Disfluencies affect the parsing of garden-path sentences

Spontaneous speech differs in several ways from the sentences often studied in psycholinguistics experiments. One important difference is that naturally produced utterances often contain disfluencies. In this study, we examined how the presence of “uh” in a spoken sentence might affect processes that assign syntactic structure (i.e., parsing). Four experiments are reported. In the first, participants judged the grammaticality of sentences that had disfluencies either right before the head noun of the ambiguous phrase or after (e.g., Sandra bumped into the busboy and the uh uh waiter told her to be careful or Sandra bumped into the busboy and the waiter uh uh told her to be careful). Sentences in the latter condition were judged grammatical less often. This result was replicated in the second experiment, in which disfluencies were replaced with environmental sounds. These findings suggest that interruptions can affect syntactic parsing, and the content of the interruption need not be speechlike. In Experiments 3 and 4 we tested whether these effects occurred because listeners use interruptions as cues to help resolve a structural ambiguity. Results from these latter two grammaticality judgment tasks suggest that when an interruption occurs before an ambiguous noun phrase, comprehenders are more likely to assume that the noun phrase is the subject of a new clause rather than the object of an old one, and furthermore, it appears that the parser is relatively insensitive to the form of the interruption. We conclude that disfluencies can influence the parser by signaling a particular structure; at the same time, for the parser, a disfluency might be any interruption to the flow of speech.