The River of Consciousness

by Oliver Sacks

  I am glad I was forewarned, for the following day (Tuesday, the seventeenth), soon after waking from the embolization—it was performed under general anesthesia—I was to be assailed by feelings of excruciating tiredness and paroxysms of sleep so abrupt they could poleax me in the middle of a sentence or a mouthful, or when visiting friends were talking or laughing loudly a yard away from me. Sometimes, too, delirium would seize me within seconds, even in the middle of handwriting. I felt extremely weak and inert; I would sometimes sit motionless until hoisted to my feet and walked by two helpers. While pain seemed tolerable at rest, an involuntary movement such as a sneeze or hiccup would produce an explosion, a sort of negative orgasm of pain, despite my being maintained, like all post-embolization patients, on a continuous intravenous infusion of narcotics. This massive infusion of narcotics halted all bowel activity for nearly a week, so that everything I ate—I had no appetite but had to “take nourishment,” as the nursing staff put it—was retained inside me.

  Another problem—not uncommon after the embolization of a large part of the liver—was a release of ADH, antidiuretic hormone, which caused an enormous accumulation of fluid in my body. My feet became so swollen they were almost unrecognizable as feet, and I developed a thick tire of edema around my trunk. This “hyperhydration” led to lowered levels of sodium in my blood, which probably contributed to my deliria. With all this, and a variety of other symptoms—temperature regulation was unstable, I would be hot one minute, cold the next—I felt awful. I had “a general feeling of disorder” raised to an almost infinite degree. If I had to feel like this from now on, I kept thinking, I would sooner be dead.

  I stayed in the hospital for six days after embolization and then returned home. Although I still felt worse than I had ever felt in my life, I did in fact feel a little better, minimally better, with each passing day (and everyone told me, as they tend to tell sick people, that I was looking “great”). I still had sudden, overwhelming paroxysms of sleep, but I forced myself to work, correcting the galleys of my autobiography (even though I might fall asleep in mid-sentence, my head dropping heavily onto the desk, my hand still clutching a pen). These post-embolization days would have been very difficult to endure without this task (which was also a joy).

  On day ten, I turned a corner—I felt awful, as usual, in the morning, but a completely different person in the afternoon. This was delightful, and wholly unexpected: there was no intimation, beforehand, that such a transformation was about to happen. I regained some appetite, my bowels started working again, and on February 28 and March 1, I had a huge and delicious diuresis, losing fifteen pounds over the course of two days. I suddenly found myself full of physical and creative energy and a euphoria almost akin to hypomania. I strode up and down the corridor in my apartment building while exuberant thoughts rushed through my mind.

  How much of this was a reestablishment of balance in the body; how much an autonomic rebound after a profound autonomic depression; how much other physiological factors; and how much the sheer joy of writing, I do not know. But my transformed state and feeling were, I suspect, very close to what Nietzsche experienced after a period of illness and expressed so lyrically in The Gay Science:

  Gratitude pours forth continually, as if the unexpected had just happened—the gratitude of a convalescent—for convalescence was unexpected….The rejoicing of strength that is returning, of a reawakened faith in a tomorrow or the day after tomorrow, of a sudden sense and anticipation of a future, of impending adventures, of seas that are open again.

  * * *

  *1 David Shenk describes this beautifully in his book The Forgetting.

  *2 See also Antonio Damasio and Gil B. Carvalho, “The Nature of Feelings: Evolutionary and Neurobiological Origins” (2013).

  *3 Aretaeus noted in the second century that patients in such a state “are weary of life and wise to die.” Such feelings, while they may originate, and be correlated, with autonomic imbalance, must connect with those “central” parts of the autonomic nervous system in which feeling, mood, sentience, and (core) consciousness are mediated—the brain stem, hypothalamus, amygdala, and other subcortical structures.

  The River of Consciousness

  “Time,” says Jorge Luis Borges, “is the substance I am made of. Time is a river that carries me away, but I am the river.” Our movements, our actions, are extended in time, as are our perceptions, our thoughts, the contents of consciousness. We live in time, we organize time, we are time creatures through and through. But is the time we live in, or live by, continuous, like Borges’s river? Or is it more comparable to a succession of discrete moments, like beads on a string?

  David Hume, in the eighteenth century, favored the idea of discrete moments, and for him the mind was “nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in a perpetual flux and movement.”

  For William James, writing his Principles of Psychology in 1890, the “Humean view,” as he called it, was both powerful and vexing. It seemed counterintuitive, as a start. In his famous chapter on “the stream of thought,” James stressed that to its possessor consciousness seems to be always continuous, “without breach, crack, or division,” never “chopped up in bits.” The content of consciousness might be changing continually, but we move smoothly from one thought to another, one percept to another, without interruption or breaks. For James, thought flowed, hence his introduction of the term “stream of consciousness.” But, he wondered, “is consciousness really discontinuous…does it only seem continuous to itself by an illusion analogous to that of the zoetrope?”

