ABSTRACT
The issue of individual variations in second language acquisition (SLA) has been one of the central concerns of SLA research. Researchers pursuing this issue have extensively explored the factors that differentiate learners in their second-language (L2) learning within the framework of ‘individual difference’ (ID) research (see Dörnyei, 2005; Dörnyei & Ryan, 2015, for overviews). In the 1990s, we witnessed an abrupt increase in empirical findings on learner characteristics that constrain L2 learning, triggered partly by stepwise paradigm shifts in L2 motivation research (e.g., Crookes & Schmidt, 1991; Dörnyei, 1990; for overviews, see Dörnyei, 2001; Dörnyei & Ushioda, 2011). In this period, there was also insightful research into aptitude and working memory (e.g., Robinson, 1997, 2002). It should be noted that the majority of these ID studies were psychometric in nature, adopting a cross-sectional linear-model design that treats ID factors as discrete independent variables (Dörnyei & Ushioda, 2011). These studies focused on the general tendencies in individual variations instead of the specific variations observed within and among individuals. This psychometric tradition of ‘variable-centered analysis’ (Larsen-Freeman & Cameron, 2008b, p. 202) has been a mainstream practice for clarifying structural relationships between ID variables and their effects on L2 learning (e.g., Csizér & Dörnyei, 2005; Dörnyei, Csizér, & Németh, 2006).
