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【英文原文】
Picking our brains: How powerful is the subconscious?
SUBCONSCIOUS thought is the brain's dumb autopilot - the chump behind repetitive tasks, Freudian slips and all the other things we do "without thinking". That was certainly the prevailing view in the 20th century, but the subconscious has lately gone up in the world. It takes centre stage in creativity, puts the "eureka!" into problem-solving, plays a crucial role in learning and memory, and it's even better at making tough decisions than rational analysis is (New Scientist, 1 December 2007, p 42).
It was in the 1980s that the late neuroscientist Benjamin Libet saw a spark of brain activity 300 milliseconds before subjects consciously chose to twitch a finger. We now know the unconscious decision happens even earlier. In 2008, John-Dylan Haynes at the Bernstein Center for Computational Neuroscience in Berlin, Germany, found brain activity up to 10 seconds before a conscious decision to move (Nature Neuroscience, vol 11, p 543).
Stanislas Dehaene, director of the Cognitive Neuroimaging Unit at INSERM, France, has elegantly revealed the subtle interplay between subconscious and conscious thought. In his experiment, volunteers saw a word flashed onto a screen, followed almost immediately by a picture, which masks conscious perception of the word. As the time interval between the two increases, the word suddenly pops into consciousness - accompanied by characteristic activity on a brain scan. This usually happened when the interval reached around 50 milliseconds, but when emotional words such as "love" or "fear" were used, it happened a few milliseconds earlier. It is as though the decision about the word's importance and attention-worthiness was taken by the subconscious itself (PLoS Biology, vol 5, e260).
Experiments like these have changed our views about the relationship between conscious and subconscious thought, putting the latter firmly in charge. Think of consciousness as a spotlight, with the subconscious controlling when to turn it on and where to direct the beam. "The conscious mind is not free," says Haynes. What we think of as "free will" is actually found in the subconscious.
