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Time, consciousness and freedom: considerations on the experiments of B. Libet and collaborators.
Author: José Ignacio Murillo1 and José Manuel Giménez-Amaya2
Published in: "certificate Philosophica", II, 17, 2008, pp. 291-306.
Date of publication: 2008
Humanity seems condemned to never be able to settle certain questions. Throughout history, people seem to be divided over their solution, not only by culture, but also within a single social group . Even if the mainstream advocates a certain answer, there are often dissonant voices. The question of freedom is one of them. Are we really free? On the one hand, there is no known human society that is not founded - even if only implicitly - on the idea of responsibility. Specifically human relationships rest on the possibility of demanding certain types of behaviour, praising those who comply with them and condemning those who deviate from them. Both positions presuppose that the subject is the master of his or her conduct, and that he or she would be guilty if he or she does not act in accordance with what is considered agreement to be best.3.
In any case, doubt about freedom has been constantly insinuated throughout history. Sometimes it is based on the experience of one's own powerlessness in the face of internal and external constraints. The force of impulses, the difficulty of overcoming ignorance, or the limitations imposed by Education or by social Structures are some of the foundations of this awareness of incapacity and lack of control over one's own behaviour. The idea that man is a puppet of the gods, or that he is sometimes forced by them to perform certain actions, has also been common in history.
Alongside these reflections, particularly since the beginnings of scientific culture in Ancient Greece, it is common to find another basis for doubt that is not so much based on the experience of conditioning or alienation, but stems from a conviction about the nature of reality. It may be called naturalistic determinism, and is based on reasoning of this kind subject. The world can be known because it is governed by rational laws; but the laws that govern the universe are only rational if they govern it in a necessary way. Accepting the reality of freedom implies admitting the existence of an origin of actions independent of deterministic laws. But, from this perspective, these are the only ones that deserve the name of rational laws of nature, because the scientific and rational knowledge is identified in this approach with the capacity of foresight. Consequently, freedom must be denied, and the consciousness of freedom, even if it cannot be denied as a phenomenon, must be qualified as an error or mirage.4.
A characteristic feature of this position is that it is what one might call a "cold" or "theoretical" determinism. It is not based on the experience of unfreedom, but is deduced from a way of seeing the world, which is considered inalienable, and which can be maintained even when it clashes with one's own inner experience.
We can ascribe to this group the position of those who deny freedom because they hold that the only proximate explanation of our behaviour is the workings of our brain. It has in common with classical scientific determinism the idea that behaviour must be accessible to science, and that there can be nothing capable of introducing true novelty into the universe. However, it differs somewhat from the former. Cerebral" determinism can coexist with the acceptance that not everything in the universe is predictable, as is clear from the new theories of physics. It does not deny freedom because everything is determined, but because the cause of our actions is an organ that we can only conceive of as subject to these laws of nature. According to Patricia Churchland5the brain is nothing more than "a causal machine", and since it is the only admissible origin of our behaviour, freedom must be eliminated from any scientific consideration of our actions.
It must be said that this position is based on an unproven postulate, and therefore a postulate that evades rational discussion. If someone says that my freedom is a mirage, it seems to eliminate the only test that I can adduce from it. Therefore, it eliminates in passing all possible rational confrontation. But what if a scientific test could be offered that freedom is an illusion? Is it possible to do so?
An experimental approach of the free action study
The discussion that originated in the wake of the classically named "Libet experiment" revolves to a large extent around these questions. Moreover, as we shall see, this discussion is also a good sample of how in some sectors of modern science, and very particularly in Neuroscience, the rigid distinction between science and Philosophy proves to be artificial or, at the very least, is in crisis.
Benjamin Libet, who died on 23 July 2007, was born in 1916 and was a researcher of the department of Physiology at the University of California in San Francisco. In the 1970s, Libet and his group had investigated the so-called sensation thresholds; in particular, the Degree activation required in certain areas of the brain to artificially trigger somatic arousal. These programs of study led him to the field of consciousness and to the design experiment that made him famous.
Libet and colleagues based their work on the finding by Hans Helmut Kornhuber and Lüder Deecke in 19656 of what they had called in German "Bereitschaftspotential": "readiness potential" in English or readiness potential (PD) in Spanish. PD is an electrical change in certain brain areas that precedes the execution of a future action.