  Before about 1830 (short of making an actual working model), we had no way of making representations or images that had movement. Nor would it have occurred to most that a sensation or illusion of movement could be conveyed by still pictures. How could pictures convey movement if they had none themselves? The very idea was paradoxical, a contradiction. But the zoetrope proved that individual images could be fused in the brain to give an illusion of continuous motion.

  Zoetropes (and many other similar devices with a variety of names) were extremely popular in James’s time, and few middle-class Victorian households were without one. These instruments contained a drum or disc on which a sequence of drawings—“freeze frames” of animals moving, ball games, acrobats in motion, plants growing—was painted or pasted. When the drum or disc was rotated, the separate drawings flicked by in rapid succession and, at a critical speed, suddenly gave way to the perception of a single, steadily moving picture. Though zoetropes were popular as toys, providing a magical illusion of motion, they were originally designed (often by scientists or philosophers) to serve a very serious purpose: to illuminate the mechanisms of animal motion and of vision itself.

  Had James been writing a few years later, he might have used the analogy of a motion picture. A movie, with its taut stream of thematically connected images, its visual narrative integrated by the viewpoint and values of its director, is not at all a bad metaphor for the stream of consciousness. The technical and conceptual devices of cinema—zooming, fading, dissolving, omission, allusion, association, and juxtaposition of all sorts—rather closely mimic the streamings and veerings of consciousness in many ways.

  It is an analogy that Henri Bergson used in his 1907 book Creative Evolution, in which he devoted an entire section to “The Cinematographical Mechanism of Thought and the Mechanistic Illusion.” But when Bergson spoke of “cinematography” as an elemental mechanism of brain and mind, it was, for him, a very special sort of cinematography, in that its “snapshots” were not isolable from one another but organically connected. In Time and Free Will, he wrote of such perceptual moments as “permeating one another,” “melting into” one another, like the notes of a tune (as opposed to the “empty and succeeding beats of a metronome”).

  James too wrote of connectedness and articulation, and for him these moments are connected by the whole trajectory and
theme of a life:

  The knowledge of some other part of the stream, past or future, near or remote, is always mixed in with our knowledge of the present thing.

  …These lingerings of old objects, these incomings of new, are the germs of memory and expectation, the retrospective and the prospective sense of time. They give that continuity to consciousness without which it could not be called a stream.

  In the same chapter, on the perception of time, James quotes a fascinating speculation of James Mill (the father of John Stuart Mill) as to what consciousness might be like if it were discontinuous, a string of bead-like sensations and images, all separate:

  We never could have any knowledge except that of the present instant. The moment each of our sensations ceased it would be gone for ever, and we should be as if we had never been…we would be wholly incapable of acquiring experience.

  James wonders whether existence would indeed be possible under these circumstances, with consciousness reduced to “a glow-worm spark…[with] all beyond in total darkness.” This is precisely the condition of someone with amnesia, though the “moment” here may be a few seconds in length. When I described my amnesic patient Jimmie, the “Lost Mariner,” in The Man Who Mistook His Wife for a Hat, I wrote,

  He is…isolated in a single moment of being, with a moat or lacuna of forgetting all round him….He is a man without a past (or future), stuck in a constantly changing, meaningless moment.

  Were James and Bergson intuiting a truth in comparing visual perception—and indeed, the flow of consciousness itself—to mechanisms like zoetropes and movie cameras? Does the eye/brain actually “take” perceptual stills and somehow fuse them to give a sense of continuity and motion? No clear answer was forthcoming during their lifetimes.

  There is a rare but dramatic neurological disturbance that a number of my patients have experienced during attacks of migraine, when they may lose the sense of visual continuity and motion and see instead a flickering series of “stills.” The stills may be clear-cut and sharp, succeeding one another without superimposition or overlap. But more commonly they are somewhat blurred, as with a too-long photographic exposure; they persist long enough that each is still visible when the next “frame” is seen, so that three or four frames, the earlier ones progressively fainter, are apt to be superimposed on each other. (This effect resembles some of Étienne-Jules Marey’s “chronophotographs” of the 1880s, in which one sees a whole array of photographic moments or time frames superimposed on a single plate.)*1

  Such attacks are brief, rare, and not readily predicted or provoked, and perhaps for this reason I could find no good accounts of the phenomenon in the medical literature. When I wrote about them in my 1970 book, Migraine, I used the term “cinematographic vision” for them, for patients always compared them to films run too slow. I noted that the rate of flickering in these episodes seemed to be between six and twelve per second. There might also be, in cases of migraine delirium, a flickering of kaleidoscopic patterns or hallucinations. (The flickering might then accelerate to restore the appearance of normal motion.)

  This was a startling visual phenomenon for which, in the 1960s, there was no good physiological explanation. But I could not help wondering then whether visual perception might in a very real way be analogous to cinematography, taking in the visual environment in brief, instantaneous, static frames or “stills” and then, under normal conditions, fusing these to give visual awareness its usual movement and continuity—a fusion which, seemingly, was failing to occur in the very abnormal conditions of these migraine attacks.

