Arthur S., a surgeon who is also a fine amateur pianist, is losing his vision from macular degeneration. In 2007, he started "seeing" musical notation for the first time. Its appearance was extremely realistic, the staves and clefs boldly printed on a white background, "just like a sheet of real music"-and Arthur wondered for a moment whether some part of his brain was now generating his own original music. But when he looked more closely, he realized that the score was unreadable and unplayable. It was inordinately complicated, with four or six staves, impossibly complex chords with six or more notes on a single stem, and horizontal rows of multiple flats and sharps. It was, he said, "a potpourri of musical notation without any meaning." He would see a page of this pseudo-music for a few seconds, and then it would disappear suddenly, replaced by another, equally nonsensical page. These hallucinations were sometimes intrusive, and might cover a page he was trying to read or a letter he was trying to write.

Though Arthur has been unable to read real musical scores for some years, he wonders, as Marjorie did, whether his lifelong immersion in music and musical scores might have determined the form of his hallucinations.5

He wonders, too, whether his hallucinations might progress. For about a year before he began to see musical notation, Arthur saw something much simpler: a checkerboard pattern. Will his musical notation be followed by even more complex hallucinations, such as people, faces, or landscapes, as his eyesight declines?

There is clearly a wide array, a whole spectrum, of visual disturbances which can occur when vision is lost or compromised, and originally the term "Charles Bonnet syndrome" was reserved for those whose hallucinations were related to eye disease or other ocular problems. But an essentially similar array of disturbances can also occur when the damage lies not in the eye itself but higher up in the visual system, especially the cortical areas involved in visual perception-the occipital lobes and their projections into the temporal and parietal lobes of the brain-as seems to be the case with Zelda.

Zelda was a historian who came to see me in 2008. She told me how her world of strange visual phenomena had started at a theater six years earlier, when the beige curtain in front of the stage suddenly seemed to be covered in red roses-the roses were three-dimensional, thrusting out of the curtain. When she closed her eyes, she still saw the roses. This hallucination lasted for a few minutes and then vanished. She was perplexed and frightened by this, and she went to consult her ophthalmologist, but he found no impairment of vision and no pathological changes in either eye. She saw her internist and cardiologist, but they could not provide any plausible explanation for this episode-or the countless episodes that followed. Finally she had a PET scan of her brain, which showed reduced blood flow in her occipital and parietal lobes, presumably the cause, or at least a possible cause, of her hallucinations.

Zelda has both simple and complex visual hallucinations. The simple ones may appear when she is reading or writing or watching television. One of her physicians asked her to keep a journal of her visions over a three-week period, and in it, she recorded, "As I write this page, it is becoming more and more covered by a pale green and pink lattice.... The garage walls, covered in white cinderblock, continually mutate ... coming to resemble bricks, or clapboard, or being covered with damask, or flowers of different colors.... On the upper part of the walls in the hallway, shapes of animals. They were formed by blue dots."

More complex hallucinations-battlements, bridges, viaducts, apartment houses-are especially common when she is being driven in a car (she gave up driving herself after her initial attack, six years ago). Once when she and her husband were driving along a snowy road, she was startled to see brilliant green bushes, their leaves glittering with icicles, to either side of the road. Another day, she saw a rather shocking sight:

As we drove away from the beauty parlor, I saw what looked like a teenage boy on the front hood of our car, leaning on his arms with his feet up in the air. He stayed there for about five minutes. Even when we turned he stayed on the hood of the car. As we pulled into the restaurant parking lot, he ascended into the air, up against the building, and stayed there until I got out of the car.

At another point, she "saw" one of her great-granddaughters, who rose up, moved to the ceiling, and disappeared. She saw three "witchlike" figures, motionless and hideous, with huge hooked noses, protruding chins, and glaring eyes-these also vanished after a few seconds. Zelda said she had no idea that she had so many hallucinations until she starting keeping a journal; many of them, she thought, would otherwise have been forgotten.