They designed an experiment aimed at finding out the temporal relationship between PD, awareness of the decision to act and the execution of the movement.7. The question they were trying to answer was the following: when does the conscious desire or intention (to carry out an action ) appear?8
To answer the question, it was necessary to measure at what precise moment the PDs, the awareness of the desire to make a movement and the activation of the effector muscles were generated, in a way that would allow them to be sequenced. To do this, they designed an experimental exploration paradigm. Subjects were to perform a movement of the wrist joint at the moment they felt the urge to do so. To solve the measurement problem, the researchers used a watch, much faster than normal watches, in which a dot travelled around the entire dial in 2.6 seconds (about 25 times faster than normal). The subject could pinpoint the position of the dot at the precise moment he or she was aware of the desire to move the tested joint.
To test the accuracy of the subjects' report , they carried out tests. In the tests, the subject was relaxed and made no voluntary movement, but received a weak stimulus on the skin of one of their hands. The stimulus was repeated at random on several occasions and the subject had to indicate when, according to the clock designed, he or she was aware of the stimulus. The difference from the actual time, which was known to the observers, had an error of only about 50 milliseconds.
The subjects of the experiment were evaluated by electroencephalogram with an electrode placed on the scalp, either on the line average of the cranial vertex or on the left side (on the cerebral hemisphere opposite to the hand executing the movement, which controls movements on the right side of the body), i.e. approximately on the motor and premotor cortexes that control the movements of the corresponding hand. The activated muscles of the limb were examined by means of an electromyogram. The moment at which they were activated was considered to be the exact time at which the voluntary movement was performed.
The test was carried out in two different situations. In some cases, awareness of the desire was measured before the instruction to "let the impulse come by itself, spontaneously" was given, and in other cases, after the explanations. In the first case, therefore, a certain amount of planning was involved, while in the other case it was a matter of unplanned decisions.
For subjects whose movements were spontaneous, with no vague planning of the moment to act, the onset of PD was 550 milliseconds before muscle activation. Awareness of the desire to act was only 200 milliseconds before muscle activation. This value was the same when the subjects claimed to have planned the movement only vaguely. If we correct the error of the subjects' report by 50 milliseconds, taking into account the skin stimulus experiment, the awareness of the desire to move occurs 150 milliseconds before the activation of the muscle. It was therefore clear that the brain processes preparing the voluntary movement started 400 milliseconds before the conscious will to act. For the groups in which planning was taking place, PD began about 1050 milliseconds before muscle activation, but awareness of the desire to act was, as in the others, about 200 milliseconds before muscle activation. They thought that the source of the PD obtained was the supplementary motor area of the premotor cortex, which is located close to the line average, next to the cranial vertex.9. Libet and colleagues concluded that "the sequence of the volitional process 'to act now' can be applied to all volitional acts, regardless of their spontaneity or previous history of conscious deliberations".10.
What conclusions can be drawn from these experimental data ? Admittedly, at least at first glance, they are surprising. One would expect that the supplementary motor area of the premotor cortex would not be activated before we are aware that we decide to execute a movement. However, the temporal sequence seems to indicate that the brain prepares the movement before we are conscious of deciding to do it.
Before turning to a discussion of some interpretations of these experiments, it is worth noting that they have received some criticism, also from a scientific point of view .11. However, it must be acknowledged that none of them seems to have eliminated the general consensus about the value of his results. Libet himself responded to some of these criticisms in a direct way12. He even, on one occasion, pointed out this consensus about the validity of his experiment, mentioning the journals that have published his results and the individual testimonies of some important neuroscientists, who have not only accepted them, but have praised their results along with the experimental ingenuity they reveal. To which this author adds by way of corollary: "It is interesting that most of the negative criticism of our findings and their implications comes from philosophers and others with negligible experience in experimental neuroscience of the brain".13.
Clearly, for those who thought that the brain is a mere causal machine 14the news came as no surprise. In their view, consciousness is not relevant to explaining movement. If anything, one could accept that it is generated by the brain as a product of its activity, but without the capacity to intervene causally in it. Some, such as Susan J. Blackmore, have gone so far as to state: "many philosophers and scientists have claimed that free will is an illusion. Unlike them, Benjamin Libet has found a way to prove it."15.
