Bisection and perception of horizontal lines in normal children

Simple line bisection is a complex task in which both perceptual/attentional factors and motor factors are involved. Using a judgment task on prebisected lines it is possible to assess independently the role of perceptual/attentional factors. The judgment-bisection relationship was investigated in 37 preschool children aged 4-5 and 70 school children aged 10-12. At bisection, a clear shift of the right hand with age from right to left bisections was observed, more pronounced in right- than in left-handers, and probably related to learned patterns. At judgment, a slight but significant left side overestimation was observed. In right-handers, judgment was related to left-hand but not to right-hand bisection. It is concluded that motor (manual) factors strongly influence visuo-motor bisection in normal children, and it is suggested that the judgment-bisection relationship has to be systematically investigated when bisection is used as a task informing on space perception or on direction of attention.