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During the experiments, healthy subjects (n = 35) completed Go/NoGo task with a set towards the recognition of negative face expression; the visual stimuli were set in the middle of a 16-second-long interval between target (face) and triggering stimuli. The local changes in low-frequency alpha-oscillations in response to stimuli (desynchronization after a positive Go stimulus and synchronization after an inhibitory NoGo stimulus) take place in posterior frontal and anterior temporal lobes of the left hemisphere, i.e., in cortical areas directly involved in speech processes. In subjects with flexible set towards recognition, we observed synchronization of alpha-rhythm after inhibitory NoGo stimulus; in subjects with more stable set, this did not occur. Thus, we obtained new experimental data confirming that induced synchronization of alpha-oscillations reflects the enhancement of descending inhibitory control of the prefrontal cortex.

In healthy adults (n = 35) was used the model the set study of recognition angry facial expression. The load on working memory by extending the interstimuli time up to 16 sec between the target (facial image) and starting (spot light) stimuli does not lead to a significant slowdown of switching of the set. Differences in the magnitude of the induced synchronization of the alpha rhythm in interstimulus period obtained in the subjects with the change in recognition of emotional facial expressions and the subjects "without errors". At the last group synchronization is clearly more pronounced. The implementation of successive cognitive acts is modulated by selective attention, whichis evident in the level of changes the induced synchronization/desynchronization of alpha range potential. The proposed mechanism "inhibitory control" provides the flexibility of cognitive processes by suppressing effect on cortical processes irrelevant factors during interstimulation pauses. This "protective" mechanism, we believe due to little effect of the loading on working memory.

We used the experimental model of cognitive visual set, designed by D.N. Uznadze, to study the influence of previous experience on emotional face expression recognition in pre-school (6.1 +/- 0.3 years) and elementary school (10.5 +/- 0.1 years) children. Our results suggest that the ability to form a cognitive set to an angry face expression develops in ontogenesis in strong concordance with functional maturation of prefrontal cortex that takes place at the age of approximately 10 years. At this age children display almost the same level of set plasticity and a similar kind of erroneous perceptions during set actualization as grown-ups. Children of younger age (6.1 +/- 0.3 years) display more perceverative erroneous perceptions, or assimilative illusions (probably of a priming origin), than the above mentioned groups. We consider this to be a result of a more strong influence of previous experience in their case.

Evoked EEG theta and alpha rhythm synchronization/desynchronization responses to facial stimuli were studied in healthy subjects (n = 35) in an experiment involving formation of a set to an emotionally negative facial expression. The magnitude of the evoked theta activity synchronization response in the group of subjects with the plastic type of set was greater and the latent period was shorter than in the group with the rigid type of set. These differences were particularly clear in the temporal and parietal-occipital areas. A sufficiently high level of the phasic theta potentials synchronization response, reflecting the level of activity of the corticohippocampal feedback system during the perception of facial stimuli, was required for rapid substitution of the set to facial expressions. In subjects with plastic sets, the evoked low-frequency alpha potentials response was apparent as synchronization, while that in subjects of the "rigid" group consisted of desynchronization. These results were interpreted in terms of the concept of Klimesch (2007) that the evoked alpha potentials synchronization response is a measure of inhibition in cognitive activity. The alpha potentials synchronization response reflects the process of inhibitory control, which plays an important coordinating role in organizing the plastic properties of the set in relation to its inhibition when it ceases to correspond to new stimuli. The involvement of the tonic and phasic forms of cortical activation, mediated by the corticohippocampal and frontothalamic brain systems, in the functional organization of the cognitive set to an emotionally negative facial expression is discussed.

