Evidence for an independent stimulus-centered spatial reference frame from a case of visual hemineglect

Previous experiments with patients suffering from visual hemineglect have provided evidence relevant to the organization of the human spatial representation system. We examined the hypothesis that one reference frame used to represent the location of objects in the environment is based on the spatial extent of the stimulation that needs to be processed at a specific point in time; in current terminology, a stimulus-centered reference frame. The paradigm used was one of filtering, and variation of the location of the target within a horizontal array of items (stimulus-relative location) was independent of the target location relative to the subject and to stable reference points in the environment. Results showed that stimulus-relative target location provided an independent contribution to the magnitude of the neglect symptoms. This is taken as an indication that a stimulus-centered spatial reference frame contributes to the representation of the location of visual objects in human vision and that this representation may serve to direct visual attention.