Tuesday, September 21, 2010

Consciousness Science

Carl Zimmer has an interesting article on consciousness in the NY Times. Here is a bit to give you a taste:
For Dr. Tononi, sleep is a daily reminder of how mysterious consciousness is. Each night we lose it, and each morning it comes back. In recent decades, neuroscientists have built models that describe how consciousness emerges from the brain. Some researchers have proposed that consciousness is caused by the synchronization of neurons across the brain. That harmony allows the brain to bring together different perceptions into a single conscious experience.

Dr. Tononi sees serious problems in these models. When people lose consciousness from epileptic seizures, for instance, their brain waves become more synchronized. If synchronization were the key to consciousness, you would expect the seizures to make people hyperconscious instead of unconscious, he said.

While in medical school, Dr. Tononi began to think of consciousness in a different way, as a particularly rich form of information. He took his inspiration from the American engineer Claude Shannon, who built a scientific theory of information in the mid-1900s. Mr. Shannon measured information in a signal by how much uncertainty it reduced.


Consciousness is not simply about quantity of information, he says. Simply combining a lot of photodiodes is not enough to create human consciousness. In our brains, neurons talk to one another, merging information into a unified whole. A grid made up of a million photodiodes in a camera can take a picture, but the information in each diode is independent from all the others. You could cut the grid into two pieces and they would still take the same picture.

Consciousness, Dr. Tononi says, is nothing more than integrated information. Information theorists measure the amount of information in a computer file or a cellphone call in bits, and Dr. Tononi argues that we could, in theory, measure consciousness in bits as well. When we are wide awake, our consciousness contains more bits than when we are asleep.


Networks gain the highest phi possible if their parts are organized into separate clusters, which are then joined. “What you need are specialists who talk to each other, so they can behave as a whole,” Dr. Tononi said. He does not think it is a coincidence that the brain’s organization obeys this phi-raising principle.

Dr. Tononi argues that his Integrated Information Theory sidesteps a lot of the problems that previous models of consciousness have faced. It neatly explains, for example, why epileptic seizures cause unconsciousness. A seizure forces many neurons to turn on and off together. Their synchrony reduces the number of possible states the brain can be in, lowering its phi.
Personally I don't this research is on the right track. Information theory is great for treating signals, coding, and noise, but I don't see it as particularly useful for measuring "consciousness". But it is intersting to put another contender in the ring. Maybe it will jog somebody into coming up with a better theory.

It is obvious that integration is an essential element of consciousness, but to reduce it to the ability to track "pinging" or a simulus through centres in the brain strikes me as simplistic. I'm in agreement with David Chalmers who is quoted at the end of the article:
Other researchers view Dr. Tononi’s theory with a respectful skepticism.

“It’s the sort of proposal that I think people should be generating at this point: a simple and powerful hypothesis about the relationship between brain processing and conscious experience,” said David Chalmers, a philosopher at Australian National University. “As with most simple and powerful hypotheses, reality will probably turn out to be more complicated, but we’ll learn something from the attempt. I’d say that it doesn’t solve the problem of consciousness, but it’s a useful starting point.”

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