She also spoke of many strange visual experiences which were not quite hallucinations in the sense of being totally invented or generated but seemed to be persistences, repet.i.tions, distortions, or elaborations of visual perceptions. (Charles Lullin had a number of such perceptual disorders, and they are not uncommon in people with CBS.) Some of these were relatively simple; thus, when she looked at me on one occasion, my beard seemed to spread until it covered my entire face and head, and then resumed its proper appearance. Occasionally, looking in a mirror, she might see her own hair rising a foot above her head and have to check with her hand to make sure it was in its usual place.

Sometimes her perceptual changes were more disturbing, as when she encountered her mail carrier in the lobby of her apartment building: "As I looked at her, her nose grew until it was a grotesque figure on her face. After a few minutes, as we stood talking, her face came back to normal."

Zelda would often see objects duplicated or multiplied, and this might create odd difficulties. "Making dinner and eating was quite difficult," she said. "I kept seeing several of each piece of food when they didn't exist. This lasted most of dinner."6 Visual multiplication like this-polyopia-can take even more dramatic form. Once, in a restaurant, Zelda observed a man in a striped shirt paying at the cash register. As she watched, he split into six or seven identical copies of himself, all wearing striped shirts, all making the same gestures-then concertinaed back into a single person. At other times, her polyopia can be quite frightening or dangerous, as when, sitting in the pa.s.senger seat of her car, she saw the road ahead of her split into four identical roads. The car seemed to her to proceed up all four roads simultaneously.7

Seeing moving pictures even on television may lead to hallucinatory perseverations. Once, watching a television program that showed people descending from a plane, Zelda began to hallucinate minute replicas of the figures, which continued their descent off the screen and down the wooden cabinet of the television console.

Zelda has dozens of these hallucinations or misperceptions every day, and has had them, almost nonstop, for the past six years. And yet she has managed to maintain a very full life, both domestically and professionally-keeping house, entertaining friends, going out with her husband, and completing a new book.

In 2009, one of Zelda's doctors suggested that she take a medication called quetiapine, which can sometimes diminish the severity of hallucinations. To our amazement and especially hers, she became entirely free from hallucinations for more than two years.

In 2011, however, she had heart surgery, and then, on top of this, she broke a kneecap in a fall. Whether it was due to the anxiety and stress of these medical problems, the unpredictable nature of CBS, or the development of tolerance to her medication, she started to have some hallucinations again. Her hallucinations, though, have taken a somewhat more tolerable form. When she is in the car, she said, "I see things, but not people. I see planted fields, flowering, and many forms of medieval buildings. Frequently I see modern buildings change into more historic looking ones. Every experience brings something different."

One of her new hallucinations, she said, "is very difficult to describe. It's a performance! The curtain goes up and 'performers' dance out on the stage-but no people. I see black Hebrew letters dressed in ballet dresses of white. They dance to beautiful music, but I don't know where it comes from. They move the upper parts of the letters like arms and dance on the lower parts so gracefully. They come onstage from right to left."

While the hallucinations of CBS are usually described as pleasant, friendly, diverting, even inspiring, they may occasionally take on a very different character. This happened to Rosalie when a neighbor of hers in the nursing home, Spike, died. Spike was a whimsical, laughter-loving Irishman, and he and Rosalie, both in their nineties, had been close friends for years. "He knew all the old songs," Rosalie remarked; they would sing these together and joke and chatter by the hour. When he died suddenly, Rosalie was devastated. She lost her appet.i.te, withdrew from social activities, and spent more time alone in her room. Her hallucinations returned, but instead of the gaily dressed figures she had seen before, she saw five or six tall men standing around her bed, silent and motionless. They were always dressed in dark brown suits and wore dark hats that shadowed their faces. She could not "see" their eyes, but she felt that they were gazing at her-enigmatically, solemnly. She felt that her bed had become a deathbed and that these ominous figures were harbingers of her own death. They seemed overwhelmingly real to her, and although she knew that if she stretched out a hand it would pa.s.s right through them, she could not bring herself to do this.

