Turing Test

The Turing Test, proposed by Alan Turing in 1950, is a thought experiment for assessing whether a machine's conversational behaviour is indistinguishable from that of a human. A human evaluator engages in a text-based exchange with both a human and a machine and must decide which is which; if the evaluator cannot reliably tell them apart, the machine is said to have passed. Although the classical Turing Test is rarely a practical benchmark in modern AI, the underlying idea drives the design of CAPTCHAs (Completely Automated Public Turing tests to tell Computers and Humans Apart), which are reverse Turing tests: instead of a human judging a machine, an automated server judges a remote agent to decide whether to grant access. For accessibility, the Turing-test framing matters because every CAPTCHA design implicitly defines what counts as "human" cognition — visual literacy, spoken-language perception, motor precision — and so risks excluding users whose abilities differ.