Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Background: Background: In 1965, Kornhuber & Deecke found a rather strange phenomenon: already 1 second before a body part is moved an activity in the EEG appears. They called it "Bereitschaftspotential" (readiness potential). Surprising is that the readiness potential starts so early.

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Aim: If a simple action like moving our hand is prepared for more than a half second in our brain, at what moment do we consciously decide to perform this action? Can we have a free will?

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Procedure: In the experiments, Libet and colleagues asked questions about when people believed they made a decision and compared it to when the readiness potential occurs as measured by EEG. In one form of their experiment, they measured EEG activity while subjects voluntarily chose to lift a finger. During the task, subjects watched a rapidly moving clock hand (a Wundt’s clock) and made a mental note of when they decided to lift their finger.

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Results: The EEG results demonstrated that, on average, the cortex became active with a ‘readiness potential’ 350 ms before the reported awareness of a ‘wish to move’. These experiments suggested that our subjective awareness of decisions occurs measurably later than the actual events of deciding.

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Conclusion: Our brain initiates a 'voluntionary act' unconsciously.  Not a conscious decision but unconscious (perhaps purely neurophysical) processes are at the origin of our behavior. This conclusion directly contradicts our (conscious) common sense: that we consciously decided to act. Many philosophers and researchers have interpreted Libet’s results as the final blow for free will – in fact as sufficient proof of physiological determinism. However, Libet himself, a fervent believer in free will, hypothesized that free will does exist but consists of the power of vetoing (cancelling) the decision and readiness potential.

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Evaluation: The method of measurement is considered valid, and the result has been successfully replicated many times and in different contexts. Most recently, using an fMRI researchers were able to predict which of two buttons a subject would press several seconds before subject pressed the button. However, it is very unclear whether the interpretations in the conclusions are justified. A main problem is how to interpret the subjects’ reports of the time of their conscious decision. If subjects “become aware” that a conscious decision has been made, was it conscious at all? And if it was not conscious, does that automatically mean that it was not free? Perhaps we need to seriously question the distinction between conscious/unconscious and free/determined.

Libet (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act.  Evaluation: Libet’s hypothesis about free will as the power of veto has been rejected because more recent experiments show that even a veto is preceded by a readiness potential. A serious problem is that of generalizability to other behaviour than simple physical movements. Normally, when we think about free will we consider questions such as big life choices: which career, school, partner, apartment to choose. Perhaps these types of choices are not preceded by a readiness potential. Overall, Libet’s results are trustworthy but mind-boggling in their absurdity and the many questions they raise. While they are usually seen as strong evidence against free will, such a conclusion hinges on how one interprets the concepts “conscious” and “free will”.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Background: There have been debates about whether our decisions are made by brain activity ahead of time or free will. In a previous experiment by Benjamin Libet, electrical brain activity was recorded while subjects were asked to press raise their hand whenever they felt the urge to do so. Their conscious decision to press the button was preceded by a few hundred milliseconds by an electrical signal, also known as ’readiness potential’ that originates from the supplementary motor area (SMA) which is normally involved in coordinating complex movements. However, because the readiness potential appears so shortly before the actual movement, it is possible that it only provides information about the late stages of planning the decision. That is why it is unclear whether the SMA is indeed the part of the brain where the decisions originates, or if the SMA merely reacts to a decision made in some other part of the brain, such as the prefrontal cortex, which is more typically involved in planning and decision making

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Aim: The key question of this study was whether any brain region encoded the subject’s motor decision well before the SMA readiness potential, and, if so, what brain regions are involved and at what time do they become activated.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Procedure: The subjects were asked to relax while fixating on the centre of the screen where a stream of letters was presented. At some point, when they felt the urge to do so, they were to freely decide between one of two buttons, left or right and press it immediately. At the same time, they should remember the letter shown when their decisions were consciously made. After the participants pressed the chosen button, they selected the letter they had seen when they had made the conscious decision to press the button. This experiment was repeated for each participant a few times with an average of 21.6 second breaks in between the trials.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Results: Both the right and the left button was pressed were equally often and most of the intentions (88.6%) were reported to be conciously formed in 1000ms before the movement. The most active region of the brain was the prefrontal cortex. The predictive information in the fMRI signals from this brain region was already presented 7 seconds before the participant pressed the button, allowing the researchers to predict which button the participant would press. Because of the time it takes for the fMRI to react in theory it takes 10 seconds before the conscious motor decision is made.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Results: It was also possible to predict the time at which the participant would press a button. However, this information was contained in the SMA-region and was available as early as 5s before the conscious decision was made. Therefore it seems that different brain regions are responsible for choosing which button to press, and when to press it.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Conclusion: The subject’s decision reached awareness only after it had been influenced by unconcious brain activity for up to 10 seconds. The earliest predictive information is encoded in specific regions of prefrontal cortex and not in SMA, as was previously believed.

Haynes (2008). Unconcious Determinants of free decisions in the human brain   Evaluation: The fMRI made it possible to observe brain activity which determined that brain activity preceded the concious intention far beyond the few hundred milliseconds. Allowed the researchers to separately investigate each brain region and determine how much information each region had about a certain motor decision. However it is still unclear if perhaps yet other processes and brain regions lead up to the activity in the prefrontal cortex. This is not a true experiment, and hence the researchers cannot be completely sure that it is the brain activity which leads up to the decision. Because of the artificial nature of this task, it is difficult to generalize the findings to other types of decisions, especially those that demand a reaction much sooner than the 10 seconds shown in this study.

Haynes (2008). Libet (1983). Questions: Discuss the studies with your fellow student and summarize them together. Have the different studies brought any clarity to the issue whether different neuroimaging techniques lets us investigate the relationship between biological factors and behaviour? Can the free will be studied this way? Discuss the reliability? Discuss the validity? Discuss the procedure? Compare these findings with the Bennet study?