Line bisection performances of 650 normal children.

When bisecting lines, an important number of brain damaged patients tend to place their bisection marks in the hemispace ipsilateral to their lesion. Biases have also been reported in normal adults. In vertical bisection both patients and normal subjects present with upward shifts, although a downward displacement may occur eventually. Surprisingly, little is known on line bisection (LB) in normal or brain damaged children. A total of 650 subjects, aged 7-12 years, performed a horizontal and vertical LB task with their preferred hand. Asymmetry indices (AIs) were used to measure directional bias. Unsigned AIs served to evaluate accuracy and mastery of the LB skill. In vertical bisection a general and significant upward bias was found, whereas in horizontal bisection subject (gender, handedness, utilized hand, age) and stimulus variables (orientation, length, position) yielded significantly different AIs. Although with increasing age significantly increasing accuracy was observed, none of the participating children mastered LB to mathematical precision. Differences in IQ-level and attention test score did not yield significantly different AIs. Impact from reading proficiency could not be demonstrated. It is suggested that stimulus length effect results are compatible with the Halligan and Marshall [Halligan, P., and Marshall, J. Toward a principled explanation of unilateral neglect. Cognitive Neuropsychology, 1994, 11, 167-206] model of hemispatial neglect. Moreover, data may support the hypothesis of greater hemispheric specialization of visuo-spatial skills in boys than in girls.