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The Case of the Colorblind Painter

The neuroanatomy and neurophysiology of Helmholtz’s time, and indeed the concept of the nervous system as a static mechanism rather than as an active processor, made it difficult to find out, or imagine, how such “judgment” could be exercised. Indeed, it is only in the last fifteen years or so that new concepts and investigations have made it possible to envisage this, and in a way that must fill us with awe for the brain. The fundamental work of Land and Zeki has been largely responsible for these new concepts. Both use “Mondrians” illuminated with light of different wavelengths. Land’s work with human subjects leads him to see the “color” parts of the brain as working like a computer, one that computes color by using three estimates of light intensity (“lightnesses”), each itself computed using intensity information from the entire image. Thus, for Land, the surround is all-important. The seeing eye, or retina-cortex (Land calls his theory “Retinex”), always takes in an entire scene, and makes a judgment of color in any given part from a consideration of color information throughout the scene.6 Land’s model enables him to predict, with some accuracy, how colors will look to human subjects, whatever the changes in illumination. The mystery of color constancy, or color judgment, seems to depend upon an immense inner act of comparison and computation, performed continually and faultlessly, every moment of our lives.7

Land proposed a model—an internal color computer. Zeki has actually located this computer by inserting microelectrodes into the brains of rhesus monkeys while they view “Mondrians” in differing lights. He finds that there are cells that respond to different wavelengths in the primary visual cortex, but cells that respond to different colors in the visual association cortex (in areas that he labels “V4” and “V4A”).8 These latter cells themselves show color constancy, each cell acting as a Landian computer, or (if you will) a Helmholtzian judge.

What happens if there is damage to Land’s color computer, Zeki’s color center (and so specialized and tiny a knot of cells may be especially vulnerable)? Land and Zeki do not ask this question, since they work only with healthy subjects—but it is precisely this question that Mr. I.’s case poses, and answers.

The varied symptoms that Mr. I. complained of, and showed, finally led us to test him on a color-Mondrian, with illumination of different wavelengths, in precisely the way that Land’s subjects are tested. And this showed us with great clarity how his ability to discriminate different wavelengths was preserved, while his color perception was obliterated, how there was a clear dissociation of the two. Such a dissociation could not occur unless there were separate processes for wavelength discrimination and color construction. Thus, Mr. I.’s situation only becomes intelligible with a theory of multistage processing such as Land’s or Zeki’s; and such a theory can only be grounded, finally and elegantly, in such a patient.

4.

This is the scientific interest of all such acquired, perceptual, cerebral disorders, that in their breakdowns they can show us how our perceptual world is made up. Patients such as Mr. I. show us that color is not a given but is only perceived through the grace of an extraordinarily complex and specific cerebral process. The same is true for the perception of motion, depth, and form: all of these we take for granted, until we see patients who have lost them, patients who have motion blindness, depth blindness, or form blindness (visual agnosia) on the basis of highly specific cerebral lesions.9

The elucidation of perceptual makeup by studying specific cerebral breakdowns was established more than a century ago. Thus several neurologists in the 1880s described cases of people who were colorblind in half the visual field (hemiachromatopsia) or were unable to recognize faces (prosopagnosia), and concluded that there must exist in the brain separate “centers” for light perception, color perception, and the recognition of form. (The centers for recognition of letters, recognition of movement, and, finally, recognition of visual form itself are very close to the color center.) But after this promising early start, there then occurred one of those unfortunate events that can exert a profound negative effect on the growth of knowledge, and indeed on our ability to recognize, or even “see,” important syndromes.

In an influential study of World War I gunshot wounds to the head, Gordon Holmes, one of the prominent neurologists of the time, wrongly concluded that colorblindness could not be caused by localized damage to the visual cortex. What he failed to realize was that, by a fluke, most of his patients had damage in areas of the visual cortex that were not concerned with color processing. They showed various other visual defects, but their color perception was intact.10

Thus achromatopsia disappeared from the medical literature, and was expunged from medical consciousness for more than sixty years. This strange situation was reversed in 1973, partly through clinical observation, but equally through the fundamental physiological work of Zeki, which established the existence of a specific “color center” in monkeys. Zeki’s work had a profound impact in clinical circles, liberating a description and discussion inhibited for sixty years.

