Disfluencies reduce the effect of uh … word surprisal during narrative comprehension

Disfluencies in speech frequently occur before the production of longer and more complex speech content. Listeners are thought to use the distribution of disfluencies in the comprehension of speech to inform their predictions. Here, we investigated whether the presence of disfluencies in speech affects word processing also in naturalistic listening conditions. Participants (n = 36) listened to the spoken recall of the events of a television series while undergoing fMRI. We modelled word processing effort using parametric modulations for word length, frequency, entropy, as well as surprisal and presence/absence of a disfluency. To investigate the effects of disfluencies on word processing, we tested the interaction between disfluency and frequency, and disfluency and surprisal. Words preceded by a disfluency were associated with increased activity in the left and right superior temporal gyrus (STG). Lower word frequency was associated with an increase in activity in the left mid STG. Increased word surprisal elicited a similar distribution of activity, with bilateral superior temporal activation. The effect of surprisal was reduced after a disfluency in a cluster in the left posterior temporal lobe, while the effect of frequency increased following disfluencies in the left superior temporal gyrus and the left inferior frontal cortex. Therefore, the presence of a disfluency affects the response to upcoming input, suggesting that it prepares the listener for higher complexity in the upcoming speech, by potentially allocating increased attention resources that facilitate integration in context.