by Oliver Sacks
He wondered whether this imagery represented a sort of “idling” in the visual part of the brain, in the absence of perception.
What Mr. Utter described so vividly are not dreams but involuntary images or quasi-hallucinations appearing just before sleep—hypnagogic hallucinations, to use the term coined by the French psychologist Alfred Maury in 1848. They are estimated to occur in a majority of people, at least occasionally, although they may be so subtle as to go unnoticed.
While Maury’s original observations were all of his own imagery, Francis Galton provided one of the first systematic investigations of hypnagogic hallucinations, gathering information from a number of subjects. In his 1883 book Inquiries into Human Faculty, he observed that very few people might at first admit to having such imagery. It was only when he sent out questionnaires stressing the common and benign qualities of these hallucinations that some of his subjects felt free to speak about them.
Galton was struck by the fact that he, too, had hypnagogic hallucinations, even though it had taken time and patience for him to realize this. “Had I been asked, before I thought of carefully trying, I should have emphatically declared that my field of view in the dark was essentially of a uniform black, subject to an occasional light-purple cloudiness and other small variations,” he wrote. Once he began observing more closely, however, he saw that
a kaleidoscopic change of patterns and forms is continually going on, but they are too fugitive and elaborate for me to draw with any approach to truth. I am astonished at their variety.… They disappear out of sight and memory the instant I begin to think about anything, and it is curious to me that they should often be so certainly present and yet be habitually overlooked.
Among the scores of people who responded to Galton’s questionnaire was the Reverend George Henslow (“whose visions,” Galton wrote, “are far more vivid than mine”).1 One of Henslow’s hallucinations started with a vision of a crossbow, then of an arrow, then a flight of arrows, which changed into falling stars and then into flakes of snow. This was followed by a finely detailed vision of a rectory and then of a bed of red tulips. There were quickly changing images in which he reported visual association (for instance, arrows became stars, then snowflakes) but no narrative continuity. Henslow’s imagery was extremely vivid, but it had no quality of a dream or story.
Henslow emphasized how greatly these hallucinations differed from voluntary images; the latter were assembled slowly, bit by bit, like a painting, and seemed to be in the realm of everyday experience, while the former appeared spontaneously, unbidden and full-blown. His hypnagogic hallucinations were “very frequently of great beauty and highly brilliant. Cut glass (far more elaborate than I am conscious of ever having seen), highly chased gold and silver filigree ornaments; gold and silver flower-stands, etc.; elaborate colored patterns of carpets in brilliant tints.”
While Galton singled out this description for its clarity and detail, Henslow was only one of many who described essentially similar visions when they were in a quiet, darkened room, ready for sleep. These visions varied in vividness, from faint imagery such as Galton himself had to virtual hallucination, though such hallucinations were never mistaken for reality.
Galton did not regard the disposition to hypnagogic visions as pathological; he thought that while a few people might experience them frequently and vividly whenever they went to sleep, most (if not all) people experienced them at least on occasion. It was a normal phenomenon, although special conditions—darkness or closing the eyes, a passive state of mind, the imminence of sleep—were needed to bring it out.
Few other scientists paid much attention to hypnagogic visions until the 1950s, when Peter McKellar and his colleagues started what was to be a decades-long investigation of near-sleep hallucinations, making detailed observations of their content and prevalence in a large population (the student body at the University of Aberdeen) and comparing them with other forms of hallucination, especially those induced by mescaline. In the 1960s, they were able to complement their phenomenological observations with EEG studies as their subjects passed from full wakefulness to a hypnagogic state.
More than half of McKellar’s subjects reported hypnagogic imagery, and auditory hallucinations (of voices, bells, or animal or other noises) were just as common as visual ones. Many of my own correspondents also describe simple auditory hallucinations: dogs barking, telephones ringing, a name being called.