The implications of the experimental for the clinical are indeed exemplified in Mr. I., who has suffered very severe, yet singularly circumscribed, damage more or less limited to Zeki’s areas for color coding in the brain. These parts of the brain are somewhat vulnerable at best, especially in an elderly patient, who may have had a sudden diminution of blood supply with the jolting of the car accident, or, coincidentally, suffered a small stroke (another patient known to one of us in England suddenly developed both colorblindness and profound visual agnosia, as a result of lack of oxygen in these areas).11

At the level of the brain Land and Zeki explore, there is nothing subjective—the physiological and perceptual processes at this level are automatic and impersonal, and are the same in every person (or monkey). The same appears to be true with regard to the “processing” (or computation) of motion, depth, form, and, after these have been separately processed, their integration into an “image.” David Marr has described how by such a computation the brain constructs visual patterns and forms of great complexity to elaborate what he calls a “primal sketch” (or three-dimensional image). This sketch can now be envisaged as colored and moving. All this is accomplished, automatically, in the visual association cortex—the formation of an image is not dependent in the least on expectation, memory, association, meaning. Such an image, or initial representation of the visual world, it would seem, can be constructed wholly by computation, without reference to the memories, expectations, or associations that are lodged in the “higher” parts of the cortex. Marr, in his pioneer study, Vision, has given us the general theory of such computations, and it seems likely that they occur in the “lower” portions of the cortex.

It is only at higher levels that integration occurs, that these (computational) images meet with our memory, expectations, associations, desires, to form a world with resonance and meaning for us. There can be disorders at this higher level, too, color association defects, or color agnosias, when colors, though they may be “constructed” correctly, lose their usual associations, feelings, and meanings. In this situation, a patient could see, but would not be surprised by, a blue banana; perhaps dress in inappropriate colors; and remain unmoved by the color of his beloved’s eyes. Color would no longer be a carrier of sense, no longer a significant part of the patient’s visual world. Though one may separate out a small part of the visual cortex as an isolated unit, as is necessary in a physiological approach, the visual cortex is part of the brain, and the brain is part of the organism, and the organism—every organism—has a world of its own, in which perceptions become infinitely more than information carriers, become an integral part of the subjectivity, the feeling, the style of the individual.

Goethe thought (mistakenly) that Newton had reduced color to the purely physical, and reacted by elevating it to the purely mental. But there is something in the language of physics—“rays differently refrangible”—that seems very far from the experience of color. Goethe’s fear that science might reduce the richly colored world of living reality to a gray nullity is expressed in the famous lines from Faust:

Grau, teurer Freund, ist all Theorie
Und grün des Lebens goldner Baum.

(Gray, dear friend, is all theory.
And green is the golden tree of life.)

One has a shadow of this fear when Land and Zeki say, in effect, “color is a computation,” and seem to reduce color to something colorless, in the depths of the visual cortex. Color is this, but it is infinitely more; it is taken to higher and higher levels, admixed inseparably with all our visual memories, images, desires, expectations, until it becomes an integral part of ourselves, our lifeworld. It is not clear that the experience, the phenomenon, of color can ever be explained (or explained away) by physiology or science: it retains a mystery, a wonder, that seems inaccessible, and that belongs in the sphere of the “given,” not the sphere of questions and answers. Something of this sentiment is expressed by Wittgenstein:

We feel that even if all possible scientific questions be answered, the problems of life have still not been touched at all. Of course there is then no question left, and just this is the answer.

The wonder of color vision, and the horror of its loss, are not diminished, are perhaps increased, by our scientific knowledge—and its limits. This was fully appreciated by Newton, who was the first to explore it, and by his friend Robert Boyle, who was the first to describe its complete loss. One can only echo the words with which W.A.H. Rushton closes his essay on color vision:

Colours are so gay that those with total colour loss cannot but be pitied: and it must be wondered what it is that makes red produce the wonderful red sensation most people perceive. What has been said here explains only what cannot be discriminated, and nothing has been said about how sensations arise from what is seen. Let it be concluded that Newton ended his first paper with these strong words: “But to determine…by what modes or actions light produceth in our minds the phantasms of colours is not so easie. And I shall not mingle conjectures with certainties.”