Rosalie continued to have these visions for three weeks, and then she started to emerge from her melancholy. The somber, silent men in brown disappeared, and her hallucinations started taking place chiefly in the dayroom, a place full of music and talk. They would start with a vision of patterns-quadrangles of pink and blue that seemed to cover the floor and then extend up the walls, finally spreading across the ceiling. The colors of these "tiles," she said, put her in mind of a nursery. And, in accordance with this, she now saw little people a few inches high, like elves or fairies, with little green caps, climbing up the sides of her wheelchair. There were children, too, "picking up pieces of paper from the floor" or climbing hallucinatory stairs in one corner of the room. Rosalie found the children "adorable," although their activities seemed pointless and, as she put it, "silly."

The children and the little people lasted for a couple of weeks, and then they, too, vanished, in the mysterious way that such hallucinations tend to. Though Rosalie misses Spike, she has found other friends in the nursing home, and she is back to her usual routines of chatting and listening to audiobooks and Italian operas. She is rarely alone now, and-coincidentally or not-her hallucinations have, for the time being, disappeared.

If some or all sight is preserved, as with Charles Lullin and Zelda, there may be not only visual hallucinations but various disorders of visual perception: people or objects may appear too large or too small, too near or too far; there may be too little or too much color or depth; misalignment, distortion, or inversion of the image; or problems with motion perception.

If, of course, the person is completely blind, as Rosalie is, then there can only be hallucinations, but these may also show anomalies of color, depth, transparency, motion, scale, and detail. CBS hallucinations are often described as having dazzling, intense color or a fineness and richness of detail far beyond anything one sees with the eyes. There are strong tendencies to repet.i.tion and multiplication, so that one may see rows or phalanxes of people, all dressed similarly and making similar motions (some early observers referred to this as "numerosity"). And there is a strong tendency to elaboration: hallucinatory figures often seem to be wearing "exotic dress," rich robes, and strange headgear. Bizarre incongruities often appear, so that a flower may protrude not from someone's hat but from the middle of their face. Hallucinatory figures may be cartoonlike. Faces, in particular, may show grotesque distortions of the teeth or eyes. Some people hallucinate text or music. But by far the commonest hallucinations are the geometrical ones: squares, checkerboards, rhomboids, quadrangles, hexagons, bricks, walls, tiles, tessellations, honeycombs, mosaics. Simplest of all, and perhaps most common, are phosphenes, blobs or clouds of brightness or color, which may or may not differentiate into anything more complex. No single individual has all of these perceptual and hallucinatory phenomena, though some people may have a great range, like Zelda, while others tend to stick to a particular form of hallucination, like Marjorie, with her "musical eyes."

In the last decade or two, Dominic ffytche and his colleagues in London have done pioneering research on the neural basis of visual hallucinations. Based on the detailed reports of dozens of subjects, they developed a taxonomy of hallucinations, including categories like figures with hats, children or small people, landscapes, vehicles, grotesque faces, text, and cartoonlike faces. (This taxonomy is described in a 2000 paper by Santhouse et al.)

With this cla.s.sification in hand, ffytche went on to do detailed brain-imaging studies in which selected patients with different categories of visual hallucinations were asked to signal the beginning and end of their hallucinations while being scanned.

There was, as ffytche et al. wrote in a 1998 paper, "a striking correspondence" between the particular hallucinatory experiences of each patient and the particular portions of the ventral visual pathway in the visual cortex which were activated. Hallucinations of faces, of color, of textures, and of objects, for example, each activated particular areas known to be involved in specific visual functions. When there were colored hallucinations, there was activation of areas in the visual cortex a.s.sociated with color construction; when there were facial hallucinations of a sketchlike or cartoonlike character, there was activation in the fusiform gyrus. Visions of deformed or dismembered faces or grotesque faces with exaggerated eyes or teeth were a.s.sociated with heightened activity in the superior temporal sulcus, an area specialized for the representation of eyes, teeth, and other parts of the face. Text hallucinations are a.s.sociated with abnormal activation in the visual word form area, a highly specialized area in the left hemisphere.

