Mind Time: The Temporal Factor in Consciousness (Perspectives in Cognitive Neuroscience) ペーパーバック – 2005/10/28
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Our subjective inner life is what really matters to us as human beings--and yet we know relatively little about how it arises. Over a long and distinguished career Benjamin Libet has conducted experiments that have helped us see, in clear and concrete ways, how the brain produces conscious awareness. For the first time, Libet gives his own account of these experiments and their importance for our understanding of consciousness.
Most notably, Libet's experiments reveal a substantial delay--the "mind time" of the title--before any awareness affects how we view our mental activities. If all conscious awarenesses are preceded by unconscious processes, as Libet observes, we are forced to conclude that unconscious processes initiate our conscious experiences. Freely voluntary acts are found to be initiated unconsciously before an awareness of wanting to act--a discovery with profound ramifications for our understanding of free will.
How do the physical activities of billions of cerebral nerve cells give rise to an integrated conscious subjective awareness? How can the subjective mind affect or control voluntary actions? Libet considers these questions, as well as the implications of his discoveries for the nature of the soul, the identity of the person, and the relation of the non-physical subjective mind to the physical brain that produces it. Rendered in clear, accessible language, Libet's experiments and theories will allow interested amateurs and experts alike to share the experience of the extraordinary discoveries made in the practical study of consciousness.
Mind Time makes for extremely interesting, engaging reading. Its discussions of consciousness, subjectivity, free will, and perception will intrigue anybody in philosophy or psychology interested in those topics. This is a valuable book to have available. (David Rosenthal, Philosophy and Cognitive Science Graduate Center, City University of New York)
Benjamin Libet's discoveries are of extraordinary interest. His is almost the only approach yet to yield any credible evidence of how conscious awareness is produced by the brain. Mind Time endeavors to clarify these startling observations for the general public, set them in proper framework of neuroscientific knowledge, and probe their philosophical meaning. Libet's work is unique, and speaks to questions asked by all humankind. (Robert W. Doty, PhD, Professor of Neurobiology and Anatomy, University of Rochester)
This book is strikingly different from most of the other books on consciousness in one key respect: it focuses on empirical discoveries, not speculation or argument. (From the Foreword by Stephen Kosslyn)
Libet only dared switch to the study of consciousness after he got tenure. It is fortunate for us that he did, and that he has presented us here with what amounts to a retrospective exhibition of his work...The refreshing result is that we are immediately engaged in an earnest one-to-one tutorial with [him]...In [his] work, philosophers have found grist for what they do best. Indeed, his experiments...must rank as one of the major contributions of experimental psychology to modern philosophy of mind...[W]hether or not one agrees with his thesis or not, one must acknowledge that his pioneering experimental work has certainly been stimulating. (Kevan Martin Nature 2004-05-20)
What makes Benjamin Libet different from all the others writing on [consciousness]...is that he has actually spent the past 40 years experimenting on the topic. His findings have played a central role in others' speculations. Now he has put his life's work into a single short book. (Steven Rose New Scientist 2004-05-22)
[Libet's] book is greatly to be welcomed because it provides the first full and detailed account of his famous experiments, explaining how and why he carried them out, and how he came to his conclusions...What is new is Libet's 'conscious mental field theory,' which is startlingly different from any other current theory of consciousness. (Susan Blackmore Times Higher Education Supplement 2004-10-01)
While reading the Zero Limits book of Dr.Joe Vitale and Dr.Hew Len ,I read that Dr.Libet has done unique experiments that prove something that my MBA awarded intellect does not like at all...My intellect is consious only 15 bits of information out of millions each moment!!!So although I think that I know a lot ,I know less than 1% of the reality each moment.So Socrates (in Ancinet Greece)was right ,when he said ''I know one that I know nothing ''But the problem is that we do not know ,that we do not know!
This is a must have book for every library !
He starts the book with very shaky philosophical assumptions. He explicitly says the scientific study of consciousness must make no assumptions on the mind-brain relationship. Yet he claims that qualia are not explainable in physical terms, that consicousness and qualia are the same thing, that the only valid form of evidence is instrospection, that cosnciousness is a content independent phenomenon. These are a prioiri assumptions. None will be admitted by most without argument, but Libet expects us to. All of this stems, of course, from LIbets extreme verificationism, disguised as scientific rigour. He holds the very dated notion that the only valid scientific knowledge attainable is that which can be falsified. Thus he shuns aside every philosophical, or scientific for that matter, progress done because he believes it cannot be put to empirical test. Circle of Vienna, here we go again.
