Asymmetric generalization between the arm and leg following prism-induced visuomotor adaptation

We have previously shown an asymmetric generalization following a prism-induced visuomotor adaptation. Subjects who adapt to laterally deviating prism lenses during walking show a broad generalization to an arm pointing task, while subjects who adapt to prisms during arm pointing do not show generalization to walking. It is not known whether this broad generalization persists with other movements outside of walking or what specific features of the walking task, e.g. lower extremity involvement, allow it to be so broadly generalizable. In the current study, we tested healthy adult subjects performing one of three forms of prism adaptation and subsequently measured generalization. In Experiment 1 we tested whether a seated arm pointing prism adaptation would generalize to the leg. In Experiment 2 we tested whether a seated leg pointing prism adaptation would generalize to the arm. In Experiment 3 we tested whether standing influenced the extent of generalization from leg to arm. Results were surprising. We found a clear and consistent generalization from arm to leg, but much less so from leg to arm during either the seated or the standing task. These findings indicate that prism adaptations during arm movements are not limb-specific, as has been previously suggested. Further, the lack of generalization from leg to arm suggests that neither the adaptation of leg movements specifically, nor standing posture, nor the bilateral component of walking could be the salient feature allowing for its broad generalization across body parts.