The interplay of composition and concept specificity in the left anterior temporal lobe: An MEG study

A fundamental function of natural language is to focus the interlocutor's attention to specific entities and circumstances from the vast set of possibilities in the environment. In other words, as an utterance progresses, the narrower its reference typically becomes. Intriguingly, there is substantial convergence in the neural localization of conceptual specificity effects at the single word level and combinatory effects at the phrasal level, both systematically affecting the left anterior temporal lobe (LATL). However, the relationship between these two types of effects is not well understood. The current study used MEG to characterize the temporal progression of both types of effects in minimal two-word phrases (e.g., tomato soup), where single word specificity was varied in both first and second position (e.g., tomato vs. vegetable; soup vs. dish). These combinatory phrases were further compared to non-combinatory single nouns of high and low specificity. Our most robust result was an effect of the specificity of the first word while processing the second word: responses to the second word were the largest when it was being composed with a more specific as opposed to a more general modifier. In the modifier position, specificity had no reliable effects, while non-combinatory single nouns did show a subtle LATL increase when specific. In all, our findings show that when non-semantic factors such as frequency are controlled for, conceptual specificity weakly modulates LATL activity in non-combinatory situations (i.e., at a single noun), but robustly affects the size of the LATL composition effect. Thus LATL activity appears to be most strongly driven by the composition of concepts as opposed to access to single concepts.