VISUAL AWARENESS AND ANISOMETRY OF SPACE REPRESENTATION IN UNILATERALNEGLECT - A PANORAMIC INVESTIGATION BY MEANS OF A LINE EXTENSION TASK

Ninety-one right brain-damaged patients with left neglect and 43 right brain-damaged patients without neglect were asked to extend horizonta l segments, either left- or rightward, starting from their right or le ft endpoints, respectively. Earlier experiments based on similar tasks had shown, in left neglect patients, a tendency to overextend segment s toward the left side. This seemingly paradoxical phenomenon was held to undermine current explanations of unilateral neglect. The results of the present extensive research demonstrate that contralesional over extension is also evident in most right brain-damaged patients without contralesional neglect. Furthermore, they show that in a minority of left neglect patients, the opposite behavior, i.e., right overextensio n can be found. The paper also reports the results of correlational an alyses comprising the parameters of line-extension, line-bisection, an d cancellation tasks, as well as the parameters relative to the Milner Landmark Task, by which a distinction is drawn between perceptual and response biases in unilateral neglect. A working hypothesis is then a dvanced about the brain dysfunction underlying neglect and an attempt is made at finding an explanation of neglect and the links between the mechanisms of space representation and consciousness through the stud y of the changes induced by unilateral brain lesions in the characteri stics of space-coding neurons. Abbreviations: C, control group; GN + 9 1, full group of neglect patients; GN+27, group of neglect patients wi th relative left overextension; GN+14, group of neglect patients with relative right overextension; GN-43, full group of non-neglect patient s; GN-9, group of non-neglect patients with relative left overextensio n; H cane, H cancellation task; LE, left extension; LE/RE, ratio of le ft-right extension; N+, neglect patients; N-, non-neglect patients; PB Land-M, perceptual bias on Landmark motor task; PB Land-V, perceptual bias on Landmark verbal task; RE Land-M, response bias on Landmark mo tor task; RE Land-V, response bias on Landmark verbal task; RE, right extension. (C) 1998 Academic Press.