A number of competing theories related to the role of explicit knowledge in the development of implicit knowledge have received much attention in the field of SLA (for example, N. Ellis, 2005; R. Ellis, 1994). This section will start by presenting the non- interface position, which rejects any link between implicit and explicit knowledge. This is followed by the strong-interface position. Contrary to the non-interface position, the strong- interface position (DeKeyser, 2003, 2007, 2009, 2015) (see section 2.8.2. below) argues for a direct link between explicit knowledge and implicit knowledge. The last position is the weak-interface position (N. Ellis, 2005; R, Ellis, 1994), which holds that explicit knowledge serves to facilitate the development of implicit knowledge, although this is based on several factors (see section 2.8.3). A discussion of these positions is presented below in further detail.
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2.9.1 Non-interface position
Krashen’s monitor theory (1981, 1982, 1985) postulates that learners have two totally separate systems that are involved in language learning (a ‘learned system’ and an ‘acquired system’). Learning is the conscious (explicit) process that is involved when a learner tries to consciously attend to language in an effort to understand and memorise rules, whereas acquisition is unconscious (implicit) and occurs as a result of exposure to input. For Krashen, explicitly learnt rules only serve to compare and possibly modify utterances that have been produced by the ‘acquired system’ (Krashen, 1982). An example of this conscious knowledge, according to Krashen, is knowledge about the rules of language (or metalinguistic knowledge). Of relevance here, Krashen claimed that the ‘learnt’ knowledge is not connected and cannot be transformed to ‘acquired’ knowledge. This position indicated that explicit knowledge cannot convert to implicit knowledge, which later became known as the non-interface position (R. Ellis, 2008). Further, he claimed that explicit knowledge does not directly influence the development of implicit knowledge, but that it only plays a role when learners monitor their own output. Moreover, he argued that implicit knowledge is only developed when the learner’s attention is focused on conveying a message for communicative purposes.
2.9.2 Strong-interface positions
The strong-interface position does not typically refer to implicit versus explicit knowledge (R. Ellis, 2008), but instead it is related to declarative and procedural knowledge. These two types of knowledge are claimed to operate along a continuum on which declarative knowledge can gradually become procedural or automatic knowledge over time, with sufficient practice (Anderson, 1992, 2000; DeKeyser, 1997, 1998, 2007; R. Ellis, 1993; Ullman, 2004, 2005).
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In the strong-interface position, the transition from declarative to procedural knowledge represents a qualitative shift as a result of automatisation, which is also referred to as practice (DeKeyser, 2001). Automatisation refers to the process of “knowledge change from initial presentation of the rule in a declarative format to the final stage of fully spontaneous, effortless, fast, and errorless use of the rule, often without being aware of it anymore” (DeKeyser, 2007, p. 3). According to this sense, the strong-interface position maintains that automatised declarative knowledge or procedural knowledge can be seen as functionally equivalent to implicit knowledge. However, it should be emphasised that automatised knowledge is not necessarily similar to implicit knowledge, as a lack of awareness is “not a requirement for automaticity” (DeKeyser, 2007, p. 4), i.e. one can possibly attain automaticity of a particular structure while at the same time being fully aware of the underlying rules. Accordingly, automaticity can be a feature that is drawn upon for both implicit and explicit knowledge (DeKeyser, 1998, 2007), with both types of knowledge involving a gradual change from more controlled to more automatic processing.
2.9.3 Weak-interface position
Another positionthat was proposed for the interface between explicit and implicit knowledge is the weak-interface position (N. Ellis, 2005; R. Ellis, 1993, 1994). The weak- interface position in R. Ellis’s (1993, 1994) work postulates that explicit knowledge can be converted into implicit knowledge, depending on the type of features of the language. The model distinguishes between the acquisition of developmental and variational linguistic features. The developmental features of language, such as the third-person –s, are linguistic features that are acquired sequentially as certain processing strategies are acquired (R. Ellis, 2008). On the other hand, variational features of language, such as the copula “be”, are linguistic features that can be acquired at any time as they are not constrained by acquisition orders.
