Modern interpretation of Libet data

In summary: Libet et al. (1985) showed that the onset of the impulse to act can be inferred from the brain’s electrophysiological activity prior to the subject’s awareness of the decision. However, their results have attracted a great deal of criticism, as the decision to act might precede the preparatory activity by some time...In our study, we used a different methodology that allowed us to determine when the decision to move occurred and the movement itself. We measured the neural activity of randomly selected neurons while participants performed a simple finger movement. We found that the decision to move and the movement were closer together than in Libet’s study, and that the decision to move was triggered
  • #1
Graeme M
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Many may be familiar with the Libet experiments that suggested that the brain begins the process of preparing for a motor action before the subject decides to make the action. This has been discussed and argued over a great deal in the past several decades. I came across this in reading about consciousness and brain processes and wondered if indeed that data and its interpretation still held true today.

I found that Aaron Schurger had done some further experiments more recently that cast a different light on the matter.

http://www.pnas.org/content/109/42/E2904.full

I like Schurger's argument. Briefly, my take from this is that he argues that random fluctuations in neural activity will tend to approach a threshold over time; once the threshold is exceeded a motor action is decided. Thus in respect to voluntary, non temporally constrained decisions to move, the decision to move and the action are in fact much closer together than Libet's data indicated.

In other words, the Libet experiment suggests that for voluntary actions the brain prepares for action BEFORE the conscious decision to act. Hence the urge to act is a post facto addition to experience. Schurger suggests that typical neuronal activity buzzes away and it is not until a threshold point is reached that the decision to act occurs (and the act itself).

That is, when we are thinking of doing a voluntary act, the choice of when to act is precipitated by the neural activity exceeding the threshold. The RP curve typical of the Libet experiment simply describes normal activity with the actual motor response grafted on (because a motor response occurred).

I think this still suggests that the motor act occurs without 'conscious' direction as such, it serves merely to bring decision point and motor response closer together temporally. But it does show that the decision to act and the act are not separate as such, rather they both arise from the same underlying neural activity.

But I also may be misreading the paper. Is the proper interpretation that when neural activity reaches close to the threshold it's already primed by an expectation to act at some time, and thus at that point it tips over the edge and hence causes the conscious decision from which the act arises.

Even then though I do not think it rescues us from the sense that the 'voluntary, conscious' act arises unconsciously from a potential.

I'd be interested in anyone else's take on this paper and its findings. Or whether there are more and later findings on this?
 
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  • #2
Graeme M said:
I like Schurger's argument. Briefly, my take from this is that he argues that random fluctuations in neural activity will tend to approach a threshold over time; once the threshold is exceeded a motor action is decided.

I haven't read Schurger's work, but your statement as written is incorrect. Motor action is definitely not related to gross physical excitation. Motor expression is relegated to a mechanism in the medial forebrain bundle that we call the "go" mechanism.

As far as Ben Libet's work, this is old news and doesn't really have a place in contemporary discourse. Libet's claim was that there was a "readiness potential" that pre-ceded a voluntary action bu that the "conscious" mind could "veto" that act if it wanted to. Everything is correct about this model except for the veto act.
 
  • #3
DiracPool I am just a curious onlooker and certainly have no familiarity with the subject matter, but I gathered a sense from my various readings that the Libet model was still under some debate (though perhaps more in philosophical circles).
The Schurger paper dates from 2012 so is relatively recent. As I noted, I drew my own inference of the meaning of Schurger's findings and I guess I don't really understand much of the detail. But I did gather that they were arguing for the 'readiness potential' not reflecting specifically a buildup to a neural decision to move, but rather a spontaneous fluctuation in activity that approaches a threshold.

This extract from a New Scientist article probably summarises it better than I have:

"Previous studies have shown that when we have to make a decision based on visual input, for example, assemblies of neurons start accumulating visual evidence in favour of the various possible outcomes. A decision is triggered when the evidence favouring one particular outcome becomes strong enough to tip its associated assembly of neurons across a threshold.

Schurger’s team hypothesised that something similar happens in the brain during the Libet experiment. Volunteers, however, are specifically asked to ignore any external information before they make a spontaneous movement, so the trigger to act must be internal... Schurger’s team reasoned that movement is triggered when this neural noise accumulates and crosses a threshold."

A couple of extracts from the Schurger paper to expand on this:"A large body of work, spanning more than four decades, has examined the properties of the readiness potential: its temporal profile, topography at different latencies, variability in different task contexts and disease states, potential cortical “generators,” and even its relevance to “free will”. However, we still lack a precise mechanistic account of what the RP reflects, beyond descriptive phrases such as “planning and preparation for movement.” Here we have offered such an account—in terms of ongoing spontaneous fluctuations in neural activity, a neural accumulator, and a threshold—that is both plausible and parsimonious. Our account departs from the prevailing assumptions about the nature of the RP and thus suggests that some very basic questions be revisited from a different perspective."

