I believe that in about fifty years' time it will be possible to programme computers, with a storage capacity of about 10 9, to make them play the imitation game so well that an average interrogator will not have more than 70 percent chance of making the right identification after five minutes of questioning. … 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. (Turing in PBF p. 290) Turing’s Hope: CTM Alan Turing
The phrase “ The Turing Test ” is most properly used to refer to a proposal made by Turing (1950) as a way of dealing with the question whether machines can think. According to Turing, the question whether machines can think is itself “ too meaningless ” to deserve discussion. However, if we consider the more precise—and somehow related—question whether a digital computer can do well in a certain kind of game that Turing describes ( “ The Imitation Game ” ), then—at least in Turing's eyes—we do have a question that admits of precise discussion. Moreover, as we shall see, Turing himself thought that it would not be too long before we did have digital computers that could “ do well ” in the Imitation Game. (Oppy and Dowe, SEP, Introduction) We now ask the question, “ What will happen when a machine takes the part of A in this game? ” Will the interrogator decide wrongly as often when the game is played like this [with a machine instead of a man] as he does when the game is played between a man and a woman? These questions replace our original, “ Can machines think? ” Note 1: behavioral criteria Note 2: only looking at “ cognitive ” tasks “ we do not wish to penalize the machine for its inability to shine in beauty competitions, nor to penalize a man for losing in a race against an airplane. ” [also: asking whether a machine can think is as interesting as asking whether a submarine can swim? Dijkstra] The Turing Test “The Imitation Game” Alan Turing Edsger Dijkstra
Not a literal computer; it is a model of computation in general. “ simple abstract computational devices intended to help investigate the extent and limitations of what can be computed. ” (Copeland, SEP, first para) “ LCMs [logical computing machines: Turing's expression for Turing machines] can do anything that could be described as "rule of thumb" or "purely mechanical". (Turing 1948:7, from Copeland, SEP, Introduction). Universal Turing Machine The Turing Machine Alan Turing Alonzo Church
Computational Theory of Mind In a nutshell: CTM = CAR + RTM Mind = Reasoning + Representation :: Program = Algorithm + Data
Contemporaneous Critiques of Turing’s CTM mathematical objection: “There are a number of results of mathematical logic which can be used to show that there are limitations to the power of discrete state machines.” (e.g., Gödel’s Theorem) (Turing) Lady Lovelace’s objection: “The Analytic Engine has no pretensions to originate anything. It can do whatever we know how to order it to perform” (Turing citing Lady Lovelace)
Anti-CTM: The Chinese Room Jack does not understand any Chinese. However, he inhabits a room which contains a book with detailed instructions about how to manipulate Chinese symbols. He does not know what the symbols mean, but he can distinguish them by their shape. If you pass a series of Chinese symbols into the room, Jack will manipulate them according to the instructions in the book, writing down some notes on scratch paper, and eventually will pass back a different set of Chinese symbols. This results in what appears to be an intelligible conversation in Chinese. (In fact, we can suppose that "the room" containing Jack and the book of instructions passes a Turing Test for understanding Chinese.) (from James Pryor Harvard class, http://www.jimpryor.net/teaching/courses/mind/notes/searle.ht ml)Turing Test http://www.jimpryor.net/teaching/courses/mind/notes/searle.ht ml John Searle YOU in a Chinese Room
Critiques of Searle’s CR The most important of these is the Systems Reply. According to the systems reply, Jack does not himself implement the Chinese room software. He is only part of the machinery. The system as a whole--which includes Jack, the book of instructions, Jack's scratch paper, and so on--is what implements the Chinese room software. The functionalist is only committed to saying that this system as a whole understands Chinese. It is compatible with this that Jack does not understand Chinese. (Ibid, Pryor) Jim Pryor
Critique of Turing as Computationalist So I do not believe that Turing was a computationalist: he did not think that thinking was just computation. He was perfectly aware of the possibility that in order to be able to pass the verbal TT (only symbols in and symbols out) the candidate system would have to be a sensorimotor robot, capable of doing a lot more than the verbal TT tests directly, and drawing on those dynamic capacities in order to successful pass the verbal TT. (Harnad) Stevan Harnad
Conclusion 1: Substrate-Neutral? CTM adopts functionalism substrate-neutrality of software multiple realizability of software in hardware Searle’s Anti-CTM “perhaps Martians also have intentionality but their brains are made of different stuff. That is an empirical question, rather like the question whether photosynthesis can be done by something with a chemistry different from that of chlorophyll.” (Searle in PBF, p. 306) (Searle in Conversations on Consciousness: “unlikely!”)
Conclusion 2: Three Questions 1. Is the Mind Software to the Brain’s Hardware? (Strong AI) 2. Is thinking/reasoning computing? 3. What is the relationship between the mind (or the brain), and a model (or simulation) of the mind (or the brain)? Identity, representation, mapping, none ? Note 1: Distinguish “is” from “represents” Note 2: Consider Strong vs. Weak AI
Question 3: Modeling the Brain Henry Markram builds a brain in a supercomputer (5:00) Note that Modeling the Brain ≠ Modeling the Mind Why?
Philosophical Fields According to Minds and Machines Metaphysics Ethics Logic Philosophy of Mind Epistemology ???? Philosophy of Science Political Philosophy ????