Negative correlation between word-level surprisal and intersubject neural synchronization during narrative listening.

Word-predictability measures, such as surprisal, have been used to show that linguistic prediction is an essential neural mechanism for successful comprehension. However, the neural dynamic of this mechanism may differ across individuals listening to the same narrative, revealing possible idiosyncrasies. Therefore, in this study, we investigated the ability of the surprisal measure to address the linguistic prediction in terms of the intersubject phase synchronization (ISPS) among healthy volunteers listening to a narrative during continuous functional Magnetic Resonance Imaging (fMRI) scanning. The data of twenty-seven participants, acquired in a previous study, were re-analyzed to estimate the ISPS associated with an audiobook listening, played forward and backward. Mean ISPS differences between playing conditions were first analyzed across the whole brain. ISPS time-series during the forward condition was explained with both a lexical-only and a semantics-weighted lexical surprisal model of the narrative word series to detect correlations between ISPS and word surprisal values. Compared to the backward condition, mean ISPS was significantly higher during forward condition in a broad network encompassing frontal, temporal, and parietal areas. The lexical-only model disclosed significant negative ISPS-surprisal correlations in the angular gyrus bilaterally, precuneus, left inferior parietal lobule, left middle frontal gyrus, left cerebellum, and left inferior frontal gyrus. The semantics-weighted surprisal model disclosed significant negative ISPS-surprisal correlations in the right angular gyrus, right precuneus, and left inferior frontal gyrus. Besides engaging language-related areas, narrative processing induces significant ISPS levels beyond the language network. The negative ISPS-surprisal correlations observed would signal divergent neural dynamics among individuals, leading to lower group synchronization, when the words to be integrated are characterized by higher surprisal levels. These results provide further support to the use of language models, such as the surprisal, to explain the neural processes of narrative comprehension and additional information into how the human brain exploits predictions during language comprehension.