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Libet's experiment: is there human freedom?

Libet's experiment: is there human freedom?

July 19, 2024

Are we really owners of our acts or, on the contrary, are we conditioned by a biological determinism? These doubts have been widely debated throughout the centuries of philosophy and psychology, and the Libet experiment it has helped to intensify them.

Throughout this article we will discuss the experiment conducted by the neurologist Benjamin Libet, as well as its procedures, its results and reflections, and the controversy surrounding this study.

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Who was Benjamin Libet?

Born in the United States in 1916, Benjamin Libet became a renowned neurologist whose first works focused on the investigation of synaptic and post-synaptic responses, to then focus on the study of neural activity and the threshold sensations of these (that is, the point at which the intensity of a stimulus generates a conscious sensation of change).


His first relevant research was aimed at establishing the amount of activation that certain specific brain areas need to release artificial somatic perceptions. As a result of these works, Libet began his famous investigations on the conscience of the people, as well as his experiments that linked neurobiology and freedom .

Following his studies and reflections on freedom, free will and conscience, Libet became a pioneer and a celebrity within the world of neurophysiology and philosophy. Despite all these, their conclusions have not been exempt from criticism from researchers of both disciplines.


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The Libet experiment

Before Libet began his well-known experiments, other researchers such as Hans Helmut Kornhuber and Lüder Deecke already coined the term "bereitschaftspotential", which in our language we could translate as "potential for preparation" or "potential for readiness".

This term refers to a dimension that quantifies the activity of the motor cortex and the supplementary motor area of ​​the brain when they are prepared for voluntary muscular activity. That is to say, refers to brain activity when a voluntary movement is planned . From this, Libet constructed an experiment in which a relationship was sought in the subjective freedom that we believe we have when initiating a voluntary movement and the neurosciences.

In the experiment, each of the participants was placed in front of a kind of clock which was programmed to take a full turn of the hand in 2.56 seconds. Next, he was asked to think about a point on the circumference of the clock chosen at random (always the same) and at the moments when the hand passed by, he had to make a wrist movement and, at the same time, remember at what point on the clock was the hand at the moment of having the conscious sensation of going to perform that movement.


Libet and his team called this subjective variable V, referring to the willingness of the person to move. The second variable was coined as variable M, associated to the real moment in which the participant made the movement.

In order to know these M values, each participant was also asked to inform of the exact moment in which he had made the movement. The temporal figures obtained by variables V and M provided information about the time difference that existed between the moment in which the person felt the desire to perform the movement and the exact moment in which the movement was made.

To make the experiment much more reliable, Libet and his collaborators used a series of objective measurements or registers. These consisted of measuring the preparation potential of brain areas related to movement and an electromyography of the muscles involved in the specific activity that was asked of the participants.

Results of the experiment

The discoveries and conclusions made once the measurements were made and the study concluded, did not leave anyone indifferent.

At first, and as expected, the study participants placed the variable V (will) before the variable M. This means that they perceived their conscious desire to perform the movement as prior to it. This fact is easily understood as a correlation between brain activity and the subjective experience of the person.

Now, the data that really supposed a revolution were those extracted from objective records. According to these figures, the brain's potential for preparation appeared before the subject was aware that he wanted to move the wrist ; specifically between 300 and 500 milliseconds before. This can be interpreted as that our brain knows before us that we want to perform an action or movement.

The conflict with free will

For Libet, these results conflicted with the traditional conception of free will. This term, typical of the field of philosophy, refers to the belief that the person has the power to freely choose their own decisions .

The reason was that the desire to make a movement considered as free and voluntary is, in fact, preceded or anticipated by a series of electrical changes in the brain. Therefore, the process of determining or wanting to make a movement begins unconsciously.

However, for Libet the concept of free will continued to exist; since the person still retained the conscious power to voluntarily and freely interrupt the movement.

Finally, these discoveries would be a restriction to the traditional conception of how freedom works and free will, considering that this would not be responsible for initiating the movement but to control and finalize it.

Critics to this investigation

The scientific-philosophical debates about whether people are really free when making decisions or, on the contrary, we are subject to a biologist materialistic determinism , go back many centuries before the Libet experiment and, of course, still continue today. So, as expected, Libet's experiment was not rid of criticism either by philosophy or by neuroscience.

One of the main criticisms made by some thinkers of the theories of free will is that, according to them, the existence of this brain advance would not have to be incompatible with this belief or concept. This brain potential could be a series of automatisms linked to a state of passivity of the person. For them, Libet would not be focusing on what is really important, the more complicated or complex acts or decisions which require prior reflection.

On the other hand, regarding the evaluation of the procedures carried out in the experiment, the methods of counting and measuring times have been questioned , since they do not take into account how much different brain areas take to issue and receive messages.


The Libet Experiment: Is Free Will Just an Illusion? (July 2024).


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