[Behavioral and ERP characteristics of recognition of complex images under forward masking. The influence of categorical similarity of target and masking stimuli].

In psychophysical (n = 55) and neurophysiological (n = 25) experiments subjects recognized the images from two categories--"animals" and "non-living objects" under forward masking. Subjects recognized images in two experimental conditions: the target and masking stimuli (SOA = 50 ms) belonged to same category and the stimuli belonged to different categories ("compatible" or "incompatible" pairs). It was found that an efficiency of forward masking depends on the categorical proximity the mask and the target stimuli. The probability of correct answers was lower, and reaction time and it's dispersion were higher in "compatible" situation as compared with the "incompatible" one. The worsening of behavioral response in "compatible" condition was associated with decreased amplitude of N2 and P3 components of ERPs. The observed effects appeared to be more marked in animal recognition in comparison with object recognition. The results are discussed in the context of negative priming and an influence of distractor.

[Mechanisms of human orientation sensitivity of the vision system. Part I. Behavioral characteristics of human orientation sensitivity. Influence of task type, experimental conditions and gender].

Orientation sensitivity in human visual system was investigated in three experiments. In the first experiment 134 subjects were to determine the orientation of the segments of short lines, by "selecting" it from a set of reference orientations (Benton's test). In the second experiment 41 subject, which was chosen from participants of the first experiment, were to estimate the proximity of oblique lines to the vertical, horizontal, and 45° axis. In the third experiment participants were to identify the orientation of cardinal (0° and 90°) and oblique (45° and 135°) lines. It was shown that the cardinal orientations were defined more accurately and faster than the oblique ones. Error type depended on experimental conditions: participant answers tilted to horizontal under normal illumination in the presence of peripheral visual information, but they tilted to vertical under low illumination (3 lux.). Women performed worse only those tasks which require precise determination of the line orientation. It was assumed that the metric spatial characteristics determined better by males then females. The oblique effect was more pronounced in females, presumably due to gender differences in brain organization of the multimodal reference frame.

[Non-conscious perception of emotional faces affects the visual objects recognition].

In 34 healthy subjects we have analyzed accuracy and reaction time (RT) during the recognition of complex visual images: pictures of animals and non-living objects. The target stimuli were preceded by brief presentation of masking non-target ones, which represented drawings of emotional (angry, fearful, happy) or neutral faces. We have revealed that in contrast to accuracy the RT depended on the emotional expression of the preceding faces. RT was significantly shorter if the target objects were paired with the angry and fearful faces as compared with the happy and neutral ones. These effects depended on the category of the target stimulus and were more prominent for objects than for animals. Further, the emotional faces' effects were determined by emotional and communication personality traits (defined by Cattell's Questionnaire) and were clearer defined in more sensitive, anxious and pessimistic introverts. The data are important for understanding the mechanisms of human visual behavior determination by non-consciously processing of emotional information.

[Recognition of visual objects under forward masking. Effects of cathegorial similarity of test and masking stimuli].

In 38 healthy subjects accuracy and response time were examined during recognition of two categories of images--animals andnonliving objects--under forward masking. We revealed new data that masking effects depended of categorical similarity of target and masking stimuli. The recognition accuracy was the lowest and the response time was the most slow, when the target and masking stimuli belongs to the same category, that was combined with high dispersion of response times. The revealed effects were more clear in the task of animal recognition in comparison with the recognition of nonliving objects. We supposed that the revealed effects connected with interference between cortical representations of the target and masking stimuli and discussed our results in context of cortical interference and negative priming.

[Recognition of the spatially transformed objects in men and women: an analysis of the behavior and evoked potentials].

In 16 men and 15 women analyzed the accuracy, reaction time and visual evoked potentials during the recognition of familiar objects at different levels of spatial transformation. We used the three levels of transformation: in a fixed position relative to each other details were carried out (1) the displacement of all the details in the radial direction and (2 and 3) a similar shift in conjunction with the rotation of all the details of the figure by +/- 0-45 and +/- 45-90 degrees. The task performance was not dependent on gender: the transformation of the image led to a deterioration of identification with the most identification impairment in the case of maximal details' rotation. Changes in evoked potentials (ERP) are different for men and women. Only in men early (100 ms after stimulus) response of the parietal cortex associated with the level of figure transformation: the more rotation evoked the higher the response. In women figure transformation evoked the ERP changes in the time window of negativity N170, they are associated with figure ungrouping but not with details rotation, and are localized in other visual areas--occipital and temporal. The data obtained are discussed in light of theory of gender specificity of the visual representations of space.

