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In an automatized experiment, with a computer on line, amplitude-temporal parameters of evoked potentials (EPs) to purposive and non-purposive stimuli (digits), were analyzed in normal and mental retarded children. At unilateral stimuli presentation to the left or right visual half-fields EPs were recorded simultaneously in projection, TPO, parietal and central areas of the left and right hemispheres. It has been shown that in normal children, differential involvement of projection and associative structures in the analysis of sensory information takes place in both hemispheres. The amplitudes of most EP components in the range of 100-400 ms to the purposive stimuli are higher than to the non-purposive ones. Considerable similarity of EPs developing in response to ipsi- and contralateral stimulations of visual fields ("direct" and "transmitted" EP) is observed. In mental retarded children significant changes are revealed in intra- and interhemisphere organization of the process of perception of purposive and non-purposive stimuli. In the right hemisphere structures there are no differential EP reactions to the two types of stimuli. Significant, in comparison with the norm, prolongation of the latencies of most EP components is noted, especially in the structures of the left hemisphere, to the purposive stimuli. In the process of perception, changes are seen of the integration of functions of both hemispheres. The totality of disturbances of systemic brain organization at perceptive activity in mental retarded children may reflect neurophysiological mechanisms of mental deficiency.

Visual EPs of the occipital, parieto-temporal-occipital, parietal and central areas of the left and right hemispheres in response to unilaterally presented stimuli (figures) were analyzed in normal and developmentally backward children. In tasks of detection and recognition of the signal, developmentally backward children manifested a lowered reactivity of associative cerebral structures, especially of the left hemisphere, during perceptive activity, and a changed, in comparison with normal, interhemispheric interaction in processing of sensory information. It is suggested that properties of brain system organization during perceptive activity reflect to a certain extent neurophysiological mechanisms of disturbance of cognitive processes in developmentally backward children.