In the River of Consciousness

The Physiology of Truth: Neuroscience and Human Knowledge

by Jean-Pierre Changeux
Harvard University Press, 336 pp., $45.00 (to be published in April 2004)

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 chain or a train, 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, into 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… and does it only seem continuous to itself by an illusion analogous to that of the zoetrope?”

Before 1830 (short of making an actual working model, or toy theater), there was no way of making representations or images that had movement. Nor would it have occurred to anyone 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, an idea that was soon to give rise to the motion picture.

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. All of these instruments contained a drum or disc on which a series of drawings—of animals moving, ball games, acrobats in motion, plants growing—was painted or pasted. The drawings could be viewed one at a time through radial slits in the drum, but when the drum was set into motion, the separate drawings flicked by in rapid succession, and at a critical speed, this suddenly gave way to the perception of a single, steady moving picture. When one slowed the drum again, the illusion vanished. Though zoetropes were usually seen as toys, providing a magical illusion of motion, they were originally designed (often by scientists or philosophers) with a sense that they could serve a very serious purpose: to illuminate the mechanisms …

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