Neural Correlates of Modal Displacement and Discourse-Updating under (un)Certainty

Abstract

A hallmark of human thought is the ability to think about not just the actual world, but also about alternative ways the world could be. One way to study this contrast is through language. Language has grammatical devices for expressing possibilities and necessities, such as the words might or must. With these devices, called "modal expressions," we can study the actual versus possible contrast in a highly controlled way. While factual utterances such as “There is a monster under my bed” update the here-and-now of a discourse model, a modal version of this sentence, "There might be a monster under my bed,” displaces from the here-and-now and merely postulates a possibility. We used magnetoencephalography (MEG) to test whether the processes of discourse updating and modal displacement dissociate in the brain. Factual and modal utterances were embedded in short narratives, and across two experiments, factual expressions increased the measured activity over modal expressions. However, the localization of the increase appeared to depend on perspective: signal localizing in right temporo-parietal areas increased when updating the representation of someone else’s beliefs, while frontal medial areas seem sensitive to updating one’s own beliefs. The presence of modal displacement did not elevate MEG signal strength in any of our analyses. In sum, this study identifies potential neural signatures of the process by which facts get added to our mental representation of the world.

Significance Statement When we say things like “There might be a monster under my bed” we distance ourselves from the observable here-and-now and imagine how the world could be. Normally, we are easily able to distinguish reality from mere possibility, but we know very little about the neural mechanisms that allow us to do so. Our research shows that the brain responds differently to utterances about the here-and-now compared with utterances conveying possibilities. This means that our brains separate factual information from hypothetical information, raising interesting new questions about the representation of possibilities in discourse comprehension. By identifying the neural correlates of updating discourse representations, we pave the way for future research on the processing and representation of non-factual discourse.