Receptive Field Disparity Research Articles

Pattern of Development of the Callosal Transfer of Visual Information to Cortical Areas 17 and 18 in the Cat

The aim of this study was to investigate the development of visual callosal transfer in the normally reared cat. Two- to nine-week-old kittens and adults (used as controls) underwent section of the optic chiasm. Three days later, the animals were placed under anesthesia and paralysed; unit activities were recorded from visual cortical areas 17 and 18 and from the white matter in one hemisphere. The units were tested for their responses to visual stimulation of each eye successively. Out of 1036 recorded neurons, 185 could be activated through the eye contralateral to the explored cortex via callosal transfer. Most of them could also be driven through the ipsilateral eye via the 'direct' geniculo-cortical pathway. For animals aged > or = 2 weeks, virtually all of these units were located at the 17/18 border zone, with a majority in the supragranular layers. When activated through the corpus callosum, they displayed receptive fields located either on the central vertical meridian of the visual field or in the hemifield ipsilateral to the explored cortex. Such extension into the ipsilateral hemifield as well as receptive field disparities of binocular units decreased with age, while spontaneous activity, strength of response, orientation selectivity and ability to respond to slits moving at middle-range velocity increased. The main conclusion is that the transient callosal projections described by anatomists, which are present until 3 months of age, do not achieve supraliminar synaptic contacts with parts of areas 17 and 18 other than the 17/18 border zone, at least from 12 days after birth. However the visual callosal transfer in young animals displays some characteristics which disappear with age.

Parallel processing of binocular disparity in the cat’s retinogeniculocortical pathways

In the cat, parallel streams of information processing have been traced from X-, Y- and W-type retinal ganglion cells to visual cortical areas 17 (X-, Y- and W-type), 18 (Y-type) and 19 (W-type). In the present study we have examined, in the anaesthetized and paralysed adult cat, the role played by X-, Y- and W-subsystems, projecting to areas 17 and 19, in the processing of binocular retinal disparity. The tapetal reflection technique was used to monitor residual eye movements and to provide a map, for each eye, of the retinal blood vessels which could later be compared with retinal wholemounts stained with cresyl violet to reveal the area centralis. The receptive-field disparities of cells recorded from areas 17 and 19 were compared with each other and with reference to the visual axes defined by the area centralis of each eye. Cells of area 19 (receiving W-type input) had horizontal receptive-field disparities that were significantly more divergent than those of the cells in area 17 and 17-18 'border region'. Referred to the area centralis, the mean horizontal receptive-field disparity in area 19 was -0.5 degrees (+/- 0.8 degrees). The mean horizontal receptive-field disparity of area 17 (receiving X-, Y- and W-type input) was convergent with respect to the visual axis at +2 degrees (+/- 0.5 degrees). Finally, the mean horizontal receptive-field disparity of the cells in the 17-18 border region (which receive mainly Y-type input) was even more convergent (2.6 degrees +/- 1.5 degrees) than that of area 17. Binocular interactions of cortical neurons were tested with the Risley biprism technique. Area 19 cells had maximal responses to binocular stimulation when the receptive-field disparities were either close to zero or slightly divergent. In contrast, area 17 cells tended to respond optimally to disparities that were either slightly or strongly convergent. At the level of the lateral geniculate nucleus there were significant differences between the receptive-field disparities inferred from the comparison of receptive-field positions of adjacent neurons recorded on either side of the border between the A and A1 geniculate laminae and those inferred from a similar comparison at the C1-C2 border. The mean horizontal disparities inferred from the interlaminar comparison at the A-A1 border were +2.1 degrees (+/- 0.3 degrees); those inferred from the interlaminar comparison at the C1-C2 border -0.2 (+/- 0.2 degrees) were more divergent.(ABSTRACT TRUNCATED AT 400 WORDS)

The organization of binocular cortex in the primary visual area of the rabbit.

AbstractA conscious rabbit which crouches in the ‘freeze’ position has an unequivocal 24° wide binocular field formed by the overlap of the two 12° sectors of uniocular optical field which extend nasal of its midline. Although this investigation reveals that the horizontal representation of the uniocular visual field in cortical visual area I extends more nasal than in earlier reports, it is found to terminate at the midline when the eyes are set in the standard freeze position. The 12° sectors of uniocular field nasal of the midline were not represented in spite of being served by retina. The binocular field of the rabbit in the freeze posture thus appears to have no binocular representation in visual area I.Nevertheless, the presence of a binocular region was confirmed in rabbit visual area I but the projections to it, via the contralateral and ipsilateral eyes, deal with the nonoverlapping sectors of monocular field when the eyes are in the freeze position. The maps of the visual field obtained in one hemisphere via the contralateral and ipsilateral projections were subject to a horizontal divergent disparity of some 18°. The presence of binocular single units in these regions was also confirmed but their two receptive fields were necessarily located in different visual hemispheres and again subject to an 18° mean horizontal divergent disparity. They could not be simultaneously stimulated by any localized feature of an object and are thus precluded from involvement in binocular single vision during the freeze position.The systematic, rather than reportedly random, topography of the ipsilateral projection to visual area I ensured that it could be well fused with the similarly organized contralateral projection by means of an 18° vergence of the eyes from the freeze position. The horizontal receptive field disparity of binocular single units is then brought to a zero mean value which enables their receptive fields through each eye to be simultaneously stimulated by the same part of an image. Tested units then evinced response summation; a minimum requirement for binocular vision. In this equivalent primary position of the eyes, the entire binocular visual field is completely represented in visual area one of both hemispheres.The rabbit thus appears to employ a two‐state cortical system for forward vision. In the freeze position the visual field attains a cyclopean extent of 360° but the receptive fields of cortical binocular units are widely divergent. The classic binocular optical field may then project to some other region of brain which subserves binocular vision. Upon examination of a frontal object the animal must verge its eyes in order to obtain binocular single vision in visual area I; it then temporarily surrenders part of its rear visual field. An explanation in terms of ocular image quality is suggested.

