Abstract

Traditionally, it was accepted hemispheric asymmetry of verbal function exist in the adult brain. However, it is unclear when this difference first emerges and how degree of asymmetry changes. Does cerebral specialization develop from an initial bilateral representation to a progressively more localized specialization, or does it follow an invariant model? And, do sex differences exist? These are the main issues that were addressed in this study. Using visual half-filed presentation method, Stroop-type word naming task was given to subjects, from age 7 through 19. Vocal reaction times of subjects(7, 10, 13, and 19-year-olds) were measured to unilaterally presented words(blue, orange, pink, and violet). The results are follows: 1)Effects of visual field presentation(right visual field advantage) for all age groups were revealed. 2)Differences in vocal reaction time between the two visual fields decreased as age increases. 3)The analysis of cerebral dominance index showed significant differences between the 7 and the 13/19-year-olds. These results were interpreted to suggest that although left-hemispheric function for word naming lateralized prior to age 7, the degree of asymmetry between the two hemispheres is decreasing with age.