Influence of the presentation of remote visual stimuli on visual responses of cat area 17 and lateral suprasylvian area

Summary Single units were recorded extracellularly from area 17 and lateral suprasylvian area (LSSA) in curarized cats. Visual stimuli, usually a 10 ° black spot, were introduced abruptly in the visual field remote from the discharge area of a neuron's receptive field and moved at a speed of about 30 °/sec. The effect of these remote stimuli (S₂) on the response to a restricted visual stimulus (S₁) crossing the discharge area was studied.It was found that most units in area 17 were not affected by the presentation of remote stimuli, the remainder being either slightly facilitated or slightly inhibited. In contrast the LSSA neurons were usually inhibited by the presentation of S₂: this effect was strong, was present in all classes of LSSA neurons and was independent of the relative directions of movement of S₁ and S₂.On the basis of these data and those previously obtained from the superior colliculus it is concluded that the way the extrageniculate centres respond to a stimulus abruptly introduced in the visual field is substantially different from that of the striate cortex. Only in the extrageniculate centres a new stimulus, besides exciting the neurons which correspond to the position of the stimulus in the field, concomitantly decreases the responses of neurons located in positions of the visual field remote from that stimulus. Possible behavioral implications of the findings are discussed.     

Evidence for corticocortical connections between areas 7 and 17 in cerebral cortex of the cat

This study provides the first evidence of direct corticocortical connections between areas 7 and 17 of the cat. Wheat germ agglutinin horseradish peroxidase (WGA-HRP) was administrated by micro-electrophoresis and micro-injection, respectively, into area 17 and area 7 in different hemispheres in eight cats. WGA-HRP labeled pyramidal neurons were observed primarily in layer 5 of areas 7 and 17 indicating that there are reciprocal connections between these areas. Optical imaging was used to guide WGA-HRP injections to single orientation columns in area 17. After such restricted injections labeled pyramidal cells were observed in layer 5 of area 7. These pyramidal cells were arranged as discontinuous patches extending across a broad region of area 7. These results suggest that feedback from area 7 to area 17 may arise from specific functional columns in area 7.     

Retinotopic order is surprisingly good within cell columns in the cat's lateral suprasylvian cortex

Summary The retinotopic map in the striate-recipient region of the cat's lateral suprasylvian cortex (referred to here as the lateral suprasylvian area (LS)) has generally been described as quite disorderly. The disorder is commonly attributed to receptive field scatter within cell columns, reflecting the very large size of receptive fields. However, scatter within columns has never been investigated. In the experiments reported here, we examined the receptive field scatter of cells in columns, and also the scatter of a limited sample of their afferents arising from areas 17 and 18. To measure post-synaptic receptive field scatter, electrode penetrations were made parallel to columns in LS, with the electrode approaching from the medial side, traversing the suprasylvian gyrus and emerging into the suprasylvian sulcus. In all 13 such penetrations, receptive fields were clustered together despite their large size. Their centers were scattered over a region that occupied on average less than 20% of the largest field in the column. In contrast, in columns in areas 17 and 18 receptive field centers reportedly are dispersed over regions about equal to the largest of the fields (Hubel and Wiesel 1962, 1965, 1974).The scatter of afferents' receptive fields was assessed anatomically by measuring the overlap between patches of different anterograde tracers in LS. These patches represented terminal labeling from two adjacent or overlapping tracer injections in area 17. While a large degree of overlap would be predicted if afferents have substantial scatter, we found the overlap to be small unless the two injection sites themselves were highly overlapping.Scatter in afferents' receptive fields was measured more directly by physiological recording. In previous experiments, cells in LS were silenced by the local injection of kainic acid, and responses were recorded from axon terminals arising from areas 17 and 18 (Sherk 1989). We examined the receptive field scatter in three penetrations made approximately normal to the cortical surface. Scatter was modest, much less than predicted by the size of post-synaptic receptive fields. Because the degree of receptive field scatter for postsynaptic cells in LS was similar to that of inputs from areas 17 and 18, the scatter of these inputs might be entirely responsible for that seen postsynaptically. Postsynaptic receptive field scatter, on the other hand, was too small to explain the reported disorder in the map in LS.     

