Simulation model of the tuning mechanism in the visual cortex neuron for the perception of Y-shape images

We performed an imitation simulation of receptive fields (RF) of cat cortical neurons in the primary visual cortex, which were able to detect symmetrical and asymmetrical Y-like figures. We investigated the models of the receptive fields of neurons sensitive to Y-like figures through either the convergence from half-bar detectors or disinhibition mechanism. The model of an of the receptive fields of neurons sensitive to Y-like figures through either the convergence from half-bar detectors or disinhibition mechanism. The model of an-like figure detector on the basis of convergence from the angle and orientation detectors was advanced. Tuning of the simulated receptive fields to Y-like figures was compared with their tuning to cross-like figures. It was shown that the detectors of asymmetric Y-like figures are also detectors of a cross, whereas the detectors of symmetric Y-like figures are more sensitive to Y-like figures than to crosses. The features of the model critical for sensitivity to Y-like figures (the shape, localization, and weight of the RF zones) were specified.     

Simulation of the role of intracortical inhibition as a source of sensitivity to cross-like figures

Simulation of receptive fields of striate neurons sensitive to cross-like figures under the blockade of intracortical inhibition was performed. It was shown that without the inhibition, a neuron with convergence of signals from two orientation detectors widens its tuning to a cross in such a way that the tuning becomes invariant to the shape and orientation of the cross. Detector of a cross whose orientation is based on the disinhibition mechanisms becomes a bar orientation detector under conditions of inhibition blockade. Another scheme of receptive field is advanced, in which the inhibitory zones mask tuning to cross-like figures, but the blockade of inhibition unveils such sensitivity. We specified the features of the receptive fields (shape, localization, and weight of their zones), which, being applied in simulation, imitate properties of the real striate neurons sensitive to shape and orientation of a cross-like figures.     

Relative meaning of lines and corners in geometric figures for their recognition by humans

Neurons tuned to line-crossings (corners, crosses, Y-like and three-ray star-like figures) of different shape and orientation rather than to a single bar were found in the area 17 of the cat visual cortex. We studied the relative role of lines and corners of 2D and 3D geometrical figures for their recognition by humans. Probability of figure recognition during its tachistoscopic presentation was compared for the whole (control) and partly masked figures. Sides or corners of the figures were masked to varying degrees and probabilities of correct response were compared. The recognition probability successively decreases with increasing extent of figure masking. This decrease is significantly more pronounced for the figures without corners than for the figures without part of the lines. The relatively greater significance of the corners than sides of geometrical figures for human visual recognition and some possible neuronal mechanisms of this effect are discussed.     

Selective sensitivity of the cat striate neurons to cruciform and angular figures of various orientations

Selectivity and invariability of tuning were studied in 51 neurons of the primary visual cortex (area 17); cruciform and angular figures (CF and AF, respectively) of different configurations and orientations were presented in their receptive fields. Twenty-three neurons, or 45% of the studied cells, demonstrated selective sensitivity to these figures. Their responses considerably (2.38±0.36 times, on average) increased, as compared with those evoked by presentation of a single bar of preferred orientation. In the examined group, 2 cells demonstrated sensitivity both to the CF and AF. A wide range of detector properties related to the CF and AF analysis was found in the analyzed neuronal population. Detectors of configuration of these figures are described. Selective sensitivity to the angle between branches of these figures was observed in 17 neurons, and responses of 2 neurons among them showed invariability to orientation of these figures. Four cells were selective for orientation and were insensitive to configuration, and 4 other cells showed no specific sensitivity to either of these properties, but were sensitive to the appearance of a CF itself in their receptive field (these cells were regarded as invariant detectors of crossing nodes). Data inconsistent with the hierarchic principle of detection of the above properties are presented. Possible mechanisms and functional significance of selective sensitivity of striate neurons to the CF and AF are discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 5/6, pp. 403–412, September–December, 1995.     

Simulation of mechanisms of tuning to incomplete cross-like figures in neurons of visual cortex

We performed a digital simulation of the receptive fields (RF) of cat cortical neurons in the area 17 that are able to detect cross-like figures with partly masked central or peripheral fragments. It was shown that the reciprocal interaction between the RF center and periphery may produce sharp, selective, and pronounced tuning to a cross shape and orientation due to blocking the end-stopping inhibition in the RF by its side-disinhibitory zone. Under conditions of cooperative interaction between the RF center and periphery the sensitivity index (cross/bar response ratio) was typically lower than in the reciprocal model. Features of the model that are critical for sensitivity to cross in cases of small or incomplete figures (the shape, localization, and weight of the RF zones) are specified.     

