32 CHAPTER 2 THE IMPLICIT-EXPLICIT DEBATE SLA research in the past decades has focused to a great extent on the implicit-explicit debate and is summarized in Ellis (2015) as follows: Implicit learning is acquisition of knowledge about the underlying structure of a complex stimulus environment by a process which takes place naturally, simply and without conscious operations. Explicit learning is a more conscious operation where the individual makes and tests hypotheses in a search for structure. (Ellis, 2015, p. 2) Over the past decades, a large body of research on what has been termed form-focused instruction (FFI), as opposed to more meaning-based instruction, has been carried out, comparing the e ectiveness of both ends of this continuum; many of these studies have been synthesized in several meta-analyses and research reviews (e.g., Norris & Ortega, 2000; De Graa & Housen, 2009; Spada & Tomita, 2010). ese have shown quite convincingly that explicit types of instruction are more e ective than implicit types of instruction, judging from the substantially larger e ect sizes that are generally observed for explicit treatments. In light of the worldwide predominance of structure-based teaching practice and structure-based course materials as witnessed by Lightbown and Spada (2013), it seems reasonable to assume that these research outcomes have found their way into schools and have even come to dominate discussions on foreign language teaching at the level of classroom practice. At the same time, however, several researchers have cautioned that the e ects of explicit instruction may have been overestimated (e.g., Doughty, 2003; DeKeyser, 2003), as research designs may have favored explicit types of instruction for several reasons: Norris and Ortega (2000) point out that instructional treatments in FFI research have tended to focus on speci c language structures and on short-term outcomes; only very few longitudinal and/or long-term FFI studies have been conducted. Short treatments may well work against implicit types of instruction in the case of L2 learning. Implicit learning processes probably require more time on task in order to be e ective as a great deal of input is needed to facilitate implicit learning (Ellis, 2015). Another reason why FFI research may have been biased against implicit treatments is its overreliance on more explicit measures of linguistic ability, which may have favored explicit types of instruction. Andringa and Schultz (2018) argue that meta-analyses have not su ciently taken di erences in amount of exposure to the target structure into account. is too, may have favored explicit types of instruction, as these may o en be more intensive in terms of exposure: each and every item in explicit exercises tends to expose learners to the target structure, while in implicit types of instruction, exposure may be more incidental and less intensive.
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