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The time course of different metacognitive experiences of knowledge was investigated using artificial grammar learning. Experiment 1 revealed that when participants are aware of the basis of their judgments (conscious structural knowledge) decisions are made most rapidly, followed by decisions made with conscious judgment but without conscious knowledge of underlying structure (unconscious structural knowledge), and guess responses (unconscious judgment knowledge) were made most slowly, even when controlling for differences in confidence and accuracy. In experiment 2, short response deadlines decreased the accuracy of unconscious but not conscious structural knowledge. Conversely, the deadline decreased the proportion of conscious structural knowledge in favour of guessing. Unconscious structural knowledge can be applied rapidly but becomes more reliable with additional metacognitive processing time whereas conscious structural knowledge is an all-or-nothing response that cannot always be applied rapidly. These dissociations corroborate quite separate theories of recognition (dual-process) and metacognition (higher order thought and cross-order integration).

What is the difference in the nature of conscious and unconscious knowledge? Artificial grammar learning (AGL; Reber, 1967) is a particularly useful methodology to help address this question as it demonstrably elicits both conscious and unconscious knowledge according to subjective measures of awareness (e.g. Dienes, 2008a, Gaillard et al., 2006 and Johansson, 2009). Two types of knowledge are involved in sequence classification in AGL: structural knowledge and judgment knowledge (Dienes and Scott, 2005 and Scott and Dienes, 2008). During the initial training phase of a typical AGL experiment, participants are exposed to rule-based sequences generated by the grammar in question. Structural knowledge is (either conscious or unconscious) knowledge of the structural consequences of the grammar and can consist of, for example, rules, patterns of connection weights, chunks, or whole items taken as examples of the structure learned during training. Before testing, participants are informed the sequences were generated by a series of complex rules before going onto classify further novel sequences in terms of their grammaticality (whether they conform to or violate the studied rules; typically 50% of sequences are grammatical at test). Here, judgment knowledge is the (conscious or unconscious) knowledge constituted by such a judgment which is directly expressed in sequence classification (i.e. the knowledge that the test item is or is not grammatical). When both structural and judgment knowledge are conscious, grammaticality decisions are based on hypothesis-driven rule-application or a conscious recollection process of recognised exemplars or bigrams, trigrams or other parts of exemplars encountered during training. Feelings of intuition or familiarity are expressed when structural knowledge is unconscious but judgment knowledge is conscious (e.g.: “I know I’m correct but I don’t know why”) (Norman et al., 2006 and Norman et al., 2007). When both knowledge types are unconscious the phenomenology is that grammar judgments are mere guesses; no conscious metaknowledge of what has been learned is expressed. (See Scott & Dienes, 2010a, for a model of how structural and judgment knowledge develop in AGL; and Scott & Dienes, 2008, and Pasquali, Timmermans, & Cleeremans, 2010, for models of how judgment knowledge may become conscious. See Fig. 1 for the relationship between the conscious status of knowledge types and the associated phenomenology.) Fig. 1. The relationship between the conscious status of structural and judgment knowledge. The bottom row represents self-reported structural knowledge attributions (Dienes and Scott, 2005 and Scott and Dienes, 2008). Figure options Numerous subjective measures of awareness have been used in AGL studies including verbal reports (Reber, 1967 and Reber, 1969); confidence ratings made on binary (Tunney & Shanks, 2003) or continuous scales (Dienes, Altmann, Kwan, & Goode, 1995); structural knowledge attributions (Dienes and Scott, 2005, Scott and Dienes, 2008, Scott and Dienes, 2010a, Scott and Dienes, 2010b, Scott and Dienes, 2010c, Scott and Dienes, 2010d and Wan et al., 2008; see also Chen et al., 2011, Guo et al., 2011 and Rebuschat and Williams, 2009) and wagering high or low amounts to indicate high or low levels of conscious awareness (Persaud, McLeod, & Cowey, 2007). Recently, a new form of wagering as a measure of awareness has been introduced into the AGL literature to indicate the presence of unconscious knowledge, namely ‘no-loss gambling’ (Dienes & Seth, 2010). During the test phase of AGL studies using the no-loss gambling procedure, participants indicate confidence (thus, metacognitive awareness) in their grammaticality decisions by either betting on their decision and, if correct they gain a reward (e.g.: one sweet), or they can gain a reward by betting on a transparently random process