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Cerebral achromatopsia is an inability to perceive colors that results from damage to specific locations within the visual areas of the cerebral cortex. Unlike many of the syndromes that result from cortical damage, however, the existence of cerebral achromatopsia was denied for many years even by prominent neurologists. The author provides an extended and detailed description of the mechanisms of cerebral achromatopsia, and also discusses the manner in which some dogmatic concepts misled researchers about the existence of this form of color blindness. The striking feature of cerebral achromatopsia is that it may occur without any amblyopia. (Amblyopia is visual impairment without any apparent defect in the eye itself.) Therefore, it would seem that within the cerebral cortex there is an area that deals with the perception of color independently of other aspects of vision. To be sure, in most cases, cerebral achromatopsia occurs in conjunction with scotoma, in which the patient is blinded in some area of the visual field due to stroke or some other sort of brain insult. Indeed, the fact that achromatopsia is generally associated with other defects permitted early neurologists to ignore it as a separate syndrome, and to believe that the reported cases of isolated achromatopsia were nothing more than incomplete and inadequate observations. However, in addition to some of the classical descriptions of achromatopsia there have been at least four cases in the medical literature since 1973 in which the achromatopsia was pure, that is, not accompanied by scotoma or any other visual defect. Among the mammals, color vision is significant only for primates, and monkeys have been used to study the anatomic localization of color perception. These investigations have directly confirmed what has been indirectly suspected from the examination of stroke victims. In addition to the cortical areas V1 and V2, there seems to be a center in the prestriate cortex, specifically the lingual and fusiform gyri in man, which deals with the perception of color, independent of shape or orientation. (Consumer Summary produced by Reliance Medical Information, Inc.)

We have recorded from wavelength-selective cells in macaque monkey visual area V2, interposed between areas V1 and V4 of the color-specialized pathway, to learn whether their responses correlate with perceived colors or are determined by the wavelength composition of light reflected from their receptive fields. All the cells we recorded from were unselective for the orientation and direction of motion of the stimulus, and all were histologically identified to be in the thin cytochrome oxidase stripes. Using multi-colored “Mondrian” scenes of the appropriate spatial configuration, areas of different color were placed in the receptive field of each cell and the entire scene illuminated by three projectors, passing long-, middle-, and short-wave light, respectively, in various combinations. Our results show that wavelength-selective cells in V2 respond to an area of any color depending on whether or not it reflects a sufficient amount of light of their preferred wavelength. In addition, the responses of a third of the cells tested were also influenced by the wavelength composition of their immediate surrounds, thus signaling the result of a local spatial comparison with respect to the amount of their preferred wavelength present. The responses of all also depended on the sequence with which their receptive fields were illuminated with light of the three different wavebands: cells were activated when there was an increase (and inhibited when there was a decrease) in the amount of their preferred wavelength with respect to the other two; the temporal route taken was therefore a determining factor, and, depending on it, cells would either respond or not to a particular combination of wavelengths. We conclude that although spatiotemporal wavelength comparisons are taking place in the color-specialized subdivisions of area V2, the determination of complete color-constant behavior at the neuronal level requires further processing, in other areas.

What is art? What constitutes great art? Why do we value art so much and why has it been such a conspicuous feature of all human societies? These questions have been discussed at length though without satisfactory resolution. This is not surprising. Such discussions are usually held without reference to the brain, through which all art is conceived, executed and appreciated. Art has a biological basis. It is a human activity and, like all human activities, including morality, law and religion, depends upon, and obeys, the laws of the brain. To understand the biological foundations of art, we must enquire into the biological foundations of knowledge, for art constitutes a form of knowledge; indeed is knowledge. We are still far from knowing the neural basis of the laws that dictate artistic creativity, achievement and appreciation, but spectacular advances in our knowledge of the visual brain allow us to make a beginning in trying to formulate neural laws of art and aesthetics; in short, to study neuroaesthetics. In this essay, I try to discuss the art of three Titanic figures in Western culture -- Dante, Michelangelo and Wagner -- in neurological terms. I try to show that we can trace the origins of their art to a fundamental characteristic of the brain, namely its capacity to form concepts. This capacity is itself the by-product of an essential characteristic of the brain. That characteristic is abstraction, and is imposed upon the brain by one of its chief functions, namely the acquisition of knowledge.

Visual neglect occurs most frequently and persistently after lesions that include the right supramarginal gyrus (SMG), a part of the inferior parietal lobule. Patients with this syndrome make very few saccades to the left, and show abnormal performance on tasks in which they must covertly shift their attention to the left, suggesting that the right SMG is involved in the generation of saccades and attention shifts. Functional imaging studies of saccades and covert attention shifts in the normal brain, however, have shown weak or absent responses in both SMGs. We used event-related functional MRI to re-examine the responses to saccades and attention shifts within a single experiment, and to assess responses to left- and right-sided stimuli independently. When subjects made saccades to peripheral stimuli, the expected responses were seen in striate and prestriate cortex, the superior parietal lobules, the frontal eye fields, the supplementary motor area and the anterior insulae. In addition there was a response in the right SMG but not in the left SMG, as predicted from the clinical literature. When subjects made a covert visual assessment of the peripheral stimulus without any saccade, greater activity was seen in all of the areas in the frontoparietal network. Each area showed a bias towards contralateral stimuli, with two exceptions: the anterior insulae gave mainly ipsilateral responses, whilst the right SMG gave equal responses to right- and left-sided stimuli. These findings are discussed in the context of current theories pertaining to the clinical syndrome of neglect.

