[The frequency-contrast sensitivity of visual stimulus perception in patients with schizophrenia with the therapy of atypical and typical antipsychotic drugs].

We studied the effect of typical and atypical antipsychotics drag treatment on the perception of visual stimulus which activates preferentially different visual channels. We recorded contrast sensitivity in normal and schizophrenic patients. Elements presented with Gabor-like gratings with sinusoidal distribution of brightness, spatial frequency: 0.4 cycles/degree, 3.6 and 17.9 cycles/degree. Patients were divided into two groups. One group--patients treated with atypical antipsychotics, and the second group--patients treated with typical antipsychotics drags. Registered a decline compared with the normal contrast sensitivity for low and medium spatial frequencies. We observed significant difference between two groups of patients in the range of low spatial frequencies.

[The efficiency of recognition of the size of segments of line by the observers with different parameters of the cognitive style].

We estimated efficiency of recognition of the size of segments of line by the persons with different parameters of cognitive style: the field dependence--field independence, the analytically--synthetically style, the flexible--rigid cognitive control. The size of segments of line was judged in task of the magnitude of the Ponzo illusion measurements. It was established, that the magnitude of the Ponzo illusion significantly less in subjects with the field independence cognitive style, than with field independence. The persons with the flexible type of the cognitive control showed the tendency to more accurate perception of the size of the segments in the Ponzo figure, than with the rigid cognitive control. The rinteraction between the analytically--synthetically style of the categorization and the magnitude of the Ponzo illusion is not fixed.

[The contrast sensitivity in schizophrenia with different durations disease].

We recorded contrast sensitivity in normal and schizophrenic patients. We presented Gabor gratings with sinusoidal distribution of brightness, with the spatial frequency: 0.4 cycles/degree, 3.6 and 17.9 cycles/degree. Taken together patients with schizophrenia compared to the healthy subjects showed a decline of contrast sensitivity at low and medium spatial frequencies. We measured the influence of duration of illness and type of treatment on contrast sensitivity. Patients with schizophrenia less than 10 years, showed a decrease of contrast sensitivity only at low spatial frequencies, while patients suffered with schizophrenia for more than 10 years--at low, medium and high spatial frequencies. Persons with schizophrenia less than 10 years receiving treatment with atypical antipsychotics, show a decrease in contrast sensitivity at low spatial frequencies, while treated with typical antipsychotics--in the low and high spatial frequencies.

[Study of parvocellular and magnocellular visual channels in normal subjects and in patients with psychopathology].

We measured susceptibility to the Müller-Lyer illusion in schizophrenic patients and normal observers. The images of the Müller-Lyer figure were digitally filtered in a high-frequency and low-frequency band by wavelet filter. Patients with schizophrenia are more susceptible to Müller-Lyer illusion, than mentally healthy examinees. The images of the Müller-Lyer figure with low spatial frequency were perceived in a similar way by the schizophrenic patients on the initial stage of disease and the control subjects. Patients with schizophrenia were more sensitive to the Müller-Lyer illusion when the image contained only high or medium spatial frequency. Schizophrenic patients in advanced stage were more susceptible to the illusion while presented with all types of images of the Müller-Lyer figure than the control group. It is hypothesized that those differences arise from the mismatch work of the magnocellular and parvocellular systems. It is known that images with the high spatial frequencies are most relevant for the parvocellular visual channels. The magnocellular visual channels are most sensitive to the images with the low spatial frequencies. Thus these findings demonstrate a significant impairment in parvocellular pathway function in patients on initial stage of schizophrenia. The patients on advanced stage of schizophrenia demonstrate impairment of both the parvocellular and magnocellular systems.

[Electrophysiological and psychophysical studies of the effect of duration of presenting textures on the recognition threshold].

We studied the dependence of correct response number, response time, and the main characteristics of visual evoked potentials on the time of the stimuli presenting. The coincidence of the recognition temporal thresholds and occurrence of differences in the visual EPs suggests that the temporal characteristics of these processes differ in different subjects. Two groups of observers were distinguished with different temporal characteristics of perception and the EP development.

