Ameliorating neglect with prism adaptation: visuo-manual and visuo-verbal measures

Previous studies have shown that adaptation to rightward displacing prisms improves performance of neglect patients on visuo-manual (VM) tasks such as line cancellation, figure copying, and line bisection [Nature 395 (1998) 166]. The present study further evaluated the effect of prism adaptation (PA) on neglect symptoms by investigating: (a) the range of beneficial effects on common visuo-spatial deficits as well as less frequent phenomena like neglect dyslexia; (b) the duration of improvement following a single exposure to the right optical deviation; (c) the extent to which visuo-spatial performance can be comparatively ameliorated in VM tasks and visuo-verbal (VV) tasks (i.e. involving or not the adapted arm, respectively) and (d) the presence and duration of the manual visuo-motor bias induced by the prismatic adaptation (i.e. the after-effect). We investigated these issues in a group of neglect patients with right hemispheric damage who were also affected by neglect dyslexia. Following a single, brief prismatic adaptation the results showed that (a) several visuo-spatial abilities, including accuracy in reading single words and non-words, considerably improved, (b) the amelioration was long-lasting, continuing for at least 24h, (c) the presence, amount, and duration of neglect amelioration was not limited to VM tasks, but extended to VV tasks and (d) the presence and duration of the after-effect induced by prismatic adaptation remarkably paralleled the presence and duration of the improvement of neglect symptoms. These findings clearly demonstrate that beneficial effects induced by a single PA are very long-lasting and spread over a wide range of visuo-spatial deficits, independent of the type of response required. In addition, our results strongly suggest that the process of adaptation, as revealed by the presence of a visuo-motor after-effect, might be essential for establishing amelioration. In light of its characteristics, the prismatic adaptation technique should be a priority tool for the rehabilitation of the multifaceted hemispatial neglect syndrome.