Horizontal space misrepresentation in unilateral brain damage - II. Eye-head centered modulation of misrepresentation in hemianopia without neglect

We used a visual distance reproduction task (endpoint task) to evaluate horizontal space representation in two left brain damaged (LBD) and three right brain damaged (RBD) patients with contralateral homonymous hemianopia and no neglect. All patients were examined in the chronic phase of the stroke and were aware of their visual field defect. Along with contralesional deviation in the line bisection task, all patients estimated size (Landmark task) and distances in the contralesional space as being longer than equivalent size and distances located in the ipsilesional space. Misreproduction of distances was abolished or reduced when the task was performed in the ipsilesional head-centred space with the head turned contralesionally. This finding points out that misrepresentation of horizontal space linked to hemianopia can be modulated by combined proprioceptive input from eye and neck muscles. The pattern of misrepresentation found in chronic hemianopic patients is opposite to the one described in chronic neglect patients with concomitant hemianopia. These different patterns of space misrepresentation are the likely consequence of the presence, in hemianopics, and the absence, in neglect patients with hemianopia, of compensatory strategies based on the non-retinotopic and multimodal coding of spatial positions falling in the retinotopically organised blind field.