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Libet's half-second delay

  1. Feb 17, 2005 #1

    Math Is Hard

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    For some reason I have never come across this until my teacher brought it up in phil class last night. I have been searching for information and reading a little bit this morning about research on brain activity and conscious experience done by Benjamin Libet and neurosurgeon Bertram Feinstein.

    It seems Libet determined in his research with Feinstein that there is approximately a half-second delay between the direct stimulation of areas of the cerebral cortex and the actual report of the sensation from the patient. That didn't seem too odd. What did seem very peculiar is that they also noted in further tests that there were electrical signals in the brain (associated with whatever motor task the patient randomly chose to perform) that preceded the patient's conscious intent to move.

    I was looking at this particular book review: http://www.the-aps.org/publications/tphys/2005html/FebTPhys/bookreview.htm and a few other web articles.

    I'm sure many people here are very familiar with this subject. I find it baffling - it just doesn't seem possible - and I wondered what your thoughts were on this.
     
    Last edited: Feb 17, 2005
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  3. Feb 17, 2005 #2

    selfAdjoint

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    Dennett, in Conciousness Explained cites Libet's research and uses it as part of his evidence that what we experience is not so tied to reality as we might believe, which I believe undermines most attempts to take the experience of consciousness as a primary datum.

    You would do us all a big favor if you would post any relvant links you turn up, pro and con, on this forum. Thank you for the one you have already posted.
     
  4. Feb 17, 2005 #3
    And yet when I attempt to do something, I usually try it out in my mind first, to the exent that I might send the signals (or query) and then inhibit myself from acting upon it, to see if that's what I really want to do. Does that make sense? While I suppose it could also entail some sub-conscious memory coming to the surface, in accordance with a similar experience you've reacted to in the past. In which case it becomes up to you to (consciously) override it or follow through with it.
     
  5. Feb 17, 2005 #4

    StatusX

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    What can we take as the primary datum of experience besides experience? We might be wrong about how our experiences relate to the external world, like, for example, whether they cause our actions or not. But we can't be wrong about what we're experiencing, because the experiences are what we know.
     
  6. Feb 17, 2005 #5

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    Thanks for the responses. SA, I will try to post more links as I find them. I approached most of the links I found gingerly since it seemed there were many who wanted to take these findings and immediately apply them to their own agenda.

    Iacchus, I am thinking about what you said, but the whole "mulling it over" process is still seems to be on the conscious level. If what Libet says is correct, the motor command that determines what you actually do happens at the pre/non-conscious level. The command to pull the trigger is well on its way to your finger before you decide to fire the gun.
     
  7. Feb 18, 2005 #6
    We all do things without conscious intent. Its called reaction. Not knee jerk reaction which is a nerve thing but mental reaction. A simple example is typing on a keyboard. I often know I am making a mistake as I hit the wrong key but am unable to stop doing it and have to correct it. Our brains run on automatic so much of the time that it is only later, the half second, that we become conscious of it. Like muscle memory doing repetative motion. like a golf or bat swing. Even as we are doing it we may know something is not right but we are unable to stop or change it because it is automatic.
     
  8. Feb 18, 2005 #7
  9. Feb 18, 2005 #8

    selfAdjoint

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    So it appears from Stanley Klein's paper, the first one you linked to, that after Trevina and Miller's work and Klein's own analysis, the gap is reduced from .4 seconds to .2 seconds. But it's still there, and now on a more careful foundation.
     
  10. Feb 20, 2005 #9
    I have read about this gap on a number of occasions with various associated explanations. What I have always wondered is, why doesn't someone with the proper facilities do the following experiment to check Libet's hypothesis? Tell someone who is being tapped for this signal to push a button after some random delay up to them, unless a specific light comes on: i.e., don't push the button if the light is on. Then use the motor signal to turn the light on.

    From what I have been told, someone with decent hand eye coordination can get their reaction time down to around a tenth of a second so even .2 seconds should produce some confusion as to what the test subject thinks is going on. I would almost bet money that the test subject would come to belive there was a motion sensor in the button.

    If someone knows of such an experiment, let me know.

