Object-based neglect varies with egocentric position.

Different reference frames have been identified to influence neglect behavior. In particular, neglect has been demonstrated to be related to the contralesional side of the subject's body (egocentric reference frames) as well as to the contralesional side of individual objects irrespective of their position to the patient (object-based reference frame). There has been discussion whether this distinction separates neglect into body- and object-based forms. The present experiment aimed to prove possible interactions between object-based and egocentric aspects in spatial neglect. Neglect patients' eye and head movements were recorded while they explored objects at five egocentric positions along the horizontal dimension of space. The patients showed both egocentric as well as object-based behavior. Most interestingly, data analysis revealed that object-based neglect varied with egocentric position. Although the neglect of the objects' left side was strong at contralesional egocentric positions, it ameliorated at more ipsilesional egocentric positions of the objects. The patients showed steep, ramp-shaped patterns of exploration for objects located on the far contralesional side and a broadening of these patterns as the locations of the objects shifted more to the ipsilesional side. The data fitted well with the saliency curves predicted by a model of space representation, which suggests that visual input is represented in two modes simultaneously: in veridical egocentric coordinates and in within-object coordinates.