Disfluency, prediction and attention in language comprehension

Spoken language comprehension is impacted by the presence of disfluencies. It follows that there have been attempts to understand the underlying mechanisms that are responsible for these disfluency effects. Different accounts of disfluency processing have been proposed to explain these effects; the current thesis was directed towards exploring two standpoints of disfluency processing: the predictional and attentional accounts. Disfluency has been shown to modulate predictive processing, with a clear effect in the literature being that upon encountering disfluency listeners show a bias for unknown or discourse new referents (Arnold, Kam, & Tanenhaus, 2007; Arnold, Tanenhaus, Altmann, & Fagnano, 2004; Heller, Arnold, Klein, & Tanenhaus, 2014). The predictional account interprets this finding in terms of expectancy: according to this view, listeners expect speakers to produce harder-to-access words in situations where their linguistic performance is consistent with planning problems. Listeners are also more likely to remember words that follow a disfluency (Corley et al., 2007). The presence of disfluency has been shown to affect the attentional state of the listener, as indexed by attenuation of event related potentials to acoustically manipulated words post disfluency (Collard et al., 2008). These effects form the basis of the competing attentional account, which suggests that that upon encountering disfluency, listeners stop predicting about upcoming content and instead, employ heightened attentional resources to help them resolve the situation. In the first experiment, we aimed to distinguish between the predictional and attentional accounts by employing a visual world paradigm to investigate directly the underlying mechanism during comprehension. Participants were expected to show different fixation behaviour depending on which account was true. The main experiment provided some unexpected results, as the fixation behaviour seen would not have been predicted by either account. These results were further investigated in a number of post-hoc tests, testing participants sensitivity to the disfluency used in the main paradigm. The results observed were again inconclusive. Taken together these findings suggested that the mechanisms afforded by each account for disfluency processing may work in unison, with reliance on either attentional or predictive processing, or a mix of both, dictated by the demands of the task. In the remaining experiments (2-6) we focused on the attentional account of disfluency processing; we asked how disfluencies impact listener attention at a phonemic level. Pitt and Szostak (2012) demonstrated that the effect of phoneme manipulation is reduced when participants’ attention is explicitly directed to the ambiguous phoneme, with participants less likely to categorise an ambiguous item as a “word” under such conditions than otherwise. We applied this paradigm at the sentence level to investigate whether disfluencies induce heightened attentional focus at a phonemic level. Specifically, we compared the impact of a phoneme manipulation on lexicality judgements with; (i) attentional focus, and; (ii) disfluency presence. The initial experiments’ findings failed to replicate the attentional manipulation seen in the Pitt and Szostak study (2012) but results from the later studies suggested there is evidence that disfluency does drive listener attention but actually makes listeners more accommodating of the phoneme manipulation heard. These results are discussed in relation to the accounts of disfluency processing being tested