Numerous other versions of the Turing test, including those expounded above, have been mooted through the years.
Reverse Turing test and CAPTCHA
A modification of the Turing test wherein the objective of one or more of the roles have been reversed between machines and humans is termed a reverse Turing test. An example is implied in the work of psychoanalyst Wilfred Bion, who was particularly fascinated by the "storm" that resulted from the encounter of one mind by another. Carrying this idea forward, R. D. Hinshelwood described the mind as a "mind recognizing apparatus," noting that this might be some sort of "supplement" to the Turing test. The challenge would be for the computer to be able to determine if it were interacting with a human or another computer. This is an extension of the original question that Turing attempted answer but would, perhaps, offer a high enough standard to define a machine that could "think" in a way that we typically define as characteristically human.
CAPTCHA is a form of reverse Turing test. Before being allowed to perform some action on a website, the user is presented with alphanumerical characters in a distorted graphic image and asked to type them out. This is intended to prevent automated systems from being used to abuse the site. The rationale is that software sufficiently sophisticated to read and reproduce the distorted image accurately does not exist (or is not available to the average user), so any system able to do so is likely to be a human.
Software that can reverse CAPTCHA with some accuracy by analyzing patterns in the generating engine is being actively developed.
"Fly on the wall" Turing test
The "fly on the wall" variation of the Turing test changes the original Turing-test parameters in three ways. First, parties A and B communicate with each other rather than with party C, who plays the role of a detached observer ("fly on the wall") rather than of an interrogator or other participant in the conversation. Second, party A and party B may each be either a human or a computer of the type being tested. Third, it is specified that party C must not be informed as to the identity (human versus computer) of either participant in the conversation. Party C's task is to determine which of four possible participant combinations (human A/human B, human A/computer B, computer A/human B, computer A/computer B) generated the conversation. At its most rigorous, the test is conducted in numerous iterations, in each of which the identity of each participant is determined at random (e.g., using a fair-coin toss) and independently of the determination of the other participant's identity, and in each of which a new human observer is used (to prevent the discernment abilities of party C from improving through conscious or unconscious pattern recognition over time). The computer passes the test for human-level intelligence if, over the course of a statistically significant number of iterations, the respective parties C are unable to determine with better-than-chance frequency which participant combination generated the conversation.
The "fly on the wall" variation increases the scope of intelligence being tested in that the observer is able to evaluate not only the participants' ability to answer questions but their capacity for other aspects of intelligent communication, such as the generation of questions or comments regarding an existing aspect of a conversation subject ("deepening"), the generation of questions or comments regarding new subjects or new aspects of the current subject ("broadening"), and the ability to abandon certain subject matter in favor of other subject matter currently under discussion ("narrowing") or new subject matter or aspects thereof ("shifting").
The Bion-Hinshelwood extension of the traditional test is applicable to the "fly on the wall" variation as well, enabling the testing of intellectual functions involving the ability to recognize intelligence: If a computer placed in the role of party C (reset after each iteration to prevent pattern recognition over time) can identify conversation participants with a success rate equal to or higher than the success rate of a set of humans in the party-C role, the computer is functioning at a human level with respect to the skill of intelligence recognition.
Subject matter expert Turing test
Another variation is described as the subject matter expert Turing test, where a machine's response cannot be distinguished from an expert in a given field. This is also known as a "Feigenbaum test" and was proposed by Edward Feigenbaum in a 2003 paper.
Immortality test
The Immortality-test variation of the Turing test would determine if a person's essential character is reproduced with enough fidelity to make it impossible to distinguish a reproduction of a person from the original person.
Minimum Intelligent Signal Test
The Minimum Intelligent Signal Test, proposed by Chris McKinstry, is another variation of Turing's test, where only binary responses are permitted. It is typically used to gather statistical data against which the performance of artificial intelligence programs may be measured.
Meta Turing test
Yet another variation is the Meta Turing test, in which the subject being tested (say, a computer) is classified as intelligent if it has created something that the subject itself wants to test for intelligence.
Hutter Prize
The organizers of the Hutter Prize believe that compressing natural language text is a hard AI problem, equivalent to passing the Turing test.
The data compression test has some advantages over most versions and variations of a Turing test, including:
• It gives a single number that can be directly used to compare which of two machines is "more intelligent."
• It does not require the computer to lie to the judge
The main disadvantages of using data compression as a test are:
• It is not possible to test humans this way.
• It is unknown what particular "score" on this test—if any—is equivalent to passing a human-level Turing test.
Other tests based on compression or Kolmogorov Complexity
A related approach to Hutter's prize which appeared in the late 1990s is the inclusion of compression problems in an extended Turing Test. Two major advantages of some of these tests are their applicability to nonhuman intelligences and their absence of a requirement for human testers.
Based on http://en.wikipedia.org/wiki/Turing_test licensed under the Creative Commons Attribution-Share-Alike License 3.0
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