Changes in the number of spikes in the early phasic discharge (50-90 ms from stimuli replacement) of neurons in the rabbit's primary visual cortex were studied under conditions of an instant change in a flashing-line pattern. We used three type of stimulation: lines with different orientations (0-90 degrees) but constant intensity; lines with constant orientation but different intensities; complex stimuli with different intensities and different orientations of lines. Factor analysis made it possible to reconstruct two-dimensional sensory spaces of orientations in 13 of 43 analyzed neurons (30%). In 5 of 30 analyzed neurons (16.6%), both two-dimensional spaces of orientations and two-dimensional spaces of intensities were revealed. Achromatic spaces were reconstructed during changes in the lines of varying intensities but constant orientation. In experiments with complex stimuli, the intensity of lines with orientations varying from 0 to 38.58 degree was 5 cd/m2. The intensity of lines with orientations varying from 51.44 to 90 degrees was 15 cd/m2. In the sensorial space, stimuli with different intensities were located on the plane formed by the first and second significant factors in opposite quadrants, whereas within each quadrant, the stimuli were arranged closely to their orientation from minimum to maximum. We suggest that this type of sensory space reflects the interaction between intensity and orientation attributes of visual stimuli with the factor of intensity prevailing over the factor of orientation. Only 7 (12%) neurons with such complex spaces were found.

Grouping, segmentation, and accentuation – processes involved in stimulus perception – are discussed. These effects are explained in terms of the universal vector coding model in neural networks. Grouping is the combination of objects or events into units on the basis of their similarity. Segmentation, conversely, is the separation of groups to the level of ensembles consisting of small numbers of objects. The processes of grouping and segmentation are regarded from the point of view of their underlying neural mechanisms. It is suggested that stimuli in neural networks are encoded by patterns of excitation of cardinal neurons. These excitation patterns can be represented as excitation vectors. Differences between stimuli are formed as the absolute magnitudes of their vector differences. The greater the perceived stimuli differ from each other, the greater the difference in their perceptual and semantic excitation vectors. The more similar the stimuli, the smaller their vector difference. This suggests that stimuli with similar excitation vectors will be grouped together in perceptual space. Conversely, stimuli with different excitation vectors will “repel” and become segmented. The spatial separation of objects increases with increases in the differences between their spatial excitation vectors. The universality of the vector coding principle can be illustrated using color contrast as an example: differences in contrasting colors increase with increases in the differences between their excitation vectors. Groups of objects with similar excitation vectors are accentuated in perception by means of summation of their excitation vectors. Groups of objects with different excitation vectors undergo mutual accentuation because of the appearance of contrast. Plastic accentuation is associated with the novelty of stimuli and is extinguished on repetition of the stimulus.

Changes in the amplitudes of evoked potentials in the visual cortex of conscious rabbits in response to substitution of flashing lines of different orientations (0–90°) but constant intensity were studied, along with interneurons of different intensities but constant orientation, and complex stimuli with simultaneous changes in flash orientation and intensity. Factor analysis of the results showed that analysis of the N85 peak of evoked potentials produced by substitution of stimuli with different orientations but constant intensity identified a two-dimensional sensory space for orientations. An achromatic sensory space was also detected using substitution of lines of different intensities but constant orientation. Substitution of complex stimuli involved two versions of the experiment. In the first version, four stimuli in the initial orientations (0–38.58°) had an intensity of 5 cd/m2, the other stimuli (with orientations of 51.44–90°) were presented at an intensity of 15 cd/m2. On the plane of the sensory space formed by the first two significant factors, stimuli with different intensities were located in different quadrants of the circle, while within the quadrants themselves, the stimuli were located in accord with their orientations, from lower values to greater. It is suggested that in this version, an interaction between orientation and intensity attributes was seen on the single plane of the sensory space, with a clear predominance of the intensity factor. The other experimental version also included eight complex stimuli, each complex having its own orientation (one of eight over the range 0–90°) and intensity (also one of eight, in the range 5–21 cd/m2). In all experiments involving substitution of complex stimuli, factor analysis identified three to four significant factors. In the vast majority of cases, only the sensory space plane X1, X2 was found, this being formed by two significant factors. On this plane, the stimuli were located in order of changes in intensity. This may be associated with the fact that rabbits are crepuscular animals, such that stimulus brightness is the most important attribute. However, in some cases, potentials in the rabbit brain also demonstrated simultaneous processing of two visual stimulus attributes, i.e., intensity and orientation. This may be evidence indicating analysis of complex stimuli in the primary visual cortex.

