Biomedical subjects
Publications and source records attributed to T Radil.
Acoustical sequences were divided by time intervals of various durations, and the performance of finger tappings following the stimuli were recorded. The results proved that it is difficult to synchronize finger tapping with irregular acoustical patterns. The subjects tended to transform the irregular stimulus patterns into more regular response patterns shifted toward interval proportions close to 1:1 or 2:1.
Ten subjects estimated the orientation of elongated random patterns composed of dots or short line segments. The estimated overall orientation of the patterns was influenced by the local orientation of the composing lines. Thus, when they formed an angle of 5.7 deg with the orientation of the least-squared-distances axis (LS-axis) of the pattern there was an effect of 'attraction', and when this angle was 22.9 deg, an effect of 'repulsion'. Estimated orientation coincided with the orientation of the LS-axis for angles of 11.5 and 45.8 deg, and when the patterns were composed of dots. The results point to interactions between different mechanisms involved in orientation perception.
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We have measured the apparent contrast of spatially and temporally sampled gratings having the spatial frequency of 2, 4 and 8 c/deg. A contrast matching task was used in two different sampling conditions which allowed us to stimulate selectively the sustained and transient mechanisms in spatial and temporal vision. The results demonstrate the visual interpolation characteristics in the two domains and suggest a better response linearity for spatial than for temporal interpolation. The strongest nonlinear responses were obtained for temporally sampled medium spatial frequency gratings, suggesting separate temporal processing mechanisms for medium and high spatial frequencies
Step duration, measured in hemiparetic patients walking on a circular path, showed that step duration of the affected foot is usually longer. Functional electrical stimulation of the peroneal nerve in the swing phase of the step (eliminating foot drop) shortened step duration in the majority of cases. Hypnosis induced by the verbal fixation technique was used in hemiparetic patients (a) to ascertain whether the patient's mobility would increase during hypnosis and to determine (in positive cases) whether this approach might be used to predicting the effect of rehabilitation performed by classical methods; (b) to use hypnosis as a method of auxiliary treatment. The general finding was that the extent of movements of the hemiparetic upper extremity considerably improved during and immediately after hypnosis. This effect could be observed both at the level of severe impairment (at the beginning of treatment) and during the later stages when mobility greatly improved due to rehabilitation and recovery.
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Two-dimensional normally distributed random dot patterns were used in two experiments on visual orientation estimation. In the first experiment the patterns differed in their sample correlation and in dot number. In the second one the number of dots was maintained constant but the patterns were generated as a superposition of two normally distributed orthogonal sets composed of different number of dots. In both experiments the estimated orientation depended on stimuli correlation - with increasing correlation the estimated orientation gets closer to the orientation of the least square distance axis of the pattern. Even at very low unsignificant correlations there still remained a hint about stimulus orientation which was not estimated at random. Equalizing consecutively the number of dots in the two orthogonal dot patterns during the second experiment did not result in chance performance either. The bimodal angular distributions of the obtained responses permitted to approach the problem of orientation ambiguity. The results are discussed in terms of optimization processes taking place in the visual system.
A statistical analysis was performed on extracellularly recorded spike trains of spontaneously active mesencephalic reticular neurons of rats. Only stationary records were used for detailed examination. The moments of interspike intervals were computed, hypothesis of renewal process and its specific forms was tested. Implications for statistical methodology are considered on the basis of the results. The main emphasis is laid on the connection between experimental results and stochastic neuronal models.
One-dimensional manual tracking was investigated in relation to cardiac activity. The task of the subjects was, by means of a joy-stick, to maintain a spotlight between two vertical lines moving horizontally across an oscilloscope screen. Error incidence was time-locked with respect to the cardiac cycle. Error rate was higher for faster (2-s trial periods) than for slower (3-s trial periods) target movement. Using linear-ramp and sinusoidal movements, it was demonstrated that error incidence is associated with positive and negative cardiac acceleration.
Rhythmic acoustical sequences consisting of patterns of various complexity (number of intervals in pattern) were generated and subjects were asked to synchronize with them by finger tapping. Deviations between onset of stimuli and onset of response were measured. It has been confirmed that tapping precedes the onset of stimuli by about 20-30 ms. The duration of this anticipatory period increased with an increase in stimulus complexity to the limit of three intervals in pattern. This finding points to a systematic error in timing of rhythmic motor reactions during acoustical following. Its degree depends to a certain limit on the nature of the stimuli. Subjects are subjectively aware of this error.
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