Wednesday, June 11, 2008

The Bejamin Libet Experiments

The libet experiments defy easy explanation he did experiments where he stimulated the finger area of one cortex and also the same finger the otherside and basicially what he found was that direct cortical stimulation if it resulted in gamma synchrony for 500 milliseconds resulted in consciousness at the end of half a second. But if he stimulated the finger and got a invoke potential followed by 500 milliseconds it was found at the time of the invoke potential. He did other studies too with peramic stimulation which basicially said that if you have to invoke potential but don't continue with the gamma synchrony for the full time their is no conscious experience so it appears if somebody knows brain,body or somebody knows rather or not this is going to continue. Libet concluded that their was backtime time referral for subjective experience.

Libbet was interested in how neuronal potentials were connected to consciousness. While performing operations on test subjects, who were undergoing brain surgery to treat epilepsy, he established a simple procedure. He found the place in either hemisphere that stimulated the subject's hand as if they were being shocked with a mild electrical current. He then taped an electrode to both hands, and, using a computer and robot, proceeded to stimulate one of those places in the brain, and the opposite hand to the one which the hemisphere in question controlled. So, if he stimulated the part of the brain that made the right hand tingle, he directly stimulated the left hand. These he did at exactly the same time, again, using the computer and robot to control timing. He would then ask the subjects which one they felt first. The subject would not know which was which thanks to the experimental design, and he did confirm that qualitatively, the subjects could detect no difference in the feelings.

He expected to find that the subject felt the brain stimulation first, since the electrical current that was producing it didn't have to travel up the arm and spinal cord. What he instead discovered is that subjects uniformly felt the direct hand stimulation first. He in fact found that this would be the case up to about a quarter of a second delay between the brain stimulation and the direct hand stimulation. Consider this carefully and I think you'll see why it's a problem for materialists. If it stumps you, I'll provide further explanation. Anyway, at least some dualist accounts would make this prediction, while no materialist account would.

Another area of evidence that is difficult to explain by physicalism is Animal navigation, for instance, is a clear case. Consider the homing pigeon for a moment. I don't recall the exact reference, but there was an English biologist who tackled the question of how a homing pigeon homes. For the experiment, he did all kinds of unusual things to the homing pigeons. He trained them to home to a carefully controlled laboratory setting, and then changed all kinds of things (like scent and ambient sounds well above and below the threshold of human hearing). He put them in windowless boxes in a van and drove them around in a highly circuitous route to try to confuse them. Under all such conditions, they homed perfectly.

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