Alpha- and theta-band EEG synchronization/desynchronization, induced by the presentation of emotionally negative stimulus (angry faces), was studied in 35 healthy adults. In subjects with a plastic set induced theta-synchronization was greater, and its latency was shorter, than in subjects with a rigid set. This difference is particularly apparent in temporal and parieto-occipital brain regions. A sufficiently high level of theta-synchronization is essential for a quick set-shifting. This synchronization reflects the activity of cortico-hippocampal feedback system and its participation in the perception of emotional faces. In subjects with a plastic set this process induces alpha-synchronization, and in subjects with a rigid set--desynchronization. W. Klimesh (2007) suggests, that induced alpha-synchronization reflects processes of inhibition in cognitive activity. This inhibition plays an important role in the set-shifting. The role of tonic and phasic forms of cortex activation, produced by cortico-hippocampal and fronto-thalamic systems, in the shifting of a cognitive set to facial face expression is discussed.

Experimental data from healthy humans on the context dependence of cognitive activity involved in the process of substituting a previously formed unconscious set with a new set appropriate to the altered conditions are discussed. The mobility/rigidity property of the visual set changes depending on the nature of the additional task introduced into the context (stimulus recognition or identification of the spatial position of a stimulus). It is hypothesized that the process of set substitution is facilitated when the context of cognitive activity includes alternation of the involvement of the ventral and dorsal visual systems in information processing.

Coherence function of the EEG in the bands of 8-13 (alpha rhythm) and 14-25 Hz (beta rhythm) was analyzed in 35 healthy adult subjects during formation and testing of a visual cognitive set to pictures of faces with different emotional expressions. The intra- and interhemispheric coherences of the potentials in the frontal area and coherence between the right frontal and temporal derivation were shown to increase at the stage of set actualization. The results of the analysis confirm the suggestion that the frontal cortical areas are predominantly involved in formation and actualization of the set to facial emotional expression. The conclusion is based on the idea that the spatial synchronization of the brain electrical potentials is an index of the functional relations between the corresponding cortical areas and their cooperative involvement in a certain kind of activity (their simultaneous activation).

Studies in healthy adults were performed to compare measures of the rigidity of a verbal set in three series of experiments: in series 1, pseudowords were presented at the set-forming stage of the experiment, while common words were presented in the test stage; series 2 used the pseudoword/word conditions of series 1 with the additional task of identifying the position of a target stimulus in a matrix, requiring discrimination from other symbols in terms of two characteristics; in series 3, the pseudoword/word test was followed by an initial task consisting of identifying the matrix position of a target stimulus in conditions in which the need to discriminate was minimized. The results supported the hypothesis that the rigidity of a visual set depends on the cognitive activity context. This property is significantly dependent on the loading applied to working memory and the cognitive tasks solved by the subject, particularly the ratio of involvement of the ventral and dorsal visual systems in the cortical processing of sequentially acting verbal and non-verbal visual stimuli. The cognitive set paradigm serves as a model for experimental studies of the roles of the ventral and dorsal visual systems in organizing recognition functions.

Measures of the stability of a non-verbal visual set were compared in healthy human subjects in three series of experiments: 1) controls, in which a pair of set-forming stimuli (images of circles) were presented; 2) in the context of a test with a non-verbal set, subjects were presented with an additional task consisting of recognition of pseudowords (words); and 3) as before, but the additional task consisted of identifying the position of a target stimulus in a matrix of letters. There was a significant decrease in the stability (rigidity) of the non-verbal set on introduction of the additional task consisting of identifying the spatial position of a target stimulus; conversely, there was an increase in rigidity when the task consisted of recognizing the quality of a stimulus. Coherence analysis of cortical potentials in the alpha range showed that changes in the spatial organization of cortical electrical activity were significantly different, depending on the nature of the additional task: when the additional task involved recognition of a verbal stimulus, coherence connections were strengthened in the frontal-temporal-parietal areas of the right hemisphere; presentation in the context of a visuospatial task resulted in greater changes being observed in the anterior areas of the right hemisphere. It is suggested that the successful performance of mental functions requiring relatively rapid shifts in unconscious sets on changes in situation occurs in conditions of alternation of different types of cognitive tasks when cortical processing of visual information is mediated predominantly by one of the visual systems - either the ventral ("what?") or the dorsal ("where?") and, correspondingly, with the involvement of the anterior and posterior cortical selective attention systems.

