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 two experiments. In Experiment 1 the stimuli consisted of a line flanked at each end by: (1) parallel arrows, (2) oblique arrows, (3) or oblique geometrical figures. Of the two pairs of labels, one pair converged on the line and 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 masking labels. In Experiment 2 we examined if orientation factors might have contributed to the observed bisection bias. The stimuli consisted of a line flanked 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 findings suggest that masking/perceptual factors may influence bisection performance in normal subjects.