with a 50% chance of winning. If one chooses to bet on the random process, rather than on the grammaticality decision, one is not aware of knowing the grammaticality of the stimulus, as it feels as if the grammaticality judgment is as reliable as flipping a coin (i.e.: it is a guess response). Conversely, when betting on the grammar decision itself, some degree of confidence and hence metacognitive awareness is indicated. Dienes and Seth found that when participants were betting on the random process, the accuracy of their grammaticality judgments was significantly above chance (around 60% correct), satisfying the guessing criterion of unconscious knowledge (Dienes et al., 1995). This shows participants could express unconscious structural knowledge when judgment knowledge was unconscious. Mealor and Dienes (2012a) used the no-loss gambling method to investigate an apparent contradiction in dual-process theories of recognition memory. Dual-process theories posit that responses based on familiarity are made rapidly and automatically whereas recollection responses are relatively effortful and time-consuming due to strategic retrieval (e.g.: Jacoby, 1991 and Yonelinas, 2002; see also the two-stage recollection hypothesis of Moscovitch, 2008, and the continuous dual-process model of Wixted & Mickes, 2010). Several researchers have found evidence to support this view (e.g. Boldini et al., 2004, Coane et al., 2011, Feredoes and Postle, 2010, Gronlund and Ratcliff, 1989, Hintzman and Caulton, 1997, McElree et al., 1999 and Yonelinas and Jacoby, 1996). However, studies using the remember-know methodology (R/K; Tulving, 1985) have provided contradictory evidence. R/K studies involve a learning phase where participants are presented with to-be-remembered stimuli (typically word lists). At test, they are required to discriminate between these previously seen targets and novel lures. When endorsing a stimulus as previously seen, the phenomenological basis for that decision is also reported; either remember (R) responses which indicate conscious recollection; know (K) responses which indicate a feeling of familiarity without conscious recollection that the stimulus had been presented earlier; or guess (G) responses which indicate no feeling of memory at all even though the test item is accepted as old. Using this methodology, several researchers have found that in self-paced tests, R responses to endorsed stimuli are made most rapidly, followed by K responses and then G responses (e.g.: Dewhurst and Conway, 1994, Dewhurst et al., 1998, Dewhurst et al., 2006, Duarte et al., 2007, Henson et al., 1999, Konstantinou and Gardiner, 2005 and Wheeler and Buckner, 2004; see also Sheldon & Moscovitch, 2010). The Dewhurst et al. (2006) interpretation of these findings is that RTs may not reflect the direct times of the actual retrieval process per se, but rather the information R, K and G responses afford to metaknowledge. A recollective experience allows a response without further delay, but a feeling of familiarity may be probed further. The R/K method as applied to memory presumably taps into similar underlying processes as recollection and familiarity as AGL (see Tunney, 2007, for implementation of R, K and G responses in an AGL task). Many researchers (but not all, e.g. Donaldson, 1996 and Dunn, 2004) subscribe to the view that R and K responses reflect qualitatively different forms of metacognitive commitment to a current test item having been previously presented. In a similar manner, recollection and familiarity in AGL reflect different metacognitive experiences that the current test sequence conforms to or violates the grammar structure from training. R responses in R/K and rules/recollection responses in AGL are consequents of consciously recognising the current item, or parts of the sequence, from training. K responses are given when there is a feeling of ‘oldness’ that the item has been presented previously without recollecting its occurrence and in AGL, intuition/familiarity responses are given when some aspect(s) of the test sequence result in a feeling of grammaticality or ungrammaticality (‘oldness’/’newness’ in an abstract sense of the current item’s structure being old) but without consciously identifying those aspects that led to that feeling. The interpretation of guess responses in both paradigms is also similar. Wixted and Mickes (2010) state that G responses are made when the memory strength of an item falls near the old/new decision criterion. In AGL, guess responses are made when the subjective familiarity of a to-be-classified sequence is close to mean subjective familiarity of previously encountered sequences acquired during the course of the experiment (Scott and Dienes, 2008 and Scott and Dienes, 2010a). However, a meta-analysis by Gardiner, Ramponi, and Richardson-Klavehn (2002) concluded that the accuracy of guess responses in R/K studies is typically at chance. This is not true of AGL studies where the guessing criterion is often satisfied (e.g.: Dienes and Altmann, 1997, Dienes and Scott, 2005, Dienes and Seth, 2010, Dienes et