(4 of 7)
Our authorship of voluntary actions can also be an illusion, the result of noticing a correlation between what we decide and how our bodies move. The psychologist Dan Wegner studied the party game in which a subject is seated in front of a mirror while someone behind him extends his arms under the subject's armpits and moves his arms around, making it look as if the subject is moving his own arms. If the subject hears a tape telling the person behind him how to move (wave, touch the subject's nose and so on), he feels as if he is actually in command of the arms.
The brain's spin doctoring is displayed even more dramatically in neurological conditions in which the healthy parts of the brain explain away the foibles of the damaged parts (which are invisible to the self because they are part of the self). A patient who fails to experience a visceral click of recognition when he sees his wife but who acknowledges that she looks and acts just like her deduces that she is an amazingly well-trained impostor. A patient who believes he is at home and is shown the hospital elevator says without missing a beat, "You wouldn't believe what it cost us to have that installed."
Why does consciousness exist at all, at least in the Easy Problem sense in which some kinds of information are accessible and others hidden? One reason is information overload. Just as a person can be overwhelmed today by the gusher of data coming in from electronic media, decision circuits inside the brain would be swamped if every curlicue and muscle twitch that was registered somewhere in the brain were constantly being delivered to them. Instead, our working memory and spotlight of attention receive executive summaries of the events and states that are most relevant to updating an understanding of the world and figuring out what to do next. The cognitive psychologist Bernard Baars likens consciousness to a global blackboard on which brain processes post their results and monitor the results of the others.
BELIEVING OUR OWN LIES
A SECOND REASON THAT INFORMATION MAY BE SEALED OFF FROM consciousness is strategic. Evolutionary biologist Robert Trivers has noted that people have a motive to sell themselves as beneficent, rational, competent agents. The best propagandist is the one who believes his own lies, ensuring that he can't leak his deceit through nervous twitches or self-contradictions. So the brain might have been shaped to keep compromising data away from the conscious processes that govern our interaction with other people. At the same time, it keeps the data around in unconscious processes to prevent the person from getting too far out of touch with reality.
What about the brain itself? You might wonder how scientists could even begin to find the seat of awareness in the cacophony of a hundred billion jabbering neurons. The trick is to see what parts of the brain change when a person's consciousness flips from one experience to another. In one technique, called binocular rivalry, vertical stripes are presented to the left eye, horizontal stripes to the right. The eyes compete for consciousness, and the person sees vertical stripes for a few seconds, then horizontal stripes, and so on.