Libet’s Experiment

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Updated: Mar 28, 2022
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Although most everyday people believe free will is legitimate, many scientists believe that it is simply an illusion. Most scientist believe that intentions, decisions, and choices are all created in the subconscious mind, and is then delivered to the conscious mind to be panned out. This is an argument that has been circulating since the time of Darwin, Huxley, and Einstein. Many recent scientists also hold these beliefs and have been performing experiments to prove it since the 1980s. The most popular experiment performed to date against the possibility of free will was done by a scientist named Benjamin Libet.

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Libet’s experiment was one that to this day, seems far too simple to explain such a complex topic. Libet monitored his participants “voluntary” finger movements, meanwhile their brain waves were being recorded from their scalp over an area of the brain where movement commands are issued. Participants were asked to spontaneously move their finger, at whatever point they would like to. While they are doing this, they are watching a spot move on a clock face, and they are to note the exact position of the clock when they made their choice. At the end, participants thought that they had made the decision to move about half a second before they actually performed the movement, which would be consistent with the idea that their movement was conscious, and free willed.

But there was a twist. EEG results exhibited a major change in activity from the motor cortex about 350 ms before the participants claimed that they willed the command to move. This signal, which scientist have now nicknamed “readiness potential”, was selected by Libet to signify the moment a decision was made. The widely accepted interpretation of this data is that the decision was solely made in the unconscious, and the conscious was excluded from the decision. With this interpretation, it is assumed that the participant did not “will” the movement, but the decision to make a movement was made unconsciously and the unconscious brain simply lets the conscious brain know that it has made a decision. Further explanation is that the brain is driven by external and internal forces to direct behavior, and a person’s consciousness is only around to learn about it afterwards.

The two biggest issues with Libet’s experiment, and similar subsequent studies after it, is that it heavily relies on introspection and the participants being able to accurately be aware of their timing. Libet claims that humans cannot consciously initiate choices because the motor cortex’s readiness potential begins to develop 400 ms before a subject conscious is aware of an attempt at a movement. But, there is also an element of “awareness of intention” that Libet and others like him acknowledge. The scientist agree that consciousness can only produce awareness of attention, and it occurs 150 ms before an actual movement. Because of this, it is possible that a person can freely choose to inhibit or deny an act that is triggered by the subconscious, which throws out the possibility that free will is an illusion.

Libet’s study also relies too heavily on such a limited area of the brain to collect neurophysiological data. The assumption in Libet’s study is that he can monitor a small piece of the brain, like he did with the motor cortex, and use that to serve as an indication for conscious decision making. The issue with this is that most complex actions are not solely dependent on one are of the brain, and this is the argument that Libet is presenting. There have been more recent investigations that have proven that there are increases in brain development prior to the increases in motor activity, and these are areas that are not known to have correlation with movement. The biggest flaw of this study is that scientist still don’t know exactly where consciousness is processed in the brain, much less where the initiation of intentions is made.

A study in 2008 by Chun Soon and colleagues was performed that was similar to Libet’s study, but they used brain imaging. They also used a different method of introspection with the participants to estimate the instant of their conscious decision. The participants were asked to stare at a stream of letters on a screen. When they felt the urge to, they were told to press one or two buttons, with their right and left index fingers. When the button was pressed, the participants were asked to remember the letter that was on the screen at the time of their decision. After they pressed the button, a screen with four letters shows up, and the participants are asked to indicate which one was present at the time of their decision.

The findings of this study were impressive. Two regions in the frontal and cingulate cortex showed a decision-predictive change a full seven to ten seconds before there was a conscious awareness of the decision. The areas of the motor cortex that issue movement commands showed slightly increased activity a second or so prior to the instant of decision, and much more pronounced activity about 2 seconds after the decision. The interpretation of the results is that the frontal and cingulate cortex could have been processing the rules of the game, and the free-will intent to move. The brain activity seems inevitable since the rules of the game form a conscious context in which willed act could occur at any moment. It is obvious that rules of the game have to be consciously processed in the beginning. However, once they have been well rehearsed, implementing intentions can be done without conscious awareness.

In this research design, participants know that as soon as one trial is done, another is starting. The participants consciously choose to make a movement and the brain no doubt is planning to make a movement long before a signal to go is delivered via a decision-making process. Because of this, the pre-movement increased brain activity could actually be reflecting conscious processing of the rules of the game, and also the participants will to obey the rules. This is why this study is a great support of the free-will interpretation. The neuroactivity increase in non-motor areas can possibly reflect conscious decision making before a movement is made. In conclusion, the decision to “go” was only one final part of a consciously willed process. This is drastically different from Libet’s conclusion where he simply boils it down to the “go” movement and ignores everything else beforehand.

Even if free will is an illusion, there are many benefits to believing in it. Belief in free will is highly relevant to many social, legal, and moral judgements. A great example of this is the legal system. If free will is an illusion, and people are unable to escape what has been predetermined for them, then why does the legal system waste time trying to establish whether or not a person was in the right state of mind during a crime? The legal definition of “heat of passion crimes” goes as follows “an intensely emotional state of mind induced by a type of provocation that would cause a reasonable person to act on impulse or without reflection”. If the jury finds that someone who killed another acted in the heat of passion, then their charge of murder can be reduced to manslaughter. If heat of passion crimes are inevitable, just like any other crimes, then it makes no sense for them to receive lighter sentences, but they still do.

