A world without words: A non-lexicalist framework for psycho- and neuro-linguistics

Abstract

In standard models of language production or comprehension, the elements which are retrieved from memory and combined into a syntactic structure are “lemmas” or “lexical items”. Such models implicitly take a “lexicalist” approach, which assumes that lexical items store meaning, syntax, and form together, that syntactic and lexical processes are distinct, and that syntactic structure does not extend below the word level. Across the last several decades, linguistic research examining a typologically diverse set of languages has provided strong evidence against this approach. These findings suggest that syntactic processes apply both above and below the “word” level, and that both meaning and form are partially determined by the syntactic context. This has significant implications for psychological and neurological models of language processing as well as for the way that we understand different types of aphasia and other language disorders. As a consequence of the lexicalist assumptions of these models, many kinds of sentences that speakers produce and comprehend - in a variety of languages, including English - are challenging for them to account for. In order to move away from lexicalism in psycho- and neuro-linguistics, it is not enough to simply update the syntactic representations of words or phrases; the processing algorithms involved in language production are constrained by the lexicalist representations that they operate on, and thus also need to be reimagined. This dissertation discusses the issues with lexicalism in linguistic theory as well as its implications in psycho- and neuro-linguistics. In addition, I propose a non-lexicalist model of language production, the “WithOut Words” (WOW) model, which does not rely on lemma representations, but instead represents that knowledge as independent mappings between meaning and syntax, and syntax and form, with a single integrated stage for the retrieval and assembly of syntactic structure. Based on this, the model suggests that neural responses during language production should be modulated not just by the pieces of meaning, syntax, and form, but also by the complexity of the mapping processes which link those separate representations. This prediction is supported by the results of a novel experimental paradigm using electroencephalography (EEG) during language production, which observes greater neural responses for meaning-syntax and syntax-form mapping complexity in two separate time windows. Finally, I re-evaluate the dissociation between regular and irregular verbs in aphasia, which has been used as supporting evidence for a distinction between the grammar and the lexicon. By training recurrent neural networks and measuring their performance after lesioning, I show that the observed clinical data can be accounted for within a single mechanism. By moving away from lexicalist assumptions, the non-lexicalist framework described in this dissertation provides better cross-linguistic coverage and aligns better with contemporary syntactic theory.