[A new property of orientation-selective neurons of the cat lateral geniculate body].

Neuronal mechanisms of description of local properties of visual object light-shadow surfaces are studied. Earlier we have shown the cat lateral geniculate body (LGB) neurons to have sensitivity to the value and direction of brightness vector in loci of object light-shadow surfaces. Further study of properties of orientational selectivity (OS) of these neurons has revealed that single LGB cells sensitive to direction of the brightness gradient vector also have the classical OS to direction of test bands. Such complex orientational sensitivity of neurons to direction of binary and light-shadow fragments of visual objects is of essential significance, in our opinion, for understanding of principles and mechanisms of object vision.

The sensitivity of neurons in the lateral geniculate body of the cat to the orientation vectors of brightness gradients.

We describe here a new property of visual neurons: sensitivity to the magnitude and orientation of the brightness gradient vector in a test stimulus presented in the receptive field of the neuron. The brightness gradient test image was a spot (diameter 4 degrees) on the dark background of the slide. Brightness changed linearly within the spot. The absolute value of the brightness gradient varied over the range 0.4-2.7 cd/m2 /degrees in the direction of the brightness gradient. The integral brightness in the test spot containing the gradient image was identical for different values of the brightness gradient. The numbers of spikes in the on- and off-responses of on and off neurons in the lateral geniculate body of cats depended on the orientation of the brightness gradient vector in the test stimulus. The sensitivity of neurons to the orientation of the brightness gradient vector, K (the coefficient of sensitivity), was assessed as the normalized difference between the number of spikes in neuron responses in the preferred and non-preferred orientations of the brightness gradient vector in the neuron's receptive field. The mean sensitivity coefficient for 53 cells was 0.55 +/- 0.20. A 6.7-fold decrease in the brightness gradient resulted in a 3.7-fold decrease in the coefficient of sensitivity (for the preferred direction of the orientation of the gradient vector); there was no change in the latent period of responses. The preferred orientation of the brightness gradient vector in the receptive fields of neurons coincided (to within +/-22.5 degrees) with the radial direction on the map of the field of vision in 45% of cases, and with the tangential direction in 26% of cells.

[Sensitivity of the cat lateral geniculate body neurons to orientation of the brightness gradient vector]. / Chuvstvitel'nost' neironov naruzhnogo kolenchatogo tela koshki k orientatsii vektora gradienta iarkosti.

A new property of visual neurons: their sensitivity to orientation and the vector brightness gradient, was revealed and described. Receptive fields of the lateral geniculate body neurons in the cat have preferred orientation maximum reaction (average mean of orientation sensitivity coefficient--0.55 +/- 0.20). The preferred orientation mainly has a radial or tangential trend in the visual field. Temporal characteristics of the neuronal responses were analysed. A role of inhibition processes in the orientation sensitivity is discussed.

[A quantitative assessment of the process of the reflection of the spatial-brightness properties of a stimulus by the neuronal structures in the lateral geniculate body of the cat]. / Kolichestvennaia otsenka protsessa otobrazheniia prostranstvenno-iakostnykh svoistv stimula neironnymi strukturami naruzhnogo kolenchatogo tela koshki.

Correlation between spatial brightness distribution in the test image and the spatial response distribution was estimated for the cat LGB. The correlation was found to be quite high. The data obtained corroborate the hypothesis by Podvigin and Kuperman of the topological correspondence of isophote structure family to the pattern of activity reflecting the test image.

[Role of the visual cortex in organizing eye movements induced by local electric stimulation of the lateral geniculate body of the cat]. / Rol' zritel'noi kory v organizatsii dvizhenii glaz, vyzvannykh lokal'noi élektricheskoi stimuliatsiei naruzhnogo kolenchatogo tela koshki.

Eye movements evoked by local electrical stimulation of the dorsal nucleus of the lateral geniculate body were analyzed in cats with extirpated visual cortex and in intact cats. The experiments were performed in alert cats. There were no differences between the obtained spatial characteristics of eye movements evoked by electrical stimulation in experimental and intact cats. These results suggest that visual cortical areas are not the main and necessary links in the chain for signal transmission (evoked by electrical stimulation of lateral geniculate body) from subcortical parts of the direct visual pathway to acting links of the oculomotor system. The possible pathways for transmission of information from the dorsal nucleus of the lateral geniculate body to structures of the oculomotor system are discussed.

[Types of eye movement patterns induced by electric stimulation of the lateral geniculate body of the cat]. / Tipy kart dvizhenii glaz, vyzyvaemykh élektricheskoi stimuliatsiei naruzhnogo kolenchatogo tela, u koshki.

Three types of eye movement patterns evoked by electrical stimulation of the lateral geniculate nucleus were distinguished in cats. The first type is characterized by parallel eye movements. The second type is formed by goal-direction eye movements, while the third one--by centering saccades. Obtained results are compared with data received by electrical stimulation of superior colliculus and their possible physiological significance is discussed.

[A model of the regulation of involuntary movements of the eye]. / Model' sistemy upravleniia neproizvol'nymi dvizheniiami glaz.

Within the scope of the concepts on the look control mechanism, i. e. the system of interrelated control of head and eye movements a mathematical model is considered which described the control system over eye involuntary movements with quadratic criterion of its work quality. Assuming the optimal character of the control system under study and taking into account the experimental data on the eye movements parameters the relationship between the parameters of the criterion introduced and retinotopic relation of a locus of lateral geniculate is estimated.

[Relation between the spatial characteristics of the receptive fields of the superior colliculi of the cat and the rate of movement of a photic stimulus]. / Zavisimost' prostranstvennykh kharakteristik retseptivnykh polei perednikh bugrov chetverokholmiia koshki ot skorosti dvizheniia svetovogo stimula.

The receptive fields of visual cells in superficial and intermediate layers of the cat superior colliculus were investigated: their boundaries, size, shape, dependence on the velocity of stimulus. The size of the excitatory zone decreased whereas the firing rate of the cells increased when the velocity 3 +/- 180 degrees.S-1 was changed. That was typical of both directionally and non-directionally selective cells. The mechanism of directional selectivity is discussed.

Eye movements in the cat evoked by electrical stimulation of the outer geniculate body.

New data were obtained in experiments with unanesthetized animals showing that electrical stimulation of the structures of the outer geniculate body of the cat elicits goal-directed eye movements. Relationships were found between eye-movement amplitude and direction and the position of the eye at the instant of stimulation, as well as the position of the stimulating electrodes in the outer geniculate body. A scheme is proposed for the multilevel interaction of the visual and oculomotor systems during their functioning, and a possible relation is discussed between the described phenomenon and the mechanisms responsible for the foveation of objects during their recognition.

[Directional selectivity of the neurons of the superior colliculi in the cat: the effect of the rate of movement of a stimulus]. / Direktsional'naia izbiratel'nost' neironov perednikh bugrov chetverokholmiia koshki: vliianie skorosti dvizheniia stimula.

Responses to stimuli moving with velocities of 3-180 degrees X sec-1 were studied in each of four axes (eight directions) separated by 45 degrees in neurons of the cat superior colliculus. 69% of units were directionally selective. In 55% of all the neurons the directional selectivity depended on stimulus velocity and was the largest for high velocities (over 10-30 degrees X sec-1). The preferred direction for some neurons was reversed with velocity increasing. The directional selectivity-velocity relationships were compared for the cat superior colliculus and visual cortex and discussed in regard to probable role of this phenomenon in the oculomotor system.