However, this is not Libet's position: "The assumption," he says, "that a deterministic nature of the observable physical world (insofar as it can be true) can account for subjective conscious functions and events is a speculative belief, not a scientifically tested proposition ".16. For its part, non-determinism, i.e., "the idea that conscious will sometimes exerts effects that are not in agreement accordance with known physical laws, is, of course, also a speculative belief unproven".17.
Nevertheless, Libet claims that we must recognise the almost universal experience that we act freely, which provides a kind of prima facie evidence for the thesis that conscious will causally controls some brain processes. To justify this impression, in the face of the apparently contrary data provided by his experiments, Libet argues that, even once the brain has prepared the act, there is still time to exercise a conscious veto that can stop the process by preventing muscular action. In fact, the subjects in the experiment described above explained that sometimes a conscious desire to act would appear, but they would suppress or veto it. Note that in the absence of the electrical signal in the muscle, the recording of the PD that preceded the veto was not initiated, so no PD was recorded from vetoed actions.18. Thus, one would assume that there was a PD, but that something stopped the course of action. Libet claims to have shown that it is possible to exercise the veto in the 100 or 200 millisecond interval preceding the execution of the move.19.
One objection to this thesis is that the act of conscience also needs a cerebral preparation and that this can be unconscious.20. To this Libet replies by distinguishing between the act of consciousness and its content: the act of consciousness can be prepared, without us having to admit that its concrete content is prepared.21.
Libet's thesis therefore presupposes that consciousness can exert a causal influence on the brain. But what is consciousness? Libet argues for the possibility that it is an emergent property of certain processes of the brain, whose functioning responds to its own laws, which cannot be reduced to the laws of the parts. On this point, he relies on Sperry's proposal , for whom the attributes of consciousness, understood as an emergent property, could not be perceptible in the neural activities of the system in which it emerges, that is, in the brain .22. Moreover, although this author, as Libet himself points out, initially believed that the system obeyed the deterministic laws of physics, in his later years he accepted that the conscious mind can control some neural functions independently of the laws of physics.23. Libet offers his own version of this theory, proposing the existence of a "conscious mental field", capable of unifying the experience generated by multiple neural units. "It would also be able to influence certain neural activities and form a basis for the conscious will".24.
The "conscious mental field" would be a new aspect of nature. It would not be "physical", in the sense that it cannot be accessed directly by external physical means, but by internal subjective experience. This does not mean that an indirect experimental test of its existence is not possible. Moreover, Libet even proposes an experiment to obtain it. 25.
Having presented the experiments of Libet and collaborators and the interpretation he gives of them, it may be convenient to frame both in a broader philosophical context, which allows them to be properly assessed. This is not an attempt to be exhaustive, nor, of course, to settle a complex question, which is subject to experimental control, and which, in fact, is still subject to discussion. However, it is clear that these experiments and their interpretations revolve around questions that have been addressed by human thought long before they were addressed by experimental neurobiology. In particular, this discussion raises at least two problems.
Measurement, time and consciousness
The first problem that arises is that of the relationship between consciousness and time. This is not just a theoretical or philosophical problem, but is connected with one of the most debated points of these experiments. The clearest form in which it presents itself in this context is that of the measurement of subjective experience.
Firstly, it should be borne in mind that the measurement of the processes that take place in the nervous system, and in particular those involved in the design and execution of movement, is not completely closed.
It has long been established that the neurobiology of the motor system has a hierarchical constitution. This assertion is based on a large issue of experiments devoted, above all, to unravelling the neural connections and neurophysiological patterns of nerve discharge of the different neural Structures involved in the control of voluntary movements. According to this stepwise outline , the highest level of the hierarchy is occupied by the multimodal associative cortex, in particular the prefrontal cortex. From there, directly or via the cerebrocerebellum and the basal ganglia (Structures subcortical), the premotor cortex is reached to organise the movement plan and programme, which will be executed directly with projections from the latter to the motor cortex, and from the latter to the brainstem and spinal cord. All these connections require a response time. However, in many cases, the time sequence as we can measure it does not conform to the theoretical patterns. This is particularly true for subcortical connections, which may appear to be out of sync with the execution of the movement. It may be objected that at least there is fine-tuning in the cortical connections, and that the subcortical Structures have only a control function. However, it would seem logical that the subcortical Structures would also influence the planning and programming of the movement, and so it remains difficult to explain how cortical and subcortical circuits are synchronised before the movement is executed.26.
