Competing factors in SLA: how the CASP model of SLA explains the acquisition of English restrictive relative clauses by native speakers of Arabic and Korean

Abstract The Complex Adaptive Systems Principles (CASP) model of SLA claims that L1 transfer results when language processing effort is minimized. This claim was investigated by a self-paced on-line sentence judgment task in which L1 Arabic and Korean speakers and a control group of L1 English speakers read and judged English subject, direct object, and oblique relative clauses (RCs) in gapped and resumptive pronoun (RP) conditions. It was hypothesized that L1 influence would cause the Arabic speakers to accept English RCs with RPs more frequently than Korean speakers because RPs are acceptable in Arabic direct object and oblique RCs, whereas Korean bans RPs in these RC types. It was also hypothesized that the L2 English speakers would accept RPs more often than the L1 English speakers because RPs would ease L2 sentence processing. As predicted, L1 Arabic speakers accepted RPs more frequently than L1 Korean speakers, a transfer effect, and both L2 English groups accepted RPs more frequently than L1 English speakers, a processing effect. The results thus support the CASP model’s claim that L1 transfer is conditioned by language processing and other complex SLA processes that interact with one another.