Separate training of hemispheres to perform visual discrimination in conditions of blocking of interhemisphere transmission by masking.

Subjects were trained to discriminate three figures presented in the left field of vision and three other figures presented in the right field of vision. In these conditions, the two hemispheres usually show identical learning to discriminate the sets of stimuli because the hemispheres in healthy humans can exchange information. In the present study, training was performed in conditions in which, during presentation of stimuli, the opposite visual hemifield was covered by a mask. After training, the recognition of all six figures was compared by presenting them to the left and right visual fields. Each hemisphere recognized figures presented to the cognate hemifield but completely or very nearly failed to recognize figures learned by the other hemisphere. The mask would thus appear to block (completely or partially) the transmission of information from one hemisphere to the other. Thus, it was possible to train the hemispheres separately to recognize different sets of images in healthy subjects.

[Recognition of visual images by separate hemispheres in conditions of masked blocking of interhemispheric transmission]. / Razdel'noe obuchenie polusharii zritel'nomu raspoznavaniiu v usloviakh blokirovaniia maskirovkoi mezhnolusharnogo perenosa.

The subjects learned to recognize three figures presented in the left visual hemifield and three figures presented in the right visual hemifield. During presentation of a stimulus, the contralateral hemifield was overlapped by a mask. After the training, recognition of all six figures presented in the right and left visual hemifields, was compared. Each hemisphere recognizes figures which were learned in the corresponding visual hemifield, but the recognition of figures learned in the opposite visual hemifield was poor. Thus, the ability of the hemispheres to act separately in recognizing different sets of visual images, was established.

Asymmetry of the internal connections of the striate cortex of the cat in the projection zone of the center of the field of vision.

Studies were carried out on the organization of the internal connections of the striate cortex in cats in the projection zone of the center (0-5 degrees) of the field of vision by microintophoretic application of horseradish peroxidase to electrophysiologically identified orientational columns. The area containing neurons showing retrograde labeling in most cases extended in the mediolateral direction. Labeled cells were located in the upper (II, III) and lower (V, VI) layers of the cortex, and the shapes and orientations of the areas containing labeled neurons in these layers coincided. Spatial asymmetry was detected in the distribution of labeled neurons relative to the orientational column studied. Labeled cells were located predominantly medial to the columns, regardless of the distance from the projection of the area centralis. Considering the visuotopical map of field 17, the asymmetry detected here provides evidence that neurons in orientational columns have more extensive connections with neurons of the peripheral part of the cortex. An asymmetrical distribution of "silent" 2 zones around the receptive fields of neurons in orientational columns is suggested, and that these appear to receive influences from the periphery of the visual field.

[The asymmetry of the intrinsic connections of the cat striate cortex in the projection zone of the central visual field]. / Asimmetriia vnutrennikh sviazei striarnoi kory koshki v zone proektsii tsentra polia zreniia.

Spatial distribution of intrinsic connections in the visual field centre projection zone of the cat striate cortex, was investigated. Retrogradely labelled cells formed an oblong area and were found in superficial as well as deep cortical layers. The labelled cells were located mostly medially to the column under study. The revealed asymmetry shows that the orientation column cells have more extended connections with cells representing the visual field periphery. We suppose that the "silent" regions are asymmetrically located in respect to the orientation column cells' receptive fields. This can account for the influence of the visual field periphery.

[Principle of uncertainty in vision]. / Printsip neopredelennosti v zrenii.

When investigating the dependence of the bandwidth of the spatial frequency characteristic (delta F) of the receptive fields of the cat striate cortex on the size (D) of the receptive field it was shown that delta FD = 1.2. Thus in the system of elements performing the processing of information in the visual cortex the inaccuracy of the signal representation in the spatial frequency and in space is related by an uncertainty principle. The size of the constant evidences that the weighting functions of elements are sinusoids or cosinusoids modulated by squarewave impulse rather than by the Gabor elements. The performing of uncertainty principle and the size of the constant are arguments in favour of the hypothesis that the receptive fields of the visual cortex organize a quasilinear basis.

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.

[Relation between the spatial and spatial-frequency characteristics of receptive fields of the cat visual cortex]. / O zavisimosti mezhdu prostranstvennymi i prostranstvenno-chastotnymi kharakteristikami retseptivnykh polei zritel'noi kory koshki.

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.

[Mechanism of responses to movement in the visual cortex neurons unresponsive to light flicker]. / O mekhanizme vozniknoveniia otvetov na dvizheniia u neironov zritel'noi kory, ne otvechaiushchikh na svetovye mel'kaniia.

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.

[Study of the mechanism of directionality of the receptive fields of the visual cortex in the cat]. / Issledovanie mekhanizma direktsional'nosti retseptivnykh polei zritel'noi kory koshki.

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.

[Spatial-frequency characteristics of receptive fields of the cat visual cortex on homogeneous and nonhomogeneous backgrounds]. / Prostranstvenno-chastotnye kharakteristiki retseptivnykh polei zritel'noi kory koshki v usloviiakh odnorodnogo i neodnorodnogo fona.

Spatial frequency characteristics of the cortical receptive fields obtained with sinusoidal gratings were investigated on the background formed by orthogonally oriented gratings or on the homogenous background. The results correspond to the conjecture that the receptive fields as spatial frequency filters are linear independent in orientation.

[Two-dimensional structure of receptive fields of the cat visual cortex]. / Dvumernaia struktura retseptivnykh polei eritel'noi kory koshki.

Two-dimensional spatial-frequency characteristics of receptive fields were obtained when investigating with sinusoidal gratings of different spatial frequency and orientation. The optimal spatial frequency does not change with orientation. Theoretical analysis of the role of limited size of RF shows that RF must be broadband in frequency and orientation. The results show that RF are grating filters.

[Structure of the complex receptive field of the visual cortex in the cat]. / Struktura slozhnogo retseptivnogo polia zritel'noi kory koshki.

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.

[Structure of the simple receptive field of the cat visual cortex]. / Struktura prostogo retseptivnogo polia zritel'noi kory koshki.

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.

[Linear and nonlinear properties of cat visual cortex receptive fields]. / Lineinye i nelineinye svoistva retseptivnykh polei zritel'noi kory koshki.

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.

[Inhibition and space-frequency characteristics of the complex receptive fields of the cat visual cortex]. / Tormozhenie i prostranstvenno-chastotnye kharackteristiki slozhnykh retseptivnykh polei zritel'noi kory koshki.

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.

[Receptive fields of the visual cortex--detectors or filters of spatial frequencies?]. / Retseptivnye polia zritel'noi kory--detektory ili fil'try prostranstvennykh chastot?

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.