[Features of perception of length of segments under conditions of ponzo and Müller-Lyer illusions in schizophrenia].

In order to better appreciate the neurophysiologic mechanisms of perception of length under conditions of geometrical visual illusions, we studied sensitivity of mentally healthy subjects and schizophrenic patients to Ponzo and Müller-Lyer illusion. Patients with schizophrenia estimated length of segments of Müller-Lyer figure less precisely. Accuracy of perception of length of segments in Ponzo figure was ambiguously connected with the duration of the disease. Persons suffering from schizophrenia for a short time were less inclined to Ponzo illusion than mentally healthy subjects. On the contrary, patients who suffered from schizophrenia for a long time were more sensitive to this illusion. Ponzo illusion can be used as a marker of schizophrenia which is found out during the specific period of development of the disease. High sensitivity of patients with schizophrenia to Müller-Lyer and Ponzo illusions supports a hypothesis about the role of the global analysis of an image during processing of its low-frequency component in formation of the illusions under study.

[Incomplete 2-D images perception at viewpoint variation of 3-D objects].

Thresholds of recognition of 3-D objects when viewed as incomplete 2-D images were measured in psychophysical experiments varying perspective of 3-D objects during subject's learning and testing. The new method of measurement of recognition thresholds of the 2-D incomplete images of 3-D objects in Gollin-test has been created. The visual system appears to be capable of extrapolating results that were obtained at the first presentation of object, at one viewing angle to other, subsequent viewing angles. It appears that a template forms immediately after the first presentation of a 2-D projection of that object. This template has "invariance" properties since its use for object identification does not depend on the orientation at which the object is subsequently presented, at least up to an angle of 60 degrees. The algorithm for template formation of 3-D objects in the human visual system needs to be modeled, taking account of the invariance mechanism.

[Investigation of the perception of incomplete contour figures of the various size].

The purpose of the current research was to estimate the range of angular sizes of incomplete images across which the perception of the given images does not depend on scale. We have measured thresholds of recognition of the identities of objects across a wide range of angular sizes from 0.19 to 50 degrees of visual angle. The methodology derived from the Gollin-test which has been used as a method for studying the perception of objects presented as incomplete contour and pattern recognition. Results demonstrated that there is a wide range of angular sizes (from 1 .0 up to 50 degrees of visual angle) across which thresholds perception of incomplete images does not depend on object size. However, there was found a narrow range of small sizes of stimulus (0.19-1.0 degrees of visual angle) at which there was found dependence of performance on object size. We assume that increase of thresholds and occurrence of undistinguished images (when they have small size) depends on increase of the contribution of sampling noise at the observer's eye retina.

[Analysis of fragmented images perception: local features and global description].

Analysis of experimental investigations of the perception of incomplete images is presented. It illustrates two different approaches to work of the brain mechanisms involved: one approach is based on the perception of whole images and another on local informative features. These approaches describe two different mechanisms, which are possibly used by brain systems for incomplete image recognition. Performance on the Gollin test (measuring recognition thresholds for fragmented line drawings of everyday objects and animals) depends upon recognition based on image informational-statistical characteristics. We suggest that recognition thresholds for Gollin stimuli in part reflect the extraction of signal from noise. The brain uses local informative features as an additional source of information about them. We have suggested that fragmented images in the Gollin-test are perceived as whole structures. This structure is compared with a template in memory which is extracted with the help of selective attention mechanism in accordance with a matched filtration model. The Gollin-test is a tool for differential diagnosis of a various forms of cognitive disorders.

[Human magno- and parvo-systems and selective disruptions in their function].

