In this study, we explore native and non-native syntactic processing, paying special attention to the language distance factor. To this end, we compared how native speakers of Basque and highly proficient non-native speakers of Basque who are native speakers of Spanish process certain core aspects of Basque syntax. Our results suggest that differences in native versus non-native language processing strongly correlate with language distance: native/non-native processing differences obtain if a syntactic parameter of the non-native grammar diverges from the native grammar. Otherwise, non-native processing will approximate native processing as levels of proficiency increase. We focus on three syntactic parameters: (i) the head parameter, (ii) argument alignment (ergative/accusative), and (iii) verb agreement. The first two diverge in Basque and Spanish, but the third is the same in both languages. Our results reveal that native and non-native processing differs for the diverging syntactic parameters, but not for the convergent one. These findings indicate that language distance has a significant impact in non-native language processing.

Linguistic analysis claims that verb agreement is composed of distinct phi-features such as person and number, but are these different phi-features processed distinctly or similarly? We used a sentence grammaticality task to explore the electrophysiological responses of Basque speakers when processing subject–verb person and number phi-feature agreement violations. We generated grammatical structures (grammatical control) and ungrammatical structures in which the verb disagreed with the subject in person (person violation), in number (number violation), or in both person and number features (person+number violation). Behavioral data revealed that, overall, participants were faster and more accurate detecting person and person+number violations than violations involving only number. Event-related potential responses revealed a N400–P600 pattern for all violation types. Person and person+number violations elicited larger P600 effects than number violations. These findings reveal different costs related to the processing of person and number phi-feature agreement and indicate that these features are distinct components of agreement computation.

Pronominal dependencies have been shown to be more resilient to attraction effects than subject-verb agreement. We use this phenomenon to investigate whether antecedent-clitic dependencies in Spanish are computed like agreement or like pronominal dependencies. In Experiment 1, an acceptability judgment self-paced reading task was used. Accuracy data yielded reliable attraction effects in both grammatical and ungrammatical sentences, only in singular (but not plural) clitics. Reading times did not show reliable attraction effects. In Experiment 2, we measured electrophysiological responses to violations, which elicited a biphasic frontal negativity-P600 pattern. Number attraction modulated the frontal negativity but not the amplitude of the P600 component. This differs from ERP findings on subject-verb agreement, since when the baseline matching condition obtained a biphasic pattern, attraction effects only modulated the P600, not the preceding negativity. We argue that these findings support cue-retrieval accounts of dependency resolution and further suggest that the sensitivity to attraction effects shown by clitics resembles more the computation of pronominal dependencies than that of agreement.