An experiment was staged to study determinants of vocational aptitudes in 8-graders, as defended on the level of activation of brain hemispheres and latent periods of the visually evoked potenatials. The data has proven that the dynamics of psychic processes as well as high activeness of the left hemisphere predetermines the choice of the type of activity related to symbolic systems. Activeness of the right hemisphere provides for the individual' s preferences for activity with natural reality objects and interpersonal communication.