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"We propose that the neural decision to move corresponds to a commitment to produce a movement now and that this commitment is associated with a threshold crossing of the accumulator underlying the response decision, a lateralization of the premovement potential, and an abrupt increase in excitability in primary motor cortex ∼100 ms before the onset of muscle flexion (or ∼150 ms before the button press, for the hardware that we used). We propose that the precise time of the “neural decision to move now” is partly determined by spontaneous fluctuations that are temporally autocorrelated."

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"Why then should there be such a long and variable gap between the time of a motor decision and the subjective estimate of the time of the motor decision, whereas no such gap exists for sensory decisions? In fact, this question arises only when we assume that the motor decision coincides in time with the onset of the RP. We have argued that this need not be the case and that the neural decision to move may come much closer in time to the movement itself (e.g., −150 ms). We propose that the neural decision to move coincides in time with average subjective estimates of the time of awareness of intention to move and that the brain produces a reasonably accurate estimate of the time of its movement-causing decision events."

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I understood all of this to be suggesting that a voluntary decision to move arises from spontaneous fluctuations accumulating enough to cross a threshold - that is, that the RP is not strictly speaking an RP arising directly from and prior to the intention to move but rather a fluctuating neural pattern that at some point initiates the voluntary action.
 
  • #4
Graeme M said:
I gathered a sense from my various readings that the Libet model was still under some debate

I'm sure it is. It was a very contentious study back in the day. My first encounter with Libet's work was the review article in Behavioral and Brain Sciences in the late 80's. Here it is if you haven't perused it yet..

http://selfpace.uconn.edu/class/ccs/Libet1985UcsCerebralInitiative.pdf

The seminal study was published in the journal Brain a couple years prior to that:

http://www.ncbi.nlm.nih.gov/pubmed/6640273

Libet got a lot of heat because he speculated that there was a psychological "backward referral" involved with the introspective report of the conscious will to initiate a voluntary act. Those studies struck a nerve because it hit at the heart of "free will." As you've demonstrated, it's still being debated. I guess it's still striking a nerve. I reconciled my position on it a long time ago. Basically, the studies are valid, you just have to draw your own personal inference from it.

There used to be this girl that would show up at the brain-consciousness conferences I used to attend, like the ASSC and the bi-annual Tucson conference..

http://www.theassc.org/
http://www.consciousness.arizona.edu/

Her name was Susan Pockett. I think she was from Australia. Not a very pleasant person, she always seemed mad and grumpy. Kind of had an elitist attitude for some reason. She attended a full day workshop that my neuroscience idol Walter Freeman was giving one year. I tried to befriend her, but to no avail. Too grumpy.

In any case, she took it it upon herself to battle Libet in the literature 20 years after those seminal studies came out. Here's a bit of the transaction..

http://www.ncbi.nlm.nih.gov/pubmed/15935698
http://www.ncbi.nlm.nih.gov/pubmed/16854596

At the end of the day, from what my experience tells me, the initiation of a voluntary act is indeed preceded by neuroactivity, call it a "readiness potential" if you want. "Free will" is an illusion that exists because it is survivally advantageous for us to believe that we have free will. I'm not going to go into detail why I believe this, this is just my opinion on the Libet debate. Whether a "backwards referral" is actually happening or not I don't think makes much difference.
 
  • #5
Thanks for those links DiracPool, I'm always very curious to learn more about both the function of the brain and human cognition – I wish I'd gone for a career in that sort of field. That said, I actually know very little as I've never had the time or opportunity to really sit down and tackle the topic.

I find your comments about "free will" interesting, although I suppose my direct interest is not in the philosophical implications, more in the actual process and how that plays out in terms of consciousness. Although it's not entirely clear to me what people mean by 'consciousness', I think I subscribe to the view that consciousness/awareness are purely states of the brain (or more exactly processes in the brain).

When I read about the Libet model, the central idea that the brain might simply do its thing and that conscious awareness or volition might arise from that process as a sort of post hoc narrative seemed intuitively correct. I found Shurger's results to provide a more illuminating interpretation and of greater explanatory power, which is why I was curious how that had since played out. I guess I can do my own research on that – Schurger seems very active in the field with a lot of publications.

Nonetheless his proposition still leaves me with a sense of the brain's processes being in large part not directly conscious (again, whatever that means). I think that the general model exposed by both Libet and Schurger's work point in the same direction. I hope to find the time to read some more on this remarkably fascinating topic.
 
  • #6
DiracPool said:
At the end of the day, from what my experience tells me, the initiation of a voluntary act is indeed preceded by neuroactivity, call it a "readiness potential" if you want. "Free will" is an illusion that exists because it is survivally advantageous for us to believe that we have free will. I'm not going to go into detail why I believe this, this is just my opinion on the Libet debate. Whether a "backwards referral" is actually happening or not I don't think makes much difference.

Graeme M said:
I find your comments about "free will" interesting, although I suppose my direct interest is not in the philosophical implications, more in the actual process and how that plays out in terms of consciousness. Although it's not entirely clear to me what people mean by 'consciousness', I think I subscribe to the view that consciousness/awareness are purely states of the brain (or more exactly processes in the brain).

