Cognitive perspectives on Difficulty and Complexity in L2 Acquisition

The theme that runs through the contributions to this special issue is diffi culty , an important yet challenging theme in second language acquisi-tion (SLA) that, after the demise of the contrastive analysis hypothesis (e.g., Stockwell, Bowen, & Martin, 1965), has only been latent in second language (L2) research; however, it has been attracting renewed and more explicit interest in the wake of the recent surge of research on language complexity (e.g., Bulté & Housen, 2012 ; Miestamo, Sinnemäki, & Karlsson, 2008 ; Ortega, 2012 ; Pallotti, 2015 ; Trudgill, 2011 ), and its scope and signifi cance are becoming increasingly clear. This special issue addresses the question of what makes learning some aspects of L2 grammar more or less diffi cult, arguing that this question can only be properly understood by reference to the synergistic infl uence of prop-erties of the L2 target feature (e.g., linguistic complexity, frequency, and salience; DeKeyser, 2005 ; N. C. Ellis, 2006 ), the learning conditions (e.g., implicit vs. explicit learning; de Graaff & Housen, 2009 ; R. Ellis, 2006 ; Long & Robinson, 1998 ), and the individual learner (e.g., attention and awareness, working memory, and language aptitude; Juffs & Harrington, 2011 ; Sawyer & Ranta, 2001 ; Wen, Borges Mota, & McNeill, 2015 ). Despite its importance in SLA, diffi culty has rarely fi gured explicitly as a primary research variable, and relevant fi ndings have mostly appeared in isolated publications (e.g., Collins, Trofi movich, White, Cardoso, & Horst, 2009 ; DeKeyser, 2005 ; R. Ellis, 2006 ; Goldschneider & DeKeyser, 2001 ; Li, 2013 ; Ozeki & Shirai, 2007 ; Roehr & Gánem-Gutiérrez, 2009 ).To our knowledge, there has been no recent single volume devoted to the intricate interactions between the various types of factors that ulti-mately determine L2 diffi culty and thus L2 learning outcomes (yet see Robinson, 1996 , 2002 ). In addition, the study of diffi culty in SLA has been plagued with terminological diffi culties, conceptual confusion, and misunderstandings of its relationship with other related yet con-ceptually distinct constructs such as linguistic complexity, learnability, and developmental stages and orders of acquisition. In this article we therefore explain what we mean by diffi culty and propose a taxonomic framework (see Figure 1 ) that can be used as a starting point for the systematic study of the nature and role of diffi culty in SLA.