In psychophysical and electrophysiological investigations, we tested the hypothesis that in patients with multiple sclerosis at its early stage either phasic cells of the magnocellular pathway or tonic cells of the parvocellular pathway are disturbed. Healthy humans and patients with early stage of diseases have a contrast spatial-frequency sensitivity measure. The decrease in sensitivity at low, medium and high spatial frequency indicates changes in parvo- and magno-system activity. The data are separated into two clusters. Psychophysical data is in good accordance with electrophysiological data of visual evoked potentials (VEPs). First group of patients showed changes of the amplitude of positive wave P100 whereas in second group of patients changes of negative wave N80 dominated comparative to healthy subjects. According to some literature data these changes were specific for M-pathway and for P-pathway.

[Localization of human brain areas activated for chaotic and ordered pattern perception].

The aim of our work was to localize cortical areas involved in the processing of incomplete figures using functional MRI (fMRI) for 8 healthy volunteers (18-30 year old) with the did of anatomical and fMRI fast imaging technique: echo planar imaging (EPI), whole brain scan (36 slices) matrix 64 x 64, 3.7 second. We used 1.5 T MR-scanner and BOLD-method (Blood Oxygenation Level Dependent), based on distinctions of magnetic properties of hemoglobin. Fast imaging technique on modern MR-scanners with > or = 1.5 T provides precise statistical maps of oxygenation increase with high spatial resolution. For test stimuli we used matrix of Gabor grating. We used two types of 10 x 10 matrices with chaotic and ordered orientation of Gabor gratings. The size, brightness and contrast of the stimuli were identical. The chaotic and ordered patterns activated different brain areas. We establish that ordered patterns activated only primary visual cortex - V1 and V2, (BA17-18), wheareas chaotic patterns activated in addition primary visual cortex, the V3,V4,V5 (BA19) of the occipital cortex and the area 7 of parietal area (BA7) classification. Decision making for that task is localized in prefrontal and frontal cortex, including (BA 6, 9, 10).

[Electrophysiological investigation of the texture discrimination mechanisms].

In electrophysiological and psychophysical experiments, we investigated mechanisms of the visual system underlying local and global texture processing. Textures included rectangular matrixes composed of Gabor patches (sine wave grating windowed by a Gaussian envelope). Orientation of each grating varied from 0 to 165 degrees with the step of 15 degrees. Matrixes differed by the amount of Gabor patches with vertical or horizontal orientation. The observers' task was to discriminate the dominant orientation. The advantage of such stimuli involved a possibility to calculate global statistics of the textures, which we considered as the difference between whole amount of vertical and horizontal orientations in the stimulus irrespective of their location. The local statistics was calculated as relative amount of spatially organized nearby gratings (i. e. collinear contours). The subjects' accuracy was low in discriminating less organized textures and gradually improved with the amount of vertically of horizontally oriented Gabor patches, while the reaction time decreased. Visual evoked potentials (VEPs) recorded from occipital lobes revealed different dependencies of their components' magnitude on the amount of equally oriented gratings. Amplitude of the late positive component P3 with latency 400 ms directly depended on the texture discriminability, and N2 wave with latency 180 ms had an S-like dependence. Opposite to that, the magnitude of P2 wave with latency 260 ms was maximal in response to less organized textures and gradually decreased with the amount of equally oriented gratings. The dependencies received were compared with the textures' statistics. Data analysis allowed us to suppose that, in the conditions of our experimental paradigm, two mechanisms were involved in discrimination of the textures--the local and the global processing. We believe that by recording VEPs one can separately investigate activity of these two processes.

[Visual mechanisms of recognition of vanishing figures].

The acuity test Landolt C's with a complex contour imitating various kinds of high-pass spatial frequency filtering generated as a printed visual acuity charts with a grey background were studied with regard to recognition thresholds. Comparisons were made for recognition thresholds with different complex contours. When the vanishing optotypes are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in the standard chart. The data obtained confirm that the recognition distance depends on physical property of complex contour profile and show the importance of the Landolt C spatial frequency spectrum for recognition of different types of the complex contour.

[Objective measurements of visual acuity by visual evoked potentials].

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.74 and a logarithmic dependence were obtained between spatial resolution measured by electrophysiological and psychophysical methods. The proposed methods of objective measurement of visual resolution has a high effectiveness, does not depend on specificity of individual EEG and domination of different channels in the visual system. Therefore it is possible to determinate objectively the visual acuity in humans independently of their responses.