As we said, time and measurement are not marginal problems of psychology. In fact, they are closely linked to the birth of discipline as a science. Indeed, one of the first stimuli for the development of this science was the problem of measurement presented by some astronomical phenomena. Until the beginning of the 19th century, some measurements were carried out by comparing visual stimuli - the star passing through a telescope's grating - with auditory ones - the sound of a clock, which the observer began to count when the body passed through a certain section of the grating. But it soon became clear that there were deviations in the measurement. At first, these were attributed to the observer's inability or negligence, until it was realised that this was a systematic problem. This gave rise to the notion of "reaction times".27.
Indeed, time was to become more and more central, not only in psychology and Philosophy - think of Bergson, Husserl, etc. - but also in physics itself. This happened in a particular way with the establishment of the theory of relativity, which destroyed the idea of a single time against which all physical phenomena could be measured and the possibility of speaking of physical simultaneity in the strict sense. This was joined by quantum mechanics, which also proposed a new way of understanding time and also systematically posed the problem of our ability to observe certain natural phenomena.
But let us return to Libet. Of course, this author takes these measurement problems into account. It is in fact one of the aspects of his study. The design of his experiments is aimed at avoiding them, and he himself has responded to many of those who have criticised them on this point. What is not so clear, however, is that his approach goes so far as to consider in a comprehensive way what temporality means, and what its relation to consciousness is. In fact, the budget of Libet's experiment is that the act of consciousness that accompanies the desire to act can be introduced into the temporal sequence of the processes that we detect in the brain. But is this possible? Even from Libet's theory of the "conscious mental field" - disregarding the problems of the emergentism that underlies this thesis -, because it is a new feature of reality, consciousness can be governed by laws different from those we know, different therefore from those that govern the functioning of the brain.
One drastic way to avoid this problem is the crudely stated Daniel Dennett28. For him, Libet's view of consciousness is still Cartesian, because it presupposes the existence of a separate self - a homunculus - somewhere in the brain, or at some distance from it, to which the various processes reach data. For Dennett thinks, however, the various processes that we attribute to the homunculus must be attributed to the brain. We can understand it, to use one of his examples, as if they were "subcontracted" to other causal instances, so that the homunculus is freed from them. This happens with perception and with all information processing. If we finally decide to dispense with the homunculus, we will realise that the homunculus is not a "subcontractor" to other causal instances.29we will realise that there is no problem: everything takes up time, although for the same reason we will be forced, contra Libet, to accept that there is no such thing as free will.
Dennett quotation to Gallagher, a commentator on Libet, as someone close to this position: "I think this problem can be solved if we stop conceiving of free decision as a momentary act. As soon as we realise that deliberation and decision are processes that extend over time, even if only, in some cases, over very short intervals of time, there is scope for conscious components that are more than props incorporated into posteriori".30.
In fact, Dennett is right to reject this view of the conscious self as a separate and stable entity, to which all temporal processes affecting the subject reach .31. What this philosopher of mind fails to explain is how it is possible that, everything being strictly temporal and extended in time, one can understand the notion of time, and also compare some times with others.
In Aristotelian terms, the comparison of times is the comparison of movements or processes. But every comparison requires a certain synchrony. A certain synchrony is inherent in life in general, since in living beings processes not only influence one another, but are coordinated. This temporal concordance is even clearer in the case of any form of knowledge sensible.32. However, our notion of time presupposes something else: in Polo's words, to articulate time, i.e. that the report appears as past and the projections as future33. But past and future are respective to the present. And is the present itself temporal? If we affirm this openly, we incur in paradoxes. If we affirm that the real is only the present, time is an appearance and cannot be real. If we affirm that the present is a part of time, the present appears in time as the negation of all time and turns time into a succession of infinite instants. It seems, therefore, that the only sensible position is to recognise that temporality can be understood only from outside time.
