What's in a line? Verbal, facial, and emotional influences on the line bisection task.

In Bryden and MacRae's [(1988). Dichotic laterality effects obtained with emotional words. Neuropsychiatry, Neuropsychology, and Behavioral Neurology, 1(3), 171-176] dichotic listening task, attending to verbal (left hemisphere) or emotional (right hemisphere) auditory stimuli can result in opposite patterns of behaviour. We examined whether performance on the line bisection task might also be influenced in opposite ways by left- and right-lateralized functions. The line bisection task is a simple and effective measure of visuospatial bias. Pseudoneglect, a leftward bias, is typically found on this task, and appears to result from right hemisphere dominance for spatial processing. We investigated how emotion, verbal, and facial processing impacted line bisection performance, while also examining the influence of hand-use. Line type (face, word, and solid), valence (positive, negative, and neutral), and hand-use (left, right, and both) were manipulated. Results indicated that face and word lines decreased and increased the extent of pseudoneglect, respectively, and that valence accentuated these results. These results were in the opposite direction from our predictions. Hand-use had little influence. We discuss the impact that visual scanning, and local and global processing, may have had on line bisection performance. Until future research clarifies how lateralized functions affect line bisections, we suggest caution in adapting the line bisection task as a general measure of relative hemispheric activation.