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T A Shcherbach

Publications and source records attributed to T A Shcherbach.

At least 19 recordsLinked to original sources
PubMed1983

[Mechanism of responses to movement in the visual cortex neurons unresponsive to light flicker].

The responses to moving and stationary stimuli in cat's striate cortical units were studied. Two stationary light bars, one located in the receptive field centre, and another--in the periphery, were used. The sequence of presentation and the time-interval between the stimuli varied thus making the presentation of a pair of stationary bars an analogue of a moving stimulus. Responses occurred in the neurons previously unresponsive to stationary stimuli when two stationary stimuli were presented successively in certain order. A model is proposed explaining the occurrence of responses to moving stimuli in the neurons, unresponsive to stationary ones.

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PubMed1983

[Relation between the spatial and spatial-frequency characteristics of receptive fields of the cat visual cortex].

Spatial (the size and the eccentricity) and spatial-frequency (optimal frequency and the bandwidth) characteristics of receptive fields of the cat visual cortex were studied. The linear and quasilinear receptive fields of equal size were shown, in accordance with predictions of the piecewise Fourier analysis, to constitute a module in every field of which the complexity index (ratio of the field size vs. the number of its optimal frequency periods) equaled the optimal frequency multiplied by a coefficient constant for a given module. Five modules were found with field sizes 2.6 degrees; 3.8 degrees; 5.2 degrees; 6.2 degrees and 7.0 degrees moving toward the visual field periphery as the modules increased in size. According to the predictions, the bandwidth decreases in the reversed proportion to the field size in a fixed complexity index. The data obtained corroborate the hypothesis implying that the receptive fields perform a piece wise quasi--Fourier expansion of an image.

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PubMed1983

[Study of the mechanism of directionality of the receptive fields of the visual cortex in the cat].

The responses of directional-sensitive striate cortex neurons to two light bars one of which was located in the centre of the receptive field and the other--in the inhibitory zone were investigated in unanaesthetized cats. The order of presentation and the time intervals between the stimuli varied; so the presentation of the pair of stationary bars was an analog of a moving stimulus. It was shown that the inhibitory off-zone located on the side of the preferred direction of movement is characterized by an early inhibitory phase followed by a phase of disinhibition and by the second inhibitory phase. The presentation of a pair of stationary bars with different time intervals between them elicited inhibition when the central zone stimulation coincided with the inhibitory phases and facilitation when it coincided with the disinhibitory phase. For the inhibitory off-zone located on the side of the null direction no disinhibitory phase was found. The significance of the time characteristics of the inhibitory zones for the appearance of directional sensitivity in striate neurons is discussed.

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PubMed1982

[Structure of the complex receptive field of the visual cortex in the cat].

This most common type of a complex receptive field was analyzed whose response contains modulated and unmodulated components. Application of the mask covering a half of the field increased (according to the filter theory) the bandwidth of the field as a spatial frequency filter due to appearance or enhancement of the response at lateral low and high frequencies. In this case the modulated components of response from each half of the field are out of phase. Analysis of this fact together with responses to thin light and dark bars permitted describing the structure of the field as consisting of linear and nonlinear subsystems converging on the complex field neuron. The linear system comprises several pairs of on- and off-subfields of corpus geniculatum. On- and off-subfields in the pair are spatially overlapped and converge on a neuron of the linear subsystem with opposite signs. The nonlinear system comprises only on- or off-subfields. Other types of complex fields are formed by various combinations of subsystems. The results evidence that the complex field is a grating spatial frequency filter.

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PubMed1981

[Structure of the simple receptive field of the cat visual cortex].

Comparison of the cat simple receptive field (No. 17) responses to sinusoidal gratings and to thin light and dark bars showed that the excitatory and inhibitory on- and off-zones are composed by on- and off-subfields of corpus geniculatum, converging to the cortical neurons. Each zone comprises a pair of opponent subfields -- excitatory and inhibitory. Such an organization reveals the linear properties of the fields. However a real simple field is a nonlinear system because of available deviations from such an ideal organization. The deviations are manifested in mutual displacement of the subfields, inhomogeneity of the subfields and absence of an antagonistic subfield in the zone. Phasic and tonic subfields may be present simultaneously even within the same field.

