The experiments of the
physiologist Benjamin Libet are famous for their contribution to the free
will/determinism debate to the extent that in popular imagination they are
often believed to have disproved the existence of free will.
The most important study was Libet, B.,
Gleason, C. A., Wright, E. W. & Pearl, D. K., Brain, 106, (1983), pp. 623-642. Here motor cortical activity
was measured using EMG (scalp electrodes) and was used to isolate the pattern
associated with the moving of a hand, which was termed the ‘readiness
potential’. Individually tested subjects were asked to sit down and after how
ever long they liked to spontaneously move a hand. Simultaneously they were to
remember the time at which they decided to move the hand.
Libet’s tests discovered readiness potential
an average of 1/5 second before the subject was aware of making the choice. The
spread had an upper limit of 1/2 second. Among others who have replicated the
experiment, apparently one study reported an average readiness potential of 1
1/4 seconds.
