The field of second language acquisition is inherently interdisciplinary drawing from and connecting many traditional disciplines. Interaction-based research stands in the middle and is able to provide linkages between and among many areas of research considered central to SLA. In this paper, I provide an overview of some of the main features of the Interactionist Approach moving from the early days where the focus was on formal linguistic elements to current research where the focus is on an a more fine-grained understanding of the benefits of interaction and in particular on understanding the role of individual learner differences in these benefits.

This study investigates how Japanese EFL learners access English homographic words. Participants were asked to complete two experimental priming tasks (a lexical decision task and semantic relevance judgment task) using PC software. The lexical decision task assessed how semantically associated words as prime words affected the participants' lexical decisions on target homographs, based on their reaction times and accuracy rate. The semantic relevance judgment task evaluated how the participants judged the relations between the target homographs and the semantically associated words as prime words based on their judgment scores and reaction times. The results revealed no priming effects of the semantically associated words in the lexical decision task. On the other hand, there were significant priming effects in the semantic relevance judgment task. Overall, the results of the two tasks revealed that Japanese EFL learners are likely to access a single meaning of homographs more strongly in the cognitive process. In addition, the configurations of lexical access can differ between the lexical decision task and semantic relevance judgment task.

This study investigates how L2 learners of Japanese with different L1 backgrounds (Korean, English, or Chinese) acquire nominative Case marking in Japanese. Analyses of data from a speaking corpus show that the nominative Case marking was almost perfect, incorrect Case marking being quite limited, throughout the entire stages examined in this study, irrespective of the learner's L1 backgrounds. On the other hand, some L1 effects were observed from early stages especially in terms of the nominative Case marking on the object of nominative object constructions. These findings suggest not only that the functional category of T is present in early L2 grammar, but also that its source is L1. Another important finding is that L1 English learners of L2 Japanese, like Japanese monolingual children, overgenerated the nominative ga for the accusative o in the course of the acquisition of nominative object constructions, which suggests a parameter resetting. Thus the Full Transfer/Full Access hypothesis (Schwartz & Sprouse, 1994) rather than the Minimal Tree hypothesis (Vainikka & Young-Sholten, 1994) or Full Access (Epstein, Flynn, & Martohardjono, 1996) is supported.