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PubMed1980

[Linear and nonlinear properties of cat visual cortex receptive fields].

Impulse responses of the simple fields cat visual cortex were found to be modulated by gratings passing the field. The complex fields proved to be of three types: with modulated responses, unmodulated responses, and with modulated responses against unmodulated background. Amplitude-phase characteristic (APC) measured were inverse Fourier transformed to obtain the field's weighting function. Simultaneously the APC was reconstructed from the responses to edges and bars, with the use of the Fourier transform. Cross-comparison of the reconstructed APC and the WF showed that a RF has some linear properties but, strictly considered, is a non-linear system. Simple fields display the largest degree of linearity. The more complex field is the greater departures from linearity. As linear methods are inadequate for dealing with cortical RFs, their identification was performed in model experiments on a computer. The evidence obtained suggest that the RFs form a system of operators which perform the expansion of the image in non-classical pattern. Such an expansion can be termed quasi-Fourier-description.

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PubMed1979

[Inhibition and space-frequency characteristics of the complex receptive fields of the cat visual cortex].

Responses of complex receptive fields of the cat straitum to moving sinusoidal grating were studied. Stimulation of the receptive field with some spatial frequencies suppresses spontaneous discharges. Responses of the receptive field corroborate previously made predictions that the spatial--frequency characteristics of the receptive field should have the main and the secondary maximums and negative areas in case the complex fields perform piece-wise Fourier--transformation of image. The changes of impulse frequency in field's response are predicted by comparing the changes of instantaneous spectrum of grating entering the field with spatial frequency characteristic of the field. The data evidence that the complex field is rather a spatial--frequency filter than a detector. Some complex fields reveal a lateral inhibitory area behind the field's nucleus in direction of stimulus movement. The complex fields with no lateral inhibitory areas seem to serve for piece Fourier--description of image, those with lateral areas--for picking out the countour between textures.

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PubMed1979

[Receptive fields of the visual cortex--detectors or filters of spatial frequencies?].

Spatial frequency characteristics of the complex cortical visual receptive field were studied in curarized cats. It is shown that, besides the main maximum, they also have additional maxima and negative regions as predicted by the theory of piecewise Fourier-analysis. Comparison of responses of the complex receptive field to sinusoidal grating entering the field completely or incompletely together with the comparison of responses to sinusoidal and squarewave gratings shows the linear properties of the receptive field as a spatial frequency filter. The response of the complex receptive field increases with the number of periods constituting the sinusoidal grating. Several periods of optimal spatial frequency matched the size of the complex receptive field. In the columns of neurons, the receptive fields were found tuned to a broad band of spatial frequencies. The data confirm the hypothesis according to which the complex receptive fields are rather spatial frequency filters than detectors.

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PubMedDate not supplied

Relationship between spatial and spatial-frequency characteristics of receptive fields of cat visual cortex.

The spatial (magnitude and eccentricity) and spatial-frequency (optimum frequency and width of pass band) characteristics of the receptive fields of the cat visual cortex were investigated. It was shown that in accordance with the predictions of the theory of piecewise Fourier analysis, linear and quasilinear receptive fields of a single size comprise a modulus in each of the fields of which the index of complexity (ratio of size of field to number of periods of its optimum frequency) equals the optimum frequency multiplied by a coefficient that is constant for the given modulus. Five moduli were found with field sizes of 2.6, 3.8, 5.2, 6.2, and 7.0 degrees, shifting with increase in the size of the modulus towards the periphery of the field of view. In accordance with predictions, when the index of complexity is fixed the width of the pass band declines inversely proportionately to the size of the fields. The obtained data directly support the hypothesis according to which the receptive fields effect a piecewise quasi-Fourier expansion of the image.

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PubMedDate not supplied

[Adjustment of the cat visual cortex receptive fields to certain spatial frequency bands within definite ranges of movement frequencies of stimulating gratings].

Reactions of simple and composite receptive fields (RF) of the 17th and 18th fields of cat's visual cortex to grating with various spatial frequency moving through the field with different velocities were studied. It has been shown that for each RF the velocity range is revealed within which spatial-frequency selectivity of RF exists. The narrow-band tuning for high frequency RF exists in the range of low velocities, and for low frequency ones in the range of higher velocities.

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