[Gender related strategies of visual-spatial task performance].

In 31 subjects (16 men and 15 women) in model of the gender differences the brain mechanisms of two different strategies of visual-spatial tasks performance were studied. Although we did not find gender differences in the performing of visual-construction task the pattern of evoked activity was unequal in men and women. In men the early answer of the parietal cortex was related with spatial transformation of figure: the more was rotation of figures details, the more was amplitude of P1 wave. Moreover the amplitude of P1 wave in parietal area decreased with incorrect answers. In opposite, in women we did not find any ERP changes reflecting the details rotation. At the same time, in women we observed the increase of N150 negativity in occipital and infero-temporal cortex area when figure ungrouped into separate details. Our results shed light on some additional information concerning the basis of gender differences in performing of visuo-spatial tasks. Our data show that different strategies are not only defined by the later, but also the early stages of visual processing.

[Evoked potentials in the human visual cortex when observing whole figures and their elements].

Evoked potentials changes were analyzed in 32 subjects in a task of observing whole and disintegrated images. In the occipital and parietal regions, reactions to a disintegrated image appeared early (within the period of P1 development), and their characteristics were determined by the magnitude of the response to the whole image. In the occipital cortex, a low-amplitude P1 (the 1st group of subjects) increased in response to image disintegration, whereas in cases of a high P1 amplitude (the 2nd group), the tendency to its reduction was observed. In the parietal regions, the effects were distinct only in the 1st group of subjects and different in the right and left hemispheres: in the left hemisphere, the P1 amplitude increased when simpler elements appeared in the image, in the right hemisphere, a change in the spatial disposition of details was more significant. In the inferior temporal cortex, the amplitude of the later wave N1 decreased in response to disintegration, the effect being significant only in the 2nd group of subjects. The appearance of simpler elements in the image resulted in a P3 wave increase in both groups. The results point to topographic and temporal specificity of the reactions of the visual cortex to image disintegration and suggest the existence of various strategies of the visual image analysis at the early stages.

[Dipole tracing of visual evoked potentials in human brain].

3D tracing of equivalent current dipoles (ECDs) of averaged human visual evoked potentials (VEP) by their distribution across a 34-electrode array was obtained under short presentation of pattern-onset stimuli (sets of 45 horizontal, vertical bars or crosses). Using a 2-dipole spherical three-layer model, we dynamically (step of 1 ms) localized dipoles in four healthy subjects. Dipole locations were matched to anatomical brain regions visualized in structural MRI. Best-fitting source parameters were superimposed on MR images of each subject to identify the anatomical structures giving rise to the surface patterns. It was found that during 50-300 ms following the onset of the stimuli, the ECDs in all subjects were localized in the occipital cortex and demonstrated reliable systematic shift in localization. Two local (1-2 cm3) zones of the preferable dipole attendance were found at 5-6 cm behind zero line: the first one was localized near the midline of the brain, whereas the other zone was situated in the right hemisphere at a distance of 6-7 cm from the first zone. Their localization and strength of activation were reliably different for crosses and lines and changed during VEP generation. Zones of relatively rare dipole attendance were found also. The data are discussed in relation to localization of initial and endpoint of ECDs trajectories, as well as with sensitivity of the visual cortex to line crossing and branching.

[Study of the letter and word recognition by the brain-computer-interface with P300 wave of human visual evoked potential].

In four adult healthy subjects in 18 experiments, we studied Brain-Computer-Interface recognition of different intended words by P300 wave in the VEP. The set of optimal characteristics of visual stimulation which rise reliability of recognition up to 100 %, as well as effective registration locus (Pz) were determined. It was found that the best processing criteria for letter recognition were: P300 square and superposition of all three criteria (P300 amplitude, square and covariation coefficient).

[Trajectories of shifting of dipole sources of visual evoked potentials over the human brain].

Dynamic study of 3D localization of the equivalent current dipole (ECD) sources of visual evoked potentials (EP) in the human brain was performed in 18 healthy subjects using a two-dipole model. Dipole tracing was performed for relatively early EP components (N1, P1, and N2) with 1-ms step. The analysis confirmed localization of these ECDs mainly in the right occipital cortex and revealed their successive shift over this area in the anterior-medial direction and then backwards in all subjects during generation of the EP components. Typically, some successive arch-like trajectories of the shift were revealed (75.8%); their duration was relatively standard (about 25 ms) and did not depend on the stimulus shape and EP phase. Between the 1st and the 2nd trajectories (110-120 ms after the stimulus onset) a jump in ECD coordinates in the medial direction was found in 85% of cases. Possible significance of the findings for the insight into dynamic topography of the visual feature processing in the human brain is discussed.