Amplitude variations of visual evoked potentials (VEP) in rabbit were studied using changes of three types of stimuli: lines with different orientations (0-90 degree) but constant in intensity, lines with different intensities but constant in orientation, and complex stimuli with different intensities and different orientations. Factor analysis of component N85 of VEP to stimuli with varying orientation and constant intensity revealed two-dimensional sensorial space of orientations. Also, the two-dimensional achromatic sensorial space was revealed for stimuli different only in intensities. In experiments with complex stimuli, two versions of stimulation were used. In the first version, four stimuli with varying orientation from 0 to 38.58 degrees were of 5 cd/m2 in intensity, the remaining four stimuli (from 51.44 to 90 degrees) were of 15 cd/m2 in intensity. In the sensorial space, stimuli with different intensities were disposed on the plane formed by the first two significant factors in the opposite quadrants, whereas within each quadrant, stimuli were arranged according to their orientation from minimum to maximum degrees. It is suggested that, in this version of stimulation, the interaction between two characteristics (intensity and orientation) took place with clear-cut dominance of the factor of intensity. In the second version of the experiments, also eight complex stimuli were used. Each stimulus was characterized by specific combination of orientation (one of the eight directions in the range from 0 to 90 degrees) and intensity (one of the eight intensities in the range from 5 to 21 cd/m2). Three or four significant factors were revealed in each test. Only the plane of intensity of sensorial space (XIX2) formed by two significant factors was revealed in the overwhelming majority of cases. On this plane, stimuli were arranged according to their intensities. This fact can be explained by specific (twilight) type of rabbit's vision with predominant discrimination of intensities. However, some findings suggest that visual evoked potentials reflect simultaneous processing of two characteristics of visual stimuli (intensity and orientation) being indicative of a possibility of the complex stimuli analysis in the primary visual cortex.

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The notion of embedded homogeneity of thin-walled structures is introduced as the property characterizing the provenance of such a structure from a homogeneous material. This property needs to be distinguished from other definitions of homogeneity formulated exclusively in terms of a purely structural constitutive equation. Necessary conditions for embedded homogeneity are derived for planar beams and their geometric interpretation is expressed as the condition for the elastic hodograph to lie on a hypersphere containing the origin of a six-dimensional space of tensors.

The responses of 83 neurons in the rabbit superior colliculus to substitution of color stimuli of different brightnesses and black-and-white stimuli of different intensities were studied. Superior colliculus neurons were found to respond with initial and late phasic discharges (over the periods 50–90 msec and 120–300 msec from the moment of stimulus substitution respectively), along with prolonged tonic discharges whose spike frequencies depended on the intensity of the stimulus. Analysis of the phasic responses of the neurons allowed three groups of cells to be identified. One group of cells (25 of the cells studied, 30%), identified on the basis of early neuron responses, were specialized for detecting brightness differences between black-and-white and color stimuli of different intensities. The sensory spaces reconstructed on the basis of spike discharge frequencies in the early discharges of these neurons were achromatic and two-dimensional. Another group of neurons (16 of the cells studied, 19%) were mainly identified on analysis of late phasic discharges and had four-dimensional spaces with two color and two achromatic axes. The third group of cells (four neurons, 5%) had early discharges with two-dimensional achromatic sensory spaces and late discharges with four-dimensional spaces. It is suggested that reconstruction of the four-dimensional space requires processing of information from the visual cortex on color and intensity differences between stimuli. The sensory spaces of superior colliculus neurons reconstructed on the basis of phasic discharges essentially coincided with the sensory spaces of neurons in the visual cortex and lateral geniculate body and spaces obtained by analysis of the N85 component of visual evoked potentials in rabbits recorded using similar stimulation. This may support the vector coding principle in the visual analyzer.