The visual brain consists of several parallel, functionally specialized processing systems, each having several stages (nodes) which terminate their tasks at different times; consequently, simultaneously presented attributes are perceived at the same time if processed at the same node and at different times if processed by different nodes. Clinical evidence shows that these processing systems can act fairly autonomously. Damage restricted to one system compromises specifically the perception of the attribute that that system is specialized for; damage to a given node of a processing system that leaves earlier nodes intact results in a degraded perceptual capacity for the relevant attribute, which is directly related to the physiological capacities of the cells left intact by the damage. By contrast, a system that is spared when all others are damaged can function more or less normally. Moreover, internally created visual percepts—illusions, afterimages, imagery, and hallucinations—activate specifically the nodes specialized for the attribute perceived. Finally, anatomical evidence shows that there is no final integrator station in the brain, one which receives input from all visual areas; instead, each node has multiple outputs and no node is recipient only. Taken together, the above evidence leads us to propose that each node of a processing-perceptual system creates its own microconsciousness. We propose that, if any binding occurs to give us our integrated image of the visual world, it must be a binding between microconsciousnesses generated at different nodes. Since any two microconsciousnesses generated at any two nodes can be bound together, perceptual integration is not hierarchical, but parallel and postconscious. By contrast, the neural machinery conferring properties on those cells whose activity has a conscious correlate is hierarchical, and we refer to it as generative binding, to distinguish it from the binding that might occur between the microconsciousnesses.

In this speculative essay, I examine two evolutionary developments underlying the enormous success of the human brain: its capacity to acquire knowledge and its variability across individuals. A feature of an efficient knowledge–acquiring system is, I believe, its capacity to abstract and to formulate ideals. Both attributes carry with them a clash between experience of the particular and what the brain has developed from experience of the many. Both therefore can lead to much disappointment in our daily lives. This disappointment is heightened by the fact that both abstraction and ideals are subject to variability in time within an individual and between individuals. Variability, which is a cherished source for evolutionary selection, can also be an isolating and individualizing feature in society. Thus the very features of the human brain which underlie our enormous evolutionary success can also be a major source of our misery.

We argue below that, at least in studying the visual brain, the old and simple methods of detailed clinical assessment and perimetric measurement still yield important insights into the organization of the visual brain as a whole, as well as the organization of the individual areas within it. To demonstrate our point, we rely especially on the motion and colour systems, emphasizing in particular how clinical observations predicted an important feature of the organization of the colour centre in the human brain. With the use of data from functional magnetic resonance imaging analysed by statistical parametric mapping and independent component analysis, we show that the colour centre is composed of two subdivisions, V4 and V4α, the two together constituting the V4 complex of the human brain. These two subdivisions are intimately linked anatomically and act cooperatively. The new evidence about the architecture of the colour centre might help to explain why the syndrome, cerebral achromatopsia, produced by lesions in it is so variable.

Looking at ambiguous figures results in rivalry with spontaneous alternation between two percepts. Using event–related functional magnetic resonance imaging, we localized transient human brain activity changes during perceptual reversals. Activation occurred in ventral occipital and intraparietal higher–order visual areas, deactivation in primary visual cortex and the pulvinar. Thus, without any physical stimulus changes, salient perceptual flips briefly engage widely separated specialized cortical areas, but are also associated with intermittent activity breakdown in structures putatively maintaining perceptual stability. Together, the dynamics of integrative perceptual experience are reflected in rapid spatially differentiated activity modulation within a cooperative set of neural structures.

The theory of multistage integration is based on evidence that the visual brain consists of several parallel multistage processing systems, each specialized for a given attribute such as colour or motion. Each stage of a given system processes information at a distinct level of complexity. Our theory supposes that activity at any stage of a given multistage processing system is perceptually explicit: that is to say, it requires no further processing to generate a conscious experience. This activity can be integrated, or bound, with the perceptually explicit activity at any given stage of another or the same multistage processing system. Such binding is therefore not a process that generates a conscious experience, but rather one that brings different conscious experiences together. Many perceptual advantages result from such a flexible and dynamic integrative system. Conversely, there would be disadvantages to limiting perception and binding to hypothetical ‘terminal’ stages of such processing systems or to hypothetical ‘integrator’ areas. Although we formulate our hypothesis in terms of the visual brain, we believe it might form a general principle of brain functioning.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50–100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure, an abstract multi–coloured scene with no recognizable objects, against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.

We have addressed the question of whether, in addition to being processed separately, colour and motion are also perceived separately. We varied continuously the colour and direction of motion of an abstract pattern of squares on a computer screen, and asked subjects to pair the colour of the pattern to its direction of motion. The results showed that subjects misbind the colour and the direction of motion because colour and motion are perceived separately and at different times, colour being perceived first. Hence the brain binds visual attributes that are perceived together, rather than ones that occur together in real time.

1. The cells of the cortex of the posterior bank of the superior temporal sulcus of the monkey appear to be specialized to signal motion in the visual field. In this paper, cells in this cortical area capable of signalling motion towards or away from the animal are described.

