Visual and tactile neglect

Abstract: Neglect patients typically fail to report, respond, or orient to information presented in locations further away from the side of the brain lesion. Neglect is most often reported after acute stroke, and is more severe and more frequent after right hemisphere damage. This thesis concerns different aspects of the "neglect syndrome" in stroke patients. It was divided into three parts. Study I examined a large sample of patients which performed a line cancellation test where the direction of arm movement and the direction of visual scanning were decoupled. The results support previous findings of a differentiation between perceptual and motor aspects of neglect, and provide further evidence that these components correlate with parietal and frontal brain lesions, respectively. In studies II-V, patients performed bisection tasks under different experimental conditions. It was found that performance improved in darkness as compared with performance in normal room illumination. The effect of darkness is probably mediated by the absence of background stimuli which direct attention rightward, or capture attention on the right side. Bisection performance also improved when it was preceded by tactile exploration of the object to be bisected. This improvement was shown across conditions in which patients bisected rods with or without the aid of vision, while patients performed poorly when exploration was excluded in the visual condition. In rod bisection performance, exploration is thus of greater importance than if vision is excluded. Patients bisected three-dimensional objects more accurately than two-dimensional objects, and two-dimensional objects more accurately than lines. It is likely that the two- and three dimensional conditions enable patients to apply a more global mode in their perceptual processing, thereby increasing the subjective display size and making bisection more accurate. No effect of different figure-ground contrast conditions was found. Finally, performance was compared when patients bisected lines with their right hand, and with a red laser point from a lamp mounted centrally on the forehead. No difference was found between these conditions. This argues against the right hand operating as a spatial cue to the right. This also argues against activation of the right hemisphere, induced by the lamp use, improving performance. It is pointed out that this may be due to the widespread right-sided lesions of patients, as intact brain areas are required for hemisphere activation to take place. Study VI found an association between chronic neglect and impaired sustained attention, while patients' awareness of their disability did not associate with chronic neglect. Key words: Visual neglect, tactile neglect, premotor neglect, perceptual neglect, bisection tasks, darkness, tactile exploration, right hand use, right hemisphere activation, three-dimensionality, figure-ground contrast, chronic neglect, sustained attention, awareness of disability. Haukur Hjaltason, Department of Neurology, Karolinska Hospital, 171 76 Stockholm, Sweden. ISBN 91-628-2443-0