Salı, Mart 02, 2010

Unconscious decision-making

Neuroscientists Daniel Kahneman and Amos Tversky received a 2002 Nobel Prize for their 1979 research that argued humans rarely make rational decisions.

People do indeed make optimal decisions—but only when their unconscious brain makes the choice.

You don't consciously decide to stop at a red light or steer around an obstacle in the road. Once we started looking at the decisions our brains make without our knowledge, we found that they almost always reach the right decision, given the information they had to work with

A very simple unconscious-decision test.

A series of dots appears on a computer screen, most of which are moving in random directions. A controlled number of these dots are purposely moving uniformly in the same direction, and the test subject simply has to say whether he believes those dots are moving to the left or right. The longer the subject watches the dots, the more evidence he accumulates and the more sure he becomes of the dots' motion.

Subjects in this test performed exactly as if their brains were subconsciously gathering information before reaching a confidence threshold, which was then reported to the conscious mind as a definite, sure answer.

The subjects, however, were never aware of the complex computations going on, instead they simply "realized" suddenly that the dots were moving in one direction or another. Human brain is wired naturally to perform calculations of this kind.

A probabilistic decision-making system has several advantages. The most important is that it allows us to reach a reasonable decision in a reasonable amount of time. If we had to wait until we're 99 percent sure before we make a decision, then we would waste time accumulating data unnecessarily. If we only required a 51 percent certainty, then we might reach a decision before enough data has been collected.

Another main advantage is that when we finally reach a decision, we have a sense of how certain we are of it—say, 60 percent or 90 percent—depending on where the triggering threshold has been set.

The findings are published in the Dec 26 2008 issue of the journal "Neuron"

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