Left of what? The role of egocentric coordinates in neglect.

OBJECTIVES Egocentric coordinate systems centred on the trunk, head, and gaze have been investigated in a patient who displays severe extrapersonal neglect and in five control subjects. METHODS The subjects were tested with a blind tactile exploration task in five different experimental conditions in which the role of the three distinct frames of reference was individually controlled. RESULTS Only the trunk centred coordinates significantly influenced the performance of the patient, therefore proving of paramount importance in determining the boundaries of the neglected field. Similar results emerged from a single word reading task, in which the patient's performance improved when the stimuli were presented to the right of his body's midline. CONCLUSION These findings point to the importance of the body centred coordinate system in determining the area of extrapersonal spatial neglect.