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 is an incredible book suitable for anyone interested in consciousness and neuroscience. Engulfed in cognitive neuroscience, yet keenly observant of the philosophy of mind, Libet's Mind Time finds a beautifully defined line between awareness and the potential there of. Through his years of research and numerous studies, this great scientist has revealed more about the nature of conscious awareness than cognitive philosophers could ever dream. How he does this is simply by repeatedly observing and verifying the temporal factor in consciousness, and leaving the reader with only one wonderful, inspiring conclusion: That we are, without a doubt, dictated by our subconscious awareness, and that there certainly is a fine line between what I think, and what I unknowingly have already thought of, called the threshold of conscious awareness.

I participated in two of Libet's experiments when I was a grad student, and knew his work well. I went on in neuroscience rather than perception, but I got well trained in both fields. So I thought I would make a few comments on that, especially in regard to the previous reviewer's remarks. I enclose those in brackets and then comment on them in my review. It's a well done review in many ways but there are some problems with it, too, and I had some additional things to add about Libet's ideas, so I thought I'd comment on that, too.

[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.]

This is the classical Karl Popper falsifiability criterian, rather than the Vienna Circle per se, but every perceptual scientist of that generation (including me) was educated that way. No big deal. They still made more progress in 20 years than in the previous 150.

[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 consciousness 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 conscious. Maybe he is right. But Libet, a scientist, seems to preocupied with philsophers and ignores other lines of evidence.]

They're both right, as the real situation is now known to be more complex. The brain can react before consciousness is aware of a percept. Occulomotor tracking by the visual system in the superior colliculus is a good example. But some percepts seem to require the intervention of consciousness, such as in complex perceptual processing and perceptual associations. So although I like Libet's ideas and I believe he was mostly right, there are exceptions. (Nothing in the brain is simple, unfortunately).

Furthermore, stroboscopic visual experiments on very short term or iconic memory, showed that memory is almost photographic for the first few hundred milliseconds following the visual presentation, but quickly fades. This is such a short period of time that this sort of memory would have to be electrical in nature.

Actually, nerve action is not really electrical in nature in the sense of a wire conducting a current. This is a common misconception, and has lead to all sorts of misunderstandings and speculation about the brain, such as whether the brain could transmit some kind of electromagnetic radiation which could be responsible for paranormal powers such as telepathy. Unfortunately, the brain doesn't really work that way. Rather, the nerve action potential is due to ion flux, a self-propagating reversal of negativity that travels down the nerve axon. There are no radio waves so there is no way telepathy or similar phenomena could work that way.

[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.]

The reviewer is simply wrong about this. Epilepsy is not a normal, and in fact is a very abnormal phenomenon of consciousness, and the existence of what are known as paroxysmal depolarization shifts, or very unusual brain waves, during epilepsy, are proof of that.

Furthermore, epilepsy is actually very complex, and there are many different types of epilepsy, including ones where the person is conscious. Some forms of epilepsy are not even unpleasant. There are rare types of temporal lobe epilepsy that produce intense visions and ecstatic feelings of well being and happiness. There is even a type of epilepsy that causes extremely intense and long-lasting orgasms, since it occurs in the thalamic nucleus responsible for orgasms, in the nucleus reticularis gigantocellularis, if I remember right (not sure since it's been so long :-)). So epilepsy is not even an issue here. This is clear to anyone who understands the electrophysiology (which was my field).

[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 might be right about this, but arguing from the standpoint of limbic system memory mechanisms and evidence is very tricky, because the limbic system participates many aspects of memory, including such extremely subtle things as the selective inhibition of retroactive interference (as discussed by Robert Isaacson in his famous book on the limbic system); in other words, it aids in the inhibition and forgetting of certain memories as well as in the laying down and preservation of memories. Hence, for now, I'd leave the limbic system alone on that question, as it's just too slippery.

Besides, it's not just the hippocampus that's involved in temporal lobe memory mechanisms; the hippocampus also connects by means of a special pathway with the adjacent entorhinal cortex and that has a role in memory too, as neuroanatomists Carl Cottman and L. M. Cowan showed in their neuroanatomical studies of that area.

There's more I could say, but I'll leave it at that for now.

Benjamin Libet deserves some kind of prize. His studies, pioneering work on the neurophysiology of consicousness, were conducted back when there was no ¨cognitive¨ in cognitive neuroscience, and much less the word ¨consciousness¨ in science in general. His work is certainly now familiar to most who are interested in the philosophy of mind, or the neural bases of the mind. In this respect, this book advances few new evidence. But it does advance LIbets speculations on the significance of his finds.

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?).

The topic is a great one, and the author was a great researcher into the topic. Unfortunately, while he may be a great scientist, he's a horrible author.

His idea of the book's audience is vague: he defines neurons as "nerve cells" and introduces Phineas Gage as if talking to someone with no background in neuroscience, only to throw out terms like "fissure of Rolando" in the very same page. He's obviously been retired for quite some time, as all his research is several decades old.

Within the first few pages of the book, he state boldly that consciousness can't be explained by materalism-- something that, while may be true, is far from the kind of statement you just throw out without backing it up.

The organization is vague at best, at times it feels as if he's just rambling.

Worst of all, he repeats himself, almost verbatim, multiple times. The story of how he got the chance to perform these experiments is told practically word for word at least three time in the first 20 pages. A tribute to his college advisor is likewise repeated using the same words. Experimental evidence is complete introduced multiple times, as if it the author had somehow forgotten that he had already introduced it. I spent quite a lot of time trying to find a pattern to these repetitions-- was the book composed by splicing together articles he wrote elsewhere? In the end, I couldn't make heads or tails out of it.

Libet's research is truly extraordinary, but if you want to learn about it, don't read him, read a secondary source like Dennett's Consciousness Explained.