A spatial exploratory task was given to 110 patients with unilateral brain lesions [66 right brain-damaged (RBD) patients and 44 left brain-damaged (LBD) patients] in two conditions, with and without the aid of vision. Exploratory deficits mainly involved the contralesional half-space and were most frequently associated with right brain damage. A double dissociation was found between the visual and the nonvisual conditions of the task; selective impairments in the visual and in the nonvisual condition were associated with the presence and the absence of visual field deficits, respectively. The suggestion is made that discrete "visual" and "tactile-kinesthetic" spatial representational systems are involved in exploration of extrapersonal space. A further distinction is made between input and output spatial system. The association between visual field deficits and visual neglect is explained in terms of the impairment of an input visuospatial component, which feeds an output component involved in spatial exploration. Finally, the ambiguous nature of the visual field deficits in neglect patients is discussed and the suggestion is made that an attentional modality-specific nonsensory component may be present.