What image characteristics are selected by neurons in the cat primary visual cortex?]

About 40% of neurons (114/289) studied in the cat area 17 gave a larger (by 3.06 +/- 0.32 times on average) response to a flashed cross, corner or y-like figures centered in the RF than to an optimal single bar. Most such neurons (72%) were found to be highly selective both to shape (angle between the lines) and to orientation of these figures. In the studied neuronal selection we have also found all possible types of invariance of sensitivity to orientation and/or shape of these figures. Separated and combined stimulation of RF center and surrounding area revealed in 44 units summation, antagonism or absence of interaction of these zones by the selectivity index (cross/bar response ratio). Cross-sensitivity was investigated in 85 V1 neurons before, during and after local blockade of GABAA ergic inhibition by microiontophoretical application of bicuculline. Inhibition either emerged or increased cross-sensitivity (32% of cells), or depressed it (36% of cases), while in some neurons it does not influenced the function. Possible mechanisms of the described effects are discussed as well as their functional implication for second-order feature extraction in the visual cortex: selective or invariant sensitivity of neurons to the shape and orientation of the line-crossings.     

A model study of the dynamic mechanisms of the double orientation tuning of the visual cortex neurons]

The dynamics of double orientation tuning of neurons in the visual cortex of cat was studied by means of computer simulation. It was possible to test the role of shape, relative localization and weight of the inhibitory and excitatory zones of a receptive field and the dynamics of these characteristics. It was shown that selective and acute double orientation tuning can be achieved only through changes in the weight of zones in the receptive fields with the end-stopping and lateral inhibitory zones whereas only the presence of the end-stopping inhibitory zone in the receptive field is sufficient during changes in zone localization and area.     

Rabbit visual cortical neurons with simple and complex receptive fields

Receptive fields of neurons of the rabbit visual cortex selective for stimulus orientation were investigated. These receptive fields were less well differentiated than those of the analogous neurons of the cat visual cortex (large in size and circular in shape). Two mechanisms of selectivity for stimulus orientation were observed: inhibition between on and off zones of the receptive field (sample type) and oriented lateral inhibition within the same zone of the receptive field (complex type). Lateral inhibition within the same zone of the receptive field also took place in unselective neurons; "complex" selective neurons differed from them in the orientation of this inhibition. A combination of both mechanisms was possible in the receptive field of the same neuron. It is suggested that both simple and complex receptive fields are derivatives of unselective receptive fields and that "complex" neurons are not the basis for a higher level of analysis of visual information than in "simple" neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 13–21, January–February, 1978.     

Dynamics of tuning to the shape of a cross-like figure in striate neurons

Dynamics of tuning to the shape of cross-like figure flashed in receptive field was studied in 83 striate neurons by the method of temporal slices. Tuning was estimated by the total number of spikes in the response and by this number in successive fragments of the response with 20 ms steps. It was found that only in 11.7% cases neurons showed stable tuning to the same shape of the preferred figure (an angle between its lines), in other cases (88.3%) during response generation this tuning changes being one-phase (7.2%) or two-phase (27.0%), or undulatory (54.1%). Different dynamical reorganization of receptive field zones is discussed as a possible mechanism of the revealed effects as well as their correlation with previously described dynamics of tuning to orientation of a single bar and a cross in striate cells.     

Disinhibition as a mechanism of tuning of cross-like figures in the visual cortex neurons

A discrete neural net was used for simulation of cross-sensitivity in 40% of neurones of the cat visual cortex' area 17th. It is based on disinhibition of the end-stopping inhibition in receptive field from the side-disinhibitory zone. Highly selective or invariant sensitivity of the simulated neurone in respect to shape and orientation of a cross-like figure was observed under changes of location, size and weight of the receptive field zones. The disinhibitory mechanism seems to be critically involved in the selection of the second-order features of the images in the primary visual cortex.     

