Adaptation to Visuomotor Rotations Remaps Movement Vectors, Not Final Positions

Abstract

When exposed to novel visuomotor rotations, subjects readily adapt reaching movements, such that the virtual display of the hand is brought to the target. Whereas this clearly reflects remapping of the relationship between hand movements and the visual display, the nature of this remapping is not well understood. We now examine whether such adaptation results in remapping of the position of the visually displayed target and the final limb position or between the target vector and the movement vector. The latter is defined relative to a starting position, whereas the former should be independent of the starting position. Subjects first adapted to a 30°rotation during reaching movements made from a single starting location to four different target locations. After adaptation, generalization trials were introduced, during which reaching movements were made under the same visual rotation condition but started from one of two locations outside the practiced workspace. These trials were directed to either the previously practiced targets or new targets that reflected the direction and distance of the practiced trials. Generalization was greatest for movements made in similar directions, regardless of changes in spatial location. Most significantly, when reaching to the previously adapted targets, subjects did not reach to the previously learned limb positions but rather to positions that reflected a near 30°rotation of the new target vector. These results indicate that learned visuomotor rotations remap the representations of movement vectors and not final positions of the limb in the workspace.

Retention of proprioceptive recalibration following visuomotor adaptation

“…They found that generalization of reach adaptation was local, in that adaptation was only observed at locations that were close to the trained target direction. Moreover, these aftereffects diminished drastically for targets located 20° from the trained target, confirming previous studies' observations that generalization patterns in motor adaptation are local (Krakauer 2000;Wang and Sainburg 2005). Interestingly, proprioceptive recalibration generalized quite broadly in comparison, such that changes in felt hand position in the trained location were found to a similar extent for locations up to 90° CCW from the trained target direction.…”

“…Generalization patterns have also been explored by Cressman and Henriques (2010a) wherein subjects' hand movements and proprioceptive recalibration to novel targets were studied following visuomotor adaptation. They found that subjects' reaches confirmed previous studies' observations of localized and narrow generalization patterns in motor adaptation (Krakauer et al 2000;Wang and Sainburg 2005). Interestingly, proprioceptive recalibration generalized quite broadly in comparison, such that the magnitude of recalibration observed for the trained target direction was found at similar levels up to 90°…”

How robust are the deviations in haptic parallelity?

“…In the literature there is agreement that this process involves some kind of spatial remapping (e.g., Redding & Wallace, 2006). There are more examples where adaptation is explained by or described as spatial remapping (e.g., Mosier, Scheidt, Acosta, & Massa-Ivaldi, 2005;Wang & Sainburg, 2005). In a number of our experiments, subjects also seem to slowly adapt to a new situation and that may likewise involve spatial remapping.…”

A dissociation between visual and motor workspace inhibits generalization of visuomotor adaptation across the limbs

“…Studies investigating visuomotor adaptation typically alter the relationship between vision and proprioception by rotating and/or translating a visual display of either the hand or the target (e.g., Roby-Brami and Burnod 1995;Redding and Wallace 1996;Goodbody and Wolpert 1999;Wang and Sainburg 2005) or by providing a proprioceptive perturbation to the moving arm (e.g., Pipereit et al 2006;, and investigate how such manipulations affect performance measures, such as movement accuracy. Findings from these studies are somewhat discrepant, in that some observed the prevalence of visual information (Redding and Wallace 1996;MonWilliams et al 1997;Goodbody and Wolpert 1999), while others indicated a balanced, and weighted, role of vision and proprioception in determining the altered hand-target relationship (Rossetti et al 1995;van Beers et al 1999;Sarlegna and Sainburg 2006), or even a dynamic relationship between the two modalities that may be context dependent (van Beers et al 2002).…”