1. The cortical projections of the foveal and extrafoveal parts of the striate cortex have been compared, using conventional degeneration techniques, as well as combinations of anatomical methods. While both foveal and extrafoveal striate cortex share a common pattern of projections (to areas V2, V3 and the visual area in the medial part of the posterior bank of the superior temporal sulcus), foveal striate cortex was found to have an additional projection (to part of the cortex of the fourth visual areas, V4). The latter projection includes the posterior lip of the inferior occipital sulcus which, on anatomical grounds, is regarded as the ventral extension of V4. 2. Anatomical studies using double tracers were employed to clarify the nature of the projections from the striate cortex and from V2 to V4. In one such experiment, tritiated proline was injected into extra‐foveal striate cortex and a small lesion was made in that part of V2 receiving a direct projection from the region of the striate cortex into which the radioactive tracer was injected. Only degenerating fibres (due to the lesion), and no radioactive label, was found in V4. Such an experiment showed that, unlike foveal striate cortex, the projections from extrafoveal striate cortex to V4 are not direct, but through V2. 3. In another type of anatomical experiment using double tracers, the corpus callosum was sectioned and tritiated proline was injected into foveal striate cortex. Such an experiment allowed a more accurate determination of the extent of V4, as judged from its callosal connexions, to which foveal striate cortex projects. 4. Considering the projections of V1 to areas V2, V3 and the visual area in the medial part of the posterior bank of the superior temporal sulcus, and considering the differences in the projections of foveal and extrafoveal striate cortex, it is suggested that, among other functions, the striate cortex acts as a distribution centre for the information coming over the retino‐geniculo‐cortical pathways, parcelling this information out to different visual areas of the prestriate cortex for further analysis.

1. Recordings were made from single neurones, or small clusters of cells, in five prestriate visual areas of rhesus monkey cortex. The cells were studied for their binocularity, as well as for their orientational, motion and colour preferences. In all, 1500 cells were studied, 250 cells for each of the areas V2, V3, V3A and the motion area of the posterior bank of the superior temporal sulcus, and 500 cells for V4. All the cells referred to in this study can be placed in one prestriate area or another unambiguously. 2. The great majority of cells in all areas were binocularly driven, without monocular preferences. Within each area, there were cells that either preferred binocular stimulation markedly, or were responsive to binocular stimulation only. The ocular interaction histograms for all areas are remarkably similar when tested at a fixed disparity. 3. Over 70% of the cells in areas V2, V3 and V3A were selective for orientation. The receptive fields of cells were larger in V3 and V3A than in V2. By contrast, less than 50% of the cells in V4 and the motion area of the superior temporal sulcus were orientation selective. 4. Directionally selective cells were found in all areas. But they were present in small numbers (less than 15%) in areas V2, V3, V3A and V4. By contrast, 90% of the cells in the motion area of the superior temporal sulcus were directionally selective. 5. 8% of the cells in V2 had opponent colour properties. Cells with such properties were not found in V3, V3A or in the motion area of the superior temporal sulcus. By contrast, 54% of the cells in the V4 complex had opponent colour properties. 6. It is argued that despite its uniformity in cytoarchitectural appearance and in ocular interaction patterns, there is a functional division of labour within the prestriate cortex. Evidence for this is seen not only in the different concentrations of functional cell types in distinct areas of the prestriate cortex, but also in the differential anatomical and callosal connexions of each area.

1. The topographic organization of prestriate visual cortex in the rhesus monkey has been studied both anatomically, by determining the pattern of termination of fibres passing through the corpus callosum, and physiologically, in the same animals, by plotting receptive field positions for different recording sites. Results are displayed on two‐dimensional, "unfolded" maps of the cortex in the dorsal half of the occipital lobe. 2. Transcallosal fibres terminate in a narrow strip of cortex along the boundary between striate and prestriate areas and in a separate, broader, zone occupying much of the anterior bank of the lunate sulcus, the annectant gyrus, and the parietooccipital sulcus. The detailed pattern of inputs is highly complicated but shows considerable similarities from one animal to the next. 3. Physiological recordings confirmed earlier reports that regions where transcallosal fibres terminate correspond to representations of the vertical meridian in the visual field. This relationship is most precise along the striate‐prestriate boundary and along the boundary of area V3 farthest from V1; it is less precise within area V4, where the pattern of transcallosal inputs is more complex. 4. A distinct, topographically organized visual area, named V3A, was found in the region between areas V3 and V4 in the lunate and parieto‐occipital sulci. Area V3A differs from V2 and V3 in that both superior and inferior visual quadrants are represented in a single region of the dorsal occipital lobe. 5. The contralateral visual field is represented in a suprisingly complex fashion in areas V3A and V4. Within each area there are multiple representations of some, but perhaps not all, parts of the visual hemifield. It is unclear whether V3A and V4 should be more appropriately considered as sets of distinct sub‐areas, each representing only a portion of the hemifield, or as larger areas with complicated internal topographies. 6. Most cells in areas V2, V3 and V3A are orientation selective but not selective for stimulus colour or direction of movement. In contrast, area V4 contains a higher incidence of colour selective cells and a lower incidence of orientation selectivity. These results support the notion of a functional division of labour within the prestriate cortex.

