Beyond unilateral neglect.

When required to set the endpoints of an imaginary horizontal line of a given length on the basis of its midpoint printed on a sheet of paper, left neglect patients most frequently misplaced endpoints leftwards. Though giving rise to the very same disproportion usually found with these patients on canonical line bisection tasks, this behaviour cannot be accommodated by current explanations of unilateral neglect. When the task was executed during leftward optokinetic stimulation (OKS), a manoeuvre known temporarily to improve neglect symptoms, the disproportion increased instead of vanishing. We therefore suggest that unilateral neglect is a manifestation of a disorder primarily implying a horizontal anisometry of space representation and that manipulations such as OKS may remove neglect without normalizing the representational medium itself.