    Dick
     
  11. Feb 20, 2005 #10

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    It seems more likely to me that the delay that is observed is between the conscious event and the report of the conscious event. I don't understand how that is ruled out.
     
  12. Feb 22, 2005 #11
    The issue is conscious awareness!

    I could be wrong as I am no expert but I have interpreted their data to imply that they are not speaking of a "report" of the conscious event but rather the conscious awareness of the decision. :biggrin: The big question in free will is, was the decision to act a subconscious event or was it a conscious event. :grumpy: If conscious awareness can be attached to activity of a particular specific area of the brain (which seems to be the case) then brain activity associated with conscious awareness is a measurable thing. o:) And, apparently, the act precedes conscious awareness of the decision which makes "free will" difficult to defend. :blushing:

    Have fun -- Dick
     
  13. Feb 22, 2005 #12

    selfAdjoint

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    As the links make clear, Libet's own defense of free will is that the individual can "veto" the brain's action after it has begun and before the actual physical action begins. This seems to me as much sheer desperate invocation of magic as every other explanation of strong free will.
     
  14. Feb 22, 2005 #13

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    Actually, those two things are exactly what I am concerned with: the conscious awareness of the decision and then the report of the conscious awareness of the decision. Maybe I didn't say this clearly in the last post. I am curious about the time between the two.

    It seems to me the only way you could know if someone is experiencing the conscious awareness of a decision is if they do something to signal to that it is happening, and this would entail some kind of report or signal.

    I can decide to push a button, but it could take me a fraction of a second to do something to indicate that I am making the decision, for instance to form and utter the word "now", or lift a finger, or tap my foot.

    I find it very difficult to believe that I could make a decision to do something and simultaneously give a cue that I am making the decision. Maybe they adjust for that in the research, but I don't see how it could be done.
     
    Last edited: Feb 22, 2005
  15. Feb 22, 2005 #14
    I'm always amused by people who, acting out of a conscious decision, proclaim it's possible we don't have free-will. That is a rather absurd notion, but maybe those people can't help doing it: it's predetermined :smile:

    I have never seen anyone approach the results of the Libet experiment from a really coherent perspective. There is an issue everyone seems to be overlooking: exactly what do we mean by "now"? Yes, because all our conscious decisions are made "in the present" and only have the power to change the physical world "in the present". But exactly how long does "the present" last, and isn't it really just a small slice of the past?

    It is wrong to expect we should find a clear causal relationship between deciding and acting, other than what we experience on a subjective level. Libet compared a subjective report with an objective measurement, and no one should be too surprised if we find that it implies we may not have free-will, for it also implies we may have the power to change our past (and I mean "our subjective past" as opposed to "the objective past")

    I'm afraid this is complicated, but I'd be happy to expand on this idea if someone is interested.
     
  16. Feb 22, 2005 #15
    If I remember it correctly, the subject is shown a series of images and asked to move a finger and then tell which image he was seeing when he decided to make the movement. They also use electrodes to measure the nerve impulse going to the finger. So the subject says "I decided to move my finger when I saw picture X", and by comparing the time picture X was shown with the time the nerve impulse was measured, they find that the latter precedes the former.

    The methodology seems sound to me except, as I mentioned in my previous post, for the fact that its results may not make much sense. People may say whatever they want, but the fact remains that no amount of objective evidence can possibly convince someone that they don't have to think before they act. The notion is simply preposterous.
     
  17. Feb 22, 2005 #16

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    What do the results of this experiment have to do with free will? If a nerve impulse caused the action, and if nerve impulses obey the laws of physics, then there is no strong free will, regardless of whether we were conscious of the impulse or not.
     
  18. Feb 22, 2005 #17

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    It seems to have more to do with ownership of action rather than 'freedom' of action. The experiment erodes our confidence that, for instance, when we decide to get up out of bed in the morning, that it is really "us"-- that mental construct of the self-- that is responsible for initiating the action. Rather (if we are to believe the implications of Libet's experiment and others), the action has been initiated subconsciously, and we only attach it to the concept of the self post hoc to give the illusion of agency to the self. Ownership of action is not all there is to be said about free will, but it seems like an important component.