When I read about the Libet model, the central idea that the brain might simply do its thing and that conscious awareness or volition might arise from that process as a sort of post hoc narrative seemed intuitively correct.

I think most people use that framework. I guess the only question is if there is another framework (what? Penrose?), whether Libet's data favours one over the other. But in a sense, we believe in the framework regardless of data, so for the modern point of view, the Libet experiments are essentially irrelevant.
 
  • #7
atyy said:
I think most people use that framework. I guess the only question is if there is another framework (what? Penrose?), whether Libet's data favours one over the other. But in a sense, we believe in the framework regardless of data, so for the modern point of view, the Libet experiments are essentially irrelevant.

If we, for the sake of discussion, were to take the Penrose model seriously, how does that change things from your perspective?
 
  • #8
There are more modern experiments that lend credence to the idea that free will is more of a feeling than a fact. My favorite is the one that predicts which, of two choices, a subject makes spontaneously. The brain activity of the subjects is analyzed as they randomly choose to click a button in their left or right hand and is able to predict (with some confidence) which hand they will pick based on brain activity. They are instructed to click the button as soon as they decide, but the algorithm can predict up to 10 seconds before hand, which hand they will choose.

https://www.ncbi.nlm.nih.gov/pubmed/18408715
 
  • #9
That's an interesting finding Pythagorean, although I don't think I can access the article to read it. I suppose the obvious question is what exactly is the experiment showing. The same applies to Libet and Schurger. It seems that as soon as you've given someone an instruction that they have understood and agree to act upon, you've set in motion a conscious act.

Schurger's case illustrates a mechanism for how the actual 'now' event arises, that is, what leads to the neural decision for the motor act to occur, but there seems no way to argue that it wasn't precipitated by a conscious decision. The brain activity cannot precede the internal acceptance of the instruction. So the resulting act is a direct consequence of a conscious choice - to accept the direction to act. I can't see how we can say otherwise.

Of course, part of the problem for me as an interested layperson in following this stuff is the definition of consciousness - what exactly do we mean by that? Is there an accepted scientific definition?
 
  • #10
Graeme M said:
...consciousness - what exactly do we mean by that? Is there an accepted scientific definition?

Nope. At least, nothing compelling that I've ever heard. There are many (most?) that will argue that consciousness is nothing but the epiphenomenon of self awareness that is purely and utterly the deterministic biochemical activity of neurological action.

Others will argue that it is something else... something more fundamental. Roger Penrose might be such a person, and is not someone whose opinion I would take lightly.

I would very much like to hear Atyy's opinion on this, as he is one of our top neuroscientists on the forum, as well as one of the more informed contributors in the quantum physics threads.
 
  • #11
Feeble Wonk said:
Nope. At least, nothing compelling that I've ever heard. There are many (most?) that will argue that consciousness is nothing but the epiphenomenon of self awareness that is purely and utterly the deterministic biochemical activity of neurological action.

imo:

The actual interesting definition of consciousness is not self-awareness persay, but the ability to have a subjective experience in the first place (of course, they may be mutually inclusive). How do clumps of matter experience things and unify those experiences? A robot recently passed a classic self-awareness test (the three wiseman test) but is that robot actually experiencing the process? Doubtful. Is it that impressive? Only for engineers working on artificial intelligence.

If we understood how subjective experiences arises in (presumably) the human brain, that would be the holy grail (or at least a monumental pillar) of neuroscience.
 
  • #12
Pythagorean, this isn't meant to be an obtuse question, but when you say a 'subjective experience' how would you define that?

From what little reading I've done on the subject science seems to have a pretty good idea generally of how the brain functions. If the brain in essence takes sensory input and combines it with existing states to generate some kind of response (even if that is in effect no response), then I can imagine that subjective experience is simply that process.

That is, subjective experience would just be what it 'feels like' to be inside that process, in which case there is really nothing to explain in terms of how it 'arises' - it just is what it is. It seems to me that science can uncover the way these processes work and how the various functional units interact, but if subjective experience is simply the unfolding of these processes then 'consciousness' is irreducible.

Why do we think there is something more there to be exposed and explained?
 
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  • #13
What you describe is computation. We can have robots do that (process data, compute, generate output). Is the robot experiencing anything? Probably not.

If we knew how subjective experience can even occur in the first place, we could create a robot that actually did experience things (or at least know why we couldn't). The computational part you describe is known as the "easy problem" (it's not actually easy, but it's theoretically tractable, whereas we still have no clue how to robustly measure the experiential aspect of consciousness (i.e., the "hard" problem).
 
  • #14
Pythagorean said:
imo:

The actual interesting definition of consciousness is not self-awareness persay, but the ability to have a subjective experience in the first place (of course, they may be mutually inclusive). How do clumps of matter experience things and unify those experiences?
>>>
If we understood how subjective experiences arises in (presumably) the human brain, that would be the holy grail (or at least a monumental pillar) of neuroscience.

You're right Pythagorean... While subtle, there is a very real difference between the subjective experience of "qualia" and the experience of "self awareness", but it would seem that the latter would be an emergent result from the former.

