Cerebral lateralization

Background: Contradictory interpretations of left unilateral neglect suggest that it reflects either decreased attention toward the left or increased attention toward the right. According to the right-hyperattention postulate, increasing severity of neglect should result from an increasingly stronger bias toward the right. Thus, response times to right-sided targets should become progressively faster as neglect increases in severity across patients. The left-hypoattention postulate predicts that as neglect increases, progressively less-attentional resources are deployed in both hemispaces. Thus, response times to right targets should progressively increase with increasing neglect. Methods: We analyzed the distribution of manual response times to left- and right-sided targets in 24 patients with right hemisphere lesions and varying degrees of left neglect. Results: Not only the responses to left targets but also those to right targets became progressively slower as neglect increased, consistent with the hypoattention account. However, the two regression lines were not parallel. With increasing neglect, responses to left targets increased more steeply than those to right targets did. Conclusions: A rightward attentional bias is present in patients with left neglect, together with left hypoattention. However, this rightward bias is one of defective, and not enhanced, attention.