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In his view, R. Ellis argues that explicit knowledge can be transformed in to implicit knowledge in the case of variational features, but not in the case of developmental features, unless the learner is developmentally ready to incorporate the feature into the interlanguage system (R. Ellis, 2008, p. 423). Accordingly, the learners’ existing knowledge serves “as a kind of filter that sifts explicit knowledge and lets through only that which the learner is ready to incorporate into the interlanguage system” (R. Ellis, 1994, p. 88).
The theory also draws on Schmidt’s Noticing Hypothesis (1990) and acknowledges that explicit knowledge and formal instruction can have a facilitative impact on implicit knowledge by helping learners to notice the relevant features in the input and to make a comparison between what they have noticed and their recent interlanguage (R. Ellis, 2008). Based on this view, explicit knowledge then helps learners with “noticing the gap” (Schmidt & Frota, 1986) and facilitates the development of implicit knowledge by informing “the language processor so that it takes account of data in the input” (Schmidt & Frota, 1986, p. 98). Nevertheless, the fact that noticing is considered a conscious process (Schmidt, 1990), as pointed out earlier, indicates that the process of “taking account of data” by the language processor is conscious. However, as noted by Rogers (2016), R. Ellis’s model does not explain how noticing, which is linked to conscious awareness, facilitates the development of implicit knowledge, instead of explicit knowledge.
Another perspective on the weak-interface position is N. Ellis’s proposal (1993, 1994, 2005, 2011, 2015; N. Ellis & Larsen-Freeman, 2006). This perspective shares some features with both Krashen’s (1982) non-interface position and R. Ellis’s (1994) weak- interface position. Similar to Krashen’s argument, N. Ellis claims that the majority of learning is implicit, and most knowledge is tacit (2005). Moreover, N. Ellis views explicit and implicit knowledge as distinct systems. He also postulates that explicit knowledge
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cannot be transformed into implicit knowledge, as the two types of knowledge work together in every cognitive task and during any learning experience (2005, p. 340). However, this should not be understood to mean that implicit and explicit knowledge work independently of one another.
N. Ellis clearly stated that “conscious and unconscious processes are dynamically involved together in every cognitive task and in every learning episode” (2005, p. 340), as well as in both input and output processing. He illustrates the interplay between implicit and explicit knowledge when using language by arguing that we rely mostly on automatic processing but that we also access explicit knowledge when automatic processes fail. As an example of this, N. Ellis mentions the case of when we stumble while walking, or even when communication breaks down. From this perspective, then, explicit knowledge serves as a form of “collaborative conscious support” for automatic processes (N. Ellis, 2005, p. 308).
Apart from explicit knowledge supporting implicit knowledge during language use, N. Ellis also argues that there is a relationship between implicit and explicit knowledge as part of language development. One of the features of N. Ellis’s (2005) weak-interface model is that it stresses the importance of attention in the development of both types of knowledge. According to this model, explicit knowledge develops as a result of conscious and deliberate attempts at learning, while implicit knowledge develops as a result of repeated exposure to patterns within the input accessible to the learner. In the case of implicit knowledge, the repeated exposure leads to the strengthening of connections within a connectionist framework through an unconscious tallying process, which leads to the development of implicit knowledge (N. Ellis, 2005, 2011; Hulstijn, 2002). Within this model, however, attention is necessary for tallying to take place, but awareness is not (N. Ellis, 2005). A key difference, then, between the weak-interface models of N. Ellis and R.
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Ellis is that explicit knowledge does not convert in to implicit knowledge (as in the case of R. Ellis’s model), but explicit knowledge does have an influential role in the development of implicit knowledge.
In sum, the previous section has outlined the various theoretical accounts that attempted to explain how implicit and explicit knowledge are developed, as well as the way that these types of knowledge might interface in their development and use. In this regard, the following section shifts the perspective towards how implicit and explicit knowledge have been operationalised and measured within SLA. The significance of the following section is that it links the previous discussion on awareness to how it has been measured, before moving on to the methodology chapter.