Prism adaptation magnitude has differential influences on perceptual versus manual responses.

Previous research has indicated that rightward prism adaptation can reduce symptoms of spatial neglect following right brain damage. In addition, leftward prism adaptation can create "neglect-like" patterns of performance in healthy adults on tasks that measure attention and spatial biases. Although a great deal of research has focused on which behaviors are influenced by prism adaptation, very few studies have focused directly on how the magnitude of visual shift induced by prisms might be related to the observed aftereffects, or the effects of prisms on measures of attentional and spatial biases. In the current study, we examined these questions by having groups of healthy adult participants complete manual line bisection and landmark tasks prior to and following adaptation to either 8.5° (15 diopter; n = 22) or 17° (30 diopter; n = 25) leftward shifting prisms. Our results demonstrated a significantly larger rightward shift in straight-ahead pointing (a measure of prism aftereffect) following adaptation to 17°, compared to 8.5° leftward shifting prisms. In addition, only 17° leftward shifting prisms resulted in a significant rightward shift in line bisection following adaptation. However, there was a significant change in performance on the landmark task pre- versus post-adaptation in both the 8.5° and 17° leftward shifting prism groups. Interestingly, correlation analyses indicated that changes in straight-ahead pointing pre- versus post-adaptation were positively correlated with changes in performance on the manual line bisection task, but not the landmark task. These data suggest that larger magnitudes of prism adaptation seem to have a greater influence on tasks that require a response with the adapted hand (i.e., line bisection), compared to tasks that only require a perceptual judgment (i.e., the landmark task). In addition, these data provide further evidence that the effects of prisms on manual and perceptual responses are not related to one another.