1. Two independent but neighbouring visual areas, V3 and V3A, sharing a common cytoarchitectural plan, but in each one of which the visual fields are separately represented, have been studied anatomically, functionally, and in combined anatomico‐physiological experiments. 2. The properties of single cells in the two areas are so similar, judged by the techniques used in this study, that it is often impossible to tell whether any one penetration was sampling from cells in V3 or V3A. This is especially so if the cells have receptive fields in the lower hemi‐quadrants, since the vertical meridian of the lower visual fields is represented along the V3‐V3A boundary and since a transition from V3 to V3A along this border is not accompanied by a shift in receptive field positions of cells. 3. Since the visual fields, including the vertical meridian, are separately represented in these two areas, and since regions of vertical meridian representation are callosally connected, a simple and certain method of specifying the boundary between V3 and V3A is to examine the degeneration following section of the callosal splenium. A heavy patch of degeneration then marks the V3‐V3A boundary. Within this patch, however, is a sub‐patch containing fewer callosal fibres, or none at all. The boundary between V3 and V3A was taken to be at this subpatch. 4. Since the horizontal meridian is represented at the V2‐V3 boundary, and since V1 projects to both these areas, sending coarse fibres to V3 and fine fibres to V2, it was found that the boundary between V2 and V3 could be precisely drawn by making a lesion in the horizontal meridian representation in V1 and noting where, in the prestriate cortex, fine fibres give way to coarse ones, without an intervening gap. 5. Double tracer anatomical experiments, in which tritiated proline was injected into V1 of animals whose callosal splenium had been sectioned, showed that whereas V3 receives a direct input from V1, V3A does not. V3A, instead, was found to receive an input from V3. Double tracer anatomical experiments were undertaken to study a possible input from V2 to V3A. Although such experiments did not reveal a direct input from V2 to V3A, they were not entirely conclusive. 6. The vast majority of cells in V3 and V3A were binocularly driven, without obvious monocular preferences. Some cells, however, though responding to stimulation of the individual eyes, summated their responses to binocular stimulation. Others responded only when both eyes were simulataneously stimulated. In any oblique penetration, cells preferring binocular stimulation only occurred either singly or in groups. 7. In an oblique penetration, the shift from a cell responding to binocular stimulation only to one responding equally well to stimulation of either eye was not necessarily accompanied by a shift in orientational preferences, shifts in the former...

Anatomical and functional studies of the visual cortex of the rhesus monkey have shown that it is made up of a multiplicity of distinct areas. These seem to be functionally specialised to analyse different features of the visual environment.

We used the technique of functional magnetic resonance imaging to chart the colour pathways in the human brain beyond V4. We asked subjects to view objects that were dressed in natural and unnatural colours as well as their achromatic counterparts and compared the activity produced in the brain by each condition. The results showed that both naturally and unnaturally coloured objects activate a pathway extending from V1 to V4, though not overlapping totally the activity produced by viewing abstract coloured Mondrian scenes. Normally coloured objects activated, in addition, more anterior parts of the fusiform gyrus, the hippocampus and the ventrolateral frontal cortex. Abnormally coloured objects, by contrast, activated the dorsolateral frontal cortex. A study of the cortical covariation produced by these activations revealed that activity in large parts of the occipital lobe covaried with each. These results, considered against the background of previous physiological and clinical studies, allow us to discern three broad cortical stages of colour processing in the human brain. The first is based on V1 and possibly V2 and is concerned mainly with registering the presence and intensity of different wavelengths, and with wavelength differencing. The second stage is based on V4 and is concerned with automatic colour constancy operations, without regard to memory, judgement and learning. The third stage, based on the inferior temporal and frontal cortex, is more concerned with object colours. The results we report, as well as the schema that we suggest, also allow us to reconcile the computational theory of Land, implemented without regard to cognitive factors such as memory and learning, and the cognitive systems of Helmholtz and Hering, which view such factors as critical in the determination of colours.Keywords:colour vision; V4; hippocampus; functional MRI; inferior temporal cortex.

Anatomical and physiological evidence shows that the primate visual brain consists of many distributed processing systems, acting in parallel. Psychophysical studies show that the activity in each of the parallel systems reaches its perceptual end–point at a different time, thus leading to a perceptual asynchrony in vision. This, together with clinical and human imaging evidence, suggests strongly that the processing systems are also perceptual systems and that the different processing–perceptual systems can act more or less autonomously. Moreover, activity in each can have a conscious correlate without necessarily involving activity in other visual systems. This leads us to conclude not only that visual consciousness is itself modular, reflecting the basic modular organization of the visual brain, but that the binding of cellular activity in the processing–perceptual systems is more properly thought of as a binding of the consciousnesses generated by each of them. It is this binding that gives us our integrated image of the visual world.

1. Anatomical studies have shown the cortex of the posterior bank of the superior temporal sulcus to receive a projection from visual cortical areas, including areas 17, 18 and 19. In this paper the response of single neurones in this area to simple visual stimulation is reported. Ten monkeys were studied.

The article defines the function of the visual brain as a search for constancies with the aim of obtaining knowledge about the world, and claims that it is applicable with equal vigour to the function of art. We define the general function of art as a search for the constant, lasting, essential, and enduring features of objects, surfaces, faces, situations, and so on, which allows us not only to acquire knowledge about the particular object, or face, or condition represented on the canvas but to generalize, based on that, about many other objects and thus acquire knowledge about a wide category of objects or faces. In this process, the artist must also be selective and invest his work with attributes that are essential, discarding much that is superfluous. It follows that one of the functions of art is an extension of the major function of the visual brain. Indeed, philosophers and artists often spoke about art in terms that are extremely similar to the language that a modern neurobiologist of vision would use, except that he would substitute the word 'brain' for the word 'artist.'

We have addressed the question of whether the brain's capacity to resolve an ambiguous retinal image depends upon the activity of early visual areas or whether it involves the investment of the received image with higher order cognitive hypotheses. To resolve the issue, we have used the technique of positron emission tomography to detect increases in regional cerebral blood flow (rCBF) in the brains of humans while they perceive the simple figures described by Schumann (1900) and by Kanizsa (1979). These figures produce striking percepts of surfaces or contours variously described as illusory, subjective, cognitive, or anomalous because they depend upon the brain's ability to complete the figures. If such completion is due to higher order cognitive processes or a combination of higher order and early areas, then, one might expect areas of increased rCBF outside the occipital lobe when subjects perceive these figures. However, if completion is mediated entirely by early visual areas, then the increases in rCBF will be restricted to these regions. Our results show that the perception of subjective contours is associated with significant activity in early visual areas only, particularly in area V2, leading us to conclude that the occipital cortex can contribute to the perception of these stimuli without higher order cognitive influence specific to the completion task.