In his book Upstate, Edmund Wilson described a hypnagogic hallucination of a sort that many people share:
I seem to hear the telephone ringing just before I am completely awake in the morning. At first, I would go to answer it, but find that it was not ringing. Now I simply lie in bed, and if the sound is not repeated, I know that it is imaginary and don’t get up.
Antonella B. hears music as she is falling asleep. The first time it happened, she wrote, “I heard a really nice classical piece, played by a big orchestra, very complex and unknown.” Usually, no images accompany her music, “just beautiful sounds that fill my brain up.”
Susan F., a librarian, had more elaborate auditory hallucinations, as she wrote in a letter:
For several decades, just as I am drifting off to sleep, I have heard sentences uttered. They are always grammatically correct, usually in English, and usually spoken by a man. (On a few occasions they were spoken by a woman and once in a language I could not understand. I can recognize the differences between the Romance languages, Chinese, Korean, Japanese, Russian, and Polish, but it was none of these.) Sometimes the sentences are commands, such as “Go get me a glass of water,” but at other times they are just statements or questions. During the summer of 1993, I kept a log of what I heard. Here are some of the sentences: “Once he was walking in front of me”; “This is yours, perhaps”; “Do you know what the photo looks like?”; “Mama wants some cookies”; “I smell the unicorn”; “Go get a shampoo.”
What I hear bears no relationship to what I have read, seen, experienced or remembered on that day, previous day, week or year. Frequently when my husband is driving and we are on a long trip, I will nod off in the car. The sentences come very rapidly then. I will nod off for a second, hear a sentence in the twilight of waking, repeat the sentence to my husband, and then nod off again, hear another sentence in the twilight and so on, until I decide to wake up and stay awake.
In Speak, Memory, Nabokov provided an eloquent description of his own hypnagogic imagery, both auditory and visual:
As far back as I remember … I have been subject to mild hallucinations.… Just before falling asleep, I often become aware of a kind of one-sided conversation going on in an adjacent section of my mind, quite independently from the actual trend of my thoughts. It is a neutral, detached, anonymous voice, which I catch saying words of no importance to me whatever—an English or a Russian sentence, not even addressed to me, and so trivial that I hardly dare give samples.… This silly phenomenon seems to be the auditory counterpart of certain praedormitary visions, which I also know well.… They come and go, without the drowsy observer’s participation, but are essentially different from dream pictures for he is still master of his senses. They are often grotesque. I am pestered by roguish profiles, by some coarse-featured and florid dwarf with a swelling nostril or ear. At times, however, my photisms take on a rather soothing flou quality, and then I see—projected, as it were, upon the inside of the eyelid—gray figures walking between beehives, or small black parrots gradually vanishing among mountain snows, or a mauve remoteness melting beyond moving masts.
Faces are especially common in hypnagogic hallucinations, as Andreas Mavromatis emphasizes in his encyclopedic book Hypnagogia: The Unique State of Consciousness Between Wakefulness and Sleep. He cites one man who described this in 1886; the faces, he wrote,
seem to come up out of the darkness, as a mist, and rapidly develop into sharp delineation, assuming roundness, vividness, and living reality. They fade off only to give place to others, which succeed with
surprising rapidity and in enormous multitude. Formerly the faces were wonderfully ugly. They were human, but resembling animals, yet such animals as have no fellows in the creation, diabolical-looking.… Latterly the faces have become exquisitely beautiful. Forms and features of faultless perfection now succeed each other in infinite variety and number.
Many other descriptions stress how common it is to see faces, sometimes clusters of faces, with each face highly individuated but unrecognizable. F. E. Leaning, in her 1925 paper on hypnagogia, speculated that such an emphasis on faces “almost suggests that there is a special ‘face-seeing’ propensity in the mind.” Leaning’s “propensity,” we now know, has its anatomical substrate in a specialized portion of the visual cortex, the fusiform face area. Dominic ffytche and his colleagues have shown in fMRI studies that it is precisely this area in the right hemisphere which is activated when faces are hallucinated.