[Visual potentials in humans with multiple sclerosis evoked by checkboard pattern of different contrast with additional noise]. / Zritel'nye vyzvannye potentsialy cheloveka na shakhnatnyi pattern raznogo kontrasta v usloviiakh pomekhi pri rasseiannom skleroze.

A hypothesis is advanced of an effect of internal noise upon signal conduction along visual nerve in an early stage of multiple sclerosis. Visual evoked potentials in response to chess patterns against a homogeneous background and against a noise background were studied in healthy subjects and in patients with multiple sclerosis. Contrast between internal noise in the patients was found to be twice as great as in healthy subjects.

[Signal/noise ratio at the visual recognition threshold of incomplete figures]. / Porogovoe otnoshenie signal/shum pri vospriiatii fragmentirovannykh figur.

We measured recognition thresholds of incomplete figure perception (the Gollin test). This test we regarded as a visual masking problem. Digital image processing permits us to measure the spatial properties and spatial frequency spectrum of the absent part of the image as the mask. Using a noise paradigm, we have measured the signal/noise ratio for Incomplete Figure. Recognition was worse with better spectral "similarity" between the figure and the "invisible" mask. At threshold, the spectrum of the fragmented image was equally similar to that of the "invisible" mask and complete image. We think the recognition thresholds for Gollin stimuli reflect the signal/noise ratio.

[Principle of least action, physiology of vision, and conditioned reflexes theory]. / Printsip naimen'shego deistviia, fiziologiia zreniia i uslovnoreflektornaia teoriia.

The variation principles such as principle of least action by Maupertuis (1740) and Fermat principle (1660) are fundamental for physics. They permit to establish a property by which the actual state is differing from all possible states of the system. The variation approach permits to establish equation of motion and equilibrium of a material system on the basis of one common rule which reduces to the search of the function extremes, describes this property of the system. So for the optical systems, crucial is the time and not the length of the way. According to Fermat principles, the light "choosen" from all possible ways connects two dots in the way which needs the least time. Generality of the variation principles guarantees success of their use in brain function investigations. Between different attempts to apply the variation principles to psychology and linguistics, the Zipf principle of least effort must be distinguished. Zipf (1949) demonstrated that languages and some artificial codes satisfied the least principle. For the brain physiology, classical conditioned reflex theory is the ideal area of variation principles application. According to this approach, conditioning leads to finding the extreme during fixation of the temporal link. In vision, physiological investigations are difficult because the signal has many dimensions. For example, during perception of spatial properties of surrounding world, in vision is realized minimization (reduction) of spatial-frequency spectrum of the scene. The receptive fields provide optimal accumulation of the signal. In ontogenesis, signal--noise ratio becomes optimal as receptive fields minimized the internal noise spectrum. According to the theory of match filtration, in the visual system recognition is carryied out by minimal differences between the image description in the visual system and storage in the human memory template of that image. The variation principles help to discover the physical property of phenomenon. The law discovered for mechanical system may be translated to quantum level. In physiology, variation principles permit us to connect information approach with concrete physiological mechanisms of pattern recognition and conditioned reflex.

[Optical-geometrical parameters and perception threshold of the fragmented contour figures]. / Optiko-geometricheskie kharakteristiki i porogi vospriiatiia fragmentirovannykh konturnykh figur.

The thresholds of recognition of line drawings of common objects were measured using the Gollin-test procedure, in which separate random line fragments are displayed cumulatively up to the point of recognition. It was shown that the mean percentage of contour displayed at threshold recognition for different images was always about 12.5%, despite inter-subject variability between 5% and 25%. The comparative and spatial-frequency analysis of the geometrical parameters of images was carried out for different levels of fragmentation (before threshold, at threshold, and for the complete contour). The magnitude information of the Fourier domain image of figures was characterized by maximum at low and high levels of fragmentation, but at recognition threshold fragmentation it was characterized by minimum variability.