But nobody is a verificationist anymore. At least not philosophers. And given that scientists interested in consicousness would part from Libets ideas, and philosophers will too, Libet is alone against the world.
Libet famously found that there is a delay in consicous awareness. That is, a stimulus becomes conscious if it elicits brain activity that lasts for 500 miliseconds or so. THat is, the difference between cosncious and unconsicous brain activity, is a matter of duration. (hence the title of the book). We do not experience the world as lagging behind, because consicousness is refered to the earlier apparition of another type of brain activity. So far so good. His evidence is strong, robust, and so far, very significant to the prospects of explaining the neural bases of consciousness. But is Libet right?
Well, Daniel Dennett does not think so. He claims the delay is due not to cosnciousness per se, but to the laying down of a memory trace for the stimulus to be reported. Libet argues that Dennett is wrong, because patients with no hippocampus (memory defects) are still consicous. Maybe he is right. But Libet, a scientist, seems to preocupied with philsophers and ignores other lines of evidence.
LIbet holds that the only thing that makes a stimulus consicous is the time the neural activity lasts, not where the activity is at. Consider ,now, spatial neglect. In this condition, patients are unaware of stimulus in the oposite visual space of a unilateral parietal lesion. This means that libet would have to argue that the duration of brain activity in visual areas is mediated by the parietal cortex, which seems odd. What about brain imaging studies. One of them, conducted by Lumer and Rees, found that the difference between a conscious and an unconsicous stimulus was reflected in a fMRI only with a difference in intensity of activation, not duration or location. This is direct counter evidence to LIbets proposal. Libet does not consider these studies. Nor does he consider the fact of epilepsy, where brain activity is quite long in duration, but different in amplitude and frequency, and the patient is unconsicous. Time cannot be the only factor. If it is, proving so requires more than what LIbet offers.
Libet also famoulsy found that brain activity preceeds the consicous will to act for about 200 miliseconds. He also proposes that the notion of free will can be mantained, because there is time to veto consciously willed actions. You do not begin your actions, but you modulate them.
Again, his evidence is strong, robust and significant. But what about his 'veto¨speculation. IT is unecessary. Firstly, materialists should not be surprised with the fact that cosncious will comes late in the game. If consicous will is the result of brain processes, it cannot antedate these processes. Secondly, the obvious question arises if the veto function is not preceeded by unconsicous brain activity in turn. Libet here argues that it must not, for even if the awareness of the decision to veto requires brain activity, the content of that awareness (the actual descition to veto), need not. This reply depends of course, on the independence of consicousness from its content, an assumption that LIbet gives us no reason to accept. It is also, of course, clear that the analogy Libet tries to make is that between internally and externally generated activity. It is obvious in perception that the brain activity that causes consicousness of an object in the world is one thing, and that the object in the external world requires no brain activity. But it is not so obvious with a ¨decision to veto¨ because such ¨thing¨ is not depndent on external imput. IT is dependent on internally generated, BRAIN generated, activity. Alas, the analogy fails.
It seems libet proposes his veto theory only because he thinks that otherwise we will be nothing but automatons, mere robots. We would loose sense of responsibility. And the guilt would fall on his discoveries. BUt nobody is claiming this at all (well, some have taken LIbets work to mean this, but the point is that it need not). Brain activity is at the end still OUR brain activity. Brain activity can still be said to be consicous or uncosncious. Resposibility need not fear determinism, wether determinsism is right or wrong.
But Libet, of course, would not consider speculating on any of this, because it would not be testable. And accordingly, Libet proposes his mental-field-theory, a theory of consicousness explaining all these findings, along with the description of how the theory could be experimentally tested (it consists of an ingenius way to see if an neurally isolated cortical slice can cause consicousness in a subject). The theory holds that a consicous-field, somehting like a force field, that depends on neural activity but does not need it to be transmitted from brain area to brain area, would explain the mind-brain relationship. Is he right? here we must wait for somebody to carry out the experiment. Any bets? Well, I would go with those who believe nerve fibers serve a purpose.
Libet, as I said, deserves a prize. He deserves his book to be read by those interested in the field, too. And his findings will shape, and must be explicable by, any theory of consicousness proposed. But his speculations on the mind-brain relationship will probably have the same fate as those of of his mentor, Sir John Eccles (anybody remembers psychons?).