Persistent residual errors in motor adaptation tasks: reversion to baseline and exploratory escape.
When movements are perturbed in adaptation tasks, humans and other animals show incomplete compensation, tolerating small but sustained residual errors that persist despite repeated trials. State-space models explain this residual asymptotic error as interplay between learning from error and reversion to baseline, a form of forgetting. Previous work using zero-error-clamp trials has shown that reversion to baseline is not obligatory and can be overcome by manipulating feedback. We posited that novel error-clamp trials, in which feedback is constrained but has nonzero error and variance, might serve as a contextual cue for recruitment of other learning mechanisms that would then close the residual error. When error clamps were nonzero and had zero variance, human subjects changed their learning policy, using exploration in response to the residual error, despite their willingness to sustain such an error during the training block. In contrast, when the distribution of feedback in clamp trials was naturalistic, with persistent mean error but also with variance, a state-space model accounted for behavior in clamps, even in the absence of task success. Therefore, when the distribution of errors matched those during training, state-space models captured behavior during both adaptation and error-clamp trials because error-based learning dominated; when the distribution of feedback was altered, other forms of learning were triggered that did not follow the state-space model dynamics exhibited during training. The residual error during adaptation appears attributable to an error-dependent learning process that has the property of reversion toward baseline and that can suppress other forms of learning.
Laboratory for Computational Motor Control, Department of Biomedical Engineering, Departments of Neuroscience and pvaswani@jhmi.edu.
Pavan A
http://orcid.org/0000-0002-1826-6275
PA
Vaswani
Department of Brain and Cognitive Sciences, Ben-Gurion University of the Negev, Beer Sheva, 8410501, Israel, and Motor Performance Laboratory, Neurological Institute, Columbia University, New York, New York 10032.
Lior
L
Shmuelof
Neurology, and Brain, Learning, Animation, and Movement Laboratory, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Adrian M
AM
Haith
Motor Performance Laboratory, Neurological Institute, Columbia University, New York, New York 10032.
Raymond J
RJ
Delnicki
Motor Performance Laboratory, Neurological Institute, Columbia University, New York, New York 10032.
Vincent S
VS
Huang
Motor Performance Laboratory, Neurological Institute, Columbia University, New York, New York 10032.
Pietro
P
Mazzoni
Laboratory for Computational Motor Control, Department of Biomedical Engineering.
Reza
R
Shadmehr
Departments of Neuroscience and Neurology, and Brain, Learning, Animation, and Movement Laboratory, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
John W
JW
Krakauer
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001132:Arm / Q000502:physiology; D003463:Cues; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009068:Movement / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013028:Space Perception / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
adaptation; error; exploration; motor learning