Spatial properties of goldfish ganglion cells

We systematically classified goldfish ganglion cells according to their spatial summation properties using the same techniques and criteria used in cat and monkey research. Results show that goldfish ganglion cells can be classified as X-, Y-, or W-like based on their responses to contrast-reversal gratings. Like cat X cells, goldfish X-like cells display linear spatial summation. Goldfish Y-like cells, like cat Y cells, respond with frequency doubling at all spatial positions when the contrast-reversal grating consists of high spatial frequencies. There is also a third class of neurons, which is neither X- nor Y-like; many of these cells' properties are similar to those of the "not-X" cells found in the eel retina. Spatial filtering characteristics were obtained for each cell by drifting sinusoidal gratings of various spatial frequencies and contrasts across the receptive field of the cell at a constant temporal rate. The spatial tuning curves of the cell depend on the temporal parameters of the stimulus; at high drift rates, the tuning curves lose their low spatial frequency attenuation. To explore this phenomenon, temporal contrast response functions were derived from the cells' responses to a spatially uniform field whose luminance varied sinusoidally in time. These functions were obtained for the center, the surround, and the entire receptive field. The results suggest that differences in the cells' spatial filtering across stimulus drift rate are due to changes in the interaction of the center and surround mechanisms; at low temporal frequencies, the center and surround responses are out-of-phase and mutually antagonistic, but at higher temporal rates their responses are in-phase and their interaction actually enhances the cell's responsiveness.     

Shape recognition and image orientation in young children]

A comparison was made of recognition of images in the direct and inverse "top-bottom" orientation. A child two and a half years old was to find the test image on the response card or to give a verbal reply. The verbal responses have shown that the child identifies well both the shape and orientation of the images. In experiments with the response card, the presentation of images in inverse orientation did not result in any mistakes in recognizing the shape nor did it prolong the latency of the reaction, and no correlation was found between the orientation of the presented and the response figures. A child trained to find images of both similar shape and orientation is incapable of indicating properly the orientation of an image presented for a limited time period. These facts are interpreted in terms of the hypothesis of multichannel transfer of information about the pattern in the visual system.     

Border ownership from intracortical interactions in visual area v2

A border between two image regions normally belongs to only one of the regions; determining which one it belongs to is essential for surface perception and figure-ground segmentation. Border ownership is signaled by a class of V2 neurons, even though its value depends on information coming from well outside their classical receptive fields. I use a model of V2 to show that this visual area is able to generate the ownership signal by itself, without requiring any top-down mechanism or external explicit labels for figures, T junctions, or corners. In the model, neurons have spatially local classical receptive fields, are tuned to orientation, and receive information (from V1) about the location and orientation of borders. Border ownership signals that model physiological observations arise through finite range, intraareal interactions. Additional effects from surface features and attention are discussed. The model licenses testable predictions.     

Double orientation tuning of cat visual cortical neurons

Orientation tuning of 148 primary visual cortical neurons was studied in acute experiments on unanesthetized, curarized cats by analysis of their spike responses to flashes in a receptive field of a bar of light of optimal size. Orientation tuning of 88 neurons (59%) was found to be bimodal: Besides the principal preferred orientation there was a second, making an angle with the first. The second tuning maximum in some cases (64%) was exhibited only with a change in stimulus intensity or background brightness. Analysis of orientation tuning by the time-slice method, i.e., on the basis of individual cuts of the spike trace, showed double tuning to be present in 69% of cases only at certain moments after the beginning of stimulation. The results of analysis of the model showed that the double orientation tuning effect may be the result of the specific configuration of the receptive field, the use of a stimulus longer than the receptive field, the presence of a series of alternating excitatory and inhibitory zones in the receptive field, and also of end inhibitory zones on the narrow ends of the field. The unequal change in zones of the receptive fields in time explains the appearance of double orientation tuning in individual fragments of the spike trace. The functional role of double, "cross-wise" tuning in some primary visual cortical neurons and their role in the detection of the features of visual patterns are discussed.     

Prediction of orientation selectivity from receptive field architecture in simple cells of cat visual cortex

From the intracellularly recorded responses to small, rapidly flashed spots, we have quantitatively mapped the receptive fields of simple cells in the cat visual cortex. We then applied these maps to a feedforward model of orientation selectivity. Both the preferred orientation and the width of orientation tuning of the responses to oriented stimuli were well predicted by the model. Where tested, the tuning curve was well predicted at different spatial frequencies. The model was also successful in predicting certain features of the spatial frequency selectivity of the cells. It did not successfully predict the amplitude of the responses to drifting gratings. Our results show that the spatial organization of the receptive field can account for a large fraction of the orientation selectivity of simple cells.     