    I'm not sure why you say this. This suggestion is not invocation of magic, but rather of a complicated neural control system. Clearly, it is within the realm of possibility that there could exist some neural system that could inhibit certain neural activity based on its own complex neural algorithms. Indeed, the picture that seems to be emerging from the literature is that of conscious agency serving a primarily restrictive or editorial role on the impulses of the subconscious rather than a productive role.
     
    Last edited: Feb 22, 2005
  19. Feb 22, 2005 #18
    It seems to me to be a very simple question. If it is a conscious decision of which we are aware of making, then that awareness should precede the action. If the action precedes our awareness of its existence, how can we claim to be the cause of the action? The settlement of the question lies entirely with the validity of the relationship between awareness and activity of a particular area of the brain. Either this is a valid relationship or a case of invalidity should be possible to find. This is not a philosophical matter; it is a matter for factual experimentation.

    Have fun -- Dick
     
    Last edited: Feb 22, 2005
  20. Feb 22, 2005 #19
    Doctordick, I will reply to your post as I think you are approaching the issue from a coherent perspective, but not necessarily seeing all the implications.

    A lot of things seem to be a very simple question. More often than not, that usually means we are overlooking something important.

    If I may borrow from the vocabulary of physicists, which frame of reference are you talking about? You do realize that the perceived order of events may change depending on your perspective. More specifically, how can we find out if the conscious minds of two human beings are in perfect synchronism? If you rule out free-will, you must necessarily open the possibility that, for instance, I am experiencing the year 1998 despite the fact that you can interact with my body in 2005. See how absurd those ideas get?
    Our awareness of the action never precedes our awareness of the conscious decision. From a subjective perspective we have every right to claim decision causes action.

    What I think the experiment may imply is not that we don't have free-will, which is a rather hasty and poorly thought conclusion to reach, if I may say so. I don't know what it implies, but it does make me think about the relationship between conscious experience and time. Most people seem to think both our conscious experiences and our actions happens in the present, but the fact is that the present is just a small slice of the past. If our consciousness really exists in the present, then we don't need the Libet experiment to tell us we have no free-will; that would be a simple fact of logic.

    That is why I find all those "Libet offers evidence that we don't have free-will" arguments simply silly. How can people possibly think they have free-will if they also think their consciousness exists in the past?

    That is only if you can prove that your conscious experience happens in the short portion of the past we call "the present". And that proof is impossible to obtain. Libet proves nothing other than we don't know much about the interaction between mind and matter.

    This is purely a philosophical matter, as we have no access to a person's conscious experience, not even in principle.
     
  21. Feb 22, 2005 #20

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    I think this experiment makes a good deal of sense if you consider my take on the boundary problem. The seeming contradiction with personal experience arises only because of our likely illusory concept of the "self." If, in fact, a "self" is nothing more than a functionally connected neuronal array that, during some given span of time, displays the threshold conditions necessary for coordinated action-initiation and unity of experience, this situation can be explained. The explanation would look something like this (I'm going to use "neural network" rather than "self," because whether or not the network in question is an experiencing network isn't important to this explanation):

    Consider two sets of threshold conditions in neural networks. The first is the set of conditions that must obtain for a given network to initiate a coordinated response to dynamic stimuli. The second is the set of conditions that must obtain for that network to also experience the stimuli and the responses. These sets likely overlap; in fact, they may even be the same set. I really have no idea, though this experiment certainly suggests that they are not the exact same set. Let us call the first set of conditions set 1 and the second set set 2. What happens in Libet's subjects might be this:

    When shown the image that the subject is supposed to respond to, set 1 obtains in a dynamic neural network that includes at least the part of the visual cortex where the image is received, the part of the memory where the instructions are kept, and the motor control center responsible for finger flexing. This network initiates the action. Within 0.2 seconds, this network expands to include whatever parts of the brain are responsible for making verbal reports and set 2 obtains in the new network, which at that point the subject refers to as his "self."
     
    Last edited: Feb 22, 2005
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