Attention processes were studied using a model based on visual searches for a specified element in grids of size 3 x 3 and 7 x 7 cm displayed on a monitor screen. Five age groups took part in the experimental studies: children of five and seven years, a group of 15-year-old adolescents, a group aged 20-35 years, and a group aged over 60 years; a total of 62 subjects took part. Statistical analysis showed that the latter three groups were not different from each other and were used as an adult control group for comparison with results from children. Five types of search were used: one difficult, in which the target was similar to the distractors, and four easy (for adults but not for children), involving seeking a red or a white element in an empty grid and seeking a target markedly different in shape or color from the distractors. The following measures were analyzed: search time, errors (false alarms and misses), and corrected search times allowing for errors. Children performed significantly worse on all measures: they found all types of search difficult, even the search for a single element. The larger number of false alarms (reactions to nonmeaningful signals) was evidence for a deficiency of inhibitory processes in children, these being controlled by the frontal lobes. The larger number of misses in children may be evidence of weakness of selective attention, which is controlled by the parietal and temporal areas of the cortex. These points may indicate that children have an immature attention system, though this would appear to mature completely by age 15 years.

Studies of 11 young subjects addressed the analysis of evoked potentials in the parietal and temporal areas to sequential presentation of visual symbols on the left and right sides; symbols were squares and circles and were observed passively and in conditions of selective attention to target stimuli presented to the subjects in random order and requiring rapid and precise motor responses. Comparison of monopolar evoked potentials in leads P3, P4, T3, T4, T5, and T6 with bipolar potentials in leads P3-T3, P3-T5, P4-T4, and P4-T6 in conditions of passive and selective attention showed that voluntary attention was accompanied by significant rearrangements in evoked activity in the parietal and temporal areas. This was evident as: 1) an increase in correlations between evoked potentials in the parietal and temporal areas; 2) stabilization of monopolar evoked potentials over time, i.e., increases in the correlations of sequential evoked potentials, in both associative visual areas; 3) stabilization of bipolar parietal-temporal evoked potentials in terms of increases in their sequential correlations. It is suggested that selective attention facilitates linked activity of the two associative areas, which is needed for performance of visual selection.

Studies in 11 young, healthy subjects addressed the characteristics of visual seeking (time taken, errors) on changes in the parameters of the target element to be sought (shape, color, and location) in an environment containing heterogeneous white distractors. Evoked potentials (EP) were recorded in six cortical leads (P3, P4, T3, T4, T5, T6) and the late endogenous components of EP were studied, i.e., the N2 and P3 components (standard terminology), as these components are known to change when the type of search changes, in the zone of so-called late selection. When the search difficulty increased (increased similarity between target and distractors), an increase in seeking time was accompanied by a delay in the P3 component and a decrease in its amplitude. Location of the target in a defined position resulted in a decrease in search time and a reduction in the latent period of the P3 component as compared with the situation in which the target position was indeterminate. Changes in the color of the target stimulus led to elimination of the inhibitory action of the distractors: EP parameters were no different from those recorded on presentation of single stimuli. A high level of correlation was found between search parameters and measures of the P3 component. Changes in EP in different types of search were essentially identical (no statistical differences) in the parietal and temporal leads. This suggests that on seeking the target in the environment, the parietal and temporal areas of the cortex function as a single system.

The state of cortical activation during visual symbol shape and position selection tasks was assessed in humans in terms of the magnitude of prestimulus negativity (contingent negative variation, CNV) and the amplitude of the N1-P3 complex in evoked potentials (EP). Evoked potentials in the frontal parietal, occipital, and temporal leads were recorded in 18 young healthy subjects in two sets of experimental conditions: in a screened chamber and in an "open field" beside the experimenter, who communicated the results to the subjects and guided them towards quicker and more precise responses to the target stimuli. The maximum magnitudes of CNV and evoked potentials during selective attention were seen in the parietal areas, and additional increases of activation indexes were observed in the "open field," where subjects' motivation was enhanced. The state of readiness (CNV) was an informative measure of cortical activation, as it determined the parameters of subsequent evoked potentials; the more marked the readiness, themore marked and stable were EP. Comparison of the situations of passive observation and selective reactions to stimuli revealed a reciprocal relationship between CNV in these conditions: the greater the magnitude of CNV in "passive" conditions, the smaller the difference between CNV in "passive" conditions and during selective attention and vice versa. We termed this "additivity of involuntary and voluntary attention." The fact that activation indexes were greatest in the parietal areas suggests that the occipital-parietal system is dominant in visual selection tasks in humans.

The state of cortical activation in the parietal and temporal areas of the right and left hemispheres was evaluated using evoked potentials (EP) during tasks consisting of selection of visual stimuli lateralized in the right and left visual fields and needing three different types of attention: to stimulus shape, to stimulus position, and simultaneously to stimulus shape and position. EP were recorded in 15 young healthy experimental subjects using six cortical leads: P3, P4, T3, T4, T5, and T6; the following endogenous EP components (in standard terminology) were analyzed: contingent negative variation (CNV), N1, P3, and the N1-P3 complex. Asymmetry in evoked potentials was assessed in terms of differences to contra-and ipsilateral stimuli in the right and left hemispheres. EP asymmetry was detected in the right hemisphere in all types of selection of lateralized stimuli. The magnitude of asymmetry in the right hemisphere depended on the level (or intensity) of attention: the degree of asymmetry increased with increases in the need for attention to analyze the stimuli. There was a significant relationship between the magnitude of asymmetry and the latent periods of the subjects' responses. The functional significance of these data demonstrating asymmetry may be that it provides better spatial differentiation of visual signals in the right hemisphere, along with dominance of the right hemisphere in attention tasks.