Calibrating the detection of spontaneous speech: From sentences to noun phrases

Many studies have examined the differences between speech that is produced spontaneously as opposed to read from a prepared script. Most of these studies have focused on prosodic measures taken from clauses, sentences, or connected discourse. Furthermore, studies have shown that listeners are able to identify the context of production when presented with sentence-length utterances. The current study examined whether a listener can identify the context for utterances that are briefer than a sentence. A set of 20 talkers (10 male) produced spontaneous descriptions of maps that they then read aloud in a separate session at least one week later. Pairs of sentences that matched in fluency across both contexts were selected, and listeners judged which member of a pair was produced spontaneously. In separate blocks, listeners heard either full sentences, sentence beginnings, sentence endings, or two-word noun phrases excised from sentences. Overall, listeners could identify the spontaneously produced utterances, but only for excerpts longer than two-word noun phrases. These findings indicate that the information present in two-word noun phrases is not sufficient to support perception of spontaneous versus read speaking style.