Processing canonical and non-canonical sentences in Basque: The case of object–verb agreement as revealed by event-related brain potentials

In this study we investigated the generality of the electrophysiological mechanisms underlying verb agreement relations by looking not only at subject–verb (SV) but, moreover, at object–verb (OV) agreement phenomena in Basque—a language in which both the subject and the object have to agree with the verb. We first provide event-related potentials (ERP) evidence for processing differences in SV vs. OV agreement in Basque by demonstrating different electrophysiological patterns as a function of verb agreement violation type. We then examine the nature of processing OV agreement violations, asking to what extent the observed ERP pattern for OV agreement violation is due to a specific word order (SOV vs. OSV). Our data reveal an N400–P600 pattern elicited by OV agreement violations in both word order conditions indicating that the brain signature of verb agreement phenomena is independent of the order of words. The P600 effect, but not the N400 effect, interacted with sentences' grammaticality, suggesting that only late processes of sentential integration are affected by order of subject and object noun phrase in the sentence. These findings suggest that agreement processing is not affected by the order of words and thereby the distance between the dependent elements, but is rather determined by agreement type.