As to your larger point, I would totally agree. The subjective experience of qualia is the aspect of consciousness that is difficult to clearly define in a reductionist/mechanistic sort of way, and does not seem to be necessary for the purposes of reflexive deterministic neurological action.

Graeme M said:
Pythagorean, this isn't meant to be an obtuse question, but when you say a 'subjective experience' how would you define that?

From what little reading I've done on the subject science seems to have a pretty good idea generally of how the brain functions. If the brain in essence takes sensory input and combines it with existing states to generate some kind of response (even if that is in effect no response), then I can imagine that subjective experience is simply that process.

That is, subjective experience would just be what it 'feels like' to be inside that process, in which case there is really nothing to explain in terms of how it 'arises' - it just is what it is. It seems to me that science can uncover the way these processes work and how the various functional units interact, but if subjective experience is simply the unfolding of these processes then 'consciousness' is irreducible.

Why do we think there is something more there to be exposed and explained?

I'm not sure if you meant to say "irreducible" here Graeme. If the mental experience of consciousness is only the epiphenomenon of "what it feels like" during the unfolding of neurological activity, then it would appear that consciousness has been reduced to the specific neurological mechanism described. But it seems (to me anyway) that it's not that clear cut or obvious.

If you haven't read it yet, I'd recommend a book by A.G. Cairns-Smith... "Evolving the Mind... on the nature of matter and the origin of consciousness"
http://www.abebooks.com/book-search/isbn/9780521637558/

Smith is no pseudoscientific light weight. He's a respected authority, and his views are taken very seriously.
 
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  • #15
I'd also add a few more books to the list...
"Vital Dust" by Christian de Duve, "The Emergence of Everything" by Harold Morowitz, and maybe even "The Matter Myth" by Davies and Gribbin.

http://www.goodreads.com/book/show/1120192.Vital_Dust

https://www.amazon.com/dp/0195173317/?tag=pfamazon01-20

https://www.amazon.com/dp/0743290917/?tag=pfamazon01-20

All are readily understandable (with the requisite degree of effort) by the interested layperson reader, but not short on scientific information. All are secular scientific expositions without quasi-religious/new age silliness (Morowitz does make some references to theological/philosophical perspectives, but those are not material to the larger scientific discussion).

To me, there is a common running theme. The emergence of consciousness appears to be "built into" the physics of the universe. Yet, that same physics precludes a causative "Ghost in the Machine". Either the machine is "real" or the ghost is "real", but not both. I would argue that which it is is a very reasonable debate.

To the chagrined monitors, I promise to not take this line of discussion any further as I am aware that it leads to philosophical concepts. I am merely pointing out that there frequently seems to be an essentially default assumption that consciousness is purely a physical process of neurological activity, but it is not clearly demonstrated that this is entirely true.
 
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  • #16
Your last post sounds like panpsychism to me, which is an interesting consideration. It's possible that a consciousness-like property is fundamental to all matter, like mass or charge, but it only does interesting things in complex configurations. There are also theories proposing that it may be a property of electromagnetic fields (and thus emerges from the electrical activity of neurons) which I find to be similar in concept.

Feeble Wonk said:
You're right Pythagorean... While subtle, there is a very real difference between the subjective experience of "qualia" and the experience of "self awareness", but it would seem that the latter would be an emergent result from the former.

As to your larger point, I would totally agree. The subjective experience of qualia is the aspect of consciousness that is difficult to clearly define in a reductionist/mechanistic sort of way, and does not seem to be necessary for the purposes of reflexive deterministic neurological action.

I think, to some extent, most of the evidence so far (while it's not a cut clear case) suggests that consciousness is a passive consequence of deterministic neurological action (thus why we haven't been able to "find" free will; free will is already kind of a contradictory idea, that seems to imply that humans should be able to evade cause and effect of the physical universe). Other evidence is genetic and environmental factors on behavior

Of course, QM theories do seek to relieve neuroscience of determinism, but QC isn't really my bag.
 
  • #17
Sadly, I'm really unable to pursue that discussion while upholding my promise to the moderators to maintain the prohibition against philosophical rhetoric.

Suffice it to say that (as I'm sure you're well aware) "cause and effect" at the quantum level becomes a very dicey thing... as does the ontological "nature" of physical existence.

That said, I want to make it very clear that I am definitely not suggesting that mental/conscious experience should not be described with reference neurological activity. My only contention is that it is questionable as to what that neurological activity represents at the fundamental "physical" level, and what the causative relationships are in the process.

But, again, I want to respect the PF policy regarding philosophical debate, so I really don't want to add anything further to that position.
 
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  • #18
I shan't dig too deeply into this bearing in mind the prohibition against philosophical matters although I must admit to being unclear where philosophy intrudes in this particular topic.

While I don't have anything like the background you both have, my personal view is that consciousness is no magic thing. Pythagorean you suggest that neurological activity is just computation and then reject consciousness as simply being that, but I suggest there is not the slightest evidence there IS more than that. Why is it not reasonable to adopt the simplest possible explanation that we cannot work out what consciousness is simply because there isn't anything to find?

