Retinotopic modulation of space misrepresentation in unilateral neglect: evidence from quadrantanopia. (Short Report).

A patient with right sided brain damage suffered contralesional neglect, inferior quadrantanopia (with 0[degrees] sparing in the left eye and 13[degrees] sparing in the right], and a visual field restriction (to 15[degrees]) in the upper contralesional quadrant of the left eye. In binocular vision, the patient showed underestimation of the horizontal size of contralesional line segments unless cued to localise their end points. When asked to reproduce, in monocular vision, 10[degrees] and 20[degrees] distances between two attentionally cued end points lying on the frontal vertical plane, the patient showed relative contralesional overextension and ipselesional underextension along the directions falling within the blind sectors of the neglected space. No asymmetry was present along the directions falling within the seeing sectors of the same space. These findings suggest precise retinotopic modulation of space misrepresentation in unilateral neglect.

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Neglect patients fail to attend to stimuli in the space contralateral to their unilateral brain damage. (1) Visual neglect is considered to depend on the disruption of multimodal representations of space integrating visual, proprioceptive, and vestibular inputs in one hemisphere, (1) most often the right. It can occur independently of visual field defects caused by damage to retinotopic representations of space in primary visual pathways (that is, hemianopia). Conversely, hemianopia is not necessarily accompanied by neglect. It has been shown that relative underestimation of horizontal distances in the contralesional space, and corresponding overestimation of equivalent ones in the ipselesional space, can be associated with neglect. (2-4) This pattern of anisometry seems severe in patients suffering both neglect and hemianopia, mild in some neglect patients with posterior lesions and no visual field defects, and absent in the large majority of patients with neglect and no hemianopia. (5-8) Patients with pure hemianopia suffer the reverse pattern of horizontal space misrepresentation--that is, contralesional overestimation and ipselesional underestimation. (9-11) In this report, we show that apparent space anisometry along the directions of the frontal vertical plane falling within the spared retinotopic areas of the neglected space can be resolved by attentional cueing, while anisometry along the …