This paper reports the results of part of a longitudinal study that analyzes the acquisition process of Japanese as a second language (JSL) by an adult learning in an intensive mode in Australia. Specifically, the purpose of the study was to find out whether or not the emergence orders of morphological and syntactic structures in his speech data would parallel the universal hierarchy of developmental stages of acquisition claimed in Processability Theory (PT henceforth: Pienemann, 1998; Pienemann, Di Biase & Kawaguchi, 2005). The informant in this study was a 33 year old Australian male, who as a complete beginner, participated in an approximate 900 hour one-on-one Japanese language training over a period of one year. As part of the training, he was engaged in spontaneous conversations with native speakers of Japanese on a fortnightly basis, which were audio-recorded and transcribed. The verbal affixes, V-te V structures, passive/causative/benefactive structures, canonical sentences and non-canonical sentences that the informant had produced were then extracted and used for distributional analysis. The results of the study showed that the developmental sequences of acquisition of Japanese morphology and syntax in the informant's interlanguage matched those predicted in the original and extended versions of PT.

This study attempted to explore the construct validity of Grammaticality Judgment Tests (GJTs) on the basis of Loewen (2009). A particular focus was placed on a relationship between L2 learners' accurate performance on timed GJTs (expected to tap implicit knowledge) and their self-reported use of ‘feel’ in making judgments in terms of task stimulus (grammatical versus ungrammatical), and 17 grammatical structures. The participants were 90 Japanese learners of English from two different universities in Japan. They conducted timed (with 4-second response time) and untimed (without time constraints) GJTs. The data from a correlation analysis reveal that out of the 17 different target structures, the accurate performance of only one item Plural-s was significantly correlated with the reported use of ‘feel’ whereas neither grammatical nor ungrammatical items as a whole were. The investigation of Plural-s in terms of learning difficulty of implicit knowledge proposed by Ellis (2006) shows that Plural-s is relatively easy due to its simple Functional value and easy Processability. However, the accuracy order from the timed GJT reveals that the structure ranks 12th. With the help of the self-report analysis, it was found that there seem to exist various factors that affect the degree of difficulty such as sentence comprehension. Furthermore, although the use of ‘feel’ was reported subjectively, the results seem to highlight the importance of considering ideal response time in order to ensure that timed GJTs can tap implicit knowledge. It seems that a combined use of subjective and objective analysis might further contribute to the exploration of GJTs' validity issue.

Investigating the effects of preemption as one of the ways of unlearning overgeneralization errors, this study examined whether Japanese-speaking second language (L2) learners of English successfully learned transitivity alternations of novel verbs that denote manner of motion. Provided with intransitive and transitive novel verbs, low intermediate learners made transitivity errors even though they had not heard the alternative uses of the given verbs. However, these overgeneralization errors were infrequent in the cases where preemption cues were provided, suggesting that the L2 learners' analytical abilities facilitate unlearning based on preemption. While previous L2 studies observed that preemption could not overcome the errors ascribed to negative transfer from L1, the present study demonstrates that preemption works for the overgeneralization errors that are not rooted in the learners' L1 properties, and therefore, preemption is available as a learning mechanism or strategy in second language acquisition.

A number of studies have been carried out since around 2000 to find out the cause of the universality in the acquisition and use of grammatical morphemes and learners' errors in producing them, a topic that was actively studied from the 1970s to the 80s. Researchers' positions are, roughly speaking, divided into two: Second language acquisition is, like acquisition of other general knowledge, fundamentally based on "memory of a stimulus", and "habit formation", in which factors such as “saliency” and "frequency" are important (Goldschneider & DeKeyser, 2001, among others); and Second language acquisition is based on the same knowledge as native language acquisition, where the mental grammar (interlanguage) plays an extremely important role in use of grammatical morphemes (Wakabayashi, 1997, etc.). In this paper, after clarifying the psychological reality of the interlanguage (Selinker, 1972), it will be shown that interlanguage is itself a kind of “natural language”. Based on data from six studies, we discuss Japanese-speaking English learners' knowledge and use of 3rd person singular -s. It will be argued that second language learners' acquisition and use of grammatical morphemes are, though general factors such as memory are also concerned, clearly based on their interlanguage, and that empirical research based on precise designs rooted in linguistics serves as a key to the elucidation of learner knowledge.