Ffytche et al. observed, moreover, a clear distinction between normal visual imagination and actual hallucination-thus, imagining a colored object, for example, did not activate the V4 area, while a colored hallucination did. Such findings confirm that, not only subjectively but physiologically, hallucinations are unlike imagination and much more like perceptions. Writing of hallucinations in 1760, Bonnet said, "The mind would not be able to tell apart vision from reality." The work of ffytche and his colleagues shows that the brain does not distinguish them, either.

There had never before been direct evidence of such a correlation between the contents of a hallucination and the particular areas of cortex activated. We have long known, from observation of people with specific injuries or strokes, that different aspects of visual perception (color perception, face recognition, movement perception, etc.) depend on highly specialized areas of the brain. Thus, for example, damage to a tiny area of the visual cortex called V4 may knock out color perception but nothing else. Ffytche's work is the first to confirm that hallucinations make use of the same visual areas and pathways as perception itself. (Ffytche has emphasized more recently, in papers on the "hodology" of hallucinations, that attributing hallucinations, or any cerebral function, to specific brain regions has its limitations, and that one must pay equal attention to the connections between these areas.)8

But while there are neurologically determined categories of visual hallucination, there may be personal and cultural determinants, too. No one can have hallucinations of musical notation or numbers or letters, for example, if they have not actually seen these at some point in real life. Thus experience and memory may influence both imagery and hallucination-but with CBS, memories are not hallucinated in full or literal form. When people with CBS hallucinate people or places, they are almost never recognizable people or places, only plausible or invented ones. CBS hallucinations give one the impression that, at some lower level, in the early visual system, there is a categorical dictionary of images or part images-of generic "noses," for example, or "headwear" or "birds," rather than of particular noses or headwear or birds. These are, so to speak, the visual ingredients called upon and used in the recognition and representation of complex scenes-elements or building blocks which are purely visual, without context or correlation with other senses, without emotion or particular a.s.sociations of place or time. (Some researchers have called them "proto-objects" or "proto-images.") In this way, CBS images seem more raw, more obviously neurological, not personal like those of imagination or recollection.

Hallucinations of text or musical scores are intriguing in this regard, for although they initially look like real music or text, they quickly reveal themselves to be unreadable, in the sense that they have no shape, no tune, no syntax or grammar. Although Arthur S. at first thought he might be able to play his hallucinatory musical scores, he soon realized that he was seeing "a potpourri of musical notation, without any meaning." Similarly, text hallucinations lack meaning; they may, on closer inspection, not even be actual letters but letter-like runes.

We know (from studies by ffytche and his colleagues) that text hallucinations go with hyperactivity in the visual word form area; there are probably a.n.a.logous (though more widespread) activations with hallucinations of musical notation, though these have yet to be "caught" on fMRI. In the normal process of reading text or scores, what is initially deciphered in the early visual system goes on to higher levels where it acquires syntactical structure and meaning. But in hallucinations of text or scores, caused by anarchical hyperactivity in the early visual system, letters, proto-letters or musical notation appear without the normal constraints of syntax and meaning-providing a window into both the powers and the limitations of the early visual system.

Arthur S. saw musical notation of fanciful elaboration, far more ornate than any real score. CBS hallucinations are often fanciful or fantastical. Why should Rosalie, a blind old woman in the Bronx, see figures in "Eastern dress"? This strong disposition to the exotic, for reasons we do not yet understand, is characteristic of CBS, and it would be fascinating to see whether this varies in different cultures. These strange, sometimes surreal images, of boxes or birds perched atop people's heads or flowers coming out of their cheeks, make one wonder whether what is occurring is a sort of neurological mistake, a simultaneous activation of different brain areas, producing an involuntary, incongruous collision or conflation.