Decreasing local stereopsis with increasing horizontal disparity, indicating decreasing density of binocular cortical projection towards the limits of Panum's area (author's transl)

Measuring local stereopsis by means of random dot stereograms with increasing horizontal disparity, the relative density of binocular cortical projection has been determined at a distance of 75 min of arc from the fovea. The accuracy of stereoscopic perception decreased with increasing horizontal disparity. The reciprocal value of the error frequency was used to measure the density of binocular cortical projection. Panum's area at the above mentioned distance from the fovea can be constructed by plotting the error frequency against the horizontal disparity. We observed a decrease of the relative density of binocular cortical projection towards the limits of Panum's area without a sharp break. The results are in agreement with those reported by Bishop and Henry and Joshua in the cat (receptive field disparity). The theory of stereopsis as proposed by Bishop explains our findings well and may be transferred to binocular vision in man.

Disparity sensitivity and receptive field incongruity of units in the cat striate cortex.

1. Receptive field correspondence and binocular interaction were studied in the cat striate cortex using fundus photography for correction of residual eye drifts. 2. The scatter of incongruities (frequently called receptive field disparities) was found to be equal in horizontal and vertical direction (S.D. 0.5 °, N = 96). Incongruity was not correlated with field orientation. 3. Using binocular stimulation, disparity tuning and binocular facilitation were analysed quantitatively in 46 cells. Seven of these were disparity specific, i.e. showed marked facilitation critically dependent on disparity. 4. With monocular stimulation, three of the seven disparity specific cells could be driven only from one eye; one gave weak responses to both left and right monocular stimulation, and one no monocular responses at all. 5. The disparity specific cells preferred vertical or oblique orientations, and vertical disparity was less critical than horizontal disparity. The disparity tuning curves, plotted with reference to the experimentally determined horopter, showed peaks within 0.5 ° crossed and 0.2 ° uncrossed disparity. The smallest half-widths at half-amplitude were 0.25 °. Some of the curves were asymmetric, or step-like, with a steep slope at zero disparity. 6. It is concluded that stereoscopic depth may be signalled by disparity specific cells in area 17. These cells could account for stereoscopic acuity of a few min arc, if one assumes that depth is encoded in the amount of activity of single units, or in the graded imbalance of activity of antagonistic units. 7. It is argued that the distribution of incongruities does not reflect stereoscopic function because the disparity specific cells often cannot be plotted in both eyes, and most of the units that can be plotted are not disparity selective.

Binocular neurons which signal change of disparity in area 18 of cat visual cortex.

BINOCULARLY activated neurones which seem to play a specific role in the detection of retinal image disparity have been described for both cat and monkey visual cortex1–6. The receptive field properties are such that for a given position of the eyes, each neurone will respond to an optimally oriented, moving line only if there is a particular disparity between the images of that line on each retina. As most of the receptive field disparities have a horizontal component, the response is related to movement of the line in a plane at a particular distance. If the plane of the optimally oriented stimulus is moved so it is effectively closer or further from the animal, there is a sharp decrease in the binocular response of the neurone, often to levels below the response to one eye alone4,5. Most of the disparity-specific neurones so far described1–6 are maximally responsive when the disparity is constant, at some particuar value, and cease to respond well when the disparity is changed from that value.

Binocular single vision and depth discrimination. Receptive field disparities for central and peripheral vision and binocular interaction on peripheral single units in cat striate cortex.

Of binocularly-activated striate neurons only a proportion have their two receptive fields in exactly corresponding positions in the contralateral hemifield. Those which are not corresponding are said to show receptive field disparity. Because the eyes diverge in the anaesthetized and paralyzed preparation, the binocular receptive fields are horizontally separate. With increasing retinal eccentricity there is a gradual decrease in this horizontal separation as well as progressive changes in the local receptive field disparities. With increasing horizontal retinal eccentricity there is a progressive increase in horizontal receptive field disparities together with a smaller decrease in vertical disparities. Receptive field disparities are relatively unaffected by increasing vertical retinal eccentricity.

Analysis of retinal correspondence by studying receptive fields of binocular single units in cat striate cortex.

The concept of corresponding retinal points was examined in terms of the binocular receptive fields of neurons in Area 17 of the cerebral cortex of the cat. Only a proportion of the binocular receptive field pairs can be accurately superimposed at the one time in a given plane. The fields which are not corresponding are said to show receptive field disparity. The attempt has been made to establish, on a quantitative basis, the parameters of the receptive field disparities that occur within 5° of the visual axis. A new method was used for defining the zero (vertical) meridian. Very effective paralysis of the extraocular muscles was achieved and the very small residual eye movements that occurred were regularly monitored so that corrections could be applied to the plotted positions of the receptive field pairs. The distribution of the receptive field disparities about the position of maximal correspondence has a range of about ±1.2° (S.D. 0.6°) in both the horizontal and vertical directions for fields in the vicinity of the visual axis. Panum's fusional area may represent the extent to which receptive fields in the one eye, all with the same visual direction, are linked to fellow members of a pair in the other eye over a range of receptive field disparities. A naso-temporal overlap of receptive fields occurs which is probably little if any more than can be accounted for on the basis of the disparity of receptive fields lying along the zero (vertical) meridian. When the extraocular muscles are paralyzed the eyes diverge and the binocular receptive field pairs are separated on the tangent screen. The distribution of the horizontal and vertical separations of the receptive field pairs have been examined.