Patterns of line bisection in patients suffering from unilateral spatial neglect.

Thirteen patients suffering from Unilateral Spatial Neglect and 6 Right Brain Damaged Control Patients were tested on a line bisection task in order to verify peculiar patterns of error. Stimuli were arranged in order to avoid confounding the effects of line length and line position in the space. Two parameters of rightward displacement of setting point were used: 1) the distance of patient's setting point from actual line midpoint, and 2) the deduced left end-point of the line that patient took into account. Results showed that: 1) the rightward extension of lines did not lead to a consistent rightward displacement of setting point; 2) error significantly increased as lines extended more than 10 cm in the left hemispace; 3) the USN severity amplified the degradation of leftmost portion of stimuli until the deduced left endpoint of all space/length conditions was aligned on the left of patient's sagittal midplane. The interpretation of these results points to the particular arrangement of neurons directing attention on specific portions of the visual field.