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5/19/11

Time, Consciousness, & The Human Brain


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When David Eagleman was eight years old, he fell off a roof and kept on falling. In the years since, Eagleman has collected hundreds of stories like his, and they almost all share the same quality: in life-threatening situations, time seems to slow down. If Eagleman’s body bears no marks of his childhood accident, his mind has been deeply imprinted by it. He is a man obsessed by time.

We think we see things in "real time," but wherever we cast our glance, the light illuminating the object is eight minutes old, having taken that long to arrive from the sun. We are condemned to live in the past without knowing it.

“The other day, I was in the lab," he told [the author], "and I said to Daisy, who sits in the corner, 'Hey, what time is it?' And she said,'I don’t know. My watch is broken.' It turns out that we’re all wearing broken watches.' Clocks offer at best a convenient fiction, he says. They imply that time ticks steadily, predictably forward, when our experience shows that it often does the opposite: it stretches and compresses, skips a beat and doubles back."

Yet “brain time,” as Eagleman calls it, is intrinsically subjective. “Try this exercise,” he suggests in a recent essay. “Put this book down and go look in a mirror. Now move your eyes back and forth, so that you’re looking at your left eye, then at your right eye, then at your left eye again. When your eyes shift from one position to the other, they take time to move and land on the other location. But here’s the kicker: you never see your eyes move.” There’s no evidence of any gaps in your perception—no darkened stretches like bits of blank film—yet much of what you see has been edited out. Your brain has taken a complicated scene of eyes darting back and forth and recut it as a simple one: your eyes stare straight ahead. Where did the missing moments go?

The question raises a fundamental issue of consciousness: how much of what we perceive exists outside of us and how much is a product of our minds? Time isn’t like the other senses, Eagleman says. Sight, smell, touch, taste, and hearing are relatively easy to isolate in the brain.But a sense of time is threaded through everything we perceive.“But the interesting thing about time is that there is no spot. It’s a distributed property. It’s metasensory; it rides on top of all the others.”

One of the seats of emotion and memory in the brain is the amygdala, he explained. When something threatens your life, this area seems to kick into overdrive, recording every last detail of the experience. The more detailed the memory, the longer the moment seems to last. “This explains why we think that time speeds up when we grow older,” Eagleman said—why childhood summers seem to go on forever, while old age slips by while we’re dozing. The more familiar the world becomes, the less information your brain writes down, and the more quickly time seems to pass.

In one story, a man is thrown off his motorcycle after colliding with a car. As he’s sliding across the road, perhaps to his death, he hears his helmet bouncing against the asphalt. The sound has a catchy rhythm, he thinks, and he finds himself composing a little ditty to it in his head.

Eagleman was brought up as a secular Jew and became an atheist in his teens. Lately, though, he’d taken to calling himself a Possibilian—a denomination of his own invention. Science had taught him to be skeptical of cosmic certainties, he told me. From the unfathomed complexity of brain tissue—“essentially an alien computational material”—to the mystery of dark matter, we know too little about our own minds and the universe around us to insist on strict atheism, he said. “And we know far too much to commit to a particular religious story.” Why not revel in the alternatives? (Compiled from this source, which has more explanations.)

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