Yuri Shelepin

Yuri Shelepin
Pavlov Institute of Physiology Russian Academy of Sciences · physiology of vision

Professor

About

129
Publications
4,615
Reads
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544
Citations
Citations since 2016
31 Research Items
245 Citations
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060
20162017201820192020202120220102030405060

Publications

Publications (129)
Article
Common patterns of rearrangements of neural networks in the whole human brain on reaching the threshold of recognition of images in conditions of uncertainly were identifi ed. This result was obtained using a combination of digital synthesis of dynamic images and a brain activity mapping method using fMRI BOLD (blood oxygen level-dependent) signals...
Article
This paper proposes a principle for synthesizing a complex target environment and identifies the optical masking characteristics for unconscious perception of a signal. A signal hidden by masking is supplied on the periphery of the field of view for a short time interval, unconsciously activating wide-angle human “periscopic vision” that possesses...
Article
This is the second special issue of Opticheskiĭ Zhurnal devoted to the key questions of neuroiconics.
Article
This paper gives estimates of the SNR for a one-photon signal and the continuous noise of photoreceptor rods. It shows that negative feedback mediated via the horizontal cell needs to be taken into account when the reaction of the retina of the eye to low-level illumination is calculated. The influence of negative feedback increases the SNR by an o...
Article
We compared several types of EEG parameters of two interlocutors during verbal and non-verbal communication. A hardware–software complex and associated method were developed for EEG hyperscanning, i.e., simultaneous EEG recording in two subjects with different location (face to face and back to back) during observation, listening, dialogue, and mon...
Article
This paper discusses the characteristics of eye movement in tasks of recognizing texts and comics with descriptions of dynamic genre scenes. The interconnection of the semantic space of the comics mentally constructed by the observer and the semantic space of test images constructed by the researcher is analyzed by measuring the characteristics of...
Article
A software–hardware complex for studying the neurophysiological mechanism that controls saccades is described and makes it possible to generate images using the motion of a window synchronized with eye movement. This complex makes it possible to demonstrate to the subject either the part of the image perceived only by the foveal region or the part...
Article
The changes in the spatial and frequency characteristics of the visual system, visual acuity, and the morphological structures of the macular zone of the retina in cosmonauts and pilots as a result of various gravitational loads were studied. We found that, after long space missions, cosmonauts exhibit a slight but statistically significant decreas...
Article
Full-text available
The purpose of this study was to investigate the relationship between the morphological parameters of the fovea, foveola, and foveolita of the human eye and the psychophysical and electrophysiological indices of the sensory and cognitive activities. We investigated the relationship between the sizes of these structures and the resolving power of th...
Article
A technique and a hardware-software complex have been developed for simultaneously recording the electrical activity of the brains of two people. It is shown that statistically significant differences appear between the various regimes and interaction conditions of the interlocutors in all frequency ranges except for the alpha range if the interloc...
Article
The interaction between the mechanisms of local and global image analysis at the level of the magnocellular and parvocellular channels of the human visual system was studied. Using wavelet filtering, the spatial frequency composition of texts presented to observers was varied. It was shown that gradual blurring of texts via wavelet filtering interf...
Article
In this paper, the results of experiments are presented in which the impact of interactive virtual environments combined with the performance of a cognitive task was estimated on the visual system of a healthy observer. Monitors of two angular sizes were used to present the images. To estimate the impacts of the environments, measurements of visual...
Article
Full-text available
Neuroimaging and functional magnetic resonance imaging have been used to study the change in the activity of the human brain during visual spatial tests of varying complexity. It is shown that, along with an increase in activity in brain structures responsible for the task, there is a decrease in activity in other areas that are not engaged during...
Article
Behavioral experiments were performed in which rhesus macaques were trained to interact with a computer using a touchscreen. Stimuli consisted of semitone images of Gabor elements with low spatial frequency with different contrast levels. The monkeys’ task was to touch the screen with the paw at the site at which the target stimulus appeared, which...
Article
The paper describes the results of studies aimed at evaluating the effect of interactive virtual environments on the visual system, including the magno-and parvo-systems. Analysis was conducted in patients diagnosed with paranoid schizophrenia diagnosed from one to five years ago. Comparative analysis of visual evoked potentials during the percepti...