We suppose that Dennett would find this conclusion unsettling. In any case, it should be added that it does not entail a relapse into the Cartesian conception of the Cartesian I-subject. The present we are talking about derives from a human (intellectual) activity and is not at odds with the fact that various other forms of change and temporality affect the subject. If the human living is something more than the consciousness of the present, we are not obliged to reduce the self to an imaginary point within which things occur that we cannot explain through science. But neither are we obliged, as Dennett seems to believe, to deny man the forms of unity that appear in the experience of free activity. Why should we? Simplifying problems may be useful in some cases, but to do so indiscriminately can turn into the disastrous mania of not wanting to see - and saying that it cannot be seen - everything that does not fit into our theory.
On the other hand, if we consider the time of the voluntary act, we may have some surprises: for example, we can clearly relate our decisions to physical time. We can also determine that we decide something before or within a certain date. But how accurate can this be? We normally date decisions in relation to what motivated them or the effects that resulted from them. However, intentions are only knowable in actions, and actions are units whose temporality is not physical. If I affirm that I have voluntarily participated in a certain experiment, I may be able to point out at what moment I decided, but the voluntary act is not an instantaneous action but accompanies a whole series of processes and activities, giving them a unitary meaning.34.
But are we really talking about freedom?
This last observation also opens up another subject of problems inherent in the experiment: those that have to do with the conception of will and, consequently, of free action. It should be noted that the experiments we are discussing have been followed by others, largely inspired by them, and which have in common the conviction that consciousness is at the margin of the origin of the actions we call free.
One of them is that of Haggard and Eimer, who investigated the relationship between selection and conscious intention by means of a modification of (as it is commonly called) the "Libet paradigm". In this case, they asked the subject to move one of the two hands, while measuring the lateralised dispositional potential (LDP), i.e., that of the hemisphere opposite to the hand they moved. They divided the attempts into those who showed an early judgement of intention and those who showed a late judgement of intention. They then found that overall PD did not vary from agreement with the timing of the intention judgement, but that PDL began significantly earlier in actions in which impulse awareness was early than in those in which it was late. From this they deduced that conscious intention was linked to action selection, and not to general preparation, as Libet et al.'s results seemed to suggest. Since within the organisation of the motor system it must have been selected which specific movement is to be performed at the time the PD lateralises, they concluded that conscious intentions were more related to the PDL than to the general PD.35.
More recent still is another experiment aimed at determining whether subjectively free activity is encoded in the brain. In this experiment, a device similar to Libet's group is used to determine the moment of awareness of the free decision. The subject has to decide, also in this case, between pressing a button with the right hand and another with the left. In the meantime, the brain activity is measured synchronously using a neuroimaging technique called functional magnetic resonance imaging (fMRI). The result was that it was possible to find an encoding of the decision to press one button or the other up to ten seconds before the awareness to act appeared! However, activation was not found in the supplementary motor area of the premotor cortex (where it had been measured by electroencephalogram by the Libet and Haggard groups), but in the multimodal associative cerebral cortex of the parietal and prefrontal regions.36demonstrating that the motor system is hierarchically organised, as mentioned above.
Putting these together data, it may seem that the control of our actions has little to do with consciousness. Rather, consciousness itself seems to be linked to the processes of specifying action, even if it is not clear what its function is and to what extent it can intervene in the action.37.
A first consideration, strictly neurobiological, is that it is legitimate to suppose that the general organisation of the whole motor system may be prepared with a certain permanent activation, which is exploited by voluntary action for the execution of a specific movement. The results of the experiment by Soon and his co-workers, which we have mentioned, seem to support an activation of east subject3829 April 2008. Online.
But, as we have already announced, before drawing conclusions from these experiments, we should ask ourselves about the concept of freedom that these programs of study presuppose. In them, free action appears as a cause, linked to consciousness, capable of modifying the physical world. However, it should be noted that this definition of freedom, although it can be found in some modern authors, is not the classical conception of free will. Thus, for example, for Aristotle what corresponds to our free will is what originates through proáiresis (usually translated as "choice"). But proáiresis, which is something specifically human, does not manifest itself as a causal agent subject , but rather as the making of a decision on the background of a way of life.39. In other words, there is no proáiresis not because there is conscious action, but because we make decisions that organise our conduct in virtue of what we rationally (and not only sensibly) judge to be good.
Of course, none of this appears in the experiments we have discussed. The actions that are considered free are conscious impulses to carry out an action. But what is the reason why the subject decides to act or not, or, as the case may be, to press the left or the right button? If there is no link between the various attempts, it becomes even clearer, that the subject is not moving by virtue of a rational judgement about what is good. In that case, it is normal that the space of motivation is occupied by drive urges.
