Stimulus modulation of pseudoneglect: influence of line geometry.

A variety of stimulus factors have recently been shown to influence the performance of normal subjects on line bisection tasks (i.e., pseudoneglect), independent of motoric factors such as scanning or hand use [McCourt & Jewell (1999) Neuropsychologia 35, 843-55]. An experiment is described which further examined the modulating influence of line geometry in determining the magnitude of pseudoneglect. Subjects bisected horizontally oriented trapezoidal lines presented in central vision whose narrow end pointed either left or right. A highly significant influence of line geometry was found which modulated a tonic leftward error (i.e., pseudoneglect). The results are interpreted in the context of a "center-of-mass" effect [Shuren, Jacobs & Heilman (1997) Brain and Cognition, 34, 293-300]. Further studies designed to tease apart the potentially independent effects of perceptual and attentional asymmetry on bisection performance are suggested.