Another benefit in the belief in free will is the difference in moral behavior. Two experiments performed by Kathleen Vohs and Jonathan schooler set out to test if inducing participants to believe that human behavior is predetermined would encourage cheating. In experiment 1, participants were randomly assigned to one of two conditions. The first group read a text that claimed that intelligent people, including most scientist, now recognize that free will is actually an illusion, and also that free will is simply a side effect of the architecture of the mind. In the control condition, the participants read a passage from a chapter on consciousness, and it did not discuss free will at all. After reading what was assigned to the, they were to complete the Free Will and Determinism scale, and also the Positive and Negative Affectivity Schedule. These two scales were used to assess whether or not the readings affected their beliefs and moods. After their assessments, the participants were given a computer based mental arithmetic task in which they were asked to calculate the answers to 20 math problems. They were told that the computer had a programing glitch, and the correct answer would show up on the screen while they were attempting to solve the problems, but they were able to stop the answer from appearing on the screen by pressing the space bar after the problem appeared.

Furthermore, participants were told that although the experimenter would not know whether or not they pressed the spacebar, the should still attempt to solve the problems honestly and on their own. In reality, the computer was rigged to show the answer and to record the number of space-bar presses. The results of this experiment showed that participants who read the anti-free-will essay did in fact cheat more frequently than the control group. On top of that, reading the text also reduced the participants’ belief in free will, which the researchers accredit the cheating to. Although the evidence in the first experiment was statistically strong, the way that cheating was operationalized can cloud the interpretation of the results. In the first experiment, cheating behavior was measured by the number of instances in which participants allowed answers to be presented when they were supposed to be calculating them on their own. Even though this was a great method of assessing cheating, it is important to realize that doing nothing is coded as cheating. Because of this, the anti-free-will essay may have caused the participants to be passive overall, and not just participating in immoral behavior specifically. Even though the participants were instructed to press the spacebar to avoid receiving answers, their failure to do so (which counted as cheating) may not have been deliberately unethical.

Experiment 2 addressed this limitation by requiring active behavior from participants in order to cheat. The researchers also included a condition that was intended to strengthen the belief in free will so that they could properly test their hypothesis between strength of free will beliefs and moral behavior. The final condition was one where participants could not cheat at all. Participants were separated into five conditions. In three of the conditions, they were given the opportunity to cheat. In the cheating possible conditions participants completed a task that involved reading and considering a series of statements meant to change beliefs or feelings. They were given a booklet with 15 statements and were asked to think about each statement for 1 minute before reading the next. Belief in free will was manipulated by varying the content of the statements. In the free-will condition, participants read statements such as “I am able to override the genetic and environmental factors that sometimes influence my behavior” and “avoiding temptation requires that I exert my free will”.

In the determinism condition, participants read statements such as “A belief in free will contradicts the known fact that the universe is governed by lawful principles of science,” and “Ultimately, we are biological computers—designed by evolution, built through genetics, and programmed by the environment.” In the neutral condition, participants read statements such as, “Sugar cane and sugar beets are grown in 112 countries.” After the participants read and thought about the statements, they completed the Free Will and Determinism scale, and also the Positive and Negative Affectivity Schedule. Participants were given a 15-question exam on an array of topics. They were told that the experimenter was investigating people’s enjoyment of tasks when they receive feedback and rewards for performance, in which they would be paid $1 for each correct answer.

The experimenter then pretended to receive a call that she had to attend a meeting immediately. She told the participants that they should work for a maximum of 15 minutes, and then score their own problems with the answer key at the front of the room and pay themselves $1 for each correct answer. She told the participants to use the shredder to shred their papers because she did not have permission to keep them. She then left the room and waited outside to debrief the participants. A limitation of this study is that they were unable to determine individual scores on the task or the amount each participant paid themselves.

The researchers calculated the average amount each participant paid themselves, and the average served as a proxy for each participants number of correct answers. The two comparison conditions were called baseline experimenter-scored and determinism experimenter-scored. These two group allow the researchers to have a better gauge of the number of questions that participants answered correctly. In the baseline experimenter-scored condition, participants completed the exam and it was scored by the experimenter. Afterwards they received $1 for each correct answer. Participants in this condition were not asked to complete the Free Will and Determinism scale so that the concept of free will would not be activated. In the determinism experimenter-scored condition, the participants were given deterministic statements, and then the exam. They experimenter scored their exam and they were also paid $1 for each correct answer. This condition allowed the researchers to assess whether or not reading the scientific-sounding determinism statements would have the incidental effect of aiding in solving logic problems.

The results of the experiment were surprising. In both experiments, researchers found that weakening free-will beliefs did in fact increase cheating. Experiment 1 presented a passive cheating opportunity. This means that to avoid cheating, the participants had to actively prevent the answer from appearing on the screen. This is a similar situation to receiving too much change from a store clerk, but not saying anything about it. Experiment 2 presented active cheating. Participants who were allowed to pay themselves and also read deterministic views beforehand, paid themselves more than groups who read neutral or free-will statements. They also paid themselves more than the two groups whos exams were graded by the experimenters. 

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Libet's experiment. (2021, Nov 29). Retrieved from