We have used the technique of positron emission tomography to study and compare the cortical activity produced when humans view a pattern of small squares moving incoherently with respect to one another and when the same pattern moves coherently and unidirectionally. A stationary version of the stimulus acted as a control. Our choice of paradigm was inspired by psychophysical models and physiological studies in the macaque monkey which show that directionally selective cells in V5 respond optimally to unidirectional coherent motion, whereas those of V1 respond to motion within their receptive fields, regardless of the motion in surrounding parts. Our results show that human V1/V2, V3, and V5 are all activated by both types of motion stimuli. Incoherent motion, however, proved to be more effective than coherent motion in activating V1/V2 and V5. Thus the higher perceptual salience of unidirectional coherent motion in comparison to incoherent motion is not reflected by any increased activation of human area V5.

We have studied a patient, G.Y., who was rendered hemianopic following a lesion affecting the primary visual cortex (area V1), sustained 31 years ago, with the hope of characterizing his ability to discriminate visual stimuli presented in his blind field, both psychophysically and in terms of the brain activity revealed by imaging methods. Our results show that (I) there is a correlation between G.Y.'s capacity to discriminate stimuli presented in his blind field and his conscious awareness of the same stimuli and (ii) that G.Y.'s performance on some tasks is characterized by a marked variability, both in terms of his awareness for a given level of discrimination and in his discrimination for a given level of awareness. The observations on G.Y., and a comparison of his capacities with those of normal subjects, leads us to propose a simple model of the relationship between visual discrimination and awareness. This supposes that the two independent capacities are very tightly coupled in normal subjects (gnosospia) and that the effect of a V1 lesion is to uncouple them, but only slightly. This uncoupling leads to two symmetrical departures, on the one hand to gnosanopsia (awareness without discrimination) and on the other to agnosopsia (discrimination without awareness). Our functional MRI studies show that V5 is always active when moving stimuli, whether slow or fast, are presented to his blind field and that the activity in V5 co-varies with less intense activity in other cortical areas. The difference in cerebral activity between gnosopsia and agnosopsia is that, in the latter, the activity in V5 is less intense and lower statistical thresholds are required to demonstrate it. Direct comparison of the brain activity during individual 'aware' and 'unaware' trials, corrected for the confounding effects of motion, has also allowed us, for the first time, to titrate conscious awareness against brain activity and show that there is a straightforward relationship between awareness and activity, both in individual cortical areas, in this case area V5, and in the reticular activating system. The imaging evidence, together with the variability in his levels of awareness and discrimination, manifested in his capacity to discriminate consciously on some occasions and unconsciously on others, leads us to conclude that agnosopsia, gnosopsia and gnosanopsia are all manifestations of a single condition which we call the Riddoch syndrome, in deference to the British neurologist, who, in 1917, first characterized the major aspect of this disability. We discuss the significance of these results in relation to historical views about the organization of the visual brain.Key words: agnosopsia; gnosanopsia; V5; conscious vision; functional MRI

New insights into how colour is represented in the cerebral cortex and what variables govern the responses of single cortical colour-coded cells have been gained by the discovery of specific visual cortical areas rich in colour-coded cells.

The primate visual brain is characterized by a set of parallel, multistage systems that are specialized to process different attributes of the visual scene. They occupy spatially distinct positions in the visual brain and do not project to a unique common area. These processing systems are also perceptual systems, because the result of activity in each leads to the perception of the relevant visual attribute. But the different processing-perceptual systems require different times to complete their tasks, thus leading to another char acteristic of the visual brain, a temporal hierarchy for perception. Together, these two characteristics—of parallel processing and temporal hierarchy—suggest that each processing-perceptual system can act with fair autonomy. Studies of the diseased human brain show that activity in separate processing-perceptual systems—especially those concerned with color and motion—can lead to the perception of the relevant attribute even when the other processing systems are inactive and that activity in individual processing- perceptual systems has a conscious experience as a correlate, which suggests that consciousness itself is a modular, distributed system. NEUROSCIENTIST 4:365-372, 1998

Patterns of anatomical connections in the visual cortex form the structural basis for segregating features of the visual image into separate cortical areas and for communication between these areas at all levels to produce a coherent percept. Such multi-stage integration may be a common strategy throughout the cortex for producing complex behaviour.

We present below a simple hypothesis on what we believe is a characteristic of visual consciousness. It is derived from facts about the visual brain revealed in the past quarter of a century, but it relies most especially on psychophysical evidence which shows that different attributes of the visual scene are consciously perceived at different times. This temporal asynchrony in visual perception reveals, we believe, a plurality of visual consciousnesses that are asynchronous with respect to each other, reflecting the modular organization of the visual brain. We further hypothesize that when two attributes (e.g. colour and motion) are presented simultaneously, the activity of cells in a given processing system is sufficient to create a conscious experience of the corresponding attribute (e.g. colour), without the necessity for interaction with the activities of cells in other processing systems (e.g. motion). Thus, any binding of the activity of cells in different systems should be more properly thought of as a binding of the conscious experiences generated in each system.