Conditioned reflex is characterized by plasticity resulting in a bilateral selective input-output linking. In simple nervous systems, input stimuli are represented by selective detectors connected with command neurons through plastic synapses strengthened during associative learning and weakened during extinction. The process of associative learning is due to temporal coincidence of excitation in both detector and command neurons. Short-term memory within a plastic synapses is mediated by phosphorilation of postsynaptic receptor molecules not requiring protein synthesis. Long-term synaptic memory parallels expression of immediate early genes that mediates structural gene expression and protein synthesis. A simple detector-command neuron association becomes more complex in the course of evolution. Input mechanism is supplemented with predetector interneurons preceding detectors. Detector selectively tuned to specific input stimulus is converging on a command neuron constitute selectivity mechanism for conditioned reflexes to complex stimuli. The complication also concerns the output mechanisms. Command neurons become more specialized, and an additional link of premotor interneurons is incorporated between command neurons and motor neurons. Via synapses, the command neurons can produce excitation in a particular set of premotor neurons controlling a specific set of motor neurons responsible for behavioral act configuration. Specialization of command neurons in combination with premotor neuron structures increases the variability of outputs. Conditioned reflexes with more complex inputs and more flexible outputs determine the diversity of acquired behaviors.

Analysis of matrixes consisting of the numbers of spikes evoked by the movement of simple and complex stimuli in cat visual cortex neurons by the principal components method demonstrated vector encoding. The responses of direction detectors to the movement of points and orientation detectors to changes in the angle of a line were encoded independently in areas V1 and V2 of the cortex. Each type of detector was represented by excitation of two cardinal neurons generating sine and cosine functions. The responses of neurons in the associative cortex with selectivity for the direction of movement of specifically oriented bars depended on four cardinal neurons formed by summation of the excitations of the cardinal neurons of the directional and orientational channels.

Changes in activity of 51 neurons in the rabbit lateral geniculate nucleus evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found that neurons displayed the earliest phasic (within 50-90 ms after the replacement) and tonic response components. The earliest component strongly correlated with differences between stimuli, whereas the tonic component depended on stimuli intensity. Analysis of phasic component revealed two neuronal populations: the first group of cells was specialized for stimuli differentiation only by their intensities, and, and the second group could measure differences in colors and intensities. Neuronal perceptual spaces were reconstructed using the average of the earliest response component as a measure of differences between stimuli. Spaces of 44 neurons (86%) were two-dimensional with brightness and darkness axes. Such neurons had the same structures of space for color and achromatic stimuli. Spaces of 7 neurons (14%) were four-dimensional with two chromatic and two achromatic axes. The structures of perceptual space reconstructed from neurons in the lateral geniculate nucleus were identical to the spaces calculated from the neurons in the primary visual cortex. The structure of the perceptual space reconstructed from neuronal spikes was also similar to space calculated from the N85 visual evoked potential component recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. This fact confirmed the general principle of vector coding in the visual system. The tonic component of the most of neurons in the lateral geniculate nucleus showed a linear correlation with changes in intensities, thereby these neurons could be characterized as pre-detectors for cortical selective detectors.

This review discusses the information content of perceptual and semantic evoked potentials arising in humans as a result of instantaneous changes in nonverbal and verbal stimuli. The amplitudes of perceptual and semantic evoked potentials were found to correlate positively with subjects' assessments of the differences between these stimuli. Multidimensional scaling matrixes of evoked potential amplitudes and subjective assessments of differences on pairwise substitution of stimuli showed that the actual colors and color names occupied a four-dimensional spherical color space and were encoded by excitation vectors of identical lengths. Color differences were equal to the absolute differences between their excitation vectors, while semantic differences in color names corresponded to the absolute difference vectors represented by long-term color memory traces. These data were reviewed in the framework of a spherical model of cognitive processes.

