How the Brain Creates Our Mental World
(Part 1)
Chris Frith
1st paragraph

Who's in Control?
Most of the work that scientists do is of little interest outside a very narrow circle of other scientists in the same field.
This is as true for physicists as for psychologists. It is said that the great majority of research papers are read by fewer than 10 other people. Many papers are never read at all. But occasionally an observation is made that is so startling that it is discussed widely outside the field of science. One such observation was so published in 1983 by Benjamin Libet and his colleagues. The experiment is delightfully simple. All the person in the experiment had to do was lift one finger whenever he or she “felt the urge to do so.” At the same time electrical activity in the brain was measured using EEG equipment. It was already well known that there is characteristic change in this activity just before someone spontaneously makes any movement like lifting a finger. This change in activity is very small, but it can be detected by combining measurements from many movements. The change in brain activity can be detected up to a second before the finger is actually lifted. The novel aspect of Libet's study was that he asked his volunteers to tell him when they had the urge” to lift their finger. They did this by reporting the "time" that was displayed on a special clock at the moment that they “had the urge.” The urge to lift the finger occurred about 200 msec before the finger was actually lifted. But the key observation that caused so much fuss was that the change in brain activity occurred about 500 msec before the finger was lifted. So brain activity indicating that the volunteer was about to lift a finger occurred about 300 msec before that volunteer reported having the urge to lift his or her finger.


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