Turing's proposed test for whether a machine is conscious (or intelligent, or aware): the subject communicates via text with the machine and with a hidden human. If the subject cannot tell which of their partners in the dialog is the human, then the computer is conscious (i.e. is an AI). Turing did not specify many key details, such as the duration of the interrogation and the sophistication of the human judge and foils. By the middle Information Age, computer AIs were regularly passing the test, although its validity remained a point of controversy and philosophical debate for some decades more.