When a nod is as good as a word: Form-function relationships between questions and their responses

It is well established that syntactic form and communicative function do not always correspond: for instance, a syntactic question might function as a request for information ("did you see the play?") or a request for acknowledgment when there is no doubt about polarity of the response ("there's a tower at Blackpool, isn't there"). Using data from a corpus of 18 child-adult conversations, we distinguished adult utterances that solicited information from those soliciting acknowledgment (i.e., where the response was predictable, and the utterance served a predominantly social function). Both types of utterance were usually responded to by children, but the form of response differed according to the communicative function of the utterance. Nonverbal and prosodic responses (e.g., nods or "mmh") were significantly more likely to occur in response to utterances soliciting acknowledgment than in response to yes/no questions that solicited information. There were consistent form-function relationships for responses as well as for soliciting utterances. Nonverbal nods and headshakes were not functionally equivalent to verbal "yes" and "no.".