This study attempts to raise and answer the question as to whether lateral specialization of the brain could explain some of the differences in persons at different stages of intellectual development from birth to adulthood according to Piaget's theory of individual development via sequential, qualitatively different stages. Electroencephalographic measures were used as indicators of hemispheric specialization of concrete and formal persons. The brain activity of six concrete and seven formal subjects was monitored from the central and parietal regions of the cerebral cortex while the subjects were responding to mental tasks. Hemispheric asymmetry was determined by the ratios (left/right) of the alphapowers from homologous leads. Logarithmic ratios of formal subjects were greater than concrete subjects indicating more lateralization of function for formal persons, especially on the logic task. (Autnor/KS)