Ocular space exploration in the dark and its relation to subjective and objective body orientation in neglect patients with parietal lesions.

Eye movements of neglect patients with right parietal lesions were recorded during ocular searching for a (non-existent) target in complete darkness. With respect to the objective orientation of the sagittal midplane, ocular exploration was biased toward the ipsilesional side. However, in relation to the patients' subjective localization of the sagittal midplane in space, exploratory eye movements were symmetrically distributed to the subjective "left" and "right" as observed in non-brain-damaged controls. The present results further support the hypothesis that the essential aspect leading to spatial neglect is a disturbance of those cortical structures that are crucial for computing egocentric, body-centred coordinates that allow use to determine our body position in space and that are necessary for visuomotor coordination and exploration of space. In neglect patients the central coordinate transformation seems to work with a systematic error resulting in a deviation of the spatial reference frame to the ipsilesional side. Consequences of this deviation are a displacement of subjective localization of body orientation and--to the same degree--of the spatial area in which motor behavior (here exploratory eye movements) is executed.