A system for evaluating responses to broadcast programs, such as television programs, includes an instructional signal modulated onto an audio signal transmitted concurrently with the television program. At each of a plurality of remote receiving stations, one or more members of a remote audience has...http://www.google.com.au/patents/US4745468?utm_source=gb-gplus-sharePatent US4745468 - System for evaluation and recording of responses to broadcast transmissions
