In a famous paper, Soon and colleagues tried to prove that decisions are created in our brain long before we consciously know about them [1]. The paper "Unconscious determinants of free decisions in the human brain" was published in Nature Neuroscience in 2008, and has been widely discussed ever since.
The authors used a very simple button-pressing task in their experiment – participants were supposed to press a left or a right button whenever they felt like it. Simultaneously, a string of single letters was viewed on a screen and subjects were told to remember the letter that was shown when they made the decision to press the button. The investigators recorded brain activity using functional MRI and then analyzed the behavioral and imaging data. In short, the authors were able to predict decisions (left versus right button presses) more than 8 seconds before the participants consciously made their decisions.
For a person who has never heard about this study, these results probably come as a shock. Someone else, by an investigation of my brain activity, knows what I will do in the future even before I know it myself! Although this is not yet completely possible, it could happen with the further development of neuroimaging and data analysis techniques.
Multivoxel Pattern Analysis
From a technical point of view, the study used an incredibly interesting and sophisticated method of analyzing the functional MRI data, namely multivoxel pattern analysis (MVPA, searchlight decoding method [2]). It is different than the classical, activation-based analysis approach (univariate analysis) in that it takes into consideration the spatial relationships between the activation of certain voxels. To put it more simply, activation-based analysis analyzes whether certain voxels are significantly active for certain conditions, whereas MVPA investigates whether changes in brain signals, called spatial patterns, correspond to certain experimental conditions. Thus, the latter method is more sensitive.
No Free Will?
Soon and colleagues showed that the button presses could be decoded from medial and left frontopolar cortex and posterior cingulate cortex with accuracies reaching 60%. This means that in 60% of cases, the experimenters were able to correctly predict which button a subject would press, a result which was statistically significant [1]. Could these results shed light on the concept of free will? As Prof. John-Dylan Haynes (a co-author of the paper) says, one experiment cannot rule out the entire concept, yet it opens up a new direction for future research. The results of this particular experiment might undermine the concept of free will and support the determinists, who claim that freedom of choice is illusory, because all our actions are determined by preceding events that we cannot influence. If we are unable to consciously make our decisions, as the paper suggests, we cannot really talk about free will at all.
Yes Free Will?
However, we cannot forget the widespread criticism this experiment received. Many researchers claimed that there were a number of flaws that were not taken into consideration by the authors. In 2012, Lages and Jaworska designed similar experiments to see whether the decoding accuracies reached by Soon and colleagues might derive from response dependencies between single trials [3]. They performed a behavioral experiment in order to show that similar accuracies could be reached. The authors reached decoding accuracies of 61.2% for responses based on preceding trials. Since classification analysis can perform better than chance by using preceding responses only, Soon’s results may also have been based on response bias, and may not have fully reflected the true nature of brain activity preceding the conscious decisions in our brains. Lages and Jaworska further claim that the multivariate pattern analysis might have picked up the neural correlates of the intention to switch or stay with the button press, which may occured much earlier in time than the intention to press the button itself. However, Soon and colleagues controlled for this response bias by excluding a large number of participants who did not meet the criterion of equal distribution of left and right button presses. Lages and Jaworska argue that this may have reduced generalizability of the results.
In all of this debate, there is one aspect that cannot be stressed enough: a single experiment does not rule out the possibility that free will does not exist. There are certain possibilities, for example the results might indeed be artefacts and represent something different than unconscious determinants of free decisions in our brains. Another explanation is that we do have free will, but that it influences the decision-making process at the end only, and modulates unconscious decisions that our brains took prior to the action.
Ultra-High Field Free Will
Another study worth mentioning is a replication of Soon's study performed by Bode and colleagues in 2011 [4]. It involved the same task as the previously described study, but the researchers used an ultra-high field MRI scanner (7T) and applied questionnaires after the testing paradigm. In this study, the authors used correlation measures in order to check whether the subjects used any fixed button press sequences, proving that the decisions were more or less random (however, the authors state that due to the low number of trials per functional run, the tests have limited informational value). The results show that no conscious process biased the decisions. Additionally, the researchers were able to decode the button presses before the decision reached consciousness from the frontopolar cortex (with accuracies reaching 57%), a region that was not informative of condition after the decision was made.
ARE WE JUST MINDLESS MACHINES CONTROLLED BY OUR
BRAINS?
As terrifying as it may seem, next time you make a decision, you will know that (maybe) it is not really your conscious and free decision, but one that has been made by your brain without the participation of your consciousness whatsoever. So are we just mindless machines controlled by our brains? Do we have any say in our decisions at all?
[1] Soon et al, Nat Neurosci, 2008
[2] Kriegeskorte et al, PNAS, 2006
[3] Lages and Jaworska, Front Psychol, 2012
[4] Bode et al, PLoS ONE, 2011
No comments:
Post a Comment