Effects of age of acquisition on grammatical sensitivity: Evidence from on-line and off-line tasks

ABSTRACT American Sign Language (ASL) provides a unique opportunity to investigate the effects of late exposure to a primary language on adult linguistic processing. In Experiment 1, a video sign-monitoring task was used to investigate the grammatical sensitivity of 11 native signers (exposed to ASL from birth) and 10 late signers (exposed to ASL at a mean age of 12 years) to errors in ASL verb agreement. The results indicated that native signers, but not late signers, were sensitive to errors in verb agreement. Experiment 2 utilized both sign monitoring and off-line grammaticality judgments. Sentences which contained errors in either verb agreement or temporal aspect were presented to 10 native signers, 10 early signers (exposed to ASL between the ages of 2 and 7), and 10 late signers (exposed to ASL between the ages of 10 and 20). The results indicated that native signers were sensitive to errors in both verb agreement and aspect, and that early and late signers were only sensitive to errors in aspect morphology. In the off-line grammaticality test, all three groups were equally able consciously to detect the grammatical errors. These findings suggest that late exposure to a primary language affects the on-line integration of verb agreement information within a sentence, but does not affect sensitivity to semantic distinctions encoded by aspect morphology.