Is a robot conscious? Is a computer conscious? Perhaps it is. Perhaps this is the 'built in' nature of consciousness you argue for Feeble Wonk.

The simplest early life operated on very simple cause and effect principles that are completely accessible to explanation. Why should evolution have supplied something extra to the mix beyond a much more complex arrangement? Why should some magic 'something' appear at some point? To me this is invoking some metaphysical quantity for which I personally see no evidence.

Anyways, clearly that is to go down the philosophical path and no doubt I am just displaying my ignorance of the deeper issues. In terms of my original question, the various links and comments have been most interesting but I return to one earlier point I made. Why in the case of the Libet experiments is the time of commencement of the conscious aspect of the act not taken to be the point of receiving the instruction? Why was the RP preceding the act itself taken as representing some backward referral when it could as easily be taken to represent a part of the causal chain originating with the original instruction?
 
  • #19
Graeme M said:
I shan't dig too deeply into this bearing in mind the prohibition against philosophical matters although I must admit to being unclear where philosophy intrudes in this particular topic.

"Philosophy" intrudes at the point where one begins to discuss the ontological nature of the quantum wave function.

This is particularly true when one questions the role of consciousness in the act of "observation" as it relates to quantum state reduction.

You might very well be correct in your assessment Graeme. If we accept a Bohmian "pilot wave"/hidden variable type of QT interpretation, it might be just as cut and dry as you suggest. Or, if we accept a "many worlds" type of interpretation, then all possible quantum states of the macroscopic organic activity are realized in one of worlds, so no explanation is necessary. But anything short of that requires some serious explanation as to how an observed outcome of a reduced quantum state is arrived at. And maybe, just maybe, consciousness is itself a hidden variable.

But, again, this treads perilously close to metaphysical and/or philosophical conjecture, so...
 
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  • #20
Graeme M said:
I shan't dig too deeply into this bearing in mind the prohibition against philosophical matters although I must admit to being unclear where philosophy intrudes in this particular topic.

While I don't have anything like the background you both have, my personal view is that consciousness is no magic thing. Pythagorean you suggest that neurological activity is just computation and then reject consciousness as simply being that, but I suggest there is not the slightest evidence there IS more than that. Why is it not reasonable to adopt the simplest possible explanation that we cannot work out what consciousness is simply because there isn't anything to find?

You misunderstood me. That may be the case, the problem is we don't have evidence that computation us consciousness and equating them blindly as if we do is putting the cart before the horse.

We simply don't know yet.
 
  • #21
Feeble Wonk said:
"Philosophy" intrudes at the point where one begins to discuss the ontological nature of the quantum wave function.

This is particularly true when one questions the role of consciousness in the act of "observation" as it relates to quantum state reduction.

Heh, I have no idea what you just said there Feeble Wonk! I'm afraid my understanding of that sort of thing hovers between "not much" and "none", depending on the time of day! I am not dismissing what you say, it just goes over my head is all.

Pythagorean said:
the problem is we don't have evidence that computation us consciousness

I understand, but I come back to the earlier question. What evidence do we have that it isn't? Or even better, what evidence are we looking for to show us that consciousness is something other?

As I've noted, I am pretty ignorant of the deeper issues and the body of knowledge around this topic - I'm just a curious sort of guy but no more than that. But I've been digging around for a while now trying to find some idea of exactly what people are actually meaning when they talk of consciousness and while I've come across a lot of ideas, there doesn't seem to be any agreed definition.

In terms of Libet, I was curious as to whether the data shows that the brain simply does what it does and the subjective sense of the act is a later addition arising from the underlying neurological processes (as has been pushed in a few articles I've read about it). Schurger's explanation makes better sense for me than what I have understood of Libet's model, but being pretty uninformed of the science I wonder at why the experiment doesn't consider the entire sequence from time of instruction.

In fact, I'd be interested in what the subject's could report of thinking. If it were me, there'd be a sense of "OK, I'm going to do it soon. Maybe now… ummm, no, maybe I'll wait till that dial reaches the 5th mark. Yeah… no, yeah, now!" I might not actually put that into words as such, but that's pretty much the 'feeling' I'd have.

While that doesn't mean that my subjective sense of things is preceding and directing the action, it seems a better fit to the idea that an RP is seen up to some time before the actual decision to act.

We don't simply sit around with nothing going on in our heads and then like a bolt from the blue do something (at least, not for voluntary acts in response to a direction).

I suppose I'm seeking some contextual information about why Libet would have assumed that the decision to act as noted subjectively is a kind of an unrelated one-off event that isn't part of some larger process begun when the instruction was first given. I'd be more impressed if the RP arose BEFORE the instruction! :)

So while I follow the general outline of the issue, I am not sure I understand its significance as I have understood it from what I've read. I have no axe to grind (though personally I'd be quite happy with subjectivity arising after the underlying process begins).
 
  • #22
I understand, but I come back to the earlier question. What evidence do we have that it isn't? Or even better, what evidence are we looking for to show us that consciousness is something other?

