Misrepresentation of horizontal space in left unilateral neglect: Role of hemianopia

Background: Right-brain-damaged patients with left unilateral neglect are reported to misperceive the horizontal extension of contralesional stimuli as being shorter than that of ipsilesional stimuli. Objective: To investigate the functional and anatomic correlates of horizontal space misrepresentation. Methods: Eight right-brain-damaged patients with contralesional neglect and complete hemianopia (N+H+), nine right-brain- damaged patients with contralesional neglect and no visual field defect (N+H- ), and five unilateral brain-damaged patients with contralesional complete hemianopia and no neglect (N-H+) reproduced a horizontal distance (10 cm) in the contralesional and ipsilesional hemispace. Results: N+H+ patients overextended the distance contralesionally and underextended the same distance ipsilesionally. N+H- and N-H+ patients reproduced equivalent distances contralesionally and ipsilesionally. Compared with N+H- patients, N+H+ patients had a greater ipsilesional shift when bisecting horizontal lines; however, these two groups of patients had comparable neglect severity on multiple-item cancellation tasks. In the N+H+ group the area of maximal overlapping of the lesion was in the posterior cerebral lobes. Conclusion: Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect.