Unilateral spatial neglect

"Unilateral spatial neglect" or "hemispatial neglect" is a commonly used term for expressing the failure of brain damaged patients to attend to and explore stimuli presented in the space contralateral to their lesion (Heilman, Bowers, Valenstein, & Watson, 1987). Because unilateral spatial neglect is observed under conditions where movements of the eyes and head are permitted, trunk-hemispace, determined by the sagittal midplane of the body, is treated as the most important conceptual space for neglect (Heilman et al., 1987). However, the neglected space is not the unilateral half of space or hemispace. It is more accurate to state that there is a gradient in spatial locations subject to neglect: In left unilateral spatial neglect, the more a stimulus is located to the left, the more frequently it is neglected (Kinsbourne, 1987). There is no constant boundary between the neglected and non-neglected spaces for individual patients. We found that neglect patients could explore more to the left in the line cancellation task when motivated by numbering (Ishiai et al., 1990). Neglected space is also reported to be affected by demand on selective attention (Rapcsak, Verfaellie, Fleet, & Heilman, 1989) and by information implicit in stimulus configurations (Kartsounis & Warrington, 1989).