I'll leave this one to Hermione Granger:

“But that’s – I’m sorry but that’s completely ridiculous! How can I possibly prove it doesn’t exist? Do you expect me to get hold of – of all the pebbles in the world and test them? I mean you could claim that anything’s real if the only basis for believing in it is that nobody proved it
doesn’t exist!”

The context is a little different, but the fact remains. You can't prove a negative, but that doesn't affirm the positive. You still have to find the evidence for the positive. Certainly we have evidence that some neural processes are associated with consciousness. But some are not (most actually) and some processes are present during both consciousness and unconsciousness. Add to that that we have no way to assay causation and we don't really have a lot to go on.

That's why it's the "hard" problem!
 
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Likes atyy and Feeble Wonk
  • #23
Thank you DiracPool for the earlier links. I have just read the paper by Benjamin Libet in the Beavioural and Brain Sciences journal link (although not as yet the commentary and the author's response) and I see that Libet did endeavour to screen for any prior planning, although it isn't clear to me whether accepting an instruction and therefore having an intention to act at some later time causes neurological activity not present otherwise. Though I suppose we are always in the stages of *some* level of intention.

One thing I didn't understand is how subjects reported an urge to act time ('W') and an act itself time ('M'). If I do this myself I am not aware of any 'urge to act' - that is, I cannot distinguish between W and M. It wasn't apparent from the paper how subjects assessed the urge to act - is there some kind of internal signal one can report? I notice this with most voluntary acts in life. That is, I am not conscious of the urge to act - it just happens. What exactly were Libet's subjects reporting for W?
 
  • #24
DiracPool said:
As far as Ben Libet's work, this is old news and doesn't really have a place in contemporary discourse. Libet's claim was that there was a "readiness potential" that pre-ceded a voluntary action bu that the "conscious" mind could "veto" that act if it wanted to. Everything is correct about this model except for the veto act.

I skimmed over this part of your post previously, and forgot to ask you about it.

Are you saying that there is no inhibitory feed back mechanism to abort a "go" signal?
 
  • #25
Feeble Wonk said:
I skimmed over this part of your post previously, and forgot to ask you about it.

Are you saying that there is no inhibitory feed back mechanism to abort a "go" signal?

I'd love to hear DiracPool and Pythagorean's (or anyone else's) comments on

http://www.ncbi.nlm.nih.gov/pubmed/?term=PMC3733500
Canceling actions involves a race between basal ganglia pathways.
Schmidt R, Leventhal DK, Mallet N, Chen F, Berke JD.
 
  • #26
Thanks atyy -let's back away from the problem in this thread that pythagorean was pointing out - problematic logic, rather than discussing actual data. Your link appears to be actual data. Yay! I cannot comment authoritatively on it.

From the abstract:
Our results support race models of action cancellation, with stopping requiring Stop-cue information to be transmitted from STN to SNr before increased striatal input creates a point of no return.

Great find. From my perspective.
 
  • #27
atyy said:
I'd love to hear DiracPool and Pythagorean's (or anyone else's) comments on

http://www.ncbi.nlm.nih.gov/pubmed/?term=PMC3733500
Canceling actions involves a race between basal ganglia pathways.
Schmidt R, Leventhal DK, Mallet N, Chen F, Berke JD.

I believe one of the authors visited and gave a talk about this research at my university, but we still come back to interpreting what it means in light of the Libet experiment. It's not particularly surprising to me in the context of the muscle reflex system. I guess the next question is whether its generalizable to all human decisions. I don't doubt I could find some similar links reading emotional regulation if I was at a computer.
 
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  • #28
Pythagorean said:
I believe one of the authors visited and gave a talk about this research at my university, but we still come back to interpreting what it means in light of the Libet experiment.

So, what was the consensus opinion regarding this at the university, with respect to the Libet experiment? Or was that specifically discussed at all?
 
  • #29
Libet was not brought up that I recall. It was a presentation on the research (methods and results).
 
  • #30
atyy said:


http://www.ncbi.nlm.nih.gov/pubmed/?term=PMC3733500
Canceling actions involves a race between basal ganglia pathways.
Schmidt R, Leventhal DK, Mallet N, Chen F, Berke JD.
Pythagorean said:
...but we still come back to interpreting what it means in light of the Libet experiment. It's not particularly surprising to me in the context of the muscle reflex system. I guess the next question is whether its generalizable to all human decisions. I don't doubt I could find some similar links reading emotional regulation if I was at a computer.

So, is it reasonable to consider whether the Libet "delay" in expression of intended action (to whatever degree that actually is) is related to this "go/stop" neurological competition?
 
  • #31
Feeble Wonk said:
I skimmed over this part of your post previously, and forgot to ask you about it.

Are you saying that there is no inhibitory feed back mechanism to abort a "go" signal?

It's been a while since I've encountered any debate on the Libet experiment, but after a quick review, the general idea is that, in the experiment, activity was recorded in scalp EEGs over the secondary motor cortex of the subjects 500 ms before the execution of a movement related to a particular cue (the position of a rotating red dot). Libet found that the subjects reported the "conscious intention to act" 300 ms after the 500 ms epoch (the readiness potential). 200 ms after that, the movement was executed. What Libet also found, though, was that the movement could be "vetoed" in the 100-150 ms between the time of the "subjective experience of the conscious will to act" (>300 ms) and the the actual act (>500 ms).

