Misrepresentation of horizontal space in left unilateral neglect: role of hemianopia.

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.To investigate the functional and anatomic correlates of horizontal space misrepresentation.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.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.Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect.