ERP indexes of number attraction and word order during correct verb agreement production

Successful subject-verb agreement production requires retrieving the verbal forms that agree with the features of the subject head noun and not of other nouns in the sentence. We investigate, for the first time, the electrophysiological indexes of number attraction and word order during agreement production. Twenty-four Basque native speakers were tested while producing auxiliary verbs during sentence completion of transitive sentence preambles involving singular subjects and singular or plural objects in canonical (SOV) and non-canonical (OSV) structures. ERP results yielded a larger production P2 (pP2) amplitude for mismatching than matching objects in SOV sentences, and larger negativity for OSV than SOV in number matching condition. We explain these results in terms of distinct contributions of number and word order during correct agreement production, with the pP2 indexing morphosyntactic retrieval difficulty of agreement-inflection, and the frontal negativity reflecting word order effects during monitoring the correctness of the selected verbal form.