A distortion of perceived space in patients with right-hemisphere lesions and visual hemineglect.

In twelve patients with left visuospatial hemineglect following acute right hemisphere cerebrovascular accident (CVA), and in twelve normal controls, we used a matching task to investigate judgement of the length of lines. Their task was to choose which of three lines of different length matched a separate single line. On each trial, the lines were all vertical or all horizontal. The set of three lines was presented either to the left or the right of the single line. When the lines were vertical, the choices made both by normal subjects and patients were nearly always correct. However, when the lines were horizontal and the set of comparison lines was on the left, patients mostly selected a line that was longer than the sample on the right, and never chose shorter lines, suggesting that the length of horizontal lines on the left was underestimated. When the set of three lines was on the right, patients chose the correct line more often, but made errors in both directions, i.e. longer or shorter, although shorter lines were chosen more often than longer lines. The rare errors made by normal subjects were in the same directions as those observed in the patients. The results provide further evidence for a non-Euclidean distortion of perceptual space in patients with left sided visuospatial neglect, and suggest that this distortion could be a gross exaggeration of normal performance or a product of diminished spatial attention, or both.