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Biomedical subjects

T Radil

Publications and source records attributed to T Radil.

At least 109 records · Page 6Linked 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↗
PubMed1986

DC potential shift preceding repetitive perceptually relevant stimuli and its possible origin.

The Necker cube pattern was flashed repetitively with regular, 5.12 s interstimulus intervals and EEG activity was recorded by means of non-polarizable Ag/AgCl electrodes and averaged. The subjects reported the actual subjective interpretation of the pattern by pushing one of two buttons, i.e. they were motivated to interpret each stimulus. A negative potential shift (lasting about 2.5 s increasing in a more or less linear way and, reaching the final amplitude of about 11 mV), developed gradually before the stimulus onset. Positive correlation was found between the duration and amplitude of DC shift. The phenomenon described might reflect cortical processes related to expectation of a regularly repeated perceptually relevant stimulus and may be considered a version of CNV. A hypothesis interpreting the DC shift as the consequence of neuroglial processes is presented.

Adult↗
PubMed1986

Perceptual ambiguity and stability of reversible figures.

In this work, the results of two experiments on ambiguous patterns are reported, which have been obtained by presenting a series of stimuli designed, in both cases, to reduce gradually the ambiguity of the patterns. Such reduction has been performed by respectively increasing or decreasing the amount of graphic details in the experiments. Data of both experiments show a lengthening of mean reversal time. The increase in the stability of one percept can be regarded as associated with the increasing difficulties encountered by an observer in organizing and restating the alternative "hypothesis" through the perceptual mechanisms. The loss of balance in the durations of percepts is discussed in terms of their different informational contents. Finally, in Exp. 1 an analysis is made to evaluate to what extent an addition of perceptual cues, designed to reinforce a three-dimensional interpretation of a pattern, can influence its figure-ground alternation.

Adult↗
PubMed1986

Simultaneous approach and avoidance learning in the teleost marine fish Serranus scriba Cuv.

The ability of the fish to discriminate between constant light (the conditional stimulus of food) and flickering light (the conditional stimulus of a painful electric shock) administered in random order during the same experimental sessions was investigated. Approaching the light for food and avoiding the shock by moving away from the light could be tought simultaneously, approach learning being faster.

Animals↗
PubMed1985

Psychic state influences electrophysiological correlates of cognition.

The number of white squares (5-10) of different spatial distribution, projected on a screen by means of a tachistosccope, had to be recognized by the subjects. Evoked potentials (EPs) were recorded from occipital skull at the midline. A computer technique was used for EPs classification into two groups according to objective correctness or incorrectness of the subject's answer, subjective certainty or uncertainty about the correctness of the subject's answer, correctness or intentional falsification of the answer, and for separate averaging of the groups of EPs. The amplitudes of late positive potentials of EPs were significantly larger for correct than for incorrect answers, for certain than uncertain judgements and for correct than for intentionally falsified answers (with the exception of highly elaborated false answers).

Cognition↗
PubMed1984

Sequential dependences of perceptual interpretations of a repetitively illuminated reversible figure.

The Necker cube pattern was illuminated by xenon flashes repetitively at different but always regular interstimulus intervals. Subjects pushed one of two buttons corresponding to the subjective perceptual interpretation of the pattern. Analysis of the resulting binary sequences showed that none of the sequences was random. The order of Markovian dependence was higher for sequences with longer (3.6 and 2.4 s) interstimulus intervals than for shorter (1.2 s) ones. This result points to the significance of perceptual sets related to short-term memory mechanism upon perception.

Adult↗
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↗
PubMed1984

Low atropine dose increases the frequency of hippocampal theta activity.

The influence of two doses (6 and 3mg/kg) of atropine (A) on hippocampal theta activity (TA) induced by means of reticular stimlulation was studied in waking rats with implanted electrodes. The higher dose of A depressed TA and the lower dose reduced markedly its incidence. The frequency of TA remaining after A administration increased significantly. The results suggest that A acts in a different way upon the mechanisms responsible for the occurrence of TA and its frequency. An accidental finding was that' A prolongs paroxysmal hippocampal EEG -induced by reticular stmimulation.

Animals↗
PubMed1984

EEG coherence in frontal and occipital region of the brain.

The results of the EEG integral coherence measure I have demonstrated that its values, either total or partial for the alpha band, are higher in frontal brain regions in comparison with the values of occipital regions. This finding can be interpreted as evidence of the corresponding higher level of neuronal communication between frontal structures. Both I values (total and partial for the alpha band) are negatively correlated with the values of power spectra of the corresponding EEG record.

Adult↗