Postscript (October 1987)

It is almost two years since Mr. I. lost his color vision. The intense sorrow that was so characteristic at first, as he sat for hours before his (to him) black lawn, desperately trying to perceive or imagine it as green, has disappeared, as has the revulsion (he no longer sees his wife, or himself, as having “rat-colored” flesh).

There has, we think, been in his case a real “forgetting” of color—a forgetting at once psychological and physiological, at once strategic and structural. Perhaps this has to occur in someone who is no longer able to imagine or remember, or in any physiologically based way generate, a lost mode of perception. It does not, by contrast, happen in those who have become ordinarily blind or deaf, but their cerebral cortices, their powers of inner representation, are unimpaired; it is quite different for the cortically blind or deaf, who become not only unseeing or unhearing, but as if they had never been seeing or hearing, as did a patient with cortical blindness described by one of us (see Oliver Sacks, The Man Who Mistook His Wife For a Hat, Summit Books, 1985, p. 39).

In the past few months Mr. I. has been changing his habits and behavior—“becoming a night-person,” in his own words. He has taken to roving about a great deal, exploring other cities, other places, but only at night. He drives, at random, to Boston, Baltimore, or small towns and villages, arriving at dusk, and then wandering about the streets for half the night, occasionally talking to a fellow walker, occasionally going into little diners: “Everything in diners is different at night, at least if it has windows. The darkness comes into the place, and no amount of light can change it. They are transformed into night places. I love the nighttime,” Mr. I. says. “I often wonder about people who work at night. They never see the sunlight. They prefer it…. It’s a different world: there’s a lot of space—you’re not hemmed in by streets, by people…. It’s a whole new world. Gradually I am becoming a night person. At one time I felt kindly toward color, very happy about it. In the beginning, I felt very bad, losing it. Now I don’t even know it exists—it’s not even a phantom.” (Mr. I. never had “phantom” colors, as amputees may have phantom limbs, and the deafened “phantasmal” voices and music; for the cerebral cortex is needed even to make a phantom.)

Mr. I., when he is not traveling, gets up earlier and earlier, to work in the night, to relish the night. He feels that in the night world (as he calls it) he is the equal, or the superior, of “normal” people: “I feel better because I know then that I’m not a freak…and I have developed acute night vision, it’s amazing what I see—I can read license plates at night from four blocks away. You couldn’t see it from a block away.” With his revulsion from color and brightness, his fondness of dusk and night, his apparently enhanced vision at dusk and night, Mr. I. sounds like Kaspar Hauser, the boy who was confined in a lightless cellar for fifteen years, as Feuerbach described him in 1832:

As to his sight, there existed, in respect to him, no twilight, no night, no darkness…. At night he stepped everywhere with the greatest confidence; and in dark places, he always refused a light when it was offered to him. He often looked with astonishment, or laughed, at persons who, in dark places, for instance, when entering a house, or walking on a staircase by night, sought safety in groping their way, or in laying hold on adjacent objects. In twilight, he even saw much better than in broad daylight. Thus, after sunset, he once read the number of a house at a distance of one hundred and eighty paces, which, in daylight, he would not have been able to distinguish so far off. Towards the close of twilight, he once pointed out to his instructor a gnat that was hanging in a very distant spider’s web.12

Richard Gregory, speaking of those who have never had color vision (owing to absence of cones, or normal cone function, in their eyes) said, “They live in a scotopic world, in a world of bright moonlight,” and this now seems to be the only world that Mr. I. can bear. Our world—our “photopic” world, dazzlingly bright and colored—must appear discordant and painful to an achromatope (whether he has been born colorblind, like Gregory’s subjects, or become colorblind, like Mr. I.); given this, along with an enhanced, compensatory sensitivity to the nocturnal and scotopic, it is not surprising, it is perhaps inevitable, that achromatopes should be drawn to the only world in which they feel at ease and at home—and that they should, like the loris and the potto, the big-eyed primates that only emerge and hunt at night, turn wholly, or as much as they can, to becoming night creatures in a night world.