Article
The research problem consisted of using the following methods of neuroiconics: digital image processing, functional magnetic-resonance tomography (fMRT) of brain activity, and psychophysical methods to determine under conditions of indeterminacy the minimum information needed to recognize faces with different intensities of the facial expression. I...
Article
We studied the characteristics of evoked potentials recorded during the recognition test based on four types of series of images subjected to the wavelet filtration: images of living objects containing either low frequency or high frequency portion of the spatial frequency spectrum, and imaging of non-living objects in the same two spatial frequenc...
Article
Biederman et al. [1, 2] have shown that the priming effect does not depend on the difference between the angular sizes of the test stimulus and the primer. However, these two and other similar studies investigated only a small range of the angular sizes of stimuli. Vakhrameeva et al. [3] have shown that there exist two perceptionally different size...
Article
In behavioral experiments rhesus macaque monkeys were trained to interact with the computer using a tactile display. We used grayscale Gabor patches of low spatial frequency as stimuli. Monkeys' task was to touch the screen with his hand in the area of the target stimulus, followed by automatic food or juice reinforcement. After two successive corr...
Article
The objective of this research was to compare the features of the shape of the foveolar area with the characteristics of eye movements in reading. To measure the size of the fovea, we used the method of optical coherence tomography of the retina. Based on this method, the diameter of the upper part of fovea (fovea diameter) and fovea bottom (foveol...
Article
The difficulty of lexical processing can explain substantial part of variability in fixation duration during the reading process. Factors like word length, frequency, syntactic and semantic ambiguity impact fixation time. On the other hand, there is not much understanding of how saccades parameters vary depending on the text characteristics. Here w...
Article
The most sensitive methods to detect pathological changes in the visual system are the method of recording visual evoked potentials and the psychophysical method of measuring contrast sensitivity. Described in the literature features of functional disorders of the visual system in patients with multiple sclerosis are controversial. The results of t...
Article
Full-text available
This research is devoted to a study of features of the operation of the neural structures of the human brain responsible for "identification, friend-or-foe" patterns when different instructions are being carried out. Digital-image processing methods are used to synthesize stimuli adequate for the task, consisting of images of optoclones of virtual...
Article
This article gives an analysis of the interconnection of the optical properties of incomplete (fragmented) images and the psychophysical recognition thresholds of objects as necessary conditions for the appearance of visual insight. A well-known method of measuring the perception thresholds of fragmented images-the Gollin test-is proposed for the f...
Article
Full-text available
This paper presents the results of a comparative computer analysis of monochromatic drawings by mentally healthy subjects and patients with schizophrenia. The contours of the images were distinguished in each of the drawings, after which the following characteristics were calculated: the total length of all the contours of the image, the mean size...
Article
Full-text available
The work of an operator in solving two classification problems when working with one image alphabet is studied. From ninety visual stimuli, half of the images contained animate objects, and the other half contained inanimate objects. The first task was to classify the images according to a semantic attribute-whether they contained an animate or ina...
Article
This paper discusses the process of interpreting scenes with the image of a human face, subjected to processing with spatial-frequency filters that simulate the characteristics of the receptive fields of the neurons of the primary visual cortex. A technique was used that makes it possible to give a quantitative evaluation of the interpretation of a...
Article
It is well known that an important function of binocular vision is to increase the SNR. When a signal simultaneously arrives along two channels, it is summed if the channels are statistically independent. The binocular visual acuity can then theoretically be increased by comparison with the monocular value by a factor of root 2, or 1.4. This paper...
Conference Paper
Biederman and co-authors (1992, 2001), has shown that the priming effect in the long-time priming paradigm does not depend on the difference in the angular size between the test stimulus and primer. However, in this and in other similar works both with long-time and short-time priming paradigms only a small range of sizes has been studied. In the p...
Article
Full-text available
Visual contrastometry was used was used to record contrast sensitivity in healthy subjects and patients with schizophrenia. Gabor elements with spatial frequencies of 0.4, 3.6, and 17.9 cycles/degree were presented. Overall, schizophrenia patients demonstrated lower contrast sensitivity at low and intermediate spatial frequencies than normal subjec...
