The lexicon constrains grammar, grammar constrains composition: ERP evidence for sequential processing of morphological agreement and sentence meaning

In neurolinguistics and the neurobiology of language, processing models that parallelize meaning and grammar have acquired theoretical and empirical support over more modular theories. Yet, parallel models too should account for serial, sequential, or blocking effects of one type of representation on others. In this study, we used ERPs to assess whether and how the mental lexicon restricts the applicability of morphosyntactic operations, and how those, in turn, constrain on-line meaning composition. The stimuli were Norwegian sentences with the form ‘N V Adj’. The adjective was either correctly or incorrectly inflected for gender or number relative to the noun, and the noun was either a real word or a pseudoword built around a pseudoroot. ERPs show that agreement only applies between an adjective and a noun that contains a real lexical root, and that lexical meanings are only composed for correctly inflected words. We could not find agreement effects for pseudonouns or differences between gender and number features. Our results suggest that some grammatical processes may draw from and depend on lexical storage, in particular of lexical roots, and that compositional semantic processes may depend on the well-formedness of the outputs of such grammatical processes. • We address blocking effects between lexical storage, morphosyntax and composition. • Stimuli were Norwegian ‘N V Adj’ sentences, with manipulations at the N and Adj. • An early ERP effect of incorrect Adj gender/number inflection, if N is a real word. • A P600 effect of Adj composition (N vs pseudo-N), if Adj is correctly inflected. • Morphosyntax depends on lexical storage, composition on well-formedness.