We owe a great debt to many colleagues whom we have consulted or conversed with in relation to this case, in particular Drs. Richard Blanck, Ivan Bodis-Wollner, Francis Crick, Antonio Damasio, R. L. Gregory, John C. Marshall, and S. Zeki.

  1. 6

    What can be shown cannot be said”—thus Land’s and Zeki’s views are difficult to state, but easy to show. This has been done very vividly in a recent BBC film (Colourful Notions) by Land and Zeki themselves, using fascinating simulations to show what would happen if color constancy were not preserved. The most recent discussion of Land’s theory is given in the account by J.J. McCann and may be found (along with Rushton’s general discussion of color vision) in the just published Oxford Companion to the Mind, edited by R.L. Gregory (Oxford University Press, 1987).

  2. 7

    In particular it must be asked whether the word or concept of “computation,” used by both Land and Zeki, is being used in its strict sense—or metaphorically. Does the brain work like a computer—or, to put it more usefully, does the brain use algorithms—for the construction of color? It is certain that it does so in a much simpler form of visual “judgment”—the judgment or perception of depth (stereopsis)—which so fascinated Helmholtz. Stereopsis, it has now been confirmed by David Marr, is based on an algorithm, a relatively simple iterating algorithm. And this is employed now in robots who “judge” or “see” depth with two “eyes.” Land has devised a rather more complicated model or algorithm for predicting color by an equation with three axes—a “color cube.” And this, in turn, may allow us to give robots not only stereo vision but color vision as well. Land and Zeki, it might be said, are concerned with the “robotics” of color vision; but this does not mean they regard living beings as robots. They regard the robotics as the starting point in exploring a far more mysterious business—the living processes of perception, processes that go beyond any algorithm (for a world, a judgment, cannot be reduced to an algorithm). This too is implied in Helmholtz’s use of the term “judgment”—first an algorithm, then a meaning. (This thesis is central in his On the Sensations of Tone, 1863; fourth edition 1877, translated, Dover, 1954.)

  3. 8

    The loss of fine contrast vision, the “silhouette” vision, which Mr. I. had, also points to damage in the visual association cortex, probably in an area immediately abutting “V4.”

  4. 9

    A remarkable account and analysis of a patient with a pure “motion blindness” has been provided by Zihl et al. (1983). The patient’s problems are described as follows: “The visual disorder complained of by the patient was a loss of movement vision in all three dimensions. She had difficulty, for example, in pouring tea or coffee into a cup because the fluid appeared to be frozen, like a glacier. In addition, she could not stop pouring at the right time since she was unable to perceive the movement in the cup (or a pot) when the fluid rose. Furthermore the patient complained of difficulties in following a dialogue because she could not see the movements of the face and, especially, the mouth of the speaker. In a room where more than two other people were walking she felt very insecure and unwell, and usually left the room immediately, because ‘people were suddenly here or there but I have not seen them moving.’ The patient experienced the same problem but to an even more marked extent in crowded streets or places, which she therefore avoided as much as possible. She could not cross the street because of her inability to judge the speed of a car, but she could identify the car itself without difficulty. ‘When I’m looking at the car first, it seems far away. But then, when I want to cross the road, suddenly the car is very near.’ She gradually learned to ‘estimate’ the distance of moving vehicles by means of the sound becoming louder.”

  5. 10

    This extraordinary story has been reconstructed by Damasio in his article “Disorders of Complex Visual Processing” (1985).

  6. 11

    These areas, indeed, seem to be particularly sensitive to disturbance and impairment, from a great variety of causes, Transient alterations of color vision are not uncommon in (visual) migraines. They are well-known to users of mescaline and other drugs. They can be a disquieting side effect of ibuprofen (Motrin). Partial or total achromatopsia (“graying-out”), also temporary, is characteristic of fainting, or shock, in which there is a reduction of blood supply to the posterior, and especially the visual parts, of the brain. These vulnerable areas may also be affected in a variety of diseases, from multiple sclerosis to brain tumors and strokes.

  7. 12

    The case of Kaspar Hauser was described by Anselm von Feuerbach in 1832 in a document of great importance for those who wish to study the effects of profound sensory, linguistic, or social deprivation in the first years of life.

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