The experimental evidence that the cognitive set shifting in healthy humans depends on the context of cognitive performance is discussed. Lability/rigidity of the experimentally formed unconscious visual set is largely determined by the type of additional task ("what?" or "where?", i. e., stimulus recognition or spatial localization, respectively) introduced into the context of the experiment. It is suggested that the acquired set more readily shifts to a new one more adequate to modified conditions in case of alternation of the ventral and dorsal visual pathways involved in the information processing in the context of cognitive performance.

Rigidity of a verbal set was compared in three series of experiments: (1) pseudowords were presented at the set-forming stage and were changed for common words at the testing stage; (2) in the same conditions as in 1, an additional task of target localization in the matrix by two distinctive features was introduced; (3) in the additional target localization task, the spatial component was strengthened whereas image recognition component was reduced. The results confirmed our hypothesis about the context-dependence of the rigidity of the visual set. This characteristic substantially depends on a working memory loading and cognitive tasks performed by a subject, in particular, the relationship between the degrees of involvement of the ventral and dorsal visual systems into the cortical processing of sequential verbal and nonverbal visual stimuli. The experimental paradigm can serve as a model for the investigation of the roles of the ventral and dorsal visual systems in the recognition function.

Healthy adults were examined in three series of experiments with formation of an unconscious visual set: 1) the set was formed by repeated presentation of pairs of unequal circles (control); 2) an additional task of recognition of words/pseudowords was introduced into the context of the set-forming trials; 3) in the task additionally introduced, a subject had to spatially localize a certain target letter in a letter matrix. Scores of stability of the visual set to circles were compared. Coherence of the cortical electric activity in the alpha band was analyzed. We revealed a significant decrease in stability (rigidity) of the nonverbal visual set in the series with the additional task of spatial localization of the target stimulus. On the contrary, the set rigidity increased in the series with additional recognition of the verbal stimulus. EEG coherence patterns and behavioral data suggest that successful cognitive performance that demands dynamic situation-dependent shifts of unconscious sets takes place under conditions of alternation of tasks involving, predominantly, either the ventral ("what?") or dorsal ("where?") visual streams and, respectively, anterior or posterior systems of selective attention.

The importance of Asratyan's conditioned switching-over phenomenon as an experimental model for investigation of the control function of the inner states (sets) in behavior is discussed. It is argued that experimental investigation of the animal conditioned switching-over phenomenon at the novel cognitive stage of exploration of neural mechanisms of behavior using the modern conceptual models of brain operation and conceptual apparatus can be a promising approach to understanding of the physiological basis of human unconscious cognitive sets and their role in perception of external signals and organization of voluntary behavior.

It was found in healthy adult subjects (n = 90) that under conditions of complication of cognitive tasks (increasing number of relevant stimuli), the stability (rigidity) of the unconscious cognitive sets markedly rises. These changes in both verbal and nonverbal sets depend on the working memory loading. The revealed dependence of the motor reaction time to the probe stimulus on the sequence of the set stimuli in a context and on the set stage suggests that unconscious cognitive sets can regulate selective attention.

A top-down processing model and the role of frontal and prefrontal cortex in the neural mechanisms of recognition of verbal and non-verbal visual stimuli, are discussed. Stimulus recognition is considered to be a result of integration of the bottom-up and top-down streams. The cognitive set phenomenon can be used for studying the downward control in the neurocognitive visual system and in functional organisation of stimuli recognition.

In order to reveal the character of motivation influence on the stability of the unconscious visual set, young adult healthy subjects were promised to be rewarded for correct solution of the cognitive task. A substantial increase in set stability was observed under conditions of augmented motivation of a subject to the result of his performance. Positive and negative aspects of the impact of the increased motivation of a subject on his cognitive activity at the stages of set formation and actualization are discussed.