Response to Contrast Objects of the Seven-Spot Ladybird Coccinella septempunctata (Coleoptera, Coccinellidae)

The goal of the work was to establish whether the seven-spot ladybird Coccinella septempunctata has a spatial constancy towards the shape of images. The beetles were presented with black figures on the white wall of the cylindrical arena. The beetles were walking with different orientation of the body relative to the force of gravity: in the horizontal plane, on a three-ray labyrinth or on the flat ring in the bottom of the arena; with an inclination of 90° on the cylindrical ring wall; upwards on the vertical labyrinth or upside down, under a thin wire labyrinth stretched over the arena. The beetles in the horizontal position did not discriminate from each other differently orientated images, except for two types of the figures: vertical or horizontal bands (the choice was 80:20%) and meanders orientated downwards and upwards (the choice was 56:44%). The bands oriented vertically towards the Earth were preferred by the beetles when observed from the inclination position, but not in the case of a vertical ascension. The meanders were not discriminated when observed from the upside down position. The ascending oblique bands were preferred over the descending ones. No ability to discriminate the shape of objects was found in the ladybirds, and, correspondingly, they have no spatial constancy. The discrimination of figures and ornaments has the simplest mechanism: detection of the movement (directional) of a contrast margin.     

Stereopsis and the random element in the organization of the striate cortex.

Receptive field position and orientation disparities are both properties of binocularly discharged striate neurons. Receptive field position desparities have been used as a key element in the neural theory for binocular depth discrimination. Since most striate cells in the cat are binocular, these position disparities require that cells immediately adjacent to one another in the cortex should show a random scatter in their monocular receptive field positions. Superimposed on the progressive topographical representation of the visual field on the striate cortex there is experimental evidence for a localized monocular receptive field position scatter. The suggestion is examined that the binocular position disparities are built up out of the two monocular position scatters. An examination of receptive field orientation disparities and their relation to the random variation in the monocular preferred orientations of immediately adjacent striate neurons also leads to the conclusion that binocular orientation disparities are a consequence of the two monocular scatters. As for receptive field position, the local scatter in preferred orientation is superimposed on a progressive representation of orientation over larger areas of the cortex. The representation in the striate cortex of visual field position and of stimulus orientation is examined in relation to the correlation between the disparities in receptive field position and preferred orientation. The role of orientation disparities in binocular vision is reviewed.     

Laminar distribution of neurons with different types of receptive fields in the rabbit visual cortex

Investigation of receptive fields of 232 primary visual cortical neurons in rabbits by the use of shaped visual stimuli showed that 21.1% are unselective for stimulus orientation, and 34.1% have simple, 16.4% complex, and 18.5% hypercomplex receptive fields, and 9.9% have other types. Neurons with different types of receptive fields also differed in spontaneous activity, selectivity for rate of stimulus movement, and acuteness of orientational selectivity. Neurons not selective to orientation were found more frequently in layer IV than in other layers, and very rarely in layer VI. Cells with simple receptive fields were numerous in all layers but predominated in layer VI. Neurons with complex receptive fields were rare in layer IV and more numerous in layers V and VI. Neurons with hypercomplex receptive fields were found frequently in layers II + III and IV, rarely in layers V and VI. Spontaneous unit activity in layer II + III was lowest on average, and highest in layer V. Acuteness or orientational selectivity of neurons with simple and complex receptive fields in layers II + III and V significantly exceeded the analogous parameter in layers IV and VI.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 19–27, January–February, 1985.     

猫视皮层神经元对光栅反应最优方位在视网膜上分布特性的研究

用金属微电极记录了114个猫皮层17、18区细胞对不同方位光栅图象刺激的反应。细胞最优方位与其感受野中心在视网膜的位置间有系统性关系,即最优方位总是倾向于垂直于各感受野中心与视网膜中心区(area centralis)的连线。这一规律对在18区或17、18区全体记录到的细胞而言,有统计意义。 在17、18区内,仅对于感受野位于视网膜离心度(eccentricity)大于9°视角的细胞、具有较窄感受野(宽度小于2.5°)的细胞以及感受野处于视网膜垂直经线附近的细胞,上述规律才有统计意义,而对感受野离心度小于9°的细胞、感受野宽度大于2.5°的细胞以及感受野在倾斜经线附近的细胞,上述规律不明显。     

Differences in orientation and receptive field position between supra- and infragranular cells of cat striate cortex and their possible functional implications

On the postlateral gyrus of the cat striate cortex the cells' preferred orientation and the location of their receptive fields was measured as a function of cortical depth in penetrations as parallel as possible to the radiating fibres. In most penetrations the majority of infragranular cells showed orientation preferences 45 degrees-90 degrees different from the preferred orientations of supragranular cells. In addition, aggregate receptive fields from the same eye of supra- and infragranular cells were spatially shifted against each other. Using different columnar models these results are discussed in terms of spatial contrast enhancement for two parallel mechanisms in upper and lower layers, determined for pattern discrimination and movement detection.