What does it mean to understand language?

Language understanding entails not just extracting the surface-level meaning of the linguistic input, but constructing rich mental models of the situation it describes. Here we propose that because processing within the brain’s core language system is fundamentally limited, deeply understanding language requires exporting information from the language system to other brain regions that compute perceptual and motor representations, construct mental models, and store our world knowledge and autobiographical memories. We review the existing evidence for this hypothesis, and argue that recent progress in cognitive neuroscience provides both the conceptual foundation and the methods to directly test it, thus opening up a new strategy to reveal what it means, cognitively and neurally, to understand language.

Introduction. What then does it mean to understand language, cognitively, computationally, and neurally? How rich and structured is your mental representation of the sentence you are reading right now, and what cognitive and neural systems are holding this representation? And are you now linking the meaning of this sentence to the previous one, to the unfolding structure of the argument in this article, and to thoughts you have had previously about language processing? In this opinion piece, we argue that a deep understanding of language, which entails building mental models and rich representations of meaning that connect to our broader knowledge of the world, requires the exportation of information from the brain’s core language system to other cognitive and neural systems that can build models of what we are hearing or reading. The idea that language understanding entails building mental models of events and situations described in language is not new.

Discussion / Conclusion. In this opinion piece, we have proposed that deep language understanding requires exporting information from the brain’s core language system to other systems that build mental models of the minds, objects, and places described in the linguistic input, that store our memories and word knowledge, and that contain our perceptual and motor representations. Some evidence for this idea already exists, but our goal here is to outline a conceptual framework for thinking about language comprehension in the brain beyond the parsing of sentences and construction of shallow approximations of linguistic meaning carried out in the language network, and to outline many testable hypotheses, as we tried to do above. Several caveats should be noted. First, strong empirical evidence for the exportation hypothesis is so far restricted to very few systems, and some studies find no evidence for exportation (e.g., [121-122]). Although suggestive evidence for the exportation hypothesis abounds (e.g., [68,72-73,79-80,86,94,23,96,101,104]) (see Box 1), methodological limitations (e.g., reliance on group-averaging approaches) restrict the conclusions we can draw from much past work.