Pseudoneglect and the cross-over effect

Several studies have found that patients with left hemi-neglect bisect long lines too far to the right, but bisect short lines too far to the left (th e 'cross-over' effect). Some studies have reported that normal participants bisect long lines too far to the left, presumably reflecting an over-estim ation of the left side due to the role of the right hemisphere in attention . The purpose of the present series of studies was to further study the cro ss-over effect in normal participants and to determine whether it may be du e to perceptual or motor factors. Participants in the first study showed no cross-over effect on either the traditional line bisection task. or on the purely perceptual Landmark task. However, improvements in the Landmark tas k in Study 2 did lead to a significant cross-over effect. In Study 3 there was no cross-over on the traditional line bisection task even after changes were made to eliminate the 'ceiling effect' that is usually found with ver y short lines. Overall, the results suggest that normal participants do sho w a cross-over effect on a purely perceptual task, but not on the tradition al manual line bisection task that includes a motor component. Possible imp lications for models of right hemispheric involvement in attention are disc ussed. (C) 2001 Published by Elsevier Science Ltd.