Measuring brain sensitivity to semantic distance in spoken narrative comprehension.

Discourse comprehension requires simultaneous integration of local and global constituents. When hearing a narrative, for example, listeners must link the meaning of each incoming word to the preceding word (local context) while also assimilating its meaning into the broader gist of a story (global context). Thus, the brain simultaneously constructs meaning at different time scales and with different levels of granularity. Our understanding of the brain's division of labor in processing local versus global semantic distance relationships is limited. In this study we ask specifically how the semantic distance between a word and its prior context drives activity in the brain during naturalistic listening. We used fMRI data collected while participants (n = 79) listened to a podcast interview. Using a novel method for estimating semantic distance between a word and prior contexts computed at multiple grain sizes, we conducted an amplitude-modulated regression to identify brain regions that were sensitive to semantic distance. Results show that semantic distance drives activation in a broad frontotemporal network including the left and right superior and middle temporal gyrus and left inferior frontal gyrus, as well as the bilateral cerebellum. The right anterior superior temporal gyrus was particularly sensitive to the increase in context window size, consistent with a right hemisphere specialization for gist processing and for the anterior temporal lobes' purported role in semantic integration. This study demonstrates a promising method for investigating neural sensitivity to semantic movement in naturalistic language.