Electronic speech control apparatus that includes a circuit for establishing and changing over time a subject code and an utterance index. The subject code generally indicates one of a plurality of sets of utterances. The utterance index identifies an utterance of at least one word in the set indicated...http://www.google.com.hk/patents/US5029214?utm_source=gb-gplus-share專利 US5029214 - Electronic speech control apparatus and methods