Functional compensation in the lateral suprasylvian visual area following bilateral visual cortex damage in kittens

Summary Previous studies have shown that functional compensation is present in the cat's posteromedial lateral suprasylvian (PMLS) area of cortex after damage to areas 17, 18, and 19 (visual cortex) early in life but not after damage in adults. These studies all have investigated animals with a unilateral visual cortex lesion, whereas all behavioral studies of compensation for early visual cortex damage have investigated animals with a bilateral lesion. In the present experiment, we investigated whether functional compensation also is present in PMLS cortex after a bilateral visual cortex lesion early in life. We recorded from single neurons in the PMLS cortex of adult cats that had received a bilateral lesion of areas 17, 18, and 19 on the day of birth or at 8 weeks of age. We found that PMLS cells in both groups of cats had functional compensation (normal direction selectivity and ocular dominance) similar to that seen after a unilateral lesion at the same ages. These results are consistent with the hypothesis that PMLS cortex is involved in the behavioral compensation seen after early visual cortex damage. In addition, the results indicate that inputs from contralateral visual cortex are not necessary for the development of functional compensation seen in PMLS cortex.     

A comparison of magnification functions in area 19 and the lateral suprasylvian visual area in the cat

A retinotopic map can be described by a magnification function that relates magnification factor to visual field eccentricity. Magnification factor for primary visual cortex (VI) in both the cat and the macaque monkey is directly proportional to retinal ganglion cell density. However, among those extrastriate areas for which a magnification function has been described, this is often not the case. Deviations from the pattern established in V1 are of considerable interest because they may provide insight into an extrastriate area's role in visual processing. The present study explored the magnification function for the lateral suprasylvian area (LS) in the cat. Because of its complex retinotopic organization, magnification was calculated indirectly using the known magnification function for area 19. Small tracer injections were made in area 17, and the extent of anterograde label in LS and in area 19 was measured. Using the ratio of cortical area labeled in LS to that in area 19, and the known magnification factor for area 19 at the corresponding retinotopic location, we were able to calculate magnification factor for LS. We found that the magnification function for LS differed substantially from that for area 19: central visual field was expanded, and peripheral field compressed in LS compared with area 19. Additionally, we found that the lower vertical meridian's representation was compressed relative to that of the horizontal meridian. We also examined receptive field size in areas 17, 19, and LS and found that, for all three areas, receptive field size was inversely proportional to magnification factor.     

Cortical connections of the anteromedial extrastriate visual cortex in the rat

Summary Efferent and afferent connections of the visually responsive cortex (area anteromedial, AM) located in the anterior portion of area 18b were studied with degeneration and horseradish peroxidase (HRP) methods following small lesions and HRP injections into this area. Degenerating axons, terminals and retrogradely HRP-labeled neurons were observed in a broad region of the cortex including areas located lateral, medial and anterior to the striate cortex. The main finding of this study is that connections of area AM with area 18a are distributed in discrete patches whose arrangement is similar to that of the lateral extrastriate visual areas postulated in previous physiological and anatomical reports. These results thus suggest that visual area AM is reciprocally connected with visual areas in area 18a. Area AM is also connected with other regions within area 18b, thus supporting the notion advanced by recent studies that area 18b contains more than one visual area. A weak afferent connection to area AM from the dorsal lateral geniculate nucleus of the thalamus was noted. Previously described connections of area 18b with areas 8 and 29 as well as with the lateral and latero-posterior thalamic nuclei were confirmed in the present study.     

Functional differentiation between the anterior and posterior Clare-Bishop cortex of the cat