The images of CBS are more stereotyped than those of dreams and at the same time less intelligible, less meaningful. When Lullin's notebook, lost for a century and a half, resurfaced and was published in a psychology journal in 1902 (just two years after Freud's Interpretation of Dreams), some wondered whether the hallucinations of CBS might afford, as Freud felt dreams did, "a royal road" to the unconscious. But attempts at "interpreting" CBS hallucinations in this sense bore no fruit. People with CBS had their own psychodynamics, of course, like everyone else, but it became apparent that little beyond the obvious was to be gained from a.n.a.lyzing their hallucinations. A religious person might hallucinate praying hands, among other things, or a musician might hallucinate musical notation, but these images scarcely yielded insights into the unconscious wishes, needs, or conflicts of the person.

Dreams are neurological as well as psychological phenomena, but very unlike CBS hallucinations. Dreamers are wholly enveloped in their dreams, and usually active partic.i.p.ants in them, whereas people with CBS retain their normal, critical waking consciousness. CBS hallucinations, even though they are projected into external s.p.a.ce, are marked by a lack of interaction; they are always silent and neutral-they rarely convey or evoke any emotion. They are confined to the visual, without sound, smell, or tactile sensation. They are remote, like images on a cinema screen in a theater one has chanced to walk into. The theater is in one's own mind, and yet the hallucinations seem to have little to do with one in any deeply personal sense.

One of the defining characteristics of Charles Bonnet hallucinations is the preservation of insight, the realization that a hallucination is not real. People with CBS are occasionally deceived by a hallucination, especially if it is plausible or contextually appropriate. But such mistakes are quickly realized to be such, and insight is restored. The hallucinations of CBS almost never lead to persistent false ideas or delusions.

The ability to evaluate one's perceptions or hallucinations, however, may be compromised if there are other underlying problems in the brain, especially those which impair the frontal lobes, since the frontal lobes are the seat of judgment and self-evaluation. This may happen transiently, for example, with a stroke or head injury; fever or delirium; various medications, toxins, or metabolic imbalances; dehydration or lack of sleep. In such cases, insight will return as soon as cerebral function returns to normal. But if there is an ongoing dementia, like Alzheimer's or Lewy body disease, there may be less and less ability to recognize hallucinations as such-which, in turn, may lead to frightening delusions and psychoses.

Marlon S., in his late seventies, has progressive glaucoma and some mild dementia. He has been unable to read for the last twenty years, and for the last five years has been virtually blind. He is a devout Christian and still works as a lay minister in prisons, as he has done for the last thirty years. He lives alone in an apartment, but he leads a very active social life. He goes out each day, either with one of his children or with a home attendant, to family occasions or to the senior center, where there may be games, dancing, going out to restaurants, and other activities.

Although he is blind, Marlon seems to inhabit a world that is very visual and sometimes very strange. He tells me that he often "sees" his surroundings-he has lived most of his life in the Bronx, but what he sees is an ugly, desolate version of the Bronx (he describes it as "shabby, old, much older than me"), and this may give him a feeling of disorientation. He "sees" his apartment, but he can easily get lost or confused. Sometimes, he says, the apartment gets "as big as a Greyhound bus terminal," and at other times it contracts, becoming "as skinny as a railroad apartment." In general, the hallucinated apartment looks dilapidated and chaotic: "My whole house is a wreck, looks like the Third World ... then it looks regular." (The only time his apartment actually is a mess, his daughter told me, is when Marlon, thinking that he is "blockaded" by the furniture, starts rearranging it, pushing things to and fro.)

His hallucinations started about five years ago and were at first benign. "In the beginning," he told me, "I saw a lot of animals." They were followed by hallucinations of children-mult.i.tudes of them, just as there would always be mult.i.tudes of animals. "All of a sudden," Marlon remembered, "I see all these kids come in, they were walking all around; I thought they were regular kids." The children were silent but "talked with their hands"; they seemed unconscious of him and "did their own thing"-walking around, playing. He was startled when he found that no one else saw them. It was only then that he realized that his "eyes were playing tricks" on him.