Article
Full-text available
In order to determine the spatial-frequancy characteristics of the visual system of healthy subjects and patients with schizophrenia, we used the contrast comparison of two Gabor gratings with sinusoidal distribution of brightness. The Gabor gratings have low, medium or high spatial frequencies; the neurons of magnocellular and parvocellular channe...
Article
Full-text available
The methods of neuroiconics and functional magnetic-resonance tomography are used to investigate the factors that limit the possibilities of visual search. The influence of an image of a human face hidden in the background on the activity of the observer’s brain was recorded during the task of tracking a moving ring. It is established that images a...
Article
The individual characteristics of macrosaccades during the reading of fairy tales were measured, and the ability of subjects (students of liberal arts colleges) to demonstrate the understanding of the text (moral of tales) by writing a short summary was assessed. The abstracts were estimated by independent experts using a six-point scale. The prepa...
Article
This paper discusses the process of perceiving dynamic images subjected to processing with spatial-frequency filters that simulate the characteristics of the receptive fields of the neurons of the primary visual cortex. A technique was used that makes it possible to give a quantitative estimate of how subjects perceive the emotional state of people...
Article
Full-text available
The effects of typical and atypical antipsychotics on the perception of visual stimuli that preferentially activate magnocellular or parvocellular visual channels have been studied. The threshold contrast sensitivity in healthy individuals and patients with schizophrenia has been recorded. The Gabor-like sinusoidal brightness gratings and spatial f...
Article
Full-text available
The effectiveness of the discrimination of segment sizes by people with different cognitive style parameters – field dependence vs. field independence, analytical vs. synthetic, and flexible vs. rigid cognitive control – was studied. Discrimination effectiveness was assessed in terms of the magnitude of the Ponzo illusion. The magnitude of the Ponz...
Article
Full-text available
Susceptibility to the Müller-Lyer illusion was studied in healthy subjects and patients with schizophrenia. The experiments used images subjected to wavelet filtration and containing spectra consisting of high or low spatial frequencies. Patients at the initial state of the clinical manifestations of schizophrenia were more susceptible to the Mülle...
Article
Full-text available
The study of sensory perception functions in schizophrenia is currently attracting much interest [1-12] and is necessary for our understanding of the relationships between cognitive and sensory percepp tion abnormalities; most likely, a clinical examination should include tests for assessing sensory abnormalii ties. Visual perception is an active p...
Article
Full-text available
The cornea of the human eye is not only refracts the light, but also acts as a convex mirror, which reflects the surroundings. In ophthalmology, an image reflected by its anterior surface is known as the 1st Purkinje image. Characteristics of this image are determined by the properties of the light source and the state of corneal surface. At the pr...
Article
Full-text available
We tested whether visual complexity can be modeled through the use of parameters relevant to known mechanisms of visual processing. In psychophysical experiments observers ranked the complexity of two groups of stimuli: 15 unfamiliar Chinese hieroglyphs and 24 outline images of well-known common objects. To predict image complexity, we considered:...
Conference Paper
Recently growing interest to possible association of amblyopia with structural changes in retina makes it important to investigate the dependence of the human normal visual acuity on the peculiarities of macular retina structures (Repka et al, 2006 American Journal of Ophthalmology142(2) 247-251; Cagini et al, 2009 Current Eye Research34(12) 1036-4...
Article
This paper shows that there currently are difficulties with the traditional interpretation of psychophysical experiments for determining the energy threshold of light perception. The functioning of the retina in the threshold regime is analyzed using models that give a new interpretation of these tests and that take into account the achievements of...
Article
Psychophysical studies of the visual perception of incomplete contour images have been carried out. The images were synthesized by means of wavelets. The wavelets consisted of the difference-of-Gaussians (DoG) function and oriented wavelets whose spectrum is limited both in the frequency range and in the orientation range. The image size and the nu...
Article
The development of methods of digitally synthesizing and processing images has made it possible to use the methods of iconics to deliberately create test images that selectively activate various structures of the visual system. The methods of processing neurophysiological data, including not only images of the activity of the entire brain but also...