al., 1995 and Tunney and Shanks, 2003). Furthermore, it has been shown that subjective familiarity can influence grammaticality judgments when participants report their decision strategy as a random selection (Scott & Dienes, 2008) which makes AGL an ideal procedure to investigate the respective time-courses of these different types of response. Using the no-loss gambling method, Mealor and Dienes (2012a) showed that in self-paced tests, ‘guess’ responses (as shown by willingness to bet on the 50:50 random process) took longer than responses made with some degree of conscious judgment knowledge (as shown by willingness to bet on the grammaticality decision) even when differences in accuracy were accounted for. In a second study, a strict response deadline (500 ms) was introduced into the test phase. It was found that the deadline only reduced the quality of responses made with conscious judgment knowledge and had no detectible effect on the quality of guess responses. Thus, it was concluded participants await a metacognitive feeling of judgment (e.g.: recollection or familiarity) to form. If this feeling is not forthcoming, only then do people opt to guess, i.e.: long RTs for guess responses are a reflection of the information afforded to metaknowledge (Dewhurst et al., 2006). However, when externally enforced, guess responses do not suffer a speed-accuracy trade off, which is not true of decisions made with some degree of metacognitive awareness. In the context of AGL this means that when both structural and judgment knowledge are unconscious, the decision quality is as good as it will ever be in around 500 ms (for the materials used in Mealor and Dienes) but when judgment knowledge is conscious, extra time is needed to optimise the decision. It was also found that participants attempted to apply conscious judgment (shown by the proportion of bets on the grammar decision to bets on the random process) in as many short deadline trials as no deadline trials showing that the process of metacognitive judgment has at least started in around 500 ms, but time is needed for that process to become optimally reliable (i.e.: under a deadline, participants think they are using a reliable judgment process to guide sequence classification when the reliability of that process has become compromised). However, as bets on the grammar decision in no-loss gambling do not distinguish between conscious and unconscious structural knowledge (i.e.: between intuition/familiarity and rules/recollection as shown on Fig. 1), the findings of Mealor and Dienes raise further questions: is it conscious or unconscious structural knowledge that takes time to be applied? And what can we infer about the nature of the decision processes based on conscious and unconscious structural knowledge through investigating their time courses? We address these questions in two AGL experiments using self-paced responding (experiment 1) and response deadlines (experiment 2). 2. Experiment 1 Experiment 1 aimed to replicate and extend the findings of Mealor and Dienes (2012a) using structural knowledge attributions in lieu of no-loss gambling (see Section 3.3 for the structural knowledge attribution definitions used in the current experiments). These attributions allow for a greater range of responding when participants have some degree of confidence (metacognitive awareness) in their grammaticality decision and allow inference of the conscious status of structural knowledge subsumed within these decisions. As AGL and R/K presumably tap into similar decision making process, it is predicted that responses based on conscious structural knowledge (rules, recollection) should be most rapid, followed by those based on unconscious structural knowledge accompanied by conscious judgment knowledge (intuition, familiarity) and finally decisions made without conscious judgment knowledge (random selection, i.e.: guess responses). Confidence is also inversely related to RT (e.g.: Petrusic and Baranski, 2003, Petrusic and Baranski, 2009 and Tunney and Shanks, 2003) and decisions based on familiarity or intuition are accompanied by lower confidence estimates than those based on rules or recollections whereas guesses are, by definition, made in the absence of confidence (e.g.: Dienes & Scott, 2005). This is also the pattern we would expect to observe in self-paced R/K studies (e.g.: Dewhurst et al., 2006). Theories which postulate (and methodologies which presume through their operationalisation) a qualitative difference between conscious and unconscious knowledge need to show that these reported types of knowledge are not reducible to a single dimension, such as confidence. If guesses, familiarity-based responding and recollection-based responding are associated with differing levels of accuracy and subjective confidence, this could be problematic for such theories. Thus, a second aim of experiment 1 was to determine whether these response types have a degree of independence in terms of the time it takes to make a decision based on such knowledge types once confidence and accuracy are accounted for.