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Biomedical subjects

N V Prazdnikova

Publications and source records attributed to N V Prazdnikova.

9 recordsLinked to original sources
PubMed1995

[The effect of the destruction of the striate and prestriate cortices on the differentiation of visual images in cats].

The experiments to examine the effects of different visual cortical lesions (area 17 and 21 of the cat cortex) on the image discrimination were conducted. Different image complexity and context of images presentation were established. Cats with area 17 lesion easily discriminated simple objects, and learned only positive image from context. Cats with area 21 lesion learned all experimental conditions. We suggest that intact area 21 carry out selection one object context.

Animals↗
PubMed1984

[Image discrimination after extirpation of the striatal or the lateral suprasylvian areas of the cerebral cortex in the cat].

Selective lesion of the cat striatal cortex lowered the visual acuity although the figure discrimination only became worse in differentiating among certain shapes differing from each other in their high frequency harmonic components of the image's spatial--frequency range. Lesion of the lateral suprasylvian area leaves the visual acuity intact but disturbs differentiation of all images. The data obtained are compatible with previously stated suggestion that rather local and mainly high--frequency description of images occurs in the striatal cortex whereas a more global and mainly low-frequency one takes place in the lateral suprasylvian area.

Animals↗
PubMedDate not supplied

Assessment of contrast sensitivity in kittens after the critical developmental period.

Spatial contrast sensitivity was measured in kittens aged 6, 9, and 12 months and in adult cats. Cats had to open one of two small windows, which had a photograph of a grid, in order to obtain food reinforcement. The nonreinforced stimulus was a photograph of a uniform field of the same mean luminance. Visual acuity was constant in kittens aged 6 to 12 months. However, six-month-old kittens had low contrast sensitivity at low spatial frequencies (< 0.6 cycles/degree). At the age of nine months, contrast sensitivity over this range increased, though the level seen in adult cats was reached only at the age of 12 months. It is suggested that the increase in contrast sensitivity occurring after the critical developmental period in kittens reflects maturation of higher-order cortical fields involved in the process of recognition.

Aging↗
PubMedDate not supplied

[Mechanisms of visual generalization].

The phenomenon of differentiations transfer from grids of different frequency and orientation to bars of different width and orientation was examined by the method of alimentary motor conditioned reflexes elaborated in free behaving dogs. After formation of differentiations of rectangular high-contrast grids by spatial frequency or orientation, transfer to single lines with the width equal to the width of bars forming the grids, leads to a broadening of the range of frequencies and orientations eliciting a positive response. Due to this fact, differentiations disappear or considerably worsen. The obtained results do not agree with the detector hypothesis according to which a part of receptive fields of the visual cortex are detectors of borders or bars of different width and orientation. But the results are predicted quantitatively by the hypothesis of description of images by receptive fields of the visual cortex as by two-dimensional filtres tuned to different spatial frequencies and orientations.

Animals↗
PubMedDate not supplied

[Compensation for disruptions of visual function in the dog after partial exclusion of the neocortex].

The recovery of visual disturbances provoked by partial neocortical deafferentation was studied in dogs with two sets of visual patterns: figures and differently oriented lines. The disturbances were more prominent, when the dogs had to solve the most complex visual tasks (6 stimuli showed to a dog simultaneously). There was a distinct recovery of figure recognition in the process of compensation, i. e. in 4--6 months after the neocortical deafferentation. On the contrary, recognition of oriented lines did not improve. Probably the differences between the two sorts of recognition mentioned above may be explained by various changes of their mechanisms' properties in the process of compensation.

Adaptation, Physiological↗