As I said in my previous post #4, Libet got into some heat on this issue because of his suggestion that there may be some neurally ambiguous "conscious will" involved in vetoing the act, as well in the backward or retro-causation implied in the antedating of the intention to move back to the beginning of it's neural causation.

https://en.wikipedia.org/wiki/Benjamin_Libet
"While consciousness plays no part in the instigation of volitional acts, Libet suggested that it may still have a part to play in suppressing or withholding certain acts instigated by the unconscious."

From here it devolved into a debate between dualists philosophers, scientists, and others. At this point, I lost interest in the subject. I thought it was all but done. That is where this quote came from:

DiracPool said:
As far as Ben Libet's work, this is old news and doesn't really have a place in contemporary discourse. Libet's claim was that there was a "readiness potential" that pre-ceded a voluntary action bu that the "conscious" mind could "veto" that act if it wanted to. Everything is correct about this model except for the veto act.

The veto act had dualist connotations I didn't really feel comfortable with.

atyy said:
I'd love to hear DiracPool and Pythagorean's (or anyone else's) comments on

http://www.ncbi.nlm.nih.gov/pubmed/?term=PMC3733500
Canceling actions involves a race between basal ganglia pathways.
Schmidt R, Leventhal DK, Mallet N, Chen F, Berke JD.

As far as the Schmidt et al. study, I have no reason to doubt their findings, the problem is that it is questionable what relevance they have to the Libet controversy. The Schmidt study dealt exclusively with subcortical processes related mostly to basal ganglia structures and as far as I could tell did not even take any readings from the neocortex at all:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3733500/
"...rats in Experiment 1 received implants containing 21 individually drivable tetrodes targeting basal ganglia structures (STR, GP, STN, and SNr)"

In contrast, the Libet experiment focused solely on the neocortex. Not only that, it was recorded with scalp EEG electrodes. So it's very difficult to extrapolate the Schmidt data to the Libet data. The Libet data was designed to test the unconscious "cerebral" initiative in a voluntary act, which has all sorts of connotations to cognition, the neocortex, and especially executive function in the prefrontal cortex. Rats are too removed from us phylogenetically to use in a comparison here. For a long time it was debated whether or not rats even had a prefrontal cortex at all. I think the consensus now is that they have a very tiny one. But in any case, the problem is that, although older phylogenetic regions of the brain are mostly conserved, the growing outer mantle of the cortex likely reorganized subcortical circuits to some degree in order to accommodate newer cognitive capacities found in primates. That's why we can't be sure the Schmidt circuits are reliable homologues to circuits in humans, and why I'd be suspect to read much into them.

Feeble Wonk said:
So, is it reasonable to consider whether the Libet "delay" in expression of intended action (to whatever degree that actually is) is related to this "go/stop" neurological competition?

See above.

As far as the OP's study:http://www.pnas.org/content/109/42/E2904.full

I don't see how this challenges or changes the Libet debate much. I only browsed it, but it seems to me as if the authors are only stating that we can't be sure that the readiness potential (RP) is the only factor "pre-cluing" in the decision to initiate a movement, there may be some stochastic processes or spontaneous neural fluctuations that compound with the RP that mask the pure role of the RP in the initiation of that movement:

http://www.pnas.org/content/109/42/E2904.full
"One can extend this idea to choice behaviors such as choosing between reaching for a coffee cup or reaching for a muffin. If you are somewhat hungry and also somewhat thirsty, then spontaneous fluctuations might play a role in tipping the scales in favor of one or the other, as is the case with cued perceptual decisions."

and

"We assume that spontaneous fluctuations are ongoing even when the subject is not preparing to move and that these can often approach the threshold without crossing it. Therefore, false alarms will be a limiting factor in the overall sensitivity of an interface that uses slow fluctuations to infer movement intention."
 
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  • #32
I found this review ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4064703/ ) to be of some interest in terms of my original question. It is relatively recent (2014) and is a general review of research aimed at more objective analyses of the Libet type experiments. That is, they attempt to identify more objective methods for measurement than relying on subjective observation.

By identifying neural correlates to the subjective perception of the urge to act and act itself (Libet's W and M moments), they can quantify when the W and M moments arise in a more objective quantitative sense.

Although the paper is more concerned with the sense of agency rather than whether spontaneous events arise according to a conscious volition, it does for me at least offer greater insight (although I found the paper hard going given my lack of background in the current science).

I found the notion of binding particularly interesting (when an action results in a sensory feedback, the perception of these events temporally shift closer together relative to either separately - the action is perceived later while the feedback is perceived earlier).

The discussion around both "comparator model within optimal motor control theory", and "active inference theory" was a bit out of my league but nonetheless I gathered that prediction models are compared internally to perceptual responses (sensory feedback) to generate (or contribute to) the sense of agency. That is, the closer the predictive model to the resulting perceptual model the greater the sense of agency (I think though that this really just says the more something looks like I did it, the more I think I did it). The active inference theory outlines how this unfolds in terms of the hierarchy of cortical processes.

