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. 2003 Elsevier Science (USA). All rights reserved. The processes involved in speaking and in writing differ substantially from each other, and so the products of the two systems are not the same. Nevertheless, most psycholinguistic studies of comprehension have used the sorts of linguistic materials that would be This research was supported in part by a Michigan State University Distinguished Fellowship awarded to Karl Bailey and by a grant from the National Science Foundation (BCS9976584) awarded to Fernanda Ferreira. The authors thank Tom Beckius and Sarah Post for their help with running the experiments and preparing stimuli. Thanks also to Tom Carr, John Henderson, and Alan Munn for their guidance on this project. * Corresponding author. Fax: 1-517-353-1652. E-mail address: [email protected] (F. Ferreira). 0749-596X/03/$ see front matter 2003 Elsevier Science (USA). A doi:10.1016/S0749-596X(03)00027-5 produced by a writer rather than a true speaker (Clark, 1997). Although speakers generally aim for an ideal delivery when they speak—that is, they attempt to produce a grammatical, fluent utterance that is similar to what a good writer would produce (Clark & Clark, 1977)—examination of spontaneous speech reveals that the output often falls short of this ideal. One important deviation is the presence of disfluencies in natural speech, which can include long silences, repeated words or groups of words, false starts, abandoned words, and the focus of the present study, items such as ‘‘uh’’ (and its close cousin, ‘‘um’’; Smith & Clark, 1993). The single utterance below contains examples of almost all of these disfluency types. (1) But I think uhuhuhprecisely because technology itself is certainly more and more... animated... uh and and is... moving faster and faster... uh that s I