Low vision impairs implicit sensorimotor adaptation in response to small errors, but not large errors

Successful goal-directed actions require constant fine-tuning in response to errors introduced by changes in the body and environment. This implicit adaptive process has been assumed to operate in a statistically optimal fashion, reducing its sensitivity to errors when sensory uncertainty is high. However, recent work has shown that visual uncertainty attenuates implicit adaptation for small errors, but not large errors, a result that is at odds with an optimal integration hypothesis. This error size interaction has motivated a new hypothesis that sensory uncertainty impacts the distribution of the perceived error locations but not the system's sensitivity to errors. To examine these competing hypotheses, previous studies have experimentally manipulated uncertainty. But it is unknown which hypothesis best describes motor adaptation to sensory uncertainty experienced during daily life. To address this question, we recruited individuals with low vision due to diverse clinical conditions impacting visual uncertainty and matched controls. The groups were tested on visuomotor tasks designed to isolate implicit adaptation and maintain tight control over the error size. In two experiments, low vision was associated with attenuated implicit adaptation only for small errors, but not for large errors. Taken together with prior work in which visual uncertainty was experimentally manipulated, these results support the notion that increasing sensory uncertainty increases the likelihood that errors are mis-localized but does not affect error sensitivity, offering a novel account for the motor learning deficits seen in low vision.

Selective activation of central thalamic fiber pathway facilitates behavioral performance in healthy non-human primates

Central thalamic deep brain stimulation (CT-DBS) is an investigational therapy to treat enduring cognitive dysfunctions in structurally brain injured (SBI) patients. However, the mechanisms of CT-DBS that promote restoration of cognitive functions are unknown, and the heterogeneous etiology and recovery profiles of SBI patients contribute to variable outcomes when using conventional DBS strategies,which may result in off-target effects due to activation of multiple pathways. To disambiguate the effects of stimulation of two adjacent thalamic pathways, we modeled and experimentally compared conventional and novel ‘field-shaping’ methods of CT-DBS within the central thalamus of healthy non-human primates (NHP) as they performed visuomotor tasks. We show that selective activation of the medial dorsal thalamic tegmental tract (DTTm), but not of the adjacent centromedian-parafascicularis (CM-Pf) pathway, results in robust behavioral facilitation. Our predictive modeling approach in healthy NHPs directly informs ongoing and future clinical investigations of conventional and novel methods of CT-DBS for treating cognitive dysfunctions in SBI patients, for whom no therapy currently exists.

Cross-transfer of motor control in visuomotor tasks. Systematic review

Introduction: The term “cross-education” describes the perfomance improvement, both in motor control and strength, of a limb after training the opposite. Despite its current interest, there is no consensus on many concepts of the transfer of a visuomotor skill. The aim of the present research was to review the current literature on the phenomenon of cross-education in visuomotor skills in order to determine the magnitude of transference and its relationships with the context of the intervention. Results: A literature search was conducted during December 2019 in the databases Pubmed, CINAHL, MEDLINE, Web of Science, SPORTdiscus and Scopus. The descriptors “Motor ability” and “Motor skill” were used, in addition to the keywords “Motor control”, “skill”, “Task”, “cross over effect”, “cross exercise”, “contralateral learning”, “inter limb transfer “,” cross transfer “,” cross education “. After applying the inclusion and exclusion criteria, a total of 19 articles were obtained for analysis. Of these articles, 12 are RCTs, 4 crossover clinical trial, 2 are non-randomized trials and only 1 lacks a control group. Most of the articles consist of a short-term intervention. Only 5 studies are of a duration of between 4 and 6 weeks. Conclusion: the cross-education phenomenon occurs in visuomotor skills. However, the magnitude of transference and its relation to the amount of learning of the trained member seems to be very variable depending on the context of the intervention. Likewise, the scarce consensus and the methodological differences in the studies make it difficult to draw firm conclusions about the effects of the context on the transference.

Urgent Decision Making: Resolving Visuomotor Interactions at High Temporal Resolution

Measuring when exactly perceptual decisions are made is crucial for defining how the activation of specific neurons contributes to behavior. However, in traditional, nonurgent visuomotor tasks, the uncertainty of this temporal measurement is very large. This is a problem not only for delimiting the capacity of perception, but also for correctly interpreting the functional roles ascribed to choice-related neuronal responses. In this article, we review psychophysical, neurophysiological, and modeling work based on urgent visuomotor tasks in which this temporal uncertainty can be effectively overcome. The cornerstone of this work is a novel behavioral metric that describes the evolution of the subject's perceptual judgment moment by moment, allowing us to resolve numerous perceptual events that unfold within a few tens of milliseconds. In this framework, the neural distinction between perceptual evaluation and motor selection processes becomes particularly clear, as the conclusion of one is not contingent on that of the other. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Predictive eye movements are adjusted in a Bayes-optimal fashion in response to unexpectedly changing environmental probabilities

This paper examines the application of active inference to naturalistic visuomotor control. Active inference proposes that actions serve to minimise future prediction errors and are dynamically adjusted according to uncertainty about sensory information, predictions, or the environment. We investigated whether predictive gaze behaviours are indeed adjusted in this Bayes-optimal fashion during a virtual racquetball task. In this task, participants intercepted bouncing balls with varying levels of elasticity, under conditions of high and low environmental volatility. Participants’ gaze patterns differed between stable and volatile conditions in a manner consistent with generative models of Bayes-optimal behaviour. Partially observable Markov models also revealed an increased rate of associative learning in response to unpredictable shifts in environmental probabilities, although there was no overall effect of volatility on this parameter. Findings extend active inference frameworks into complex and unconstrained visuomotor tasks and present important implications for a neurocomputational understanding of the visual guidance of action.

The effect of visual uncertainty on implicit motor adaptation

Sensorimotor adaptation is influenced by both the size and variance of error information. In the present study, we varied visual uncertainty and error size in a factorial manner and evaluated their joint effect on adaptation, using a feedback method that avoids inherent limitations with standard visuomotor tasks. Uncertainty attenuated adaptation but only when the error was small. This striking interaction highlights a novel constraint for models of sensorimotor adaptation.

Visual Strategies Underpinning the Spatiotemporal Demands During Visuomotor Tasks in Predicting Ball Direction

We investigated gaze behavior of expert goalkeepers during the prediction of penalty kicks in different spatiotemporal constraints: penalties taken from 11 and 6 m. From 11 m, goalkeepers were more successful in predicting ball direction, with longer movement time initiation and a visual strategy with more fixations and greater saccade rates than penalties from 6 m, where they exhibited fewer fixations with higher microsaccade rates. As long as the opponent’s distance is large and time pressure low, gaze can be frequently shifted between the kicker’s body and the ball, due to the low cost of saccades. Conversely, when the objects are close, there is increased reliance on foveal and parafoveal information. In conclusion, when the spatiotemporal constraint is less severe, goalkeepers adopt a visual strategy with more fixations and small saccades. When the spatiotemporal constraint is more severe, they rely on peripheral vision to monitor kickers’ movements through the use of microsaccades.