Quote:But if hundreds of milliseconds of brain activity are required for neuronal adequacy, how can conscious sensory experience occur at 30 ms? To address this issue, Libet also performed experiments in which stimulation of thalamus resulted in an EP at 30 ms, but only brief ongoing activity, i.e., without neuronal adequacy (Figure (Figure9A).9A). No conscious experience occurred. Libet concluded that for real-time conscious perception (e.g., at the 30 ms EP), two factors were necessary: an EP at 30 ms, and several 100 ms of ongoing cortical activity (neuronal adequacy) after the EP. Somehow, apparently, the brain seems to know what will happen after the EP. Libet concluded the hundreds of milliseconds of ongoing cortical activity (“neuronal adequacy”) is the sine qua non for conscious experience—the NCC, even if it occurs after the conscious experience. To account for his results, he further concluded that subjective information is referred backwards in time from the time of neuronal adequacy to the time of the EP (Figure (Figure9B).9B). Libet's backward time assertion was disbelieved and ridiculed (e.g., Churchland, 1981; Pockett, 2002), but never refuted (Libet, 2002, 2003).
I dug a bit into the references but it's still not clear me to what Libet's actual, original claim was.
'Historically, we may regard materialism as a system of dogma set up to combat orthodox dogma...Accordingly we find that, as ancient orthodoxies disintegrate, materialism more and more gives way to scepticism.'
I dug a bit into the references but it's still not clear me to what Libet's actual, original claim was.
I think there are lots of assumptions going here. The ideas that have been put forward to explain different subjective results of studies exploring Masking or Enhancement stimuli, make a lot of unstated assumptions about how the brain works. Libet's work is early 60's/70's, and although the actual observations they make are correct, there are a lot of half-baked attempts at explanations made in these papers, that are really 'reaching' way beyond what it was (still is) actually possible to say about how the brain works, together with a good helping of professional ego.
I don't think these studies necessarily show what people think they show. I think it's reasonable to consider that stimuli is unified as best as possible by a person subjectively, according to past experiences, and that this process is not one simple mechanism, but multiple mechanisms that have complex effects on the results of these studies, many of which have not been pinned down.
I've linked to two papers for you to download (I will remove them in a few days)...
It would be better if you read Kahneman 1968 review of masking first. It's quite dense, but the concepts of masking it explains are relatively easy to understand, although the different explanations are harder... because none of them actually explain all the results satisfactorily... probably because these explanations are just too simplistic, and made with very limited understanding of the brain - less than we have today (which isn't much anyway)...
I think after that, you should read Libet 1992, and you should then be able to better understand Libets experiment, and why sticking sub-cortical and cortical probes into brains, and using other sensory skin stimuli opens up even more possibilities, than the subjective masking stimuli studies discussed in Kahneman's review. You'll probably then appreciate the limitations of Libet's ideas to explain the results in this paper, he's just over-reaching, and giving more certainty to his ideas than they really deserve...
'Historically, we may regard materialism as a system of dogma set up to combat orthodox dogma...Accordingly we find that, as ancient orthodoxies disintegrate, materialism more and more gives way to scepticism.'
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