Toward a principled explanation of unilateral neglect

Abstract

In the unilateral neglect syndrome, patients seem unable to detect or respond to stimuli in spatial locations contralateral to the damaged cerebral hemisphere. The condition has been reported in the visual, auditory, tactile, and olfactory modalities, although the most extensive investigations have concerned visuo-spatial neglect. Left neglect after right hemisphere lesion is more frequent, severe, and long-lasting than right neglect after left hemisphere lesion. Left neglect is a major negative prognostic factor after brain damage and is reliably associated with poor performance on many functional recovery measures. Many current accounts stress that neglect is an “attentional” disorder, although there are numerous (potentially competing) hypotheses that emphasise “perceptual,” “representational,” “intentional,” and “premotor” factors. In short, there is little theoretical consensus and it is possible that many distinct impairments have been conflated under the label of “unilateral neglect.” The theoretical integration proposed here attempts to derive many of the core clinical symptoms of neglect from two (conceptually) independent properties of normal hemispheric specialisation: the contralateral “orientational bias” of each cerebral hemisphere, and the association of “focal” and “global” processing biases (attentional and/or perceptual) with left and right hemisphere mechanisms, respectively.