Changes in activity of 83 neurons in the rabbit colliculus superior evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found out that neurons displayed the early and late phasic responses (within 50-90 and 120-300 ms respectively, after the replacement) and long-term tonic response component, which depended on stimuli intensity. Analysis of phasic component revealed three neuronal groups. The first group (n=25, 30%) selected on the basis of the earliest component, was specialized to differentiate stimuli only by intensities. The perceptual spaces of these neurons reconstructed on the basis of spike discharge in the earliest response were two-dimensional. The second group of neurons (n=16, 19%) selected on the basis of the late phasic component demonstrated four-dimensional structure of perceptual space. Neurons of the third group (n=4, 5%) possessed a two-dimensional structure of perceptual space reconstructed by the analysis of the early component, whereas analysis of the late response revealed a four-dimensional structure. We suggest that information about differences between stimuli in color and intensity coming from cortical neurons is necessary for the reconstruction of four-dimensional space. The structure of perceptual spaces reconstructed on the basis of phasic responses of neurons in the colliculus superior was similar to the spaces of neurons in the primary visual cortex and lateral geniculate nucleus. The structure of perceptual space reconstructed on the basis of neuronal spikes was also similar to the space calculated from the N85 component of the visual evoked potential recorded under similar conditions. This finding confirms the general principle of vector coding in the visual system.

Changes in activity of 54 neurons in the rabbit visual cortex evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. The diffused stimuli generated by color SVGA monitor were used in the experiments. The earliest response of phasic neurons (50-90 ms after the replacement) was strongly correlated with differences between stimuli in color or intensity. This response ("the signal of differences") was used as a basis of a matrix (8 x 8) constructed for each neuron. Such matrices included mean numbers of spikes per second in responses to changes of different stimuli pairs. All matrices were subjected to factor analysis, and the basic axes (the main factors) of sensory spaces were revealed. It was found that 16 neurons (30%) detected only achromatic differences between stimuli. Perceptual spaces of these neurons were two-dimensional with brightness and darkness orthogonal axes. The spaces of 12 neurons (22%) were four-dimensional with two chromatic and two achromatic axes. The structure of the perceptual space reconstructed from neuronal spikes was similar to the space calculated from the early VEP components recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. The fundamental coincidence of color spaces revealed by different methods may reflect the general principle of vector coding in the visual system and suggests the coexistence of two independent cortical mechanisms of the detection of chromatic and achromatic differences.

The activity of 41 visual cortex neurons and 20 hippocampal field CA1 neurons was studied in rabbits during application of the oddball stimulation paradigm using color stimuli of different intensities. Among these cells, about one third were plastic cells (34% of cortical cells and 37% of hippocampal cells). These neurons showed significant increases in late responses, at times 200–500 and 200–1000 msec for visual cortex neurons and 300–550 msec for hippocampal neurons, to rare deviant stimuli of lesser intensity as compared with responses to the frequent standard stimuli of greater intensity. The initial peak of the response (40–120 msec), the “difference discharge,” remained stable in responses to deviant and standard stimuli throughout the experiment. It is suggested that the strengthening of the late components of neuron responses to rare deviant stimuli (limited plasticity) reflects inclusion of the mechanisms of the orientational reflex.

Concept of neurodarvinism is regarded in the context of simulation of the "natural" and "artificial" selection of neurons, synapses and neuronal groups. "Natural" selection of neurons is based on mobile devices built of neuron-like elements. These devices should be capable for adaptation to real surrounding. "Artificial" selection of neurons is performed using computerized "neurointelligence" model operating in a virtual environment. Comparison of the models suggests the advantage of the integration of these approaches.