I have updated my web page on Skeptical Fallacies to include the following:
A skeptic may say that materialism can explain consciousness because the brain could be a conscious computer. As evidence to support this position, he may cite the paper Computing Machinery and Intelligence by Alan Turing. This paper is about a test for computer intelligence that has come to be called the Turing test. The Turing test involves two people and a computer. One person communicates remotely with both the computer and the other person. If he can't tell which is the person and which is the computer, then the computer passes the Turing test.
Turing argued that if you can't distinguish a computer from a person and if you doubt a computer is conscious, you must also doubt other people are conscious. Since we accept that people are conscious, if a computer passes the Turing test, the computer should be considered conscious too.
However, there are several reason it is incorrect to use this paper as evidence that the brain is a conscious computer.
- Turing believed in the evidence for ESP and he felt a computer couldn't reproduce it.
(9) The Argument from Extrasensory Perception
I assume that the reader is familiar with the idea of extrasensory perception, and the meaning of the four items of it, viz., telepathy, clairvoyance, precognition and psychokinesis. These disturbing phenomena seem to deny all our usual scientific ideas. How we should like to discredit them! Unfortunately the statistical evidence, at least for telepathy, is overwhelming. It is very difficult to rearrange one's ideas so as to fit these new facts in. Once one has accepted them it does not seem a very big step to believe in ghosts and bogies. The idea that our bodies move simply according to the known laws of physics, together with some others not yet discovered but somewhat similar, would be one of the first to go.
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If telepathy is admitted it will be necessary to tighten our test up. The situation could be regarded as analogous to that which would occur if the interrogator were talking to himself and one of the competitors was listening with his ear to the wall. To put the competitors into a "telepathy-proof room" would satisfy all requirements."
- Turing wrote that the proof of his belief that a computer could pass the Turing test would only occur when a computer actually passed the Turing test. He incorrectly believed this would happen by the end of the twentieth century. However, it is already the second decade of the twenty first century and no computer has ever passed the Turing test. So there is no actual evidence that a computer can pass the Turing test.
The only really satisfactory support that can be given for the view expressed at the beginning of §6, will be that provided by waiting for the end of the century and then doing the experiment described.
From §6:
I believe that in about fifty years' time it will be possible, to programme computers, with a storage capacity of about 109 [10^9], to make them play the imitation game so well that an average interrogator will not have more than 70 per cent chance of making the right identification after five minutes of questioning. The original question, "Can machines think?" I believe to be too meaningless to deserve discussion. Nevertheless I believe that at the end of the century the use of words and general educated opinion will have altered so much that one will be able to speak of machines thinking without expecting to be contradicted.
Clearly this prediction has not come to pass.
- Even if a computer could pass the Turing test, that would not prove human consciousness is produced by the brain. There is a large amount of evidence that human consciousness survives the death of the body. A computer cannot imitate this. Any theory to explain human consciousness has to account for that evidence. You can't ignore empirical evidence because it contradicts a theory. A theory must be consistent with the empirical evidence, otherwise the theory is wrong.
Philosophers have also addressed, and rejected the possibility that consciousness could be produced by a computer. Edward Feser discusses this in his blog posts Popper Contra Computationalism and Kripka Contra Computationalism
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