To what extent do pragmatic cues from disfluencies inform our predictions of spoken language during naturalistic language processing?

Language processing is facilitated by the prediction of upcoming linguistic content. Natural speech is full of disfluencies that have potential predictive power for the listener. The extent to which different pragmatic cues, such as disfluencies, are integrated with semantic context to inform predictions is, however, currently unknown. Here we combine electroencephalography (EEG), eye tracking and virtual reality to investigate to what extent predictive processing during naturalistic language comprehension is influenced by hesitation disfluencies in speech. Participants (n= 64) listened to sentences spoken by a virtual agent in various virtual scenes (e.g., office, street) while their eye-movements and EEG were recorded. Spoken sentences were predictable or unpredictable based on the verb constraints, and were either fluent or disfluent with a hesitation disfluency ("uhh") preceding the noun phrase. Referents were visible or absent in the scene to be congruent or incongruent with listeners' predictions, respectively. In predictable but not unpredictable sentences, fixations towards the referent increased before it was mentioned, which confirmed that participants predicted the referent. After hesitation onset, fixations towards the referent no longer increased but shifted towards the virtual speaker. EEG data at noun onset (N400 amplitudes and alpha and theta frequency power) provided no evidence that listeners discard their prediction after hearing a hesitation disfluency. Rather, the disfluency further facilitates predictable noun processing, possibly through mechanisms of increased attention and processing time.