Summary A total of 783 cells were studied extracellularly in anterior (A10–13), posterior (A4–8), and intermediate regions (A8. 1–9.9) of Clare-Bishop (CB) cortex of the cat, which were defined according to the anteroposterior coordinate of the stereotaxic axis and probably corresponded to the antero- (AMLS), postero-medial lateral suprasylvian cortex (PMLS), and the border region between the two subareas, respectively. The study was conducted under N₂O anesthesia supplemented with continuous infusion of short-lasting anesthetics (Saffan, Glaxo or Etomidate, Janssen), using three types of visual stimulators presenting two- (2D) and three-dimensional (3D) motion stimuli, and visual cues contained in the 3D motion. Neuronal responsiveness was essentially similar between the anterior and posterior CB subdivisions. Both areas contained 1) AP, 2) RC and 3) FP cells, selectively responsive to approaching, recessive and fronto-parallel motion, and 4) NS and 5) U cells, nonselectively responsive and unresponsive to any of these motions. However, a quantitative difference was found: 1) In the posterior CB the FP cell population was the largest, and the frequency reduced in the order of AP, NS, RC and U cells, while the largest population in the anterior CB consisted of the AP and U cells, and the frequency reduced in the order of FP, RC and NS cells. 2) 3D (AP and RC) cells in the posterior CB responded preferentially to approaching motion at a distal range, while those in the anterior CB preferred motion at a proximal range. 3) The 3D cells in the posterior CB were more sensitive to the motion cue and demonstrated lower thresholds for the size cue than the anterior CB cells. 4) The anterior CB cells generally demonstrated high-pass velocity tuning (cut-off around 10°/s) for monocular 2D stimulation, while the posterior CB cells demonstrated a broad band-pass tuning (4–120°/s). These findings suggest functional differentiation in neuronal representation of 3D motion signals between the two subdivisions of CB cortex.     

Projections from the cytochrome oxidase modules of visual area V2 to the ventral posterior area in the macaque

The ventral part of the third visual cortical complex, the ventral posterior area (VP) or V3v, is located between the ventral half of visual areas V2 and V4. Because of its location and the physiological properties of its neurons, VP has been considered to be involved in the ventral stream visual areas. The ventral stream visual areas such as V4 and TEO receive projections from the cytochrome oxidase (CO)-rich thin stripes and CO-poor interstripe regions of V2; however, which CO-modules project to VP remains unclear. Moreover, it is not clear whether V1 projects to VP. We injected retrograde tracers into VP and found that VP receives projections from V2 neurons not only in the CO-rich thin stripes and CO-poor interstripe regions but also in the CO-rich thick stripes. We also confirmed the virtual absence of inputs from V1 to VP. These results support the hypothesis that VP constitutes a distinct extrastriate visual area and also suggest that, in addition to color and shape information, VP may also process visual information related to space and disparity.     

Retinotopy of cortical connections between the striate cortex and extrastriate visual areas in the rat

Previous studies have determined that the striate cortex of the rat is reciprocally connected with multiple extrastriate cortical areas that are retinotopically organized. The objective of this study was to investigate the retinotopy of the striate-extrastriate connections in the rat, by placing triple or double injections of fluorescent tracers (fluorogold, fast blue, rhodamine dextran, or rhodamine-labeled microspheres) in different regions of the striate cortex (Oc1) and mapping the distribution of cells and fibers labeled with the different tracers in the lateral (Oc2L) and medial (Oc2M) extrastriate cortex. The tracer injection sites were visualized in tangential sections of the flattened cortex and correlated with the myelin layout of the striate cortex and with an electrophysiological map from previous studies. The results showed retinotopically organized Oc1 connections with ten different extrastriate cortical areas. The location of these extrastriate areas and the retinotopy of their striate connections remained mostly invariant despite changes of the injection sites in Oc1. Thus, the quadrantic retinotopy was obtained for striate connections to areas posterior, posterolateral, lateromedial, laterointermediate, laterolateral, anterolateral and rostrolateral in Oc2L; and to areas posteromedial, anteromedial, and anterior in Oc2M. The present anatomical map correlates well with electrophysiological maps of the rat extrastriate cortex from previous studies. Furthermore, they provide a definition of the retinotopy of some areas that have not been completely mapped before. These results reaffirm the existence of multiple extrastriate visual areas in the rat.     

The primate visual system after bilateral removal of striate cortex

Summary This study examined the strategies used by monkeys lacking striate cortex to perform visual pattern discriminations. Complete bilateral removal of area 17 initially produced severe visual impairment with recovery of even rudimentary visual capacities (e.g., flux discrimination) dependent on gradually retraining the monkeys through a set of increasingly more complex pattern discriminations. After extended periods of postoperative testing, however, three of five monkeys lacking striate cortex were able to discriminate a number of complex visual patterns even when such local stimulus cues as amount of contour and number of elements were equal. Further testing demonstrated that these animals could distinguish a pattern's spatial organization. They were also able to transfer good performance to tasks with novel patterns.This work was supported by USPHS Grants NS 10576 and EY 02941, and by the Veteran's Administration Research Service to E. G. Keating     

Increased oxidative metabolism in middle suprasylvian cortex following removal of areas 17 and 18 from newborn cats

