حافظه ضمنی مفهومی و زمینه محیط زیست

Changes in environmental context between encoding and retrieval often affect explicit memory but research on implicit memory is equivocal. One proposal is that conceptual but not perceptual priming is influenced by context manipulations. However, findings with conceptual priming may be compromised by explicit contamination. The present study examined the effects of environmental context on conceptual explicit (category-cued recall) and implicit memory (category production). Explicit recall was reduced by context change. The implicit test results depended on test awareness (assessed with a post-test questionnaire). Among test-unaware participants, priming was equivalent for same-context and different-context groups, whereas for the test-aware, the same-context group produced more priming. Thus, when explicit contamination is controlled, changes in environmental context do not impair conceptual priming. Context dependency appears to be a general difference between implicit and explicit memory rather than a difference between conceptual and perceptual implicit memory. Finally, measures of mood indicated no changes in affect across contexts, arguing against mood mediation for the context effects in explicit recall.

Research on memory often reveals a sensitivity to contextual change. One important aspect of context is environmental context, referring to the physical surroundings in which learning or retrieval takes place. Reinstating the learning context often has a beneficial effect on retrieval. One oft-cited study featured a rather extreme manipulation of environmental context in which scuba divers learned words either on dry land or underwater (Godden & Baddeley, 1975). Divers later tested in the same context recalled more words then those tested in the opposite environment. More typically, researchers have examined such “place effects” on memory with less extreme manipulations of context such as different experimental rooms or indoor vs. outdoor locations. These studies have often demonstrated context-matching effects on memory tests such as recall and recognition (see Smith & Vela, 2001, for a review). The vast majority of the research on environmental context and memory has used explicit memory tests, in which participants intentionally and consciously recollect past events. In contrast, implicit memory refers to unconscious or unintentional retrieval of past experience and is typically assessed with tests of repetition priming. Dissociations between implicit and explicit memory demonstrate that these forms of memory differ in important ways. For example, patients with organic amnesia exhibit reduced explicit memory (the primary symptom of their disorder) but largely intact priming on tests of implicit memory (e.g., Levy et al., 2004 and Shimamura, 1986).1 A variety of encoding variables also dissociate these forms of memory, and neuroimaging analyses indicate different neural substrates (for reviews, see Horner and Henson, 2008, Mulligan, 2004, Roediger and McDermott, 1993 and Schacter, 1987). In addition, researchers also differentiate among different forms of implicit memory, most notably between perceptual and conceptual implicit memory. Tests of perceptual implicit memory feature fragmentary or rapidly-presented cues which participant attempts to complete or identify. The word-fragment completion and perceptual identification tasks are examples. Priming on these tests is generally sensitive to manipulations of perceptual form (e.g., study modality) but not manipulations of semantic elaboration (e.g., the levels-of-processing manipulation). In contrast, conceptual implicit tests present participants with cues that are meaningfully related to the to-be-retrieved material. An example is the category production task in which category names are used to elicit examples. Conceptual priming is typically affected by semantic encoding manipulations but unaffected by manipulations of surface form (such as modality) (see Mulligan, 2004 and Roediger and McDermott, 1993, for reviews). Because context-dependency is a defining characteristic of explicit memory, it is important to determine whether context-dependency as reflected, for instance, by environmental-context effects also characterizes implicit memory (McKone & French, 2001). A few such studies have been conducted and have produced conflicting results. Several studies using perceptual priming tests have shown no effect of context change. Jacoby (1983) manipulated context across two experimental rooms and found no effect of match between study and test on the perceptual identification test. Similarly, McKone and French (2001) manipulated context by using one indoor and one outdoor location, and found that context match produced no effect on priming in the word-stem completion test but reduced recall on the matched explicit test of word-stem cued recall. Parker, Gellatly, and Waterman (1999) manipulated context match in a similar way and found no effect on the perceptual implicit tests of word-fragment completion and anagram solution, coupled with an effect of context match on free recall. These studies imply that the effects of environmental context dissociate implicit and explicit memory. In contrast, studies examining conceptual implicit memory have reported effects of environmental context. The Parker et al. (1999) study, mentioned above, also assessed context effects with the conceptual implicit tests of category production and general knowledge questions, and found that conceptual priming on both tests was reduced with a change in context between study and test. In a similar vein, Smith, Heath, and Vela (1990) reported an effect of context match on priming in the homophone spelling test, a test often characterized as conceptual (e.g., McKone & French, 2001; see Roediger & McDermott, 1993, for discussion). These studies imply that insensitivity to context manipulations is not a general characteristic of implicit memory. Rather, Parker et al. argue, dissociations produced by context change may be better accounted for by the distinction between conceptual and perceptual processing rather than the implicit–explicit distinction (see McKone & French, 2001, for a similar suggestion). However, there are reasons to hesitate before accepting this conclusion (Parker, Dagnall, & Coyle, 2007). An important issue in implicit memory research is the potential for explicit contamination to undermine results from implicit memory experiments. When given an implicit memory test, participants may become aware of the relationship between the test and the study episode (and may engage in intentional retrieval). Furthermore, this possibility is more likely with conceptual than perceptual implicit tests (e.g., Butler and Berry, 2001, Mace, 2003 and Mulligan et al., 1999). If conditions or groups differ on explicit memory then explicit contamination is especially problematic as it might produce the appearance of a difference in implicit performance. For example, Mitchell and Bruss (2003), motivated by prior research implying reduced conceptual priming in old age, showed that when steps were taken to limit the likelihood of explicit contamination, older and younger adults produced equivalent priming on conceptual tests. Mitchell and Bruss concluded that the appearance of age differences in conceptual priming was due to explicit contamination in the nominally implicit test which differentially benefited the younger adults, the group with superior explicit memory ability (see Schmitter-Edgecombe & Woo, 2007, for a similar conclusion). In a similar vein, if explicit contamination occurred