  Such visual effects may also occur in certain seizures, as well as in intoxications (especially with hallucinogens such as LSD). And there are other unusual visual effects that may occur. Moving objects may leave a trailing smear or wake, images may repeat themselves, and afterimages may be greatly prolonged.*2

  I heard similar accounts in the late 1960s from some of my postencephalitic patients when they were “awakened,” and especially overexcited, by taking the drug L-dopa. Some patients described cinematic vision; others described extraordinary “standstills,” sometimes hours long, in which visual flow was arrested—and even the stream of movement, of action, of thought itself.

  These standstills were especially severe with Hester Y. Once I was called to the ward because Mrs. Y. had started a bath, and there was now water overflowing in the bathroom. I found her standing completely motionless in the middle of the flood.

  She jumped when I touched her and asked, “What happened?”

  “You tell me,” I answered.

  She said that she had started to run a bath for herself, and there was an inch of water in the tub…and then I touched her and she suddenly realized that the tub must have run over and caused a flood. She had been stuck, transfixed, at that perceptual moment when there was just an inch of water in the bath.

  Such standstills showed that consciousness could be brought to a halt for substantial periods while automatic, nonconscious function—maintenance of posture or breathing, for example—continued as before.

  Another striking example of perceptual standstill can be demonstrated with a common visual illusion, the Necker cube. Normally, when we look at this ambiguous perspective drawing of a cube, it switches perspective every few seconds, seeming first to project, then to recede, and no effort of will suffices to prevent this switching back and forth. The drawing itself does not change, nor does its retinal image. The switching is a purely cortical process, a conflict in consciousness itself, as it vacillates between two possible perceptual interpretations. This switching is seen in all normal subjects and can be observed with functional brain imaging. But a postencephalitic patient during a standstill state may see the same unchanging perspective for minutes or hours at a time.*3

  The normal flow of consciousness, it seemed, could not only be fragmented, broken into small, snapshot-like bits, but also suspended intermittently, for hours at a time. I found this even more puzzling and uncanny than cinematic vision, for it had been accepted almost axiomatically since the time of William James that consciousness, in its very nature, is ever changing and ever flowing. Now my own clinical experience had to cast doubt on even that.

  Thus I was primed to be further fascinated when, in 1983, Josef Zihl and his colleagues in Munich published a single, very fully described case of motion blindness: a woman who, following a stroke, became permanently unable to perceive motion. (The stroke damaged highly specific areas of the visual cortex which physiologists have shown in experimental animals to be crucial for motion perception.) In this patient, whom they call L. M., there were “freeze frames” lasting several seconds, during which Mrs. M. would see a prolonged motionless image and be visually unaware of any movement around her, though her flow of thought and perception was otherwise normal. She might begin a conversation with a friend standing in front of her but not be able to see her friend’s lips moving or facial expressions changing. And if the friend moved around behind her, Mrs. M. might continue to “see” him in front of her, even though his voice now came from behind. She might see a car “frozen” a considerable distance away but find, when she tried to cross the road, that it was now almost upon her. She would see a “glacier,” a frozen arc of tea coming from the spout of the teapot, but then realize that she had overfilled the cup and there was now a puddle of tea on the table. Such a condition was utterly bewildering and sometimes quite dangerous.

  There are clear differences between cinematic vision and the sort of motion blindness described by Zihl, and perhaps between these and the very long visual and sometimes global freezes experienced by some postencephalitic patients. These differences imply that there must be a number of different mechanisms or systems for the perception of visual motion and the continuity of visual consciousness, and this accords with evidence obtained from perceptual and psychological experiments. Some or all of these mechanisms may fail to work as they should in certain intoxications, some attacks of migraine, and some f
orms of brain damage—but can they also reveal themselves under normal conditions?

  An obvious example springs to mind, which many of us have seen and perhaps puzzled over when watching evenly rotating objects—fans, wheels, propeller blades—or when walking past fences or palings, when the normal continuity of motion seems to be interrupted. Thus occasionally as I lie in bed looking up at my ceiling fan, the blades seem suddenly to reverse direction for a few seconds and then to return equally suddenly to their original forward motion. Sometimes the fan seems to hover or stall, and sometimes to develop additional blades or dark bands broader than the blades.

  It is similar to what happens in a film when the wheels of stagecoaches sometimes appear to be going slowly backwards or scarcely moving. This wagon-wheel illusion, as it is called, reflects a lack of synchronization between the rate of filming and that of the rotating wheels. But I can have a real-life wagon-wheel illusion when I look at my fan with the morning sun flooding into my room, bathing everything in a continuous, even light. Is there, then, some flickering or lack of synchronization in my own perceptual mechanisms—analogous, again, to the action of a movie camera?

  Dale Purves and his colleagues have explored wagon-wheel illusions in great detail, and they have confirmed that this type of illusion or misperception is universal among their subjects. Having excluded any other cause of discontinuity (intermittent lighting, eye movements, etc.), they conclude that the visual system processes information “in sequential episodes,” at the rate of three to twenty such episodes per second. Normally, these sequential images are experienced as an unbroken perceptual flow. Indeed, Purves suggests, we may find movies convincing precisely because we ourselves break up time and reality much as a movie camera does, into discrete frames, which we then reassemble into an apparently continuous flow.