Visual field influence on radial line bisection

An attentional bias toward far peripersonal space has been proposed as the mechanism underlying inaccurate bisection of lines oriented radially in the sagittal plane. The position of stimuli in the visual scene has also been proposed as an important determinant of visual attention. This study was designed to evaluate the relative contributions of spatial and visual field factors in bisection of radial lines. The usual linkage of distant space and upper visual field was dissociated by assessing line bisection above eye level. Ten normal subjects bisected twelve 20-30-cm lines 35 cm above eye level and the identical stimuli 35 cm below the eyes. The previous findings of misbisection of radial lines distant to true center was replicated when stimuli were presented below eye level. Lines above eye level were misbisected significantly closer to the subjects. The findings suggest that visual field position influences the allocation of attention in the radial axis of space.