time of conscious intention

A test subject was instructed to carry out a certain motion, i.e. to raise a finger, whenever he felt like doing so. About 550 ms before this action a readiness-potential can be measured in the brain which differs from the final signal of motor reaction. To determine the instant when a person consciously decided to raise his finger he had to remember the position of a fast running clock hand. It was found that this instant lies about 200 ms before the signal of motor reaction and therefore at least 350 ms after the readiness-potential. Thus the conscious perception clearly appears after a previous physiological activity.

Libet, B., Gleason, C. A., Wright, E. W. & Pearl, D. K. Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act. Brain 106, 623-42. (1983).