Syntactic sophistication as a sensitive index of EFL/ESL context-related differences in spoken and written L2 production

Grounded in usage-based accounts of language acquisition, which hold that syntactic development is driven by cumulative exposure to verbs and argument structure constructions in authentic communicative use, this study investigated how absolute-complexity indices and construction-based syntactic sophistication indices differ in their sensitivity to EFL–ESL group contrasts in spoken and written production. Spoken and written production data from 800 intermediate Asian learners were analyzed using separate linear mixed-effects models fitted for six absolute complexity and four syntactic sophistication indices. The clearest group-related effects were observed for the frequency-based indices, with significant differences occurring in the spoken dataset, where ESL learners produced constructions and verb–construction combinations with lower frequency values than EFL learners. Because the spoken and written data came from different learner samples and task conditions, this pattern should be interpreted as a dataset-level difference in the EFL–ESL contrast, not as a modality effect. Within these limits, these findings suggest that syntactic sophistication measures can capture context-related differences in L2 syntactic production that are not fully reflected in absolute-complexity measures.