Biomedical subjects

S G Korshunova

Publications and source records attributed to S G Korshunova.

9 recordsLinked to original sources

PubMedDate not supplied

Visual evoked potentials induced by illusory outlines (Kanizsa's square).

This report describes studies of visual evoked potentials (VEP) in ten subjects produced in response to Kanizsa's square and a control stimulus which did not involve a visual illusion but which had a similar spatial organization. The results showed that the amplitude-time characteristics of VEP depended on the illusory outlines. Differences in the parameters of VEP produced using the two stimuli were seen in the occipital, parietal, and temporal areas. VEP amplitude differences between the peaks of the N180 and P230 waves increased and the latent period of the N300 wave decreased on presentation of the illusory outlines as compared with the control stimulus. Interstimulus differences in amplitude were seen in the left and right occipital and left temporal areas, while differences in latency were seen in the left occipital lead. The data supported the suggestion that the visual perception system includes two areas encoding illusory outlines, which are associated with different aspects of visual analysis--encoding of individual signs and their complexes (O1 and O2) and comparing sensory codes with codes stored in memory (T5).

Adult↗

PubMedDate not supplied

Relationship between visual evoked potentials and subjective differences between emotional expressions in "face diagrams".

The relationship between visual evoked potentials resulting from substitution of one image of a human "face diagram" for another and assessment of perceived differences between the emotional expressions of these faces were studied. Emotions were altered by changing the curvature of the mouth and/or the slope of the brows. Unlike the traditional approach, in which visual evoked potentials are recorded in response to presentation of a single stimulus bearing a face image, visual evoked potentials in the present study were recorded as the response to instantaneous substitution of a reference stimulus with a test stimulus, and thus represented the direct response to the difference between the stimuli. A characteristic of this approach was the use of a series of functionally associated test stimuli, in which there was a monotonic increase in the difference between the test and references images in terms of the variable characteristics of the stimuli. Analysis revealed differences in the amplitudes of the P120, N180, and P230 peaks in leads O1, O2, P3, P4, T5, and T6, which demonstrated high levels of correlation both with a points-scale assessment of perceived differences between the emotional expressions of faces and with the physical (configurative) differences between images of the same faces as defined by the differences in the orientation angles of lines determining mouth curvature and brow angle. Responses were seen to differences between stimuli for both types of change in pairs of images, both going from reference image to test image and from test image to reference image. Changes in the interpeak amplitude of the P120-N180 potential in the temporal areas of both hemispheres provided the earliest electrophysiological measure of perceived differences between the emotional expressions of human faces. This suggests application of the spherical model for the perception of emotions to specify emotional facial expressions in terms of the activity of line orientation detectors.

Electroencephalography↗

PubMedDate not supplied

[A spherical model of the discrimination of the emotional expressions of a schematic human face].

The four-dimensional spherical emotional space was constructed by multidimensional scaling of visually perceived differences between emotional expressions of schematic faces. In this spherical model Euclidean distances between the points representing the schematic faces are directly proportional to perceived differences of emotional expressions. Three angles of the four-dimensional sphere correspond to specific characteristics of emotions, such as emotional modality (joy, fear, anger, etc.), intensity of emotions, and emotional fullness (saturation). At the same time Cartesian coordinates represent excitations in the neuronal channels encoding line orientations. It was shown that the structure of the emotional space is similar to the structure of color space, i.e., emotional modality corresponds to color hue, emotional intensity to brightness, and emotional fullness to color saturation. The obtained evidence suggests the common mechanisms of information coding in the visual system.

Adult↗

PubMedDate not supplied

[The connection of visual evoked potentials with the subjective differences between emotional expressions of the "schematic face"].

Human cortical visual potentials (VEP) were studied to obtain electrophysiological data concerning face discrimination and to compare them with the direct estimates of differences between faces obtained in the previous publications. The present schematic faces varied in curvature of a mouth and/or declination of eyebrows. These features determined the emotional expression of the schematic faces. We recorded the VEP as the response to the instant replacement of one schematic face (referent stimulus) by an other one (test stimulus) rather then to presentation of a single stimulus. Thus we recorded direct electrophysiological differences between schematic faces. A characteristic feature of this approach was the application of the set of functionally connected test stimuli with monotonously increasing values of differences between the referent and test stimuli. In a result of analysis the complex of components P120-N180-P230 in sites O1, O2, P3, P4, T5, T6 was described. Interpeaks amplitudes of the components shows high correlations with subjective differences between the same pairs of stimuli as well as with physical (configurative) differences between stimuli measured as the angles of lines, defining curvature of a mouth and a declination of eyebrows. The highest correlation with subjective estimates of emotional differences between faces was shown by interpeaks amplitudes N180-P230 in sites O1 and P3. In the some time the interpeaks amplitudes P120-N180 in sites O1 and T5 reflected highest correlation between configurative measures and subjective estimates of stimuli differences.

Electroencephalography↗

PubMedDate not supplied

[A geometrical model for the perceived line of orientation based on subjective evaluations and human VEP data].

