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Biomedical subjects

V Bozkov

Publications and source records attributed to V Bozkov.

At least 19 recordsLinked to original sources
PubMed1987

Toward the problem of physical and semantic component of the form during eye scanning.

In subjects inspecting random polygonal shapes eye movements were recorded by means of a corneal reflection technique and computer processed. Eye fixations were mostly located around angles. Distribution of fixations over different angles was unhomogenous. Angular rotation changed both semantic meaning of the shapes and the eye fixation distribution. Sequential Markov dependence was found only in cases when semantic interpretation of the shapes was reported by the subjects and was absent when the shapes were perceived as meaning-less geometrical patterns.

Eye Movements↗
PubMed1984

Eye fixation duration during random texture discrimination.

Eye fixation duration during discrimination of pairs of simultaneously presented computer generated random textures differing in 'grain' has been analyzed. Of the shortest duration are fixation periods preceded and followed by local saccades over the same texture and those preceded by local saccade and followed by crossing saccade shifting the eye to the other texture. The longest were fixation periods preceded and followed by crossing saccades. Small difference in 'grain' of both textures was combined by a higher number of crossing saccades between them. The approximate duration of some neural operations taking part in the visual cognitive task studied was hypothesized on the basis of comparing the duration of different types of eye fixation periods.

Discrimination, Psychological↗
PubMed1984

Acoustic stimulus threshold related to EEG alpha and non-alpha epochs.

In humans sitting in the dark with their eyes closed the presence of EEG alpha and non-alpha epochs was registered automatically and the threshold detection of weak acoustic stimuli and reaction time of responses were measured according to the principles of the von Békésy audiometer under both conditions. The threshold was higher during alpha epochs in comparison with non-alpha ones. The reaction time of responses under both conditions was equal. Presentation of the stimulus did not influence the duration of corresponding alpha or non-alpha epochs significantly.

Adult↗
PubMed1983

Visual stimulus threshold related to EEG alpha and non-alpha epochs.

In humans sitting in darkness with open eyes the presence of EEG alpha and non-alpha epochs was detected automatically and the threshold of detection of a dim visual stimulus was measured under both conditions. No differences in threshold were found. However, the reaction times for stimulus detection during alpha epochs were significantly longer than during non-alpha ones.

Adult↗
PubMed1982

Scanning open and closed polygons.

The process of selection of target points during voluntary eye movements when contoured polygonal shapes with open and closed angles are observed was analysed in humans by means of an eye recording technique. It has been found for both types of stimuli that the majority of fixation points where located at angles and that the mean value of distribution was found to be more distant from the vertex for acute angles than for obtuse ones. In this respect a difference was found between open and closed contours. In the former case the mean values of fixation point distribution were more distant from the vertex and the dispersion of eye fixation was greater.

Adult↗
PubMed1982

Eye movements during random texture discrimination.

Eye movements during discrimination of simultaneously presented random textures pairs, differing in increasing mutual transitional probability, were recorded. Increase of difference in the "grain" between images resulted in reduction of crossing eye movements, while the number of saccadic eye movements within each image prior crossing eye movements decreased only slightly. The mean fixation time did not change at all. The principal factor determining the latencies of discrimination was the number of crossing eye movements. The schematized process of discrimination covering several steps is suggested.

Adult↗
PubMed1981

Unconscious and conscious processes during visual perception.

Ongoing unconscious processes may be influenced by related conscious processes without self-awareness. (a) When the conscious semantic interpretation of physically identical shapes changes due to their angular rotation, the sequence of saccadic movements arid the localization of eye fixations over the shapes change as well. (b) The amplitude of the P 300 wave of visual evoked potentials is related to the conscious cognitive interpretation of identical stimuli. (c) The instants of figure reversals are influenced by conscious cognitive programs delineated by means of corresponding experimental instructions. It is assumed that unconscious and conscious processes may be considered functional manifestations of the same complex and specific neuronal network at different levels of its hierarchical organization and that mutual interactions between both types of processes do not require the existence of any mediating "interface" system.

Awareness↗
PubMed1977

Two-dimensional probabilistic images discrimination. I. Simultaneously presented pairs of patterns.

Reaction time and judgment of similarity or dissimilarity were studied in an experiment on two-dimensional probabilistic images (TDPIs) composed of rectangular black and white cells with statistical distribution of these elements 0.5-0.5. The subjects were asked to report verbally whether pairs of TDPIs, presented for 700 ms, appeared to them similar or not. Three sets of TDPIs differed as to the size of their "grain". Within the pairs "physically identical patterns", "statistically same patterns" or "different patterns" have been used. The statistically same patterns pairs reached the lowest (39 percent) judgment correctness. Reaction times for these pairs were generally longer than for others. In the case of identical patterns and statistically same patterns pairs the results indicated a general increase of the processing time as the size of grain had increased. There was a general tendency of reaction time shortening in successive sessions. These results suggest that correct discrimination of TDPIs does not depend primarily upon their grain.

Adult↗
PubMed1975

Various background pattern-effect on saccadic suppression.

It has been proved that the saccadic suppression is a phenomenon closely related to the presence of contours and structures in the visual field. Experiments were performed to clarify whether the structured background influences the pattern of attention distribution (making the stimulus detection more difficult) or whether the elevation of visual threshold is due to the "masking' effect of the moving background image over the retina. Two types of backgrounds were used therefore: those with symbolic meaning in the processing of which "psychological' mechanisms are presumably involved like picture reproductions of famous painters and photographs of nudes, and those lacking semantic significance like computer figures composed of randomly distributed black and white squares with different grain expressed as the entropy of the pattern. The results show that saccadic suppression is primarily a consequence of peripheral mechanisms, probably of lateral inhibition in the visual field occurring in the presence of moving edges over the retina. Psychological factors have to be excluded as being fundamental for saccadic suppression.

Eye Movements↗