LingLang Lunch (11/28/2018): Steven Frankland (Princeton)

Steven Frankland is a postdoctoral fellow at the Princeton Neuroscience Institute. He studies the composition of complex thoughts in human’s brain, and how they are related to language production, reasoning and decision making. For more information, his website is here.

Structured re-use of neural representations in language and thought

To understand an unfamiliar event, we must retrieve concepts from memory, and flexibly assemble them to encode structural aspects of the event (e.g., who did what to whom). Imagine, for example, the difference between the sentences “the lawyer needs an accountant” and “the accountant needs a lawyer”. In a series of fMRI studies, we examine how the human brain encodes the different meanings of such sentences, and does so in a way that generalizes to novel combinations. We find two regions, left-mid superior temporal cortex (lmSTC) and medial-prefrontal cortex (mPFC) that re-use relational representations across sentences, supporting composition. However, we find that they do so using different representational strategies. lmSTC encodes abstract semantic role variables (who did it? to whom was it done?) that are re-used across verbs. mPFC, by contrast, encodes narrow noun-verb conjunctions, specific to a particular event-type (who needed something?). The representational re-use in both regions supports composition, but reflects a tradeoff between generalization (lmSTC) and specificity (mPFC). The hippocampus plays a different role, representing recurring conjunctive representations as more dissimilar to one another than expected by chance, consistent with a role in pattern separation. We suggest that these regions play distinct, but complementary, roles in a hierarchical, generative system for composing representations of events.