Neural basis of basic composition: what we have learned from the red-boat studies and their extensions.

Language is our mind's most powerful generative system for the expression of meaning and thought. What are the neural mechanisms of our ability to compose complex meanings from simpler representations? This question is impossible to answer unless we decompose the notion of 'meaning composition' in some theoretically guided way and then begin to assess the extent to which brain activity tracks the posited subroutines. Here, I summarize results from a body of MEG research that has begun to address this question from the ground up, first focusing on simple combinations of two words. The work sets off with a hypothesis space offered by theoretical linguistics, positing syntactic and logico-semantic composition as the main combinatory routines, but then reveals that the most consistent and prominent reflection of composition, localized in the left anterior temporal cortex at 200-250 ms, cannot be described with this toolkit. Instead, this activity tracks a much more conceptually driven process, robustly sensitive to the density of the conceptual feature space of the composing items. I will describe our functional understanding of this activity and how it may operate within a broader 'combinatory network.' This article is part of the theme issue 'Towards mechanistic models of meaning composition'.