This article, written on the 60th anniversary of Korbinian Brodmann's death, discusses his schematic cytoarchitectonic chart of the cerebral cortex in relation to the brain sections from which it was derived and draws attention to the discrepancies between the two.

V5 and V4 are areas of macaque monkey prestriate visual cortex that are specialized for involvement in different aspects of visual perception, namely motion for V5 (refs 1–4) and colour vision, with other possible functions, for V4 (refs 2, 5–9). Thus, it is unlikely that they should be fed the same information for further processing, yet both receive a strong input from patches of the upper layers of V2 (refs 10, 11), the area immediately adjoining the primary visual cortex, V1. V2, however, seems to comprise functionally distinct subregions, which can be revealed by staining the tissue for the mitochondrial enzyme cytochrome oxidase12–15. Here we report that V4 and V5 are connected with separate cytochrome oxidase-defined subregions of V2, suggesting that cortical pathways dealing with motion and colour perception are segregated in their passage through V2, and reinforcing evidence for functional specialization in the visual cortex16–18.

IntroductionEosinophilic oesophagitis (EoE) is an inflammatory condition characterised by symptoms of oesophageal dysfunction (typically dysphagia and food bolus obstruction) and at least 15 eosinophils/hpf on oesophageal biopsy. Although there are endoscopic features associated with EoE, 10%–25% of endoscopies in patients with this condition will be normal [1]. Currently, it is unclear if oesophageal biopsies should be taken in every patient presenting with dysphagia and a normal oesophagus. A more patient focussed strategy can be more cost effective.Our aim was to determine clinical risk factors predictive for EoE, that may then guide the endoscopist for when to take oesophageal biopsies.Method127 patients presenting with dysphagia or FBO and a new diagnosis of EoE (eosinophils>15/hpf) were compared to 127 patients presenting with dysphagia or FBO but no evidence of EoE on biopsies.A multivariate logistic regression analysis was carried out to predict who might have EoE prior to taking biopsies, based on history where available and endoscopic findings. Receiver operator characteristic (ROC) curves were generated and the area under the curve (AUC) was calculated to test the accuracy of the model.ResultsFrom the EoE group, 95 (75%) were male and 32 (25%) were female, with an average age of 39 years. From the control group 59 (46%) were male and 68 (54%) were female with an average age of 60 years. The mean number of biopsies taken between the 2 groups was non-significant.In the EoE cohort, the most common abnormal endoscopic findings were strictures (40%) followed by trachealization (15%) and furrows (15%). 19% had a normal endoscopy.A multivariate logistic regression analysis identified age (p<0.001) and sex (p<0.001) as the strongest predictors of EoE. The AUC for younger age and male sex was 0.86 (95% CI 0.81–0.90). Using the Youden index, the optimal cut-off for age was 46 years giving a sensitivity of 86% and specificity of 69%.ConclusionIn patients presenting with dysphagia or FBO and a normal endoscopy, utilising a simple bedside tool comprising of age (<46 years) and male sex can reliably predict the presence of EoE.Reducing the number of potentially low yield histological examinations for EoE has significant implications for time and cost.Reference. Dellon ES. Diagnostics of eosinophilic esophagitis: clinical, endoscopic, and histologic pitfalls. Dig Dis2014;32(1-2):48–53.Disclosure of InterestNone Declared

IntroductionManagement of eosinophilic oesophagitis (EoE) includes proton pump inhibitors (PPIs), topical steroids, or dietary intervention. In adults dietary management commonly consists of either the six-food elimination diet (SFED) or allergy-test directed food exclusion. To date patient characteristics and outcomes from various interventions have not been reported in a UK population.MethodA retrospective evaluation of adults (≥16 years) with oesophageal eosinophilia (≥15 eos/hpf) over a two-year period was undertaken. Patients were identified from histology reports and clinical records. Treatment episodes were analysed in those who had both pre- and post-intervention biopsies. Patients who underwent dietary interventions were advised by a specialist dietitian.ResultsOur search identified 100 subjects 18–84 years of age (median 35) with a predominance of males (76%; 76/100) and Caucasians (94%; 67/71). Atopic conditions were reported in 75% (65/87) and allergy testing with skin prick or specific IgE tests was positive to food allergens for 71% (44/62) and aeroallergens 72% (38/53). PPIs were given first-line for 75% (38/51) and overall 22% fully responded to a PPI (5/23). Fifty-one patients had both biopsies covering 73 treatment episodes (table 1). Signficant reductions in eosinophil counts were seen for SFED and allergy-test directed diets. There were no significant differences in efficacy between treatment groups.Abstract OC-041 Table 1Median peak eosinophil countInterventionResponders (%)*PrePostp value**PPI8/23 (35)44300.230Steroids5/12 (42)53150.117SFED13/23 (65)47100.006Test-directed5/10 (50)62230.036Other empiric diet1/6 (17)55580.437Elemental diet2/2 (100)331n/a*<15 eso/hpf or ≥50% reduction in peak count. **Wilcoxen signed rank testThrough food reintroduction and biopsies 14 patients identified dietary triggers: 57% milk (n=8), 29% gluten containing cereals (n=4), 14% egg (n=2), 7% soya, nuts, shellfish or fruit (each n=1). For those who completed the process (n=10), 50% had only one trigger, 30% two, and 20% three or more.ConclusionBaseline characteristics were comparable to other described cohorts with a high proportion of males, Caucasians and a high rate of atopy. Dietary intervention particularly with the SFED appears to be effective in our population, with a non-significant trend to higher response rates compared to other interventions. Since the most common triggers were dairy and cereals, empirical exclusion of these two food groups may be an effective approach.Disclosure of InterestNone Declared

