Valian, V. & Wales, R. (1976). What’s what: talkers help listeners hear and understand by clarifying sentential relations. Cognition, 4, 155-176.

Abstract: It was predicted that a talker would clarify the sentential relations of an utterance if a listener indicated difficulty in hearing and understanding. Subjects read syntactically clear and distorted sentences to a listener (cxperirnenter) in un adjoining room. The experimenter often asked “What?” Subjects changed distorted versions to clear versions, while repeating clear versions essentially as first read. Other subjects were asked to make the sentences clear and simple to understand. The same basic results were obtained. Talkers thus seem to interpret a “What?” partly as a request for clearer sentential relations und respond accordingly. The results indicate that talkers have knowledge of underlying structure. Several alternate explanations can be rejected. A relative derivational theory of complexity, is presented.