Unconscious Cerebral Initiative and the Role of Conscious Will in
Voluntary Action by Benjamin Libet
Libet aims to show that voluntary acts are preceded by readiness
potentials (RPs), and that the conscious intention to act occurs
after the preparations to act have already been put in motion.
Subjects were told to flex their wrist at any time they chose, but
to record the point at which they decided to do so by noticing the
position of a dot on a clock face. Libet regards this method as
recording voluntary, internally generated action. To be a little bit
pedantic, I can't agree with this, as the subjects are still doing
as the experimenter says, i.e. sitting still in a chair and moving
their wrist at some point, so he is not recording voluntary action
in any ecologically valid way.
Libet was able to take the average of 100's of RPs which occurred in
the supplementary motor area and show that they occurred 550ms
before the action occurred. Furthermore, the point at which the
subjects recorded conscious intention to move occurred about 200ms
before they moved. Thus there was a difference of about 350 ms
between the preparation to act and the conscious intention of
acting.
To answer the criticism that the time taken to observe the dots'
position may be a factor, Libet points to a study which shows that
if subjects have to record the dots position when they are given a
skin stimulus, they actually record the sensation before it has
happened to the degree of 10's of ms. Libet thus believes that this
exaggerates rather than narrows the gap between conscious awareness
and action.
Libet goes on to discuss the philosophical implications i.e. that
preparation to act occurs before intention to act. He decides that
this result does not impinge on our notions of free will because the
timing of conscious intention (200ms before movement) allows time
for us to consciously veto or permit these actions. However the fact
that this procedure does not allow individual RPs to be recorded,
but only the averages makes it difficult for Libet to convincingly
demonstrate either a veto or a permit to action. Libet goes on to
say that we are thus still accountable for our actions, but that
religions etc would be unfair to hold us accountable for mental
impulses to carry out actions as these occur at the unconscious
level.
I found the article very interesting, but could not get as carried
away as Libet by the idea that RPs occur before conscious awareness.
Unless one is an unfashionable duellist, it is really to be expected
that conscious awareness would be preceded by neural activity, as it
is arising from the workings of the brain
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