Pieces of the true crossover effect in neglect.

A subject with left hemispatial neglect exhibited the crossover effect on bisecting lines of varying lengths. On long lines he misbisected to the right and on shorter lines he misbisected to the left. Rather than being an idiosyncrasy of this one task, the crossover effect also occurred on variations of Milner's Landmark task and Bisiach's Endpoint task. Performances across different bisection task variations were highly correlated. The crossover effect is not specific to the traditional line bisection task but is a pervasive aspect of this subject's performance. As the crossover effect is not explained by current theories of neglect, determining the bases for the crossover effect constitutes a challenge in understanding neglect.