Although there is substantive evidence of implicit learning of form-to-form mappings in cognitive psychology, laboratory-based studies in the field of second language acquisition examining the existence, possibility and effectiveness of adult implicit L2 learning have been inconclusive (Williams, 2005; Leung & Williams, 2006, 2010, 2011; Rebuschat & Williams, 2009, 2012; N. Ellis, 2002; Long, to appear; DeKeyser, 1994, 1995; Robinson, 1996; de Graaff, 1997; Hama & Leow, 2010).

The present study probes deeper into the realm of IL mechanisms by investigating not only the possibility of IL, but also how powerful and efficacious adults’ IL mechanisms are by using a miniature artificial language, having multiple training sessions (4 hour-long sessions), more realistic and naturalistic exposure, non-salient and complex linguistic features and three outcome measures: comprehension, judgment and production.

40 adult native speakers of English without formal training in language sciences were recruited for the experiment. Although there was only one treatment condition in the form of implicit training, based on participants’ awareness of the target rules, three groups were formed post-hoc. The miniature artificial language contains 26 words: eight animate nouns, eight inanimate nouns and ten transitive verbs. The nouns in our morphosyntactic paradigm were divided into two classes: animates and inanimates, and were differentially marked for nominative and accusative.

Overall, our experiment has shown that, under certain circumstances, adult language learners can learn specific L2 morphosyntax implicitly. It appears that concrete, easily trackable L2 properties that lend themselves to distributional learning can benefit from IL mechanisms. However, more abstract L2 properties, like the morphological paradigm of case, seem not to be learnable by implicit means, but rather that explicit (inductive, deductive) learning is necessary. Results from repeated-measures ANOVA demonstrate evidence of implicit learning of animacy but not case. Results also demonstrated that learners in the aware group, who engaged in explicit learning, performed significantly better then both the unaware and the case-aware groups on all three measures. By means of explicit induction, only the aware participants were able to learn the full morphosyntactic paradigm consisting of animacy and case markers and then generalize to items in syntactic positions not encountered before.