Normal development of bilateral field advantage and evoked potential interhemispheric transmission time

Implications of the developmental progression of myelination of the corpus callosum were studied using evoked potential interhemispheric transmission time (EP-IHTT) and the bilateral field advantage (BFA) in letter matching. Forty-two normal children aged 7 to 17 years were asked to respond regarding whether 2 letters matched when presented either unilaterally (both in the same visual field) or bilaterally (1 letter in each field). Evoked potentials were recorded with bilateral midparietal electrodes during unilateral presentations of the letter-matching task. Age-related changes were found for both EP-MTT and BFA. BFA in reaction time in the visual letter-matching task increased significantly with age. Decreasing EP-IHTT with age was also evident (although only in a statistical trend). These findings lend support to the hypothesis that increased callosal myelination during late childhood has functional significance. Callosal maturation appears to result in faster interhemispheric transfer and increasing ability to integrate information across the midline.