Effects of hand and spatial conditions on visual line bisection

This study examined the effects of hand and spatial conditions on a visual line bisection task with normal right-handers and proposed a normal range of deviation for this task in middle and advanced age. Twenty-four normal dextrals in their fifties and sixties performed a visual line bisection task using either the left or right hand under three spatial conditions: at the midline and in the left and right hemispaces. Our results revealed that performance was significantly affected by the hand used but not spatial conditions: Left hand performance was significantly further leftward than right hand performance. There was no significant interaction between the hand and spatial conditions. The mean deviation of the right hand was 2.2% of the half line length to the right of the true center. The possibility of left unilateral spatial neglect should be considered if a patient bisects a line with a deviation greater than 10% of the half line length to the right.