Activation of a homologous area in the left hemisphere may produce lexical hallucinations—of letters, numbers, musical notation, sometimes words or pseudowords, or even sentences. One of Mavromatis’s subjects put it this way: “When dozing or before going to sleep … I appear to be reading a book. I see the print clearly and distinguish the words, but the words rarely seem to have any particular significance. The books I appear to be reading are never books with which I am familiar, but frequently deal with whatever subject I have been reading during the day.”
(While hypnagogic images of faces and places are usually unrecognizable, there is a distinct category of hypnagogia which McKellar and Simpson call “perseverative”: hallucinations or recurrent images of something one has been exposed to earlier in the day. If, for example, one has been driving all day, one may “see” a hedgerow or line of trees continually unfurling before one’s closed eyes.)
Hypnagogic imagery may be faint or colorless, but it often has brilliant and highly saturated color. Ardis and McKellar, in a 1956 paper, cited a case in which the subject described “colors of the spectrum intensified as though bathed in the fiercest sunlight.” They compared this, as others have, to the exaggeration of color with mescaline. In hypnagogic hallucinations, luminosity or outlines may also seem to be abnormally distinct, with shadows or furrows exaggerated—sometimes such exaggerations go with cartoonlike figures or scenes. Many people speak of an “impossible” clarity or a “microscopic” detail in their hypnagogic visions. Images may seem finer-grained than perception itself, as if the inner eye has an acuity of 20/5 rather than 20/20 (this hyperacuity is a feature common to many types of visual hallucination).
One may “see” a constellation of images in hypnagogia—a landscape in the middle, a face erupting in the upper left corner, a complex geometric pattern around the edge—all present simultaneously and all evolving or metamorphosing in their own ways, a sort of multifocal hallucination. Many people describe hallucinatory polyopia, multiplications of objects or figures (one of McKellar’s subjects saw a pink cockatoo, then hundreds of pink cockatoos talking to each other).
Figures or objects may suddenly zoom towards one, getting larger and more detailed, then retreat. Hypnagogic images, often compared to snapshots or slides, flash into consciousness, hold for a second or two, then disappear; they may be replaced by other images that seem to have no connection or apparent association to one another.
Hypnagogic visions may seem like something from “another world”—this phrase is used again and again by people describing their visions. Edgar Allan Poe stressed the fact that his own hypnagogic images were not only unfamiliar but unlike anything he had ever seen before; they had “the absoluteness of novelty.”2
Most hypnagogic images are not like true hallucinations: they are not felt as real, and they are not projected into external space. And yet they have many of the special features of hallucinations—they are involuntary, uncontrollable, autonomous; they may have preternatural colors and detail and undergo rapid and bizarre transformations unlike those of normal mental imagery.
There is something about the rapid and spontaneous transformations specific to hypnagogic imagery that suggests the brain is “idling,” as my correspondent Mr. Utter suggested. Neuroscientists now tend to speak of “default networks” in the brain, which generate their own images. Perhaps one may also venture the term “play” and think of the visual cortex playing with every permutation, playing with no goal, no focus, no meanings—a random activity or perhaps an activity with so many microdeterminants that no pattern is ever repeated. Few phenomena give such a sense of the brain’s creativity and computational power as the almost infinitely varied, ever-changing torrent of patterns and forms which may be seen in hypnagogic states.
Although Mavromatis writes of hypnagogia as “the unique state of consciousness between wakefulness and sleep,” he sees affinities with other states of consciousness—those of dreams, meditation, trance, and creativity—as well as the altered modes of consciousness in schizophrenia, hysteria, and some drug-induced states. Although hypnagogic hallucinations are sensory (and thus cortical, being produced by the visual cortex, auditory cortex, etc.), he feels that the initiating processes may be in the more primitive, subcortical parts of the brain, and this, too, is something that hypnagogia may share with dreams.
