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To measure the actual time of the voluntary motor act, an electromyograph (EMG) recorded the muscle movement using electrodes on the skin over the activated muscle of the forearm.
The EMG time was taken as the zero time relative to which all other times were calculated.
To monitor brain activity during the same period, Libet used an electroencephalogram (EEG).
The EEG uses small electrodes placed at various points on the scalp that measure neuronal activity in the cortex, the outermost portion of the brain, which is associated with higher cognition.
The transmission of electrical signals across regions of the cortex causes differences in measured voltage across EEG electrodes.
It has been suggested that consciousness is merely a side-effect of neuronal functions, an epiphenomenon of brain states.
Pressing the button also recorded the position of the dot on the oscillator, this time electronically.
By comparing the marked time of the button's pushing and the subject's conscious decision to act, researchers were able to calculate the total time of the trial from the subject's initial volition through to the resultant action.
To gauge the relation between unconscious readiness potential and subjective feelings of volition and action, Libet required an objective method of marking the subject's conscious experience of the will to perform an action in time, and afterward comparing this information with data recording the brain's electrical activity during the same interval.
For this, Libet required specialized pieces of equipment.
This timer was set so that the time it took for the dot to travel between intervals marked on the oscilloscope was approximately forty-three milliseconds.