Effects of hand-used on unilateral spatial neglect: a case study.

It was originally claimed that left hand use on line bisection tasks reduced the extent of left neglect by Halligan and Marshall. However, in a following study, the same research group failed to reproduce this left hand amelioration effect if the left hand was initially placed on the right side, and they claimed that spatio-motor cueing was more important in reducing unilateral neglect than the hand used. The present study concerns with the validity of these two theoretical views on modification of unilateral neglect, i.e., hemispheric activation and spatio-motor cueing. A patient with left unilateral neglect and a slight left hemiparesis participated in three experiments. Under conventional testing condition, line bisection performed with the right hand showed more severe left neglect than when performed with the left hand. These hand effects were modified by changing a starting position of the patient's hand when bisecting horizontal lines. However, under body-fixed condition, effects in hand-used as well as starting position were again significant. The results suggest that not only spatio-motor cueing but also differential hemispheric activation can exert a profound effect on unilateral neglect.