Аннотация: This article tries to hypothesize an invisible brain mechanisms in charge of grammatical processing of speech sound stream. It`s known that animal sign reflexes are logical and are operated by logic of dichotomy for pattern recognition of signs and that of dualism for dualistic integration of a sign and its movement vector. It is probable that speech sound stream is decomposed into minimum dualistic segments of “concept + grammar” and each segment should be processed by the logic of dualism in sign reflex processing. Monaural audition of mother tongue indicates that dualistic integration of movement vector is converted to integrate a grammatical vector with an adjacent concept. This hypothesis is supported by the actual data of exceptional Piraha language, which has no grammar but keeps binaural audition for speech to let its bearers survive in the Amazonian jungle.