Nor is it strange in this case that it is possible to predict, by virtue of the brain's activation patterns, which course of action will finally be taken. An observation by Thomas Aquinas comes to mind at purpose in a controversy that may seem strange to us, but which serves to present in a masterly way the classical conception of free will, which is not taken into account here. Our author wonders whether it can be accepted in any sense that astrology can predict human behaviour, supposedly free. This would presuppose that the stars, which are a physical and material reality, influence the human soul.
And he answers as follows: "The fact that astrologers are often right in their predictions is due to two reasons. In the first place, because most men allow themselves to be governed by their bodily passions, and consequently behave, in the majority of cases, in accordance with the influences which reach them from the heavenly bodies. However, only a few - the wise - rationally moderate such a class of inclinations. That is why astrologers are often right in their predictions, especially in the most common events, which depend on the multitude".40.
It is clear that, for these classical authors, free will consists in the capacity to act in virtue of the intellectual knowledge of the good; or, to put it more precisely, of the good insofar as it is good. It is also for this reason that they admit that freedom can grow, to the extent that the agent habitually accommodates himself to act in accordance with this criterion agreement . This is what is traditionally called virtue. In this sense, the virtuous person is freer, because he is able to impose a rational order - the one that truly interests him as the rational agent that he is - on the activity that is in his power. It is true that this dominion is present in some way in every action that is conscious and can be controlled, but these actions, which are the ones studied in these experiments, cannot be considered the paradigm of free action.
It can be concluded, therefore, that these experiments, which may perhaps serve to criticise certain conceptions of freedom, do not affect all of them. topic And this sample, once again, that in order to carry out an experimental and scientific approach to certain problems, such as that of freedom, it is necessary to know what the various currents of the Philosophy have already said about it.
1- department de Philosophy, University of Navarra, firstname.lastname@example.org
2- department de Anatomy, Histology and Neuroscience, Universidad Autónoma de Madrid, email@example.com
3- On the other hand, it is curious - a paradox - that there are words such as "freedom", the meaning of which we all seem to understand, but which, in reality, do not have the same meaning for everyone. Another analogous example is the word "God".
4- Cfr. J.M. Giménez-Amaya and J.I. Murillo, Neurociencia y libertad. Una aproximación interdisciplinar, "Scripta Theologica", (2008), in press.
5- Cf. P. Churchland, in S. Blackmore (ed.), Conversations on consciousness: What the Best Minds Think about the Brain, Free Will, and What it Means to Be Human, Oxford University Press, New York 2006, Oxford University Press, Oxford 2005, pp. 50 ff.
6- Cf. H.H. Kornhuber and L. Deecke, Hirnpotentialänderungen bei Willkürbewegungen und passiven Bewegungen des Menschen: Bereitschaftpotential und reafferente Potentiale, " Pflugers Archive für die Gesamte Physiologie des Menschen und der Tiere ", 284 (1965), pp. 1-17.
7- Cfr. B. Libet, E.W. Whright and C.A. Gleason, Readiness potentials preceding unrestricted spontaneous pre-planned voluntary acts. Whright and C.A. Gleason, Readiness potentials preceding unrestricted spontaneous pre-planned voluntary acts, " Electroencephalography & Clinical Neurophysiology ", 54 (1982), pp. 322-325.; B. Libet, C.A. Gleason, E.W. Whright and D.K. Pearl, Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiative of a freely voluntary action, " Brain " 106 (1983), pp. 623-642; B. Libet, E.W. Whright and C.A. Gleason, Preparation or intention-to-act, in relation to pre-event potentials recorded at the vertex, " Electroencephalography & Clinical Neurophysiology ", 56 (1983), pp. 367-72. On the subject of this topic, Libet has published other subsequent articles, for example: B. Libet, Unconscious cerebral initiative and the role of conscious will in voluntary action, " Behavioral and Brain Sciences ", 8 (1985), pp. 529-566.
8- Cf. B. Libet, Do We Have Free Will?, "Journal of Consciousness Studies", 6 (1999), pp. 47-57.
9- Cf. B. Libet et al., Do We Have Free Will?, cit. pp. 47-51.
