A STUDY OF PLANE BISECTION IN 4 CASES OF VISUAL NEGLECT

We report four case studies of bisection performance in patients with severe left neglect consequent upon right hemisphere lesion. The stimuli to be bisected range from a horizontal line through horizontally oriented rectangles to a square; the stimuli are displayed on a VDU and bisections made by moving a 'mouse' that controls a cursor line on the screen. For one of the patients, both the starting position of the cursor (left or right) and the shape of the stimulus have a major effect upon bisection accuracy. One patient shows an effect of starting position but not stimulus geometry; two patients show an effect of stimulus geometry but not starting position. For 3 out of 4 patients, the estimated midpoint of a line is thus not equivalent to that of a plane with the same horizontal extent. A putative 'attentional' interpretation of the results is provided.