A number of researchers (DeKeyser, 2012; J. S. Johnson & Newport, 1989; Long, 1990) have argued that age is a critical factor in second language acquisition. This conclusion is based on extensive research over the last two decades that has demonstrated age-related effects in learners’ nonnativelike acquisition of phonology, morphosyntax, pragmatics, and discourse-level features of language. In the wake of such findings, there has recently been an increased interest in determining the precise linguistic areas that are difficult for adult learners and the cognitive mechanisms implicated in age-related effects. Because implicit learning plays a key role in first-language (L1) acquisition, particularly in the acquisition of statistical patterns in language, it has been proposed that age effects may be the result of attenuated implicit learning capabilities in late-teen and adult learners (DeKeyser, 2000; Janacsek, Fiser, & Nemeth, 2012). If this is true, age-related effects should be significant in linguistic areas that are not readily amenable to conscious learning processes and explicit instruction. To determine whether this is in fact the case, this study examined the linguistic knowledge of native speakers (NSs), early L2 learners, and learners who acquired English as adults. In particular, it examined these groups’ knowledge related to an area of English that is hypothesized to be difficult to learn explicitly, namely, English sound-symbolic (SS) patterns.

Participants were composed of English NSs (n = 20) and three NNS groups with L1 Korean and L2 of English. The NNS groups were divided into three groups based on age of onset (AO) , with an AO range from 3 to 9 years of age (n = 20), 10 to 16 (n = 20), and > 17 (n = 20). Three experiments were performed that tested the participants’ English magnitude SS sensitivities when forming assumptions about nonce words (Experiment 1 and 2) and their ability to utilize English SS patterns to bootstrap their learning of new vocabulary (Experiment 3). The two late L2 learner groups (AO 10-16; 17+) were found to have significantly reduced levels of SS knowledge compared to the early L2 learners (AO 3-9) and NSs in all experiments. Only in Experiment 1 and 2, the early L2 learners had diminished magnitude SS sensitivities compared to NSs, but not for Experiment 3.

Explicit and implicit aptitudes as measured by LLAMA (Meara, 2005) were also tested for potential relationships with test scores. Explicit aptitudes (LLAMA B, E, and F) did not have a significant effect on the performance of all AO groups, whereas implicit aptitude (LLAMA D) did have a moderate to strong correlation for test scores in only the two late learner groups. The early learner group was not affected by language aptitude levels during the experiments.

In sum, the study has found that there is evidence for SPE in the areas of magnitude and English phonesthemic SS patterns. Implicit language-learning aptitudes appeared to have a facilitative effect on the acquisition of these SS sensitivities for the two late L2 learner groups, but not for the early L2 learners.