10- Cf. B. Libet et al., Do We Have Free Will?, cit. p. 53.
11- Thus, for example, J.A. Trevenna and J. Miller, Cortical movement preparation before and after a conscious decision to move, " Consciousness and Cognition ", 1 (2002), pp. 367-375; S. Pockett, On subjective back-referral and how long it takes to become conscious of a stimulus: A reinterpretation of Libet's data, " Consiousness and Cognition ", 11, (2002), pp. 144-161; G. Gomes, The timing of conscious experience: A critical review and reinterpretation of Libet's research, " Consiousness and Cognition ", 11, (2002), pp. 555-56. 144-161; G. Gomes,The timing of conscious experience: A critical review and reinterpretation of Libet's research, " Consiousness and Cognition ", 7 (1998), pp. 559-595; G. Gomes, The reinterpretation of Libet's results on the timing of conscious events: A commentary, " Consciousness and Cognition ", 11 (2002), pp. 221-230.
12- Cf. B. Libet, Time factors in conscious processes: Reply to Gilberto Gomes, " Consciousness and Cognition ", 9 (2000), pp. 1-12; The Timing of Mental Events: Libet's Experimental Findings and Their Implications, " Consciousness and Cognition ", 11 (2002), pp. 291-299. In the latter article, Libet responds to criticisms of his experiment by Pockett, Trevena and Miller and Gomes.
13- Thus, for example, in his article B. Libet, The Timing of Mental Events: Libet's Experimental Findings and Their Implications, cit. However, Libet points out some exceptions, such as the philosophers Karl Popper, Stephen Pepper, Martin Edman, and others.
14- Cf. P. Churchland, in S. Blackmore (ed.), Conversations on Consciousness: What the Best Minds Think about the Brain, Free Will, and What it Means to Be Human, cit. p. 61.
15- Cf. S.J. Blackmore, Mind over matter? Many philosophers and scientists have argued that free will is an illusion. Unlike all of them, Benjamin Libet found a way to test it, commentary in Guardian Unlimited, 28 August 2007(http://commentisfree.guardian.co.uk/sue_blackmore/2007/08/mind_over_matter.html).
16- Cf. B. Libet, Do We Have Free Will, p. 55.
18- Cf. B. Libet, Do We Have Free Will, cit.
19- Cfr. B. Libet et al., Preparation or intention-to-act, in relation to pre-event potentials recorded at the vertex, cit.
20- Cf. M. Velmans, How could conscious experience affect brains, " Journal of Consciousness Studies ", 9, (2002), pp. 3-29.
21- Cf. B. Libet, Do We Have Free Will, cit. p. 52 ff.
22- Cf. R.W. Sperry, Mind-brain interaction: mentalism yes; dualism, no, " Neuroscience ", 5 (1980), pp. 195-206; J.R. Searle,Freedom and Neurobiology: Reflections on Free Will, Language, and Political Power, Columbia University Press, New York 2007; J.R. Searle, " Towards a Science of Consciousness ". lecture given in 2006 at the Center for Consciousness at the University of Arizona in Tucson, Arizona, USA. Broadcast on the programme "The Philosopher's Zone" on ABC National Radio in Australia on 20 January 2007.
23- Cf. R.W. Doty, The five mysteries of the mind, and their consequences, " Neuropsychologia ", 10 (1998), pp. 1069-1076.
24- Cf. B. Libet, Can Conscious Experience Affect Brain Activity? Peer review on Velmans, " Journal of Consciousness Studies ", 10 (2003), pp. 24-28.
25- Cfr. B. Libet, A testable field theory of mind-brain interaction, " Journal of Consciousness Studies ", 1 (1994), pp. 119-126; B. LIBET, Can Conscious Experience Affect Brain Activity?, cit.
26- Cfr. G.I. Allen and N. Tsukahara, Cerebrocerebellar communication systems, "Physiological Reviews", 54 (1974), pp. 957-1006.; C. Ghez, The Cerebellum, in E.R. Kandel, J.W. Schwartz and T.M. Jessel (ed.), Principles of Neural Science, Elsevier, New York 1991, pp. 626-646. Schwartz and T.M. Jessel (ed.), Principles of Neural Science, Elsevier, New York 1991, pp. 626-646; J. Krakauer and C. Ghez, Voluntary Movement, in E.R. Kandel, J.W. Schwartz and T.M. Jessel (ed.),Principles of Neural Science, McGraw-Hill, New York 2000, pp. 756-779; R. Nieuwenhuys, J. Voogd and C. Van Huijzen, The Human Central Nervous System, Springer, Heidelberg 2008.
