Are we really owners of our actions or, on the contrary, are we conditioned by biological determinism? These doubts have been widely debated throughout the centuries of philosophy and psychology, and Libet’s experiment has contributed to intensifying them.
Throughout this article we will talk about the experiment carried out by the neurologist Benjamin Libet, as well as its procedures, results and reflections, and the controversy surrounding this study.
Born in the United States in 1916, Benjamin Libet became a renowned neurologist whose early work focused on the investigation of synaptic and postsynaptic responses, later focusing on the study of neural activity and their threshold sensations (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 research on people’s consciousness, as well as his experiments that related neurobiology and freedom.
As a result of his studies and reflections on freedom, free will and consciousness, Libet became a pioneer and a celebrity within the world of neurophysiology and philosophy. Despite all these, his conclusions have not been exempt from criticism from researchers from both disciplines.
Libet’s 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 “preparation potential” or “disposition potential”.
This term refers to a dimension that quantifies the activity of the motor cortex and the supplementary motor area of the brain when they prepare for voluntary muscular activity. That is to say, refers to brain activity when planning to perform a voluntary movement. From this, Libet built an experiment in which a relationship was sought between the subjective freedom that we believe we have when initiating a voluntary movement and neuroscience.
In the experiment, each of the participants was placed in front of a kind of clock which was programmed to make one full turn of the hand in 2.56 seconds. Next, he was asked to think about a point on the circumference of the watch chosen at random (always the same) and at the moments in which the hand passed through there, he had to make a wrist movement and, at the same time, remember at what point on the clock the hand was at the moment of having the conscious sensation of going to make that movement.
Libet and his team called this subjective variable V, referring to the person’s willingness to move. The second variable was coined as variable M, associated with the actual instant in which the participant performed the movement.
To know these M values, each participant was also asked to report the exact moment in which they had performed the movement. The temporal figures obtained through the 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 performed.
To provide much more reliability to the experiment, Libet and his collaborators used a series of objective measurements or records. These consisted of measuring the readiness potential of brain areas related to movement and an electromyography of the muscles involved in the specific activity that the participants were asked to do.
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 person’s subjective experience.
Now, the data that really represented a revolution were those extracted from objective records. According to these figures, the brain’s readiness potential appeared before the subject was aware that he wanted to move his wrist ; specifically between 300 and 500 milliseconds before. This can be interpreted as our brain knowing before we do 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 your own decisions.
The reason was that the desire to perform a movement considered free and voluntary is, in reality, preceded or anticipated by a series of electrical changes in the brain. Therefore, the process of determination or desire 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 movement.
Finally, These discoveries would represent a restriction on the traditional conception of how freedom works and free will, considering that this would not be in charge of initiating the movement but rather controlling and finishing it.
The scientific-philosophical debates about whether people are really free when making decisions or whether, on the contrary, we are subject to a biological materialist determinism, date back many centuries before Libet’s experiment and, of course, still continue today. So, as expected, Libet’s experiment was not immune to criticism from either philosophy or neuroscience.
One of the main criticisms made by some thinkers of free will theories is that, according to them, the existence of this cerebral advance should not 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 most 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, Counting and time measurement methods have been questioned since they do not take into account how long it takes for different brain areas to send and receive messages.
