Most helpful positive review
21 of 24 people found the following review helpful
Excellent summary of great scientist's theories
on April 30, 2006
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.
Furthermore, I was well trained and educated in epistemology, the philosophy of science, and so on, before settling on grad school in neurobiology. The philosophy is really only important for a neurobiologist at the undergraduate level to avoid basic logical mistakes. At the graduate level in neurobiology, you're at a level the philosophers can't even understand and read the articles on anymore and so philosophy is completely irrelevant. Sad to say but that's just the way it is. So what I have to say to the other philosophically inclined neuroscientists like myself is to understand that at some point you have to move on and leave philosophy behind.
[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.