27- The name was given to this phenomenon, which was called "physiological time" by the physiologist Exner. For a history of this discovery and its influence on the history of psychology, see R. Luccio, Los Orígenes de la Psicología, in P. Legrenzi (ed.), Historia de la Psicología, Herder, Barcelona 1986, pp. 62-¿?
28- Cf. J.M. Giménez-Amaya and J.I. Murillo, Mente y cerebro en la neurociencia contemporánea. Una aproximación a su estudio interdisciplinar, " Scripta Theologica " 39 (2007), pp. 607-635.
29-"Libet's data does rule out one hypothesis, which would perhaps have been our favourite: the self-contained self, according to which all the routines of the brain are concentrated in a compact location, where everything converges at the same point: vision, hearing, decisions, judgements of simultaneity... Having everything so close at hand, no temporal problem would arise: a person, a soul, could settle there quietly and make free and responsible decisions, and be simultaneously aware of them and of everything that happens in his consciousness at that moment. But there is no such place in the brain. As I never tire of pointing out, the whole work performed by the imaginary homunculus of the Cartesian Theatre must be divided and distributed in space and time among various brain instances. It is time again to repeat my ironic motto: if you make yourself small enough, you can externalise practically everything". D. Dennett, The Evolution of Freedom, Paidós, Barcelona 2004, p. 268. Dennet examines Libet's experiment in a special way on pages 258-273.
30- S. Gallagher, The neuronal platonist, in conversation with Michael Gazzaniga, "Journal of Consciousness Studies", 5 (1998), pp. 706-717. Cited in D. Dennett, The Evolution of Freedom, cit. In any case, Dennett reproaches him, as a relapse into Cartesianism, for claiming shortly afterwards that if feedback is unconscious it will be "deterministic", but if it is conscious, it will not be.
31- Some authors, such as Eccles, accept Libet's data , but interpret them in a dualistic core topic , as the manifestation of a consciousness that is above time. Cf. J.C. Eccles, Mental summation: the timing of voluntary intentions by cortical activity, "Behavioral and Brain Sciences", 8 (1985), pp. 542-543.
32- Cf. L. Polo, Cybernetics as the logic of life, "Studia Poliana", 4 (2002) 9-17.
33- Cfr. L. Polo, Curso de teoría del knowledge, II, Eunsa, Pamplona 1985, pp. 261 and ff.
34- An interesting analysis of Libet's experiment from the consideration of what is a voluntary action can be found in M.R. Bennet, P.M.S. Hacker, Volition and Voluntary Movement, in (ed.) Philosophical Foundations of Neuroscience, Blackwell, Malden 2003, pp. 224 ff.
35- Cf. P. Haggard and M. Eimer, On the relation between brain potentials and conscious awareness, " Experimental Brain Research ", 126 (1999), pp. 128-133. It is also interesting to consult the discussion in P. Haggard and B. Libet, Conscious Intention and Brain Activity, "Journal of Conscious Studies", 8 (2001), pp. 47-63, and the recent review of P. Haggard, Conscious intention and motor cognition, "Trends in Cognitive Sciences", 9 (2005), pp. 290-295.
36- Cf. C.S. Soon, M. Brass, H.J. Heinze and J.D. Haynes, Unconscious determinants of free decisions in the human brain, " Nature Neuroscience " 11 (2008), pp. 543-545.
37- Cf. D. Chalmers, Philosophy of Mind: Classical and Contemporary Readings, Oxford University Press, Oxford 2002.
38- Cfr. J.M. Giménez Amaya and J.I. Murillo, Libertad anticipada, " A ciencia cierta" (http://www.unav.es/acienciacierta).
39- Cf. A. Vigo, Zeit und Praxis bei Aristoteles. Die Nikomachische Ethik und die zeit-ontologischen Voraussetzungen des vernunftgesteuerten Handelns, Karl Alber, München 1996.
40- Thomas Aquinas, Summa de Theologia, II-II, q. 95, a. 5, ad 2.