Tag Archives: Libet’s experiment

Libet’s experiment

For the last few days we have been trying to understand the concept of free will from different points
of view and in relation to different fields of science and philosophy. Today we will discuss a very important
and fundamental experiment in neuroscience that may tell us a lot about the relationship between
conscious thought and action- the very question regarding the presence of free will.
Benjamin Libet did a series of experiments to determine if there is electrical activity in the brain before
a bodily action. In a set of experiments done in 1980s he was able to show that there was an electrical
signal build-up in the brain about half a second before a physical movement is done. So half a second before
I move my finger, there is an electrical build up in some neurons of the brain. This electrical build up
was given the name “readiness potential” by Libet. That was interesting but that does not tell us about the
relationship between physical movement, “free will” and conscious thought. That was the next experiment that
Libet did in the 1990s.

In the more advanced experiment Libet put electrodes on the heads of his subjects and asked them to observe
a very fast moving clock. he then asked them to move their wrists whenever they wanted to but note the time
at which the “desire to move the wrist” came into their minds. So there were three time measurements for each
1) The time of the build up of the electrical signals in the brain ( this is the readiness potential)
2) The time when the conscious wish to act occurs in the brain ( this is now called Libet’s W time)
3) The actual time of the physical movement or action.
Now we have see that in the experiments conducted in 1980s, Libet had found that the readiness potential happens
upto .5 second or 500 ms before the actual action. Libet found that the conscious will to act occurred about 300 ms after
the readiness potential and about 200 ms before the physical act. So the brain has already initiated an activity
300 ms before you know about it consciously! The conscious desire to move has been caused by electrical signals build up
300 ms prior to it! So the decision to move has been triggered in the brain 300 ms before “you” got to know about it.
This suggests something simple: there seems to be no conscious free will.
The experiment was done very carefully and it was adjusted for errors in measurement.
It would be interesting to correlate this experiment with the reaction times available in “high speed” ball games like
Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun

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