Article
Full-text available
Various images of the Müller–Lyer figures have been obtained by digital filtering. The filtered images contained a definite spatial-frequency spectrum, predominantly low, medium, or high frequencies. The filtering was carried out by convolution of the images with wavelets that are the difference of two Gaussoids with half-width differing by a facto...
Article
Full-text available
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 Muller-Lyer illusion. Patients with schizophrenia estimated length of segments of Muller-Lyer figure less precisely. Accur...
Article
Recognition thresholds for incomplete two-dimensional images of three-dimensional objects were measured as the observation angle was changed. A new experimental psychophysical method was developed and programmed for this purpose, this being a modification of the Gollin test, which measures perception thresholds of incomplete outline images. After t...
Article
Full-text available
graph (Mitsar, St. Petersburg, Russia) was used for recording evoked potentials. This encephalograph was used in combination with an apparatus for control of eye movements (SMI, Berlin, Germany and Jan Ober, Poznan, Poland). Matrices consisting of Gabor grids with different orientations were used as visual stimuli. It is well known that images form...
Article
Full-text available
The aim of the present work was to assess the range of angular sizes of fragmented images of objects at which perception of the images was scale-independent. Measurements were made of human subjects' recognition thresholds for the shapes of the objects over a wide range of angular sizes (0.19-50 degrees). The experiments used the Gollin test--a met...
Article
To determine the quantitative ranges of invariance in the visual perception of objects viewed at different distances and different viewing angles, we have provided a set of psychophysical measurements of recognition thresholds of incomplete line drawings (Gollin-test) with different sizes and rotations. New experimental data are presented, relating...
Article
The magno and parvo systems, consisting of large and small cells respectively and showing the greatest differences in temporospatial characteristics, are two of the most interesting channels in the organization of retinotopic input pathways of the human visual system. We tested the hypothesis that selective lesions of fibers of a specified diameter...
Article
This report presents an analysis of studies of the visual perception of fragmented images. Two approaches to the description of brain functioning during the solution of this task are considered: studies of the perception of the statistical properties of global whole images and studies of the perception of images in terms of local higher-order infor...
Article
Based on an analysis of the dark-adaptation regime of the eye, a setup is developed and tested for calculating the illuminances corresponding to the image-perception threshold by an observer equipped with “electronic-vision” devices.
Article
Full-text available
The aims of this study were to identify the locations of areas in the human cortex responsible for describing fragmented test images of different degrees of ordering and to identify the areas taking decisions regarding stimuli of this type. The locations of higher visual functions were determined by functional magnetic resonance imaging (fMRI) usin...
Article
We report here our electrophysiological and psychophysiological studies of the mechanisms by which the visual system recognizes structured images with different levels of ordering. Visual stimuli consisted of textures, i.e., a set of matrixes consisting of Gabor grids. Matrixes differed in terms of the degree of ordering resulting from changes in t...
Article
Full-text available
A new system of subjective methods of measuring resolving power (visual acuity) on the basis of modern standards is proposed in order to solve problems of physiological optics. New principles for constructing tables of optotypes have been developed in accordance with modern methods of iconics. The new set of optotypes makes it possible to extend th...
Article
Full-text available
The aim of the present work was to study the interaction between the optical properties of images of " disappearing" optotypes and their recognition thresholds. The "disappearing" optotypes were figures with complex outlines and had a unique property - they were close to the threshold of recognition and observation, which increases the accuracy of...
Article
Full-text available
Electrophysiological studies were performed to measure the threshold (upper end of range) spatial frequency using visual evoked potentials and comparison with visual acuity neuron 26 healthy subjects. The aim of the present work was to create a method for objective measurement of visual acuity. This was addressed by initial measurements using a uni...
Article
Full-text available
The Gollin test (measuring recognition thresholds for fragmented line drawings of everyday objects and animals) has traditionally been regarded as a test of incomplete figure perception or 'closure', though there is a debate about how such closure is achieved. Here, figural incompleteness is considered to be the result of masking, such that absence...
Article
Perception thresholds were measured for fragmented outline figures (the Gollin test). A new approach to the question of the perception of incomplete images was developed. In this approach, figure fragmentation consisted of masking with multiplicative texture-like noise--this interference was termed "invisible" masking. The first series of studies e...