Unilateral Visual Cueing and Asymmetric Line Geometry Share a Common Attentional Origin in the Modulation of Pseudoneglect

Numerous factors influence the leftward bias (pseudoneglect) in perceived line midpoint of normal subjects in line bisection tasks. Cues are a potent factor; left and right cues promote shifts in perceived midpoint to the left and right, respectively. Trapezoidal lines have recently been shown to influence perceived line midpoint, displacing it toward the larger side. The present experiments test the hypothesis that the effect of line geometry, like that of unilateral cues, results from an exogenous recruitment of spatial attention. Normal right-handed subjects (N = 60) participated in two experiments employing a tachistoscopic forced-choice line bisection task. Experiment 1 crossed the effect of cue position and cue contrast, and confirmed that a significant interaction could be obtained. Experiment 2 crossed the effect of line geometry and cue position, revealing that line geometry and cue location both significantly influence perceived line midpoint, and produce a significant interaction. According to Additive Factors Logic the finding that spatial cueing interacts with line geometry suggests that both types of stimuli modulate spatial attention at a common site of processing, supporting the conclusion that the effect of line geometry itself derives from asymmetric cueing. An explanation for the interaction is offered that is based on the existence of a hypothesized compressive nonlinearity that maps attentional bias to perceptual error.