Showing papers on "Orientation column published in 1972"

Lateral inhibition between orientation detectors in the cat's visual cortex.

Abstract: Ncurones in the visual cortex of higher mammals respond very selectively to white or black bars at particular orientations in the visual field (Hubel and Wiesel, 1962, 1968). Psychophysical experiments in man have led several authors to suggest that there is mutual inhibition between detectors with slightly different preferred orientations (Andrews, 1965; Blakemore et al., 1970). We now have physiological evidence for such inhibition in the cat.

Hypercomplex cells in the cat's striate cortex.

Abstract: .here has already been some discussion concerning hierarchical versus parallel processing of information in the striate cortex and I would like to add a few comments. Hubel and Wiesel,' in their classical papers, differentiated three categories of cells in the cat's striate cortex. They further suggested a hierarchical model which would explain the organization of the receptive fields of each type of cell. Thus only simple cells would receive a direct excitatory input from lateral geniculate neurons (LGN), and a number of simple cells with a common optimal orientation and slightly offset receptive-field positions would then provide the excitatory input to the complex cells. Finally, different complex cells with a common preferred orientation but again with offset receptive-field positions would provide excitatory and inhibitory inputs to the hypercomplex cells. The inhibitory input to the hypercomplex cell would explain that the sharp reduction in the discharge, as an optimally oriented stimulus, is elongated beyond the excitatory region in the receptive field. If the Hubel and Wiesel model is correct, one would expect a basic similarity between the responses of complex and hypercomplex cells. However, on the basis of the organization of their receptive field, we have been able to differentiate four classes of cells in the cat's striate cortex: simple, complex, and two distinct classes of hypercomplex cells. The majority of hypercomplex cells (Fig. 1, Type 1) have responses very similar to those of simple cells and their receptive fields can be subdivided into

Orientation specificity of visual cortical neurons after head tilt.

Abstract: The orientation specificity of the receptive fields of single neurons in primary visual cortex of the cat varied as a function of sustained head tilt in a sample of 33 cells. The types of variation suggested analogies to certain psychophysical phenomena. Orientation specificity of visual cortical cells may in part be determined by information from non-visual afferent systems.

Color Opponency from Fovea to Striate Cortex

Abstract: fused, there is no difficulty in obtaining yellow from a binocular mixture of red and green. RODIECK: The notion of pure color changes in your experiments is difficult to understand. You use stimuli matched from the photopic luminosity curve and then assume that this will activate only the color system. At the single unit level I don't know what pure color means. Could you clarify this? D E VALOIS: Surely the distinction between pure intensity variations in the stimulus in which the number of photons sent to the retina varies but their wavelength remains constant, and pure wavelength variations in which the number of photons is constant but their wavelength varies can be readily understood. But what is critical for vision is not the number of photons put into the eye, but the number actually absorbed. To effect a pure color change with the total photon catch constant, one must of course compensate for the absorption characteristics of the receptors involved. That is what we approximate in our pure color stimuli. If a unit in the visual path is just adding up in the outputs of the various cone types in the retina, it will be able to respond to pure intensity changes but not to pure color changes. This, in fact, is the case with nonopponent cells. On the other hand, a cell which receives differential input from different cone systems can detect a wavelength change even though the total retinal light absorption remains constant. This, in fact, is what the opponent cells can do. HUBEL: Do all the cells that are not color coded in the geniculate have the same photopic sensitivity function? D E VALOIS : Not completely. There are variations from one cell to another, presumably depending upon the proportion of L to M cones across which the cell is summing. The deviations from the photopic sensitivity function from one nonopponent cell to another are sufficiently small, however, that these cells show little or no response to pure color changes. BURKE: IS there any difference between the retinal ganglion and the geniculate cells in regard to color-coding properties? DE VALOIS: Marrocco (Responses of monkey optic tract fibers to monochromatic lights, Vision Res. In press, 1972) examined ganglion and geniculate cell responses to chromatic stimuli and found no significant differences.

Interaction of Vestibular and Visual Inputs in the Visual System

Abstract: Publisher Summary Psychophysical and neurophysiological experiments about the interaction of visual and vestibular signals in the central nervous system are described in this chapter. A steady visual input (after-image) moves in an otherwise dark visual field perpendicularly as the vestibular receptors are stimulated sinusoidally. The subjective vertical of a human observer, placed in different constant positions in space depends also on the spatial orientation of a striated visual pattern. Microelectrode recordings from single neurons of the primary visual cortex of enckphale isolk cats are used to investigate the interaction of vestibular and visual signals. Single neurons in the primary visual cortex responded to labyrinth d.c.-polarization either with an on-, off- or on-off activation. The activation is strongest during the first second of labyrinth stimulation. The neuronal response to light stimuli is increased by simultaneous polarization of the labyrinth. In some cortical neurons, however, besides an increase of the instantaneous impulse frequency during the light induced excitatory periods also a prolongation of the latency or of the inhibition periods occurred. Hence, the gross electrical stimulus of the labyrinth receptors did not elicit a simple general increase of cortical neuronal activity. The experimental data are believed to indicate a meaningful integration of visual and vestibular signals in the primary visual cortex.

Controle, par le cortex visuel, du groupe thalamique lateral posterieur chez le chat

Abstract: This study mainly concerns the influence of a cryogenic blockade of the primary visual cortex on some posterior thalamic structures in cats. Units were recorded from nn.lateralis posterior, pulvinar, suprageniculatum and the pretectal area; they were tested for their responses to restricted light spots and part of them also to sound. Cats were anaesthetized with chloralose. 1. The extent and characteristics of the visual receptive fields of these units had first to be evaluated in each case. Three different types of responses were identified (isolated burst, inhibition of spontaneous activity, burst + inhibition). The receptive fields were usually large (30 to 100 degrees), always including the foveae and generally displaying a concentric organization with on-off center and on or off periphery. 2. A local temporary cryogenic blockade of the primary visual area ipsilateral to the explored thalamus modified the responses of 75% of the cells tested therefore. These changes consisted in an increase in latency, a decrease in duration of the response (number of spikes or length of inhibition), sometimes leading to a complete temporary disappearance of the response. 3. Similar coolings applied to the contralateral visual cortex were also effective in 50% of the cells thus tested. This contralateral action is likely to take place via subcortical pathways, since it can still be observed after chronic section of the corpus callosum. 4. This control from the visual cortex seems to be modality specific; namely, in cases when cells were responding both to light and to sound, auditory responses were not affected by the cortical cooling. 5. Our conclusion is that the visual cortex exerts a sustained dynamogenic control over visual input into the lateral posterior thalamus.

Unit Responses to Moving Visual Stimuli in the Motor Cortex of the Cat

Abstract: Neurons in the pericruciate cortex of the cat were tested with moving visual stimuli for responses to specific properties of the visual receptive field. Specific response patterns were shown by cells of origin of the pyramidal tract as well as by other cells.