Prism adaptation improves visual search in hemispatial neglect.

Visuomotor prism adaptation has been found to induce a lateral bias of spatial attention in chronic hemispatial neglect patients. Here, two experiments were conducted to explore the effects of 10 degrees prism adaptation on visual search tasks and standard visual inattention tests. Baselines and intervention effects were measured on separate days for all patients. The first experiment explored whether prism adaptation affects performance on a time restricted visual search task (maximum 3500ms presentation followed by visual and auditory feedback). No positive effects of prism adaptation were found on accuracy in visual search nor on traditional neglect tests. These results accord well with previous studies showing that increased cognitive load can lead to prism de-adaptation or unchanged performance following prism adaptation. Response times in visual search became faster following intervention but this was not the case for the standard neglect tests. In the second experiment, the same single-featured search task was used, but the participants had unlimited search time and received no feedback on their response. This time, the patients showed accuracy improvements in visual search and all four on regular neglect tests. Therapeutic effects lasted for at least 90-120min. Response times on all tasks became faster after prism adaptation. The results are consistent with studies showing effects of prism adaptation on neuropsychological neglect tests and other attentional tasks that are not speeded or time restricted, where feedback is not provided, or are performed following non-feedback-based tasks. The current findings show that prism adaptation improves visual search in neglect and that these beneficial effects can disappear with feedback.