Very high-level, functional ability in foreign languages is increasingly important in many walks of life. It is also very rare, and likely requires an early start and/or a special aptitude. This study investigated the extent to which aptitude for explicit learning, defined as "analytic ability" and aptitude for implicit learning, defined as "sequence learning ability," are differentially important for long-term L2 achievement in an immersion setting.

A group of 20 native speaker (NS) controls and 100 Chinese-Spanish bilinguals with ages of onset 3-6 (n = 50) and > 16 (n = 50) participated in the study. Early L2 learners use the same language learning mechanisms as NSs (but still differ in ultimate success), whereas late L2 learners have been claimed to be fundamentally different from NSs in terms of learning mechanisms (and also differ in ultimate success). A set of six L2 attainment measures reflecting a continuum from automatic to controlled use of language knowledge was administered, as well as a battery of six cognitive tests (four language aptitude subtests, a general intelligence test, and a probabilistic serial reaction time task).

Results confirmed the predicted distribution of cognitive abilities into two main types of aptitudes, interpreted as implicit and explicit. Participants could be high in one, high in both, or low in both. Results further revealed that early and late L2 learners with high aptitude for explicit learning outperformed individuals with low aptitude on tasks that allow controlled use of language knowledge. On these tasks, aptitude for implicit learning also had an effect, but among early L2 learners only. In addition, early and late L2 learners with high aptitude for implicit learning showed greater sensitivity towards agreement violations on the language task at the most implicit end of the continuum. Finally, general intelligence only played a role in late L2 learners' attainment on tasks that allow controlled use of knowledge.

The study concluded that 1) cognitive aptitudes play a role in both early and late L2 learners, 2) different types of cognitive aptitudes have differential effects on L2 outcomes, and 3) individual differences in implicit learning ability are related to L2 attainment in adults.