Most patients with neglect demonstrate a crossover effect on
line bisection. Crossover refers to a pattern of performance
in which long lines (>10 cm) are bisected ipsilateral to
brain injury and short lines (<2 cm) are bisected contralateral
to brain injury. Crossover bisections on short lines are of
interest because they are not predicted by contemporary theories
concerning neglect. However, we propose that the effect depends
on two independent factors that normally influence bisection
performance but are merely exaggerated in neglect—a tendency
to overestimate the length of short lines and underestimate
long lines and a tendency to orient attention preferentially
in one spatial direction. We predicted that both patients with
unilateral left and right hemisphere injury would demonstrate
crossover on line bisection and that they would overestimate
short lines and underestimate long lines upon direct visual
inspection. Further, the 2 groups were predicted to demonstrate
crossover in opposite directions owing to different lesion-induced
biases in attentional orientation. Testing 5 patients with right
hemisphere injury and 7 patients with left hemisphere injury
confirmed each prediction. Additionally, errors in length
estimation were exaggerated among patients with right hemisphere
injury, most of whom had neglect. It is concluded that while
crossover is accentuated in cases of neglect, it is not a
consequence of neglect per se. As such, crossover
bisections are not at odds with contemporary neglect theory.
(JINS, 2002, 8, 107–114.)