[Identification of the images of gradually transforming geometrical figures].

The effect changing of dependence of distance, on which subject move the optic mouse, on presented geometrical figure has been studied in psychophysiological experiments by transformation of quadrat in triangle by exclusion of one of figures of representations row. It has been found 75% authentic effects. The findings are discussed in connection with the phenomena of lateral inhibition, including possible neuronal mechanisms.

Recognition of lateralized halftone and outline images of everyday objects in conditions of masking.

Recognition of the shapes of halftone and outline images of everyday objects in conditions of lateralized tachystoscopic presentation and different levels of noise masking (with "raindrops") by humans was studied. Mean group data for 15 subjects demonstrated significantly better recognition of outline images of everyday objects by the left hemisphere of the brain than the right at all levels of masking. Increases in masking produced gradual and significant degradation of recognition as compared with controls (recognition of unmasked figures).

[Recognition of halftone and contour figures under their lateralization and masking].

Recognition of shape of natural objects was studied during lateralized tachistoscopic presentation and different degree of noise-like ("rain drops") masking in 15 healthy subjects. Two sets of figures were used: halftone and contour ones. In all masking conditions, the mean group data showed a significantly better recognition of contour images by the left hemisphere as compared to the right hemisphere.

[Recognition of halftone, contour, and silhouette figures under conditions of their masking].

Shape recognition of natural objects was studied under conditions of tachistoscopic (12 ms) presentation and different degree of noise-like ("rain drops") masking in 15 healthy subjects. Three set of figures were used: halftone, contour and silhouette. For all sets of figures, mean group data reveal a drop of the correct response probability with increase in masking.

[Trajectories of alpha rhythm dipoles shifting over the human brain cortex].

Dynamic study of 3D localization of the equivalent current dipoles (ECD)--sources of the EEG alpha rhythm in the human brain was performed in seven subjects with closed eyes using a one-dipole model. An exact localization of ECDs was obtained by combination of EEG and MRI mapping that allowed tracing of ECD shifts over the cortex with 4 ms step. Our data confirmed localization of these ECDs mainly in the occipital cortex and revealed their successive shift over this area during generation of each alpha-wave.

The role of lines and corners of geometric figures in recognition performance.

A relative role of lines and corners of images of outline geometric figures in recognition performance was studied psychophysically. Probability of correct response to the shape of the whole figure (control) and figures with lines or corners masked to a different extent was compared. Increase in the extent of masking resulted in a drop of recognition performance that was significantly lower for figures without corners, than for figures without part of their lines.

[Gender distinctions in recognition of partly masked geometric figures].

Visual recognition of entire and partly masked geometric figure by men and women was studied. Probabilities of correct recognition of the entire (control) and partly masked figures (without some parts of their lines or corners) under conditions of their near-threshold tachistoscopic presentation were compared. A gradual decrease in recognition probability with increasing masking was observed.

Visual illusions and travelling alpha waves produced by flicker at alpha frequency.

The aim of the study was to obtain some experimental evidence of the 'scanning hypothesis' that links electroencephalogram (EEG) alpha-activity with rhythmically spreading waves in the visual cortex. The hypothesis was tested in experiments with 29 healthy adults. Under flicker stimulation through closed lids with the frequency of the individual alpha-rhythm, all subjects perceived illusory visual objects (a ring or a circle, a spiral or a spiral spring, or a grid).

[Relative meaning of lines and corners in geometric figures for their recognition by humans].

Neurons tuned to line-crossings (corners, crosses, Y-like and three-ray star-like figures) of different shape and orientation rather than to a single bar were found in the area 17 of the cat visual cortex. We studied the relative role of lines and corners of 2D and 3D geometrical figures for their recognition by humans. Probability of figure recognition during its tachistoscopic presentation was compared for the whole (control) and partly masked figures.

[The dynamic localization of a dipole source of the alpha rhythm in the human brain].

In 11 subjects the dynamic localization (with 2-ms step) of the equivalent current dipole of alpha rhythm during travelling alpha waves was studied using one-dipole 3-layered spherical head model and MRI. The dipole was localized in the occipital cortex and during the development of a single alpha wave it shifted in one or another direction while dipole's moment revealed fan-like rotation mainly in sagittal and horizontal planes. The results obtained indicate changing localization of the alpha-rhythm source in the region corresponding to striate cortex.

[Visual illusions evoked by rhythmic bursts and the "movement" through the cortex of waves of alpha activity].

In computer-controlled experiments the visual illusions were studied which appeared in human subjects under conditions of diffuse rhythmic photostimulation through the closed eyes with the individual dominant alpha-rhythm frequency. A significant correlation was demonstrated between the type of experienced illusion (or its absence) and the trajectory of the alpha-wave travelling in the prestimulation and stimulation periods.

[The relationship of visual illusions to the frequency and phase shift of rhythmic photostimulation synchronized with the EEG alpha wave].

Under flicker stimulation through the closed eyes, synchronized with different phases of the EEG alpha wave, all 18 subjects systematically perceived the illusory visual objects (ring, circle, spiral, or curvilinear grid). Most frequently, they saw a ring or a circle, a little less frequently, a three-dimensional spiral, and at last-a curvilinear grid. The incidence of the ring and spiral illusion was the highest when the stimulation frequency strictly coincided with the individual dominant frequency of the alpha-rhythm.

Recognition of direction of uniform and accelerated visual motion and EEG alpha wave phases.

The perception of visual motion in seven subjects was studied comparing motion towards or away from the fixation point in the left or right hemifield. The light target was moved either at a constant velocity or positively or negatively accelerated to compensate for the magnification factor of the visual cortex. We compared probability and latency of motion recognition when it was asynchronous or synchronized to different phases of the alpha wave of the EEG recorded over the occipital cortex.

[Visual illusions and the alpha-rhythm EEG].

During flicker stimulation with the alpha-rhythm frequency through the closed eyes 11 from 12 subjects clearly saw illusory objects (in order of descending probability, ring, circle, three-dimensional spiral or spiral spring, funnel, curved crossed bars). The individual optimal stimulation frequency for producing an illusion was always within the alpha range and was closely correlated with the individual dominant alpha frequency (r = 0.86).

[The estimation of the direction of uniform and nonuniform movement and the alpha-rhythm EEG].

In experiments with 7 human observers the recognition of side and direction of the even and non-even (compensating the magnification factor) light motion in the left or right visual hemifield and to or from the fixation point was studied. The onset of the movement coincided with different phases of the EEG alpha-wave in the occipital region. In a control study stimuli were presented irrespectively to alpha-wave phases.

EEG alpha-wave in the visual cortex: check of the hypothesis of the scanning process.

In computer-controlled experiments the recognition by seven human observers of tachistoscopically presented geometrical figures of different size (from 0.5 to 9 angular degrees) or of different eccentricity (from 3 up to 16 degrees) in the visual field was studied. The onset of figures presentation coincided with different phases of the EEG alpha-wave in the occipital region.