al, 2018). All participants experienced the same number of reaches and had the same amount of practice to each target during training.…”

“…The purpose of Experiment 2 was to examine the effect of blocked or random practice schedules in a task that isolates implicit adaptation. Previous studies have used a task-irrelevant clamped feedback experiment in order to induce adaptation without the participant's knowledge (Shmuelof et al, 2012;Vaswani et al, 2015;Morehead et al, 2017;Kim et al, 2018). Experiment 2 was identical to Experiment 1, except for the fact that all of the rotations during the training and retest blocks were clamped at a fixed angle from the target ( Figure 2D).…”

“…Task-irrelevant visual feedback has been used to study implicit adaptation without any influence from explicit learning (Shmuelof et al, 2012;Vaswani et al, 2015;Morehead et al, 2017;Kim et al, 2018). For this manipulation, the cursor is fixed to an invariant path that is rotated from the target and independent of the participant's hand position.…”

Implicit visuomotor adaptation remains limited after several days of training

“…Even more challenging for a unitary implicit motor learning account: implicit adaptation appears to be highly stereotyped regardless of the particular task demands, such as the size of the visual perturbation . Implicit adaptation being a stereotyped process is supported by studies examining the adaptive response when feedback is not dependent on subjects' movements and is irrelevant to the task (Morehead, Taylor, Parvin, and Ivry, 2017;Kim, Morehead, et al 2018). Morehead and colleagues revealed stereotyped asymptotic adaptation even when the incentive to strategize was completely removed.…”