We measured changes in metabolic activity in middle suprasylvian (MS) cortex of cats subjected to early or late removal of areas 17 and 18 to localize shifts in activity possibly indicative of regions within MS cortex that may receive expanded inputs and be involved in the sparing of some visual behaviors following early primary visual cortex damage. Cytochrome oxidase (CO) activity was measured in MS cortex of mature, intact cats and of others with areas 17 and 18 removed in adulthood (P180), or on postnatal day 28 (P28) or postnatal day 1 (P1). Not less than 9 months after the ablation, brain sections were prepared and reacted for the presence of CO. The density of CO reactivity in each of the six cortical layers in MS cortex was measured and standardized against densities from ventral periaqueductal gray or hypothalamus on the same section. Following lesions on P1, significant increases in CO activity occurred in deep layer III and in layer IV of the medial bank of the MS sulcus, including all of area PMLS and the posterior portion of AMLS. In contrast, there were no significant differences in the level of CO activity among P28, P180, or intact cats for any of the cortical layers, and all had lower levels than the P1 cats. This metabolic change provides an anatomical marker for localizing adjustments in MS cortex and can be linked to amplified projections into MS cortex from the thalamus (LPm and A and C laminae of the dorsal lateral geniculate nucleus) and ventral posterior suprasylvian cortex following P1 ablations. Furthermore, this neurochemical analysis implicates a distinct region of MS cortex as the cortical locus of some spared visual functions following early primary visual cortex damage.     

The effect of aging on the neuronal population within area 17 of adult rat cerebral cortex

The brains of Sprague-Dawley rats in various age groups from 3 to 33 months were fixed by perfusion with standard aldehyde solutions in order to determine the effects of aging on neuronal numbers. Several indices of cortical volume were then measured to determine whether neuronal packing densities were affected by age-related change in cortical volume. The lengths, heights and widths of individual hemispheres for 160 animals ranging in age from 1 day to 36 months were first determined, after which blocks of tissue were removed from area 17 of some of the brains. These blocks were osmicated, embedded in Araldite and sectioned at 1 micrometer to ascertain, in the vertical plane, the thickness of area 17 and, in the tangential plane, the packing density of the clusters of apical dendrites extending from layer V pyramidal neurons. Results indicate the overall dimensions of the cerebral hemispheres increased until 3 months of age, after which there was no further increase in size. Between 3 and 33 months of age there was no age-related change in either the thickness of area 17 or in the separation between dendritic clusters, indicating the volume of area 17 did not change after 3 months of age. Within individual age groups the amount of variation present is greater than that among age groups. Since the number of nucleus-containing neuronal profiles per unit area of layers II/III, IV, V, VIa and VIb was similar in two groups of three animals at 3 and 33 months of age and the diameters of neuronal nuclei were unchanged, there seems to be no significant change in the number of neurons contained in these layers of rat visual cortex between 3 and 33 months of age. It is therefore concluded that no neurons are lost from area 17 as the mature cerebral cortex ages.     

The effect of aging on the neuronal population within area 17 of adult rat cerebral cortex

The brains of Sprague-Dawley rats in various age groups from 3 to 33 months were fixed by perfusion with standard aldehyde solutions in order to determine the effects of aging on neuronal numbers. Several indices of cortical volume were then measured to determine whether neuronal packing densities were affected by age-related change in cortical volume. The lengths, heights and widths of individual hemispheres for 160 animals ranging in age from 1 day to 36 months were first determined, after which blocks of tissue were removed from area 17 of some of the brains. These blocks were osmicated, embedded in Araldite and sectioned at 1 micrometer to ascertain, in the vertical plane, the thickness of area 17 and, in the tangential plane, the packing density of the clusters of apical dendrites extending from layer V pyramidal neurons. Results indicate the overall dimensions of the cerebral hemispheres increased until 3 months of age, after which there was no further increase in size. Between 3 and 33 months of age there was no age-related change in either the thickness of area 17 or in the separation between dendritic clusters, indicating the volume of area 17 did not change after 3 months of age. Within individual age groups the amount of variation present is greater than that among age groups. Since the number of nucleus-containing neuronal profiles per unit area of layers II/III, IV, V, VIa and VIb was similar in two groups of three animals at 3 and 33 months of age and the diameters of neuronal nuclei were unchanged, there seems to be no significant change in the number of neurons contained in these layers of rat visual cortex between 3 and 33 months of age. It is therefore concluded that no neurons are lost from area 17 as the mature cerebral cortex ages.     

