This link has been bookmarked by 12 people . It was first bookmarked on 17 Mar 2009, by Rudy Garns.
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18 Aug 13
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26 Mar 12
Bue Thastumhar highlights fra diigo
article research experiment Libet consciousness neuroscience diigo
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the stimulus had to persist for about 500 milliseconds before the subject became consciously aware of it
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although the stimulus to the skin might be brief, it was still the case that the resultant brain activity had to persist for 500 milliseconds before the subject became consciously aware of it
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Where a patient was anaesthetised, the initial brain response to a stimulus was the same as for a fully conscious subject, but it failed to continue for the required period: moreover, a stimulus applied directly to the brain 500 milliseconds after one applied to the skin could cancel (or in some circumstances, enhance) it
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500 milliseconds - half a second - is a noticeable period of time, and it is evident that human beings often respond to events far more quickly than that. If we had to wait half a second before responding to events, we should never be able to play a good game of tennis, and we should be dangerous (or extremely cautious) drivers.
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A stimulus applied to the skin produces an 'evoked potential' or EP in the brain within tens of milliseconds, and that seems to be enough for it to register unconsciously but effectively
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our unconscious responses are far quicker than our conscious ones
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we register unconsciously a whole host of things which may influence our response to events but which never cross the threshold into consciousness
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Libet's hypothesis was that conscious awareness is subjectively referred backwards in time
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We consciously perceive the stimulus as occuring at the same moment it registers unconsciously, even though it doesn't in fact enter our awareness until it has persisted for half a second.
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27 Nov 10
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14 Sep 09
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Libet was able to demonstrate that although the stimulus to the skin might be brief, it was still the case that the resultant brain activity had to persist for 500 milliseconds before the subject became consciously aware of it.
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hat sorted out Libet's account in purely empirical terms: in philosophical terms the problems were only beginning. The research (subsequently repeated and corroborated by others) seemed to provide a scientific proof that free will was a delusion. How could we consider ourselves responsible for decisions we were not even aware of until after they had been made?
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17 Mar 09
Rudy GarnsThe experiments carried out by Benjamin Libet into the timing of conscious awareness (briefly described here ) have provoked, and go on provoking, a vast amount of discussion. His own theory of consciousness as a kind of field has received somewhat less attention; and the strange brain-cutting experiment he proposed to test it seems likely to remain unperformed for the foreseeable future. A large number of papers and discussions have been published: in 2004, Libet finally summarised his own account in the book 'Mind Time'. (consciousentities.com)
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whatever the voltage or frequency of the pulses, the stimulus had to persist for about 500 milliseconds before the subject became consciously aware of it.
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But we also respond to events, and here a delay is highly relevant and noticeable.
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our unconscious responses are far quicker than our conscious ones
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Libet's hypothesis was that conscious awareness is subjectively referred backwards in time. We consciously perceive the stimulus as occuring at the same moment it registers unconsciously, even though it doesn't in fact enter our awareness until it has persisted for half a second. Subjectively we backdate it to match the EP at the beginning rather than the end of the 500 millisecond span.
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Perhaps the sensations actually enter conscious awareness immediately, and the half-second delay merely allows time for them to become reportable, or fixed in short term memory? Perhaps we are merely dealing with the difference between being aware of the stimulus, and being aware that we are aware of it? Libet contends that awareness and memory, especially declarative, explicit memory, are different and independent phenomena.
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the perceived time at which we make a decision must also be subjectively referred back by 500 milliseconds. Unlikely as it seems, and contrary to our own impression, we must have made our decisions slightly before we actually become aware of them.
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This 'Readiness Potential' or RP appeared about 800 milliseconds in advance of the act, and seemed to be a clear indication that the intention to act had formed.
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the RP appeared some 500 milliseconds before the reported awareness of a decision to move
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free will was a delusion
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Although the subject's decision to move occurred too early for it to have been initiated by conscious thought, there was still - just - a window of opportunity in which conscious awareness might conceivably veto the move.
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Is the RP really a signal that a decision has been made?
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Might not the RP merely signal a quickening of attention, rather than a moment of decision?
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isn't it possible that we need a certain amount of time just in order to report the awareness to ourselves?
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his proposed CMF is an emergent phenomenon: something that arises from the combination of active neurons but amounts to something distinctively more than, and different from, the sum of brain activity.
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27 Nov 07
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24 Jul 07
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13 May 07
Paul HackettInteresting article on whether or not we gave a free will
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14 Sep 06
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