IntroductionEndoscopic Therapy for T1a oesophageal adenocarcinoma (OAC), and some T1b with favourable pathological features (sm1, no LVI, G1 or G2 differentiation), is now the recommended standard of care by BSG. Many endotherapy centres have large geographic catchment areas, so accurate staging for these early cancers is crucial to avoid unnecessary visits for patients. Our aim was to assess the utility of staging techniques to define whether endotherapy is possible.MethodAll referrals for endoscopic therapy to tertiary centre (St Thomas’ Hospital), who subsequently underwent EMR and had confirmed T1 OAC, were assessed. All patients were referred with baseline CT CAP. PET scans were scheduled to assess accuracy of nodal disease following confirmation of OAC. EUS was undertaken prior to EMR when intramucosal cancer or greater was diagnosed on biopsy locally.ResultsForty seven patients had confirmed T1 OAC on EMR, undertaken by 3 expert endoscopists at STH between April 2012 – November 2016. Age range 46–86 years old, 38/47 male. Barrett’s oesophagus was present in all, median length C2M4.Original histology was upstaged by EMR in 24 (51%) patients from dysplasia only, including 7/47 with LGD.CT staging of T stage was inaccurate in 57%, under-staging in 19 patients (40%) and over-staging in 8 (17%). CT over staged nodal disease >N0 in 9% vs. PET, all were T1a. Only 1/39 PET scans showed possible nodal disease but no involvement was found after primary surgery.20 patients had EUS and 7/20 had nodal disease but in 6 of these PET was negative for nodes. No Tx/T1 disease on baseline CT was upstaged by EUS.Pathological staging and treatmentDetailed pathological staging is shown in table 1. 25 subjects had T1a, of which 23 had no LVI. 22 subjects had T1b, of which 15 had no LVI or T1b sm1 (or any LVI)n=23n=15n=9Baseline Histology (>dysplasia)13 (57%)11 (73%)7 (78%)CT (>T1)5/18 (28%)2/14 (14%)1/9 (10%)CT (node accuracy vs. PET)10/1312/128/8PET (node negative)17/1813/138/8EUS (T and N)6/94/63/5ConclusionIn this retrospective study we have shown that baseline histology and CT are inaccurate for staging T1 disease, compared to EMR histology. Endoscopically treatable T1 disease was over staged by CT in 22%. Decisions on referral to Endotherapy centre for potential EMR should not be based on CT and histology alone. PET may prove a useful adjunct to confirm node negative disease but more follow up data is required.Disclosure of InterestNone Declared

Cerebral akinctopsia is a syndrome in which a patient loses specifically the ability to perceive visual motion following cortical lesions outside the striate cortex. There has been only one good case of akinetopsia in the published literature. Yet that case was immediately accepted by the neurological world. In this, cerebral akinetopsia differs markedly from cerebral achromatopsia, the evidence for which was strongly contested for the better part of a century (Zeki, 1990). This article complements the one on cerebral achromatopsia, traces the history of akinetopsia and enquires into why it was so much more readily acceptable than achromatopsia.

We used the technique of PET to determine whether visual signals reach visual area V5, specialized for visual motion, when a human patient, blinded by a lesion in area V1, discriminates the direction of motion of visual stimuli and shows, through his verbal reports, that he is consciously aware of both the nature of the visual stimulus and its direction of motion. The results showed that area V5 was active without a parallel activation of area V1, implying that the visual input can reach V5 without passing first through V1 and that such an input is sufficient for both the discrimination and the conscious awareness of the visual stimulus.

Published clinical evidence has led us to hypothesize that there are parallel pathways which lead to the striate (VI) and prestriate cortex in the human brain. We have used the technique of visually evoked EEG coupled to magnetoencephalography (MEG) to test our hypothesis, by detecting the timing of arrival of signals into these visual areas, using published PET evidence to guide us in the location of the evoked response sources. We found that, if the moving stimulus has a speed of 22° s−1, signals arrive in V5 before V1: with speeds of <6° s−1, signals arrive in V1 first. We conclude that, in addition to the classical picture of a sequential input to prestriate cortex through V1, there is also a fast parallel input which by-passes V1. The parallelism manifests itself only as a function of the characteristics of the visual stimulus, a phenomenon we describe as dynamic parallelism. The results obtained help us explain the residual motion vision of patients with lesions in V1 or V5.

We studied the capacity of normal humans to discriminate the direction of motion of visual stimuli when areas VI or V5 were reversibly inactivated with transcranial magnetic stimulation. We found that (i) magnetic stimulation of V5 at intervals of −20 to +10 ms before or after the onset of visual stimulation was effective in abolishing motion perception—other delays were not; (ii) magnetic stimulation of VI abolished motion perception only marginally and at delays which were significantly different from those obtained with V5, the stimulation now being effective only at delays of 60–70 ms after the onset of visual stimulation. We conclude (i) that stimulation of V5 is a much more potent way of inducing akinetopsia (motion imperception) than stimulation of VI ; (ii) that perceptually effective visual motion signals reach V5 at or before 30 ms and reach VI at or before 60 ms— consequently, perceptually effective motion signals reach V5 before they reach VI ; (iii) that, given the time course of arrival of signals in VI and V5, it takes about 30–50 ms for signals from VI to reach V5. We conclude further that there are probably two components reaching V5 from the retina, a fast one which bypasses VI and a slow one which reaches it through VI.

