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M V Danilova

Publications and source records attributed to M V Danilova.

16 recordsLinked to original sources
PubMed2005

Detection of narrow bars when presented in the right and left visual hemifields.

Three series of psychophysical experiments were performed to study the effects of additional images on the contrast thresholds for detection of narrow bars of width 1 arc min and length 1 arc degree presented randomly to the left and right sides of the fixation point with an eccentricity of 4 degrees. The additional images were bars of the same size but with lower contrast, presented to the right and left of the test bar at varying distances, i.e., 1-2 degrees. Different series used different contrast ratios for the test and additional bars. The first series revealed significant predominance of one visual hemifield over the other in performing the bar detection task, though the predominant side varied in different subjects. This predominance disappeared or changed to the opposite side in the second or third series. There was a tendency for the additional images to have asymmetrical influences on the detection threshold for the test bar: additional bars had more extensive inhibitory influences when they were on the peripheral side of the test bar. These data provide evidence for the absence of specificity in hemisphere operation in the detection task. The mechanism of description of peripheral images is discussed.

Contrast Sensitivity↗
PubMed2003

[Contrast detection thresholds during their presentation in right and left hemifields of vision].

We measured contrast detection thresholds for thin black vertical bars (1 min of arc wide, 1 deg long) against a bright background, which were presented eccentrically at 4 deg to the left or right of fixation and flanked on one side by a subthreshold bar having the same dimensions. On each presentation, the stimulus randomly appeared in the left or right visual hemifield. The separation between the test and the flanks varied from 1 to 60-120 min of arc. Different subjects showed better performance in different hemifields. This preference was lost or changed to opposite in the course of training. The central excitatory areas are more or less symmetrical, but inhibitory areas reveal asymmetrical tendency: when flanked bars were more peripheral than the test line, the inhibitory areas were larger. Our results show absence of hemispheric specificity in the line detection task. We discuss the ways of stimulus description in fovea and periphery.

Fovea Centralis↗
PubMed2001

Detection of a gabor patch superimposed on an illusory contour.

Interactions between visual stimuli have been found to be specific to the spatial frequency, orientation and phase of the interacting stimuli. We asked if there are any interactions between luminance-defined Gabor patches and Kanizsa-type illusory contours. In psychophysical experiments we studied whether induction of a vertical illusory line affects detection thresholds for a Gabor patch superimposed on this line and whether these effects depend on the orientation, spatial frequency and phase of the Gabor elements. Employing a 2AFC method with a staircase procedure we measured contrast detection thresholds and varied the orientation, spatial frequency and phase of the test Gabor patch and the separation between the two pacmen in four experimental series. The results show that in a situation where the two inducers generate perception of an illusory line, the contrast detection of the Gabor patch is facilitated relative to a control condition where the rotated pacmen do not induce illusory contours. This facilitation was more pronounced for test Gabor signals that were collinear to the illusory line, but the observer's performance was not altered by changes in the spatial frequency or phase of the Gabor stimuli. With increasing spatial separation of the two pacmen (and, consequently, with a decreasing support ratio), the difference between performance in the test and control conditions diminished. From the data obtained we cannot infer that we have measured some neural interactions between Gabor patches and Kanizsa-type illusory contours, and nor can we draw a unique conclusion about what causes the facilitation of detection of the test Gabor patch in the experimental situation that allows induction of the illusory line. We discuss possible mechanisms of the facilitation, such as contextual influences or a reduction of uncertainty about spatial location of the test Gabor patch.

Adult↗
PubMed1999

Spatial interval discrimination in the presence of flanking lines.

Spatial interval discrimination was studied in the absence or presence of distractors. In the latter case, two flanking lines surrounded two vertical lines delimiting the spatial interval. Using a temporal 2AFC technique with a method of constant stimuli we measured the accuracy of performance (discrimination thresholds) and biases (points of subjective equality) depending on the separations between the target and the flanking lines. For separations less than or comparable to the size of the spatial interval we found both a reduction of precision and the increase of perceived sizes of the spatial intervals: the discrimination thresholds were increased, the size of the spatial interval was overestimated. For larger separations, the size of the spatial interval was underestimated, but the precision of performance was not affected by the presence of flanking lines. We discuss the possible mechanisms underlying spatial interval discrimination in the presence of flanking lines.

Humans↗
PubMed1997

What spatial frequency do we use to detect the orientation of a Landolt C?

We calculated the two-dimensional Fourier spectrum of a Landolt C. For Landolt Cs of orthogonal orientation, the main differences in the amplitude spectrum were found at a low frequency such that 1.3 periods were equal to the size fo the Landolt C, rather than at the high frequency corresponding to the size of the gap, i.e., such that 2.5 periods were equal to the size of the Landolt C. We compared visual acuity assessments obtained with Landolt C optotypes and the cut-off of the contrast sensitivity function measured with sinusoidal gratings. We found that the frequency corresponding to the size of the gap is twice the latter frequency. We suggest that, in fact, this lower frequency can be used to determine the position of the gap.

Fourier Analysis↗
PubMed1996

Three remarks on perceptual learning.

This essay makes three points. (1) From the failure of perceptual learning to transfer when stimulus parameters are changed, it cannot necessarily be concluded that the site of learning is distal: rather, the learning may be central and the specificity may lie in what is learnt. (2) Mere exposure to a stimulus may not be sufficient for learning: even in the absence of explicit feedback, other sources of information are often available in a perceptual learning task. (3) Procedural learning may sometimes be apparent only after a delay: this phenomenon has a long history and is known as reminiscence.

Humans↗
PubMedDate not supplied

Central synaptic neurotransmission: universal self-regulation theory.

A prospective randomized study based on case monitoring and treatment of the patients with chronic tension-type headache was carried out, which revealed the regularities in the effects of basic groups of central neurotropic drugs on clinical manifestations and the EEG data. The patients of control (n=90) and experimental (n=91) groups were followed up for 3 months. The experimental group patients were treated with central neurotropic preparations in addition to the routine medicines having peripheral effects. The control group patients received only the routine preparations. The efficiency was assessed by clinical and EEG criteria. The data obtained were analyzed based on fundamental views of modern experimental neurobiology on the gradual nature of postsynaptic responses and their role in universal process of the central neurotransmission. This analysis led to the views on neurochemical origin of EEG rhythms, which has not been yet defined. A theory is advanced, which is based on clinical experience gained in the process of treatment of various functional CNS disorders in more than 5000 patients. This theory makes it possible to use EEG as an objective criterion of efficiency of neurotropic drugs administered to correct central neurotransmission in the patients with clinical pathological functional disorders of CNS.

Adolescent↗