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Biomedical subjects

J Radilová

Publications and source records attributed to J Radilová.

At least 19 recordsLinked to original sources
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↗
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

Subjective figure reversal in two- and three-dimensional perceptual space.

A permanently illuminated pattern of Mach's truncated pyramid can be perceived according to the experimental instruction given, either as a three-dimensional reversible figure with spontaneously changing convex and concave interpretation (in one experiment), or as a two-dimensional reversible figure-ground pattern (in another experiment). The reversal rate was about twice as slow, without the subjects being aware of it, if it was perceived as a three-dimensional figure compared to the situation when it was perceived as two-dimensional. It may be hypothetized that in the three-dimensional case, the process of perception requires more sequential steps than in the two-dimensional one.

Adult↗