This study examined the development of integrated knowledge or automatic competence in adult SLA. Automatic competence was operationalized in terms of the participants' sensitivity to grammatical errors in a self-paced reading task. Their sensitivity was determined by observing whether there was a delay in reading ungrammatical sentences. Native and nonnative speakers of English read grammatical and ungrammatical sentences that contained errors involving plural -s and verb subcategorization. Their reading times were measured and compared. The results showed that native speakers were sensitive to errors involving both structures, but nonnative speakers were only sensitive to errors involving verb subcategorization. The results confirmed that the development of second language automatic competence or integrated knowledge is selective. Alternative explanations of this selectivity are discussed.