Adaptation to virtual prisms and its relevance for neglect rehabilitation: a single-blind dose-response study with healthy participants.

Prism adaptation (PA) has been applied with mixed success as a rehabilitation method of spatial neglect. Results from many single-case and multiple case studies as well as randomised controlled trials do not produce a clear picture of the efficacy of PA. We here tested a new method of PA, by inducing adaptation effects in the virtual reality. Healthy participants were attributed to one of four groups: no deviation, 10-, 20-, or 30-degrees rightward deviation. In contrast to classical wedge prisms, we induced the visual shift progressively. Participants performed two variants of the bisection and the landmark task to measure cognitive transfer of adaptation effects. Pointing error was directly related to the degree of optical deviation, and was greatest immediately following adaptation. Transfer was only observed in the bisection tasks, and only in the 30-degrees group. Due to the gradual induction of the spatial deviation the majority of participants were unaware of the adaptation effects. These findings show that large rightward deviation may affect sensorimotor performance in healthy participants similarly to neglect patients. Moreover, the finding that only participants adapted to 30-degrees showed biased bisection performance suggests that a critical threshold must be reached in order to induce significant visuomotor transfer.