a twin input of the utterance compares the inputs to each other and to the prototype and in the situation where it is determined that the inputs fulfill the criteria replace the prototype with one of the new inputs fig2 details the procedures for adaptive retraining of prototype vocabulary items during the recognition process if the talker produces a keyword mistake the adaptive retraining routine is invoked under computer control the procedures are entered and a stack of vocabulary item choices related to the words just before the keyword mistake recognition is sent to the adaptive training stage using this stack the system prompts the user to indicate which stack vocabulary item was uttered just prior to its identification as an unrecognized utterance this prompting can either be by audio response or character display from a gas panel cathode ray tube or the like if the word equivalent to the misrecognized utterance is not contained in the stack the user is prompted to recite the utterance again and the recognition procedure continues upon acknowledgment by the talker that a stack vocabulary item matches the utterance input 1 the user is prompted to provide a new prototype keyword candidate input 2 appropriate to that vocabulary item the system calculates the matrix distances input 1 vs input 2 d1 prototype vs input 2 d2 and prototype vs input 1 d3 where input 1 is the misrecognized utterance and.