[Human visual evoked potentials to bars and cross-like figures].

Temporal and amplitude characteristics of averaged visual evoked potentials to presentation of lines, corners and crosses with different orientation recorded in 19 adult healthy subjects were compared in 34 derivations. In all subjects, the latencies of P1, N2, and P3 were shorter while their amplitudes were higher for crosses than for lines. The effect of lengthening of P1 peak latency from occipital to temporal cortex was mostly pronounced for EPs to a bar, whereas as increase in the P1 amplitude was most evident for a cross-like figure. Correlation of these data with: i) greater magnitude and shorter latencies of responses to crosses vs. bars in a half of cat striate neurons, ii) sensitivity of cells in monkey inferior temporal cortex to star-like figures, and iii) relatively better human recognition of figures with comers than with lines, as well as significance of the effects obtained for detection of image features in different areas of the human visual cortex is discussed.

[Role of filtration in localization of the evoked potential dipoles in the human brain: experiment and simulation].

3D dipole tracing with 1 ms step of visual evoked potentials recorded from 40 electrodes was performed under exposition of crosses in 5 healthy human subjects. The data on dipole displacement were compared with prediction of the simulation study on distortion of dipole localization by the signal filtration in the low-frequency band. These predictions were experimentally confirmed: the effect depends on the degree of filtration (0.1 or 0.5 Hz) and on the latency of EP waves. Localization and strength of P1 dipoles were not changed under filtration, while for later components--N2 and especially P3--they changed significantly. For the improvement of these distortions time constant of the amplification tract must be some times longer than the time of the dipole activity.

[Decrease of nitric oxide (NO)-cGMP-dependent vasodilatation in the vessels of lesser circulation in endothelial dysfunction].

Inducible NO-synthase inhibitor aminoguanidine (AG) was used for investigation into enhanced nitric oxide (NO) production influence on elevated pressure in the pulmonary circulation (pulmonary hypertension, PH) under endothelial dysfunction. PH was simulated by subcutaneous injection of 60 mg/kg MCT to Wistar rats. Experimental groups were given AG in drinking water (15 mg/(kg x day)), and control groups were given drinking water. Rate of nitrite/nitrate excretion (RENOx) with urine was measured. The RENOx was elevated since second week as long as through the PH development. Chronic AG administration led to RENOx and soluble guanylate cyclase (sGC) NO-dependent activity restoration, and also it led to partial restoration of the right ventricular pressure. AG administration restored the perfusion pressure responses of isolated pulmonary arteries to acetylcholine. These results suggest that chronic inducible NO-synthase inhibition restores the impaired endothelium-dependent and sGC-dependent relaxation of pulmonary artery in MC-induced PH.

[Effect of chronic administration of aminoguanidine on the reactivity of pulmonary vessels in rats with monocrotaline-induced pulmonary hypertension]. / Vliianie khronicheskogo vvedeniia aminoguanidina na reaktivnost' legochnykh sosudov u krys s monokrotalinovoi model'iu legochnoi gipertenzii.

Monocrotaline (MCT)-induced pulmonary hepertension (PH) is associated with impaired endothelium-dependent relaxation and increased activity of inducible NO-synthase (iNOS). To examine the role of iNOS in MCT-induced PH, we used iNOS inhibitor: aminoguanidine (AG). The PH was simulated with a subcutaneous injection of 60 mg/kg MCT to Wistar rats; control rats were injected with saline. Then each group was separated into 2 subgroups: the 1st one was given drinking water (MCT-C and C-C groups) whereas the 2nd one was given AG in drinking water (15 mg/(kg(-1) x day(-1)) (MCT-AG and C-AG groups). In 4 weeks, the perfusion pressure (PP) responses of isolated pulmonary arteries to acetylcholine (Ach) and activator of soluble guanylate cyclase (sGC), FPTO, were examined. In the MCT-C group, a decrease of relative PP to perfusion of 1 x 10(-8) M and 5 x 10(-8) M Ach and 1 x 10(-8) M FPTO was diminished. This reduction of relaxant responses in MCT-treated rats was prevented by AG treatment. The findings suggest that AG administration restores the impaired endothelium-dependent and sGC-dependent relaxation of the pulmonary artery at MCT-induced PH.