[Clinical aspects and mechanisms of visual-spatial neglect]

Several interpretations have been advanced to explain the nature of unilateral spatial neglect. According to some authors, unilateral neglect could be due to a sensory deficit or to an oculomotor disorder hampering the patient from completely exploring the half space contralateral to the damaged hemisphere. According to other authors, the unilateral neglect syndrome could result either from a mutilation of the inner representation of the outside space or from a lack of attention for stimuli falling in the half space opposite to the hemispheric locus of lesion. We have wondered whether the relationships between unilateral neglect and hemispheric lateralization could not help to understand the nature of the neglect phenomena. A retrospective analysis of data gathered in neuropsychological literature, and results of an experimental study in which we had contrasted results obtained on an "overlapping figures" task and on a visual search task and a qualitative analysis of neglect phenomena observed in right brain-damaged patients, have led to the following conclusions: a) unilateral neglect is specifically linked to right hemisphere lesions in tasks requiring extraction of information from the central part of the visual field, whereas no difference between right-sided and left-sided lesions is observed on tasks requiring a full exploration of extra-personal space; b) tasks selectively affected in right brain-damaged patients require an automatic orienting of attention toward the more peripheral parts of the stimuli, which could be partly impaired owing to an early orientation of attention toward the right side of the pattern and a subsequent difficulty to detach attention from this early focus to orient it toward parts fo the stimulus lying in the left half space.