Marlon enjoys listening to talk shows, gospel, and jazz on the radio, and when he does so, he may find his sitting room crowded with hallucinatory people who are also listening. Sometimes their mouths move as if they are speaking or singing along with the radio. These visions are not unpleasant, and they seem to provide a sort of hallucinatory comfort. It is a social scene, which he enjoys.9

In the last two years, Marlon has also started to see a mysterious man who always wears a brown leather coat, green pants, and a Stetson hat. Marlon has no idea who it is but feels that this man has a special message or meaning, though what the message or meaning is eludes him. He sees this figure at a distance, never close up. The man seems to float through the air rather than walk, and his figure can become enormous, "as tall as a house." Marlon has also spotted a small, sinister trio of men, "like FBI, a long way off.... They look real, real ugly and bad." Marlon believes in angels and devils, he tells me, and he feels that these men are evil. He has started to suspect that he is under surveillance by them.

Many people with mild cognitive impairment may be organized and oriented during the daytime-this is the case with Marlon, especially when he is at the senior center or at a church social, actively engaged with other people. But as evening comes, there may be a "sundowning" syndrome, and fears and confusions start to proliferate.

Generally, in the daytime, Marlon's hallucinatory figures deceive him briefly, for a minute or two, before he realizes they are figments. But late in the day, his insight breaks down, and he feels his threatening visitors as real. At night, when he finds "intruders" in his apartment, he is terrified-even though they seem uninterested in him. Many of them look "like criminals" and wear prison garb; sometimes they are "smoking Pall Malls." One night one of his intruders was carrying a bloodstained knife, and Marlon yelled out, "Get out of here, in the name of the blood of Jesus!" On another occasion one of the apparitions left "under the door," slipping away like a liquid or vapor. Marlon has ascertained that these figures are "like ghosts, not solid," and that his arm will go right through them. Nevertheless, they seem quite real. He can laugh about this as we talk, but it is clear that he can be quite terrified and deluded when he is alone with his intruders in the middle of the night.

People with CBS have, at least in part, lost the primary visual world, the world of perception. But they have gained, if only in an inchoate and fitful way, a world of hallucinations, a secondary visual world. The role CBS may play in an individual's life varies enormously, depending on the sort of hallucinations that occur, how often they occur, and whether they are contextually appropriate, or frightening, or comforting, even inspiring. There are, at one extreme, those who may have had only a single hallucinatory experience in their life; others may have had hallucinations, on and off, for years. Sometimes hallucinations can be distracting-seeing patterns or webs over everything, not knowing whether the food on one's plate is real or hallucinatory. Some hallucinations are manifestly unpleasant, especially those that involve deformed or dismembered faces. A few are dangerous: Zelda, for instance, does not dare drive, since she may see the road suddenly bifurcate or people jumping on the hood of her car.

For the most part, however, the hallucinations of CBS are unthreatening and, once accommodated to, mildly diverting. David Stewart speaks of his hallucinations as being "altogether friendly," and he imagines his eyes saying, "Sorry to have let you down. We recognize that blindness is no fun, so we've organized this small syndrome, a sort of coda to your sighted life. It's not much, but it's the best we can manage."

Charles Lullin, too, enjoyed his hallucinations and would sometimes go into a quiet room for a brief hallucinatory break. "His mind makes merry with the images," Bonnet wrote of his grandfather. "His brain is a theatre where the stage machinery puts on performances which are all the more amazing because they are unexpected."

Sometimes the hallucinations of Charles Bonnet syndrome can inspire. Virginia Hamilton Adair wrote poetry as a young woman, publishing in the Atlantic Monthly and the New Republic. She continued to write poems during her career as a scholar and professor of English in California, but these, for the most part, remained unpublished. It was not until she was eighty-three and completely blind from glaucoma that she published her first book of poetry, the acclaimed Ants on the Melon. Two further collections followed, and in these new poems she made frequent reference to the Charles Bonnet hallucinations that now visited her regularly, the visions given to her by "the angel of hallucinations," as she put it.