In a previous study we showed that fast moving stimuli activate V5, an area specialized for motion, at very short latencies through a pathway that reaches it without passing through VI. Using the same technique of visual evoked responses, we have tested our conclusions by studying patient GY, whose VI is damaged but whose V5 is intact. In spite of the contralateral hemi-blindness due to his VI lesion, GY has a residual visual capacity that allows him to perceive, consciously, fast but not slow moving stimuli presented in his affected hemifield. By stimulating GYs ‘blind’ hemifield and comparing the responses with those obtained from normal subjects, we were able to study the relative contribution of VI and V5 to the visual evoked response to motion in normal subjects. We found that GYs early response to fast motion is preserved and correlates with activity elicited in control subjects over area V5, while slow motion, pattern offset, and pattern reversal stimuli failed to elicit responses in GY. The results confirm our previous conclusions: namely, that the early part of the motion evoked response is generated in area V5 and that signals reach this area through a dynamically parallel pathway that bypasses area V1. They go on to demonstrate that neurophysiological activity in the prestriate cortex correlates with the conscious visual perception of motion.

Credo (manifesto of physiological facts) All visual art must obey the laws of the visual system. The first law is that an image of the visual world is not impressed upon the retina, but assembled together in the visual cortex. Consequently, many of the visual phenomena traditionally attributed to the eye actually occur in the cortex. Among these is visual motion. The second law is that of the functional specialization of the visual cortex, by which we mean that separate attributes of the visual scene are processed in geographically separate parts of the visual cortex, before being combined to give a unified and coherent picture of the visual world. The third law is that the attributes that are separated, and separately processed, in the cerebral cortex are those which have primacy in vision. These are colour, form, motion and, possibly, depth. It follows that motion is an autonomous visual attribute, separately processed and therefore capable of being separately compromised after brain lesions. It is also one of the visual attributes that have primacy, just like form or colour or depth. We conclude that it is this separate visual attribute which those involved in kinetic art have tried to exploit, instinctively and physiologically, from which it follows that in their explorations artists are unknowingly exploring the organization of the visual brain though with techniques unique to them.

We have used the technique of PET to chart the areas of human cerebral cortex specifically responsive to an optical flow stimulus simulating forward motion in depth over a flat horizontal surface. The optical flow display contained about 2000 dots accelerating in radial directions away from the focus of expansion, which subjects fixated at the centre of the display monitor: Dots remained of constant size, but their density decreased from the horizon, lying across the middle of the screen, to the foreground at the lower screen margin; the top half of the display was void. For the control stimulus the dot motions were randomized, removing any sensation of motion in depth and diminishing the impression of a flat terrain. Comparison of the regional cerebral blood flow (rCBF) elicited by the optical flow and control stimuli was thus intended to reveal any area selectively responsive to the radial velocity field that is characteristic of optical flow in its simplest natural form. Six subjects were scanned, and analysed as a group. Four subjects were analysed as individuals, their PET data being co-registered with MRIs of the cerebrum to localize rCBF changes to individual gyri and sulci. There were three main areas of activation associated with optical flow: the dorsal cuneus (area V3) and the latero-posterior precuneus (or superior parietal lobe) in the right hemisphere, and the occipito-temporal ventral surface, in the region of the fusiform gyrus, in both hemispheres. There was no significant activation of V1/V2, nor of V5. These results show that higher stages of motion take place in both the ‘dorsal’ and ‘ventral’ visual pathways, as these are commonly conceived, and that both may be fed by area V3. The information potentially derivable from optical flow concerns the direction of heading, and the layout of the visual environment, a form of three-dimensional structure-from-motion. The perceptual division of labour between the various activated areas cannot be directly inferred, though it is a reasonable supposition that the parietal activation reflects the utility of optic flow for guiding self-motion.

We have used the technique of PET to chart the cortical areas activated by visual motion in the brain of a patient with a severe impairment in the ability to recognize the motion of objects (akinetopsia), following bilateral lesions which have so far been presumed to include area V5. High resolution MRI of her brain showed that the zone occupied by area V5 had indeed been destroyed bilaterally. Positron emission tomography activation images, co-registered to the MRIs, showed three principal regions of the cortex activated by motion. These were located (i) bilaterally in the precuneus of superior parietal cortex (area 7 of Brodmann); (ii) bilaterally in the cuneus (a region considered to represent upper V3); (iii) in the left lingual and fusiform gyri (possibly lower V3 and adjacent areas). In contrast to normal subjects, there was no significant activation of area VI or V2. The stimuli used for scanning were chosen by prior testing of the patient‘s visual capacities. The control stimulus was a static random distribution of light squares on a dark background. In the moving stimulus these squares moved coherently, the direction of motion changing periodically between the cardinal directions (left, right, up and down). It was ascertained that the patient could correctly identify these directions. We also found (i) that her occasional errors were always in the direction opposite to the motion presented, so that her identification of axis of motion (i.e. vertical or horizontal) was 100% correct; (ii) that when a few static squares were added to the moving display her identification of direction fell to chance but her identification of the axis of motion remained 100%; (iii) that when a few squares moving opposite and orthogonal to the predominant direction of motion were incorporated, her performance on both direction and axis fell to chance; (iv) that she was unable to identify motion in oblique directions between the horizontal or vertical axes, always guessing one of the cardinal directions. In accounting for her residual vision in terms of cortex which remains active, we hypothesize: (i) that the bilateral loss of V5 has affected direction sensitive mechanisms at other sites in the cortex which are interconnected with V5 and (ii) that in consequence her performance on our tests reflects the properties of dynamic orientation selective mechanisms that were also differentially activated by the stimuli used during scanning.