The Turing Test

The Turing test (another good article at the Stanford Encyclopedia of Philosophy) is a proposal for a test of a machine’s capability to demonstrate intelligence. 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 one human and one machine, each of which try to appear human; if the judge cannot reliably tell which is which, then the machine is said to pass the test.

I understand that CAPTCHAS (= Completely Automated Public Turing Test to Tell Computers and Humans Apart) are reverse Turing tests (because it is administered by a machine and targeted to a human, in contrast to the standard Turing test that is typically administered by a human and targeted to a machine). Before being allowed to do some action on a website, the user is presented with a alphanumerical characters in a distorted graphic image and asked to recognise it. This is intended to prevent automated systems from abusing the site. The assumption is that software sufficiently sophisticated to read the distorted image accurately does not exist (or is not available to the average user), so any system able to do so must be a human being.