- #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?
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?