The projection of the visual cortex on the Clare-Bishop area in the cat

Summary Following large lesions of the cat visual cortex, the distribution of degenerating terminal boutons in the Clare-Bishop area was studied electron microscopically. Degenerating boutons were found throughout the cortical layers but mostly in layer III (51% of the total number of degenerating boutons) and layer V (24%). A smaller number of boutons were found in layers II (12%) and IV (9%), and very few in layers VI (3%) and I (1%). No degenerating terminals were observed in the upper two-thirds of layer I. Seventy-six per cent of the total degenerating boutons terminated on dendritic spines, 22% on dendritic shafts, and 2% on somata. Some degenerating boutons made synaptic contacts with somata and dendrites of nonpyramidal neurons. For example, one degenerating bouton was observed in contact with an apical dendrite of a fusiform cell. Three examples of dendritic spines, with which degenerating boutons made synaptic contacts, were found to belong to spinous stellate cells. No degenerating boutons were observed making synaptic contacts with profiles that could conclusively be traced to pyramidal cell somata.     

Orientational influences of layer V of visual area 18 upon cells in layer V of area 17 in the cat cortex

We examined the orientation tuning curves of 86 cells located in layer V of area 17, before, during, and after focal blockade of a small (300-m diameter) region of near-retinotopic register in layer V of area 18 of quantitatively established orientation preference. Such focal blockade revealed three distinct populations of area 17 layer V cells-cells with decreased responses to stimuli of some orientations (21%), cells with increased responses to stimuli of some orientations (43%), and cells unaffected by the focal blockade (36%). These effects were clearcut, reproducible, and generally directly related to the known receptive field properties of the cell recorded in area 18 at the center of the zone of blockade. These effects were also analyzed in terms of alterations in orientation bandwidth in the cells in area 17 as a result of the blockade-bandwidth increases (22%) and decreases (24%) were found; however, these changes were essentially unrelated to the measured receptive field properties. Inhibitory and excitatory effects were most pronounced when the regions in areas 17 and 18 were of like ocular dominance and were of similar orientation preference. Inhibitory effects (suggesting a normally excitatory input) were most dependent upon the similarity of receptive fields; excitatory effects (suggesting a normally inhibitory input) were less heavily dependent.     

Enhancement of oblique effect in the cat's primary visual cortex via orientation preference shifting induced by excitatory feedback from higher-order cortical area 21a

It is often suggested that the oblique effect, the well-known phenomenon whereby both humans and animals are visually more sensitive to vertical and horizontal contours than to oblique ones, is due to the overrepresentation of cardinal orientations in the visual cortex. The functional role of feedback projections from higher-order cortical areas to lower-order areas is not fully understood. Combining the two issues in a study using optical imaging here, we report that the neural oblique effect was significantly enhanced (3.7 times higher than the normal) in the cat's primary visual cortex through orientation shifting induced by excitatory feedback from the higher-order cortical area 21a. This suggests that a reciprocal co-excitatory mechanism may underlie the perceptual oblique effect.     

Single-unit analysis of pattern-motion selective properties in the middle temporal visual area (MT)

Summary The middle temporal visual area (MT) in macaque extrastriate cortex is characterized by a high proportion of neurons selective for the direction of stimulus motion, and is thus thought to play an important role in motion perception. Previous studies identified a population of cells in MT that appeared capable of coding the motion of whole visual patterns independent of the motions of contours within them (Gizzi et al. 1983; Movshon et al. 1985). These pattern-motion selective neurons are unlike motion sensitive cells that have been observed at earlier stages of the visual system. Using very different criteria, we have also previously indentified an apparently functionally distinct group of MT neurons (Albright 1984). We predicted that these Type II neurons correspond to the pattern-motion neurons. In the present study, we have applied both sets of criteria to individual neurons in MT and found that these two differently defined sets of cells actually form the same population. These results support the idea that MT contributes to a specialized type of motion processing which reflects the integrity of normal perception.     