And yet the two are quite distinct. Dreams come in episodes, not flashes; they have a continuity, a coherence, a narrative, a theme. One is a participant or a participant-observer in one’s dreams, whereas with hypnagogia, one is merely a spectator. Dreams call on one’s wishes and fears, and they often replay experiences from the previous day or two, assisting in the consolidation of memory. They sometimes seem to suggest the solution to a problem; they have a strongly personal quality and are determined mostly from above—they are largely “top-down” creations (although, as Allan Hobson argues, with a wealth of supporting evidence, they also employ “bottom-up” processes). In contrast, hypnagogic imagery or hallucination, with its largely sensory qualities—enhanced or exaggerated color and detail and outlines, luminosity, distortions, multiplications, and zoomings—and its detachment from personal experience, is overwhelmingly a “bottom-up” process. (But this is a simplification, for given the two-way traffic at every level in the nervous system, most processes are both top-down and bottom-up.) Hypnagogia and dreaming are both extraordinary states of consciousness, as different from each other as they are different from waking consciousness.
Hypnopompic hallucinations—those that may come upon waking—are often profoundly different in character from hypnagogic hallucinations.3 Hypnagogic hallucinations, seen with closed eyes or in darkness, proceed quietly and fleetingly in their own imaginative space and are not usually felt to be physically present in one’s room. Hypnopompic hallucinations are often seen with open eyes, in bright illumination; they are frequently projected into external space and seem to be totally solid and real. They sometimes give amusement or pleasure, but they often cause distress or even terror, for they may seem charged with intentionality and ready to attack the just-wakened hallucinator. There is no such intentionality with hypnagogic hallucinations, which are experienced as spectacles unrelated to the hallucinator.
While hypnopompic hallucinations are only occasional with most people, they may occur frequently in some, as is the case with Donald Fish, an Australian man whom I met in Sydney after he wrote to me about his vivid hallucinations:
I wake from a calm sleep and perhaps a fairly normal dream with a shock, and there before me is a creature that even Hollywood couldn’t create. The hallucinations fade in about ten seconds, and I can move when I have them. In fact I usually jump about a foot into the air and scream.… The hallucinations are becoming worse—now about four a night—I am now becoming terrified of going to bed. The following are some examples of what I see:
A huge figure of an angel standing over me next to a figure of death in black.
A rotting corpse lying next to me.
A huge crocodile at my throat.
A dead baby on the floo
r covered in blood.
Hideous faces laughing at me.
Giant spiders—very frequent.
Huge hand over my face. Also one on the floor five feet across.
Drifting spider webs.
Birds and insects flying into my face.
Two faces looking at me from under a rock.
Image of myself—only looking older—standing by the bed in a suit.
Two rats eating a potato.
A mass of different colored flags descending onto me.
Ugly-looking primitive man lying on floor covered in tufts of orange hair.
Shards of glass falling on me.
Two wire lobster pots.
Dots of red, increasing to thousands like spattered blood.
Masses of logs falling on me.
It is often said that hypnagogic and hypnopompic hallucinations are more vivid and most easily remembered in childhood, but Mr. Fish’s hallucinations have been lifelong—they started when he was eight, and he is now over eighty. Why he should be so prone to hypnopompic hallucinations is a mystery. Although he has had thousands of hypnopompic hallucinations, he has been able to live a full life and function consistently at a high creative level. A graphic designer and visual artist with a brilliant imagination, he sometimes finds inspiration in his surreal hallucinations.
While Mr. Fish’s hypnopompic imagery is extreme in its frequency (and very distressing to him), it is not atypical in character. Elyn S. wrote to me about her own hypnopompic images:
The most typical one would involve me sitting up in bed and seeing a person—often an old lady—staring at me at some distance from the foot of my bed. (I imagine that such hallucinations are thought to be ghosts by some people—but not by me.) Other examples are seeing a foot-wide spider crawling up my wall; seeing fireworks; and seeing a little devil at the foot of my bed riding a bicycle in place.