Prism adaptation in virtual and natural contexts: Evidence for a flexible adaptive process

Abstract

Prism exposure when aiming at a visual target in a virtual condition (e.g., when the hand is represented by a video representation) produces no or only small adaptations (after-effects), whereas prism exposure in a natural condition produces large after-effects. Some researchers suggested that this difference may arise from distinct adaptive processes, but other studies suggested a unique process. The present study reconciled these conflicting interpretations. Forty participants were divided into two groups: One group used visual feedback of their hand (natural context), and the other group used computer-generated representational feedback (virtual context). Visual feedback during adaptation was concurrent or terminal. All participants underwent laterally displacing prism perturbation. The results showed that the after-effects were twice as large in the “natural context” than in the “virtual context”. No significant differences were observed between the concurrent and terminal feedback conditions. The after-effects generalized to untested targets and workspace. These results suggest that prism adaptation in virtual and natural contexts involves the same process. The smaller after-effects in the virtual context suggest that the depth of adaptation is a function of the degree of convergence between the proprioceptive and visual information that arises from the hand.

Keywords:

• Prism adaptation
• Object unity assumption
• Realignment and recalibration
• Virtual and natural contexts
• After-effects

This work was supported by the Natural Sciences and Engineering Research Council of Canada, through a Discovery Grant (L.P.).

Notes

¹We calculated a supplementary analysis to determine whether the after-effects remained significant at the end of the posttest. Specifically, we computed an ANOVA that contrasted 2 (contexts) × 2 (visual feedback conditions) × 2 (tests: recalibration vs. realignment) × 3 (targets) × 2 (trials: average of pretest vs. 10^th trial of posttest) using repeated measures on the last three factors. The ANOVA revealed a significant Context × Trials interaction, F(1, 36) = 10.50, p = .003, which indicated that the position of the effector at movement endpoint at the end of the posttests was located significantly more to the left than during the pretest: −6.3° ± 3.3° in the natural context to −4.7° ± 3.2° in the virtual context. In light of these results, it was assumed that there was no significant decrease in after-effects even after 60 postadaptation trials.