The regulatory function of the set and dominanta in human cognitive activity is discussed. Role of the stimuli context in formation of the set is demonstrated.

It was shown in adult healthy subjects (n = 60) that the set depends on the context of cognitive activity. Under conditions of its complication, when a subject had to solve successively several tasks, the stability of the verbal set markedly increased. This was expressed in a longer effect of "blindness" characteristic for the set to pseudo-word reading and increase in the time of reaction to a probe stimulus.

Two kinds of cognitive sets for verbal and non-verbal stimuli were revealed in healthy subjects: an "intellectual blindness" and a distortion of perception and assessment of the stimuli size. Analysis of the response time to a probe stimulus and a spectral analysis of the cortical EEG revealed a participation of these sets in cortical functions: a stable set organizes and improves the stimuli perception and assessment but impedes this process in a modified situation. An optimal balance between the two sets seems to be necessary for effective cognitive activity.

The cognitive set can be formed in healthy humans (75 subjects have been examined) on the basis of the Müller-Lyer's visual illusion. The effect of this set is expressed as a contrast illusion similar to the effect of the set, which is formed on the basis of the real size of visual stimuli (pictures of circles). Time of the simple motor reaction to the probe stimulus (light spot) depends on the factor of set stability. In subjects with the stable set the reaction time and its variability are substantially longer than in persons with the unstable set. Analysis of correctness of perception of the visual stimuli and the reaction time shows that the set which has been formed at the unconscious level leads to a certain rigidity in cognitive activity. Thus, factor of lability/stability of sets is an important feature of human cognitive activity.

A psychological set was formed in 30 healthy adult subjects by means of successive exposition on the screen (with the intervals in 3-7 sec) of 30 single pseudo words written in the Latin letters. This series of stimuli was immediately followed by similar presentation of 36 single Russian words which consisted of the letters written in the same way as some characters of the Latin alphabet. At the beginning of the second train of stimuli all the subjects began to read the well-known Russian words as senseless. In 11 subjects this effect disappeared after 1-2 Russian word presentations and in 19 subjects only after 6-36 presentations. Analysis of the reaction time to the presentation of the visual probe stimulus suggests that the formation of preparatory set improves selective attention to the stimuli acting in a given situation and thus consolidates the cognitive processes.

The formation of late evoked cortical responses, N150 and P300, correlates with some factors determining cognitive activity (selective attention, different types of memory, decision making process). Influence of different significance stimuli in a particular situation results in creation of an integral "psychonervous image" reflecting a context of these stimuli, whole complex of cognitive tasks to be solved. It influences significantly on the magnitude of cortical evoked reactions to different stimuli that allows to make a correspondence with the "psychological set" phenomenon and its role in the evaluation of the perceived stimuli.

The role of unrecognized forms of reinforcement in the function of the discrimination of microintervals of time was investigated in emotionally excitable adults. The word "good" [""khorosho""] (positive reinforcement) and a word associated with the subject's negative emotions (negative reinforcement) were utilized as feedback stimuli. Experimental confirmation was obtained of the hypothesis that unrecognized phenomena of the external milieu can exert an influence on conscious mental activity and on the learning process in man. Unrecognized semantic stimuli can fulfill the function of a reinforcing factor, and thus participate in the process of learning a cognitive activity accomplished at the conscious level.

In adult emotionally excitable persons the role was studied of unrecognized reinforcement forms in the function of differentiation of time microintervals. As feedback stimuli the word "good" (positive reinforcement) and a word connected with negative emotions of the subject (negative reinforcement) were applied. Experimental confirmation was obtained of the hypothesis that unrecognized phenomena of environment can influence conscious psychic activity, the process of man learning. Unrecognized semantic stimuli can function as a reinforcing factor and in this way participate in the process of learning of cognitive activity realized at conscious level.