Transgeniculate signal transmission to middle suprasylvian cortex in intact cats and following early removal of areas 17 and 18: a morphological study

 Removal of cat areas 17 and 18 early, but not late, in postnatal development results in the sparing of certain reflexive and nonreflexive visually guided behaviors. These spared behaviors are accompanied by an expansion of geniculocortical projections to middle suprasylvian (MS) cortex. However, little is known about the types of visual signals relayed along these pathways. The purpose of our study was to reveal the morphologies of the neurons participating in the rewired circuits and, by relating them to the morphologies of functionally characterized neurons described by others, infer the types of visual signals transmitted via the lateral geniculate nucleus (LGN) to MS cortex. To do this, we retrogradely labeled LGN neurons from MS cortex with fluorescent microspheres, and subsequently intracellularly filled them with Lucifer Yellow. We then classified well-filled neurons according to a battery of morphological parameters (such as soma size and shape, and dendritic field-form and specializations), and compared them with already defined structure/function relationships. By doing this, we found that the large majority of visual thalamic relay neurons to MS cortex of both normal cats and cats that incurred removal of areas 17 and 18 were types I and IV. These results indicate that visual Y and W signals, respectively, are relayed directly from LGN to MS cortex in both types of cats. Following the early lesions, some of the MS-projecting type I neurons were found in layers A and A1, where they are never found in intact cats. Thus, some layer A and A1 type I neurons redirect axons to MS cortex following early removal of areas 17 and 18. For the type IV MS-projecting neurons in early lesioned cats, the somas were hypertrophied and they had more profuse and broader dendritic arbors than equivalent neurons in intact cats. These results suggest that dynamic interactions take place between inputs and outputs of LGN neurons during development that influence final LGN neuron morphology. Moreover, they suggest that signals transferred to MS cortex by type IV neurons may be modified by early lesions of areas 17 and 18. Overall, these results contribute to our understanding of the types of behaviors that may be spared by early lesions of areas 17 and 18. Received: 22 May 1996 / Accepted: 3 September 1996     

Influence of layer V of area 18 of the cat visual cortex on responses of cells in layer V of area 17 to stimuli of high velocity

Focal blockade of restricted regions in layer V of area 18 was used to assess the contribution of this region to the responses to high-velocity stimuli of cells in retinotopically matched, layer V in area 17. In 40% of cases, blockade within area 18 revealed responses of area 17 cells to high-velocity stimuli to which they previously showed only poor responses. Stimulus specificity of the cells in area 17 was otherwise unaltered. All effects were reversible and repeatable. We suggest that a component of the output of layer V from area 18 normally suppresses the responses of retinotopically matched cells within area 17 to stimuli of high velocity, thereby enhancing the specificity of those cells to stimuli of low velocity     

Neurophysiological mechanisms of recovery from visual cortex damage in cats: Properties of lateral suprasylvian visual area neurons following behavioral recovery

Summary Damage to visual cortical areas 17, 18, and 19 in the cat produces severe and long-lasting deficits in performance of form and pattern discriminations. However, with extensive retraining the animals are able to recover their ability to discriminate form and pattern stimuli. Recent behavioral experiments from this laboratory have shown that a nearby region of cortex, the lateral suprasylvian visual area (LS area), plays an important role in this recovery (Wood et al., 1974; Baumann and Spear, 1977b). The present experiment investigated the underlying neurophysiological mechanisms of the recovery by recording from single neurons in the LS area of cats which had recovered from long-term visual cortex damage.Five adult cats received bilateral removal of areas 17, 18, and 19. They were then trained to criterion on two-choice brightness, form, and pattern discriminations. Recording from LS area neurons was carried out after the behavioral training, from 3 to 7 months after the visual cortex lesions. The properties of these neurons were compared to those of LS area neurons in normal cats (Spear and Baumann, 1975) and in cats with acute or short-term visual cortex damage and no behavioral recovery (Spear and Baumann, 1979). The results showed that all of the changes from normal which were produced by acute visual cortex damage were also present after the behavioral recovery. Moreover, all of the response properties of LS area neurons which remain after acute visual cortex damage were present in similar form after the behavioral recovery. There was no evidence for any functional reorganization in the LS area concomitant with its role in the behavioral recovery.These results suggest that functional reorganization plays little or no role in recovery from visual cortex damage in adult cats. Rather, the recovery of form and pattern discrimination ability appears to be based upon the functioning of residual neural processes in the LS area which remain after the visual cortex damage.