Again, while mostly this discussion was above my level of understanding, I felt that it broadly described how the conscious sense of directing an act is largely retrospective. That sort of accords with my intuitive sense about how conscious direction might operate.

The 'binding' discussion to me is especially relevant by illustrating how subjective perception is adjusted internally and my take - and here I'd welcome any comment by those who are far more familiar with the subject matter - is that the W and M perceptions arise from internal temporal adjustments to correlate motor actions with external feedbacks (that is, it's better to have an organism sense its behaviours as aligned with environmental interactions in a cause/effect relationship than otherwise, which would seem to my naïve view a clear evolutionary likelihood).

For example, while the Libet data indicates the W moment precedes the actual moment of action by around 200ms and the M moment around 85ms, research shows that the later the W moment (ie closer to M), the less the sense of agency.

By the way, going back to an earlier comment, I still have no idea how anyone can identify a W moment in the first place...
 
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  • #33
And just to show I am happy to comment on things I know nothing about, here's an interesting study regarding unconsciousness that I think has some relevance in terms of earlier comments regarding defining consciousness.

http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1003271

This study notes (and I suppose it's stating the bleeding obvious) that Propofol induced unconsciousness is characterised by a loss of wide scale integration of information processing (increased clustering of connectivity) and reduced efficiency in information distribution. They also note that changes to both long and short connections were generally similar and that long range connections were not more affected, contrary to other reports.

Given I am not familiar with current scientific thinking around consciousness and the general position of neuroscience I am probably out of order with this observation, but is this not somewhat suggestive of the reverse idea that consciousness arises from wide scale integration of neural information processing? For example, the sense of agency discussed in the paper in my earlier comment above must depend upon the integration of a wide range of internal information from a variety of brain regions. If I consider that for the conscious mind to generate a sense of agency, actions, their outcomes AND the modelling of those relationships must occur quickly enough to provide some gross temporal synchronicity then it makes sense to me that it is the effectiveness and the speed of the integrated network that makes consciousness possible.
 
  • #34
Apropos my earlier comment regarding consciousness simply being what it is to be a brain processing information, I found this today. I offer it for anyone who is interested and to ask if anyone who has read the book "Consciousness and the Social Brain" or knows more about this fellow's ideas would care to comment.

http://aeon.co/magazine/philosophy/how-consciousness-works/

Michael Graziano is a professor of neuroscience at Princeton, and unless I misunderstand his ideas from this relatively simple overview, this is exactly what I was getting at.
 

1. What is the Libet experiment and how is it relevant to modern interpretation?

The Libet experiment is a psychological study conducted by Benjamin Libet in the 1980s that aimed to understand the relationship between conscious awareness and the initiation of voluntary actions. In the experiment, participants were asked to perform a simple motor task while their brain activity was measured. The results showed that brain activity related to the initiation of the action occurred before the participants were consciously aware of their intention to act. This has been interpreted as evidence for the lack of free will and the deterministic nature of human behavior. Modern interpretations of the Libet data suggest that the experiment may not accurately reflect real-life decision-making processes and that the findings should be interpreted with caution.

2. How has the interpretation of Libet data evolved over time?

Initially, the Libet experiment was seen as evidence against the existence of free will. However, as more studies have been conducted, researchers have proposed alternative explanations for the results. Some argue that the brain activity observed in the experiment may not necessarily reflect a conscious decision, but rather a preparatory process for the action. Others suggest that the conscious awareness of the intention to act may occur earlier than measured in the experiment. These alternative interpretations have led to a more nuanced understanding of the Libet data in modern times.

3. Can the Libet experiment be replicated and have the results been consistent?

The Libet experiment has been replicated numerous times, and while the general findings have been consistent, there have been variations in the results. Some studies have shown that the timing of the brain activity and conscious awareness may vary depending on the complexity of the task or the individual's level of self-awareness. This suggests that the Libet data may not be a reliable indicator of the absence of free will and that further research is needed to fully understand the relationship between conscious awareness and decision-making.

4. How does the Libet experiment relate to real-life decision-making?

One of the criticisms of the Libet experiment is that it may not accurately reflect the complex decision-making processes that occur in real-life situations. In the experiment, participants were asked to make a simple motor action, which may not be representative of the complex and often unconscious processes involved in decision-making. Additionally, the experiment was conducted in a controlled laboratory setting, which may not accurately reflect the dynamic and unpredictable nature of real-life decision-making.

5. What are the implications of the Libet data for the concept of free will?

The implications of the Libet data for the concept of free will are still a subject of debate. Some argue that the experiment provides evidence for the lack of free will and the deterministic nature of human behavior. Others suggest that the results may not be applicable to real-life decision-making and that free will may still exist in more complex and unpredictable situations. Ultimately, the interpretation of the Libet data and its implications for free will remain a topic of ongoing research and discussion in the scientific community.

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