A common framework for semantic memory and semantic composition

Abstract

How the brain constructs meaning from individual words and phrases is a fundamental question for research in semantic cognition, language and their disorders. These two aspects of meaning are traditionally studied separately, resulting in two large, multi-method literatures, which we sought to bring together in this study. Not only would this address basic cognitive questions of how semantic cognition operates but also because, despite their distinct focuses, both literatures ascribe a critical role to the anterior temporal lobe (ATL) in each aspect of semantics. Given these considerations, we explored the notion that these systems rely on common underlying computational principles when activating conceptual semantic representations via single words, vs. building a coherent semantic representation across sequences of words. The present pre-registered study used magnetoencephalography and electroencephalography to track brain activity in participants reading nouns and adjective-noun phrases, whilst integrating conceptual variables from both literatures: the concreteness of nouns (e.g., "lettuce" vs. "fiction") and the denotational semantics of adjectives (subsective vs. privative, e.g., "bad" vs. "fake"). Region-of-interest analyses show that bilateral ATLs responded more strongly to phrases at different timepoints, irrespective of concreteness. Decoding analyses on ATL signals further revealed a time-varying representational format for adjective semantics, whereas representations of noun concreteness were more stable and maintained for around 300 ms. Further, the neural representation of noun concreteness was modulated by the preceding adjectives: decoders learning concreteness signals in single words generalised better to subsective relative to privative phrases. These findings point to a unified ATL function for semantic memory and composition.