Influence of perceptual factors on line bisection

In the present study we investigated whether masking/perceptual factors may influence line bisection performance in normal subjects. We carried out tw o experiments. In Experiment 1 the stimuli consisted of a line flanked at e ach end by: (1) parallel arrows, (2) oblique arrows, (3) or oblique geometr ical figures. Of the two pairs of labels, one pair converged on the line an d appeared to mask the flanked portion of the line. The results showed the presence of a bisection bias in the direction opposite to location of maski ng labels. In Experiment 2 we examined if orientation factors might have co ntributed to the observed bisection bias. The stimuli consisted of a line f lanked by only one pair of oblique geometrical figures. The results showed that bisection bias was always in the direction opposite to label location, independently of the direction pointed out by oblique figures. These findi ngs suggest that masking/perceptual factors may influence bisection perform ance in normal subjects.