Turing test

The Turing test is a proposal for a test of a machine's capability to perform human-like conversation. Described by Alan Turing in the 1950 paper "Computing machinery and intelligence", it proceeds as follows: a human judge engages in a natural language conversation with two other parties, one a human and the other a machine; if the judge cannot reliably tell which is which, then the machine is said to pass the test. It is assumed that both the human and the machine try to appear human. In order to keep the test setting simple and universal (to explicitly test the linguistic capability of some machine), the conversation is usually limited to a text-only channel such as a teletype machine as Turing suggested or, more recently, IRC.

Objections and replies

Turing himself suggested several objections which could be made to the test. Below are some of the objections and replies from the article in which Turing first proposed the test.

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• Theological Objection: This states that thinking is a function of man's immortal soul and therefore a machine could not think. Turing replies by saying that he sees no reason why it would not be possible for God to grant a computer a soul if He so wished.
• Mathematical Objections: This objection uses mathematical theorems, such as Gödel's incompleteness theorem, to show that there are limits to what questions a computer system based on logic can answer. Turing suggests that humans are too often wrong themselves and pleased at the fallibility of a machine.
• Mechanical Objections: A sufficiently fast machine with sufficiently large memory could be programmed with a large enough number of human questions and human responses to deliver a human answer to almost every question, and a vague random answer to the few questions not in its memory. This would simulate human response in a purely mechanical way. Psychologists have observed that most humans have a limited number of verbal responses.
• Data Processing Objection: Machines process data bit by bit. Humans process data holisticly. In this view, even if a machine appears human in every way, to treat it as human is to fall victim to the pathetic fallacy.
• Argument From Consciousness: This argument, suggested by Professor Jefferson Lister states, "not until a machine can write a sonnet or compose a concerto because of thoughts and emotions felt, and not by the chance fall of symbols, could we agree that machine equals brain". Turing replies by saying that we have no way of knowing that any individual other than ourselves experiences emotions, and that therefore we should accept the test.
• Lady Lovelace Objection: One of the most famous objections, it states that computers are incapable of originality. This is largely because, according to Lady Lovelace, machines are incapable of independent learning. Turing contradicts this by arguing that Lady Lovelace's assumption was affected by the context from which she wrote, and if exposed to more contemporary scientific knowledge, it would become evident that the brain's storage is quite similar to that of a computer. Turing further replies that computers could still surprise humans, in particular where the consequences of different facts are not immediately recognizable.
• Informality of Behaviour: This argument states that any system governed by laws will be predictable and therefore not truly intelligent. Turing replies by stating that this is confusing laws of behaviour with general rules of conduct, and that if on a broad enough scale (such as is evident in man) machine behaviour would become increasingly difficult to predict. (Later research on recursive algorithms has found that, in any case, deterministic systems are capable of a chaotic diversity of behaviour.)
• Extra-sensory perception: Turing seems to suggest that there is evidence for extra-sensory perception. However he feels that conditions could be created in which this would not affect the test and so may be disregarded.