Can moving in a redundant workspace accelerate motor adaptation?

Variability in behavior can be a manifestation of unwanted noise. However, variability can also reflect exploration and benefit learning. For example, it has been shown that interindividual differences in motor learning can be partly explained by differences in movement variability at baseline. Here, we examined whether permitting versus constraining movement variability via target shape alters motor learning rate in one and the same individual. Healthy young subjects made reaching movements to visual targets in two-dimensional space with their unseen hand. During an initial priming phase, the shape of targets allowed for movement variability either in direction (arc-shaped targets), or, in a separate session, in extent (radially oriented line-shaped targets), while requiring highly precise movements in the other spatial dimension, respectively. In subsequent test phases in each session, we quantified the rate of (single-trial) motor adaptation to visuomotor perturbations along these two spatial dimensions (rotation and gain). During priming, we observed higher variability in movement direction for arc-shaped targets, compared with radial line-shaped targets, and vice versa for variability in movement extent. As predicted, participants adapted more to a visuomotor rotation following priming with arc-shaped targets, compared with radial line-shaped targets, and vice versa for adaptation to a change in visuomotor gain. This effect was prominent in the part of the examined workspace where variability in initial movement trajectories was highest, suggesting high planning noise. Our results suggest that workspace redundancy can modulate motor adaptation in a spatially specific manner, however, this modulation may depend on the level of planning noise.NEW & NOTEWORTHY Interindividual differences in motor adaptation are partly explained by differences in movement variability. Movement variability is higher in a redundant workspace. Can workspace redundancy increase adaptation? In a within-subject experiment, we show that moving in a workspace that permits versus constrains movement variability in a given spatial dimension modulates adaptation rate in that dimension, at least in part of the workspace where initial movement trajectories vary most, indicating planning noise. Redundant workspaces might aid rehabilitation.

Psychophysical Evidence for Impaired Magno, Parvo, and Konio-cellular Pathways in Dyslexic Children.

PURPOSE: Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring luminance and color perception. METHODS: Visual stimuli consisted of a series of natural images, divided into layers of luminance, red-green and blue-yellow, which probed magnocellular, parvocellular, and koniocellular pathways, respectively. Thirteen children with dyslexia and 13 sex- and age- matched controls performed three psychophysical tasks. In the first task, subjects were instructed to match the contrast of luminance (magno) and red-green (parvo) images to that of the blue-yellow (konio) images. In the second task, subjects detected the isoluminant point of red-green images to probe parvocellular pathway. In the third task, temporal processing was assessed by measuring reaction time and percentage of correct responses in an identification task using four categories of images, activating all three pathways. RESULTS: The dyslexic group had significantly elevated luminance and color contrast thresholds and higher isoluminant point ratio in comparison to the control group. Furthermore, they had significantly less correct responses than the control group for the blue-yellow images. CONCLUSION: We may suggest that dyslexic subjects might suffer from both magnocellular and parvocellular deficits. Moreover, our results show partial impairment of the koniocellular pathway. Thus, dyslexia might be associated with deficits in all three visual pathways.