A geometric model in proposed based on subjective dissimilarity estimates among differently oriented line segments in the frontal plane and on visual evoked potentials (VEP) recorded in respond to abrupt changes in the orientation of such a line segment. The orientations are represented by points constituting a clised planar curve, with interpoint distances corresponding to interstimulus dissimilarities. The angle of the radius-vertor connecting the center of the configuration with its circumference encodes the orientation of the line stimuli in the visual field, and two Cartesian axes drawn through the center are interpreted as two orientation-opponent channels in the neuronal network processing line orientation. The first channel (the ordinate axis) gives maximal positive and maximal negative responses to, respectively, vertical and horizontal orientations, whereas the second channel (the abscissa axis) gives maximal positive and maximal negative responses to, respectively, 45 and 135 degrees orientations. The VEP analysis shows that the activity of the first channel affects the interpeak amplitudes of both the P1-N2 (P130-N180) and N2-P2 (N180-P230) components, whereas the second channel affects only the late component N180-P230. We propose the hypothesis according to which outputs of the two channels are connected linearly (which is reflected in the city-block metric obtained when distances are computed directly from neuronal activity), but the growth rate of the overall output is inhibited nonlinearly when it reaches large absolute values. This inhibition effectively transforms the "true" city-block metric of the line orientation space into the Euclidean metric one obtains when distances are computed from subjective dissimilarity estimates. VEP amplitudes as intermediate characteristics of visual processing between neuronal activity and subjective estimates represent intermediate metric (between city-block and Euclidean).

Adult↗

PubMedDate not supplied

[Heart rhythm indices during human solving of arithmetic tasks].

Heart rate and respiration were recorded in a group of 90 subjects (25 males and 65 females) aged 17-19 during rest and under informational load (arithmetical tasks) lasting 3 min each. Off-line spectral analysis was performed for all the subjects. Anxiety according to Spilberger and strength of excitation-inhibition according to Strelau were also tested. It was shown that heart rate increased significantly in the group as a whole, however, variability of RR-intervals remained unchanged. Then two subgroups of subjects who responded to information load by a decrease and increase of RR-interval variability were distinguished. These subgroups were characterized respectively by the high and low levels of personal anxiety. The decrease of RR-interval variability in the high-anxiety subgroup was associated with a decrease of power in all frequency bands of the rate spectrum. The increase of RR-interval variability in the low-anxiety subground was due to an increase of heart rate modulation in a low-frequency band of the heart rate spectrum. Fatigue is regarded as a cause of such heart rate modulation.

Adolescent↗

PubMedDate not supplied

[The dependence of the heart rhythm on anxiousness as a stable individual characteristic].

In 90 subjects (25 males and 65 females) aged 17-19 heart and respiration rates were telemetrically recorded with a "Sport" polygraph under conditions of rest and arithmetical load (periods of 3 min each). Spectral analysis of heart rate and respiration and statistical processing was performed off-line by an IBM PC XT with the software package PFE2. Anxiety was tested according to Spielberger State-Trait-Anxiety Inventory with Hanin modification and strength of excitation and inhibition according to Strelau Temperament Inventory. It was shown that the group characterized by the high trait-anxiety had significantly higher resting heart rate and Baevskiĭ index of strain than the group with low trait-anxiety. The groups differed also in R-R interval variability (standard deviation) under arithmetic load. In the group with high trait-anxiety R-R interval variability was lower than in the other group mainly in two frequency bands of R-R power spectrum, i. e., those of respiratory arrhythmia (RA) and Traube-Hering-Mayer waves (THM). Mental load evoked an increase in the heart rate and Baevskiĭ index and decrease in the power of RA and THM frequency bands. Such peculiarities of the heart rate in both groups during the periods of rest and informational load can be explained in the framework of reciprocal relationship between orienting (lower trait-anxiety, lower heart rate, higher R-R interval variability mainly in RA and THM bands of R-R power spectrum) and defensive reflexes (higher trait-anxiety, higher heart rate, lower R-R interval variability, in particular in RA and THM bands of R-R power spectrum.

Adolescent↗

PubMedDate not supplied

[The specific nature of the color and brightness components of the human visual evoked potential].

In order to gain an insight into the electrophysiological cortical mechanisms of color discrimination and to compare the results with psychophysiological data summarized in the previous publications as the spherical model of color discrimination a problem was specified to identify color and brightness components of human evoked potentials. The experiments were carried out with alternating pairs of light flashes constituted of five colors (white and four main colors; red, blue, yellow, and green). Each of the light stimuli varied by seven brightness levels. Color and brightness components (N87 and P120, respectively) were reasonably reliably detected in all cases of substitution of stimuli with identical or different spectra. However, the latency and amplitude analysis of N87 and P120 components in these cases showed that N87 reflects not only color but also brightness information. It makes it possible to draw on the analogy between the N87 as one of the earliest components and N1 in primate cortical evoked potential and suggest that these components reflect the activity of cells receiving information directly from the lateral geniculate body. This process can be considered as the first stage of cortical analysis of chromatic and achromatic light characteristics. The brightness component P120, probably, represents the activity of cortical cells related to the analysis of nonchromatic stimuli characteristics, such as form, movement, orientation, etc. These characteristics are also based on luminance gradients and contrasts, however, in contrast to N87, these characteristics are not directly related with brightness of light.

Analog-Digital Conversion↗

PubMedDate not supplied

[Visual evoked potentials to illusory contours (Kanizsa's square)].

Visual evoked potentials (VEP) were studied in 10 subjects to presentation of illusory Kanizsa's square and control visual stimulus with similar spatial organization, which did not produce a visual illusion. The VEPs to the applied stimuli were expressed in the occipital, parietal, and inferiotemporal areas. It was shown that during presentation of the illusory configuration the amplitude of VEP variation between the N180 and P230 peaks was higher and the N300 latency lower than during presentation of stimuli with real configuration. The difference between VEPs in amplitude were observed in the left and right occipital and left inferiotemporal areas, and differences in latency were pronounced in the left occipital derivation. It is suggested that there exist two contour-encoding regions in the visual system which participate in different kinds of the visual analysis. First, associative visual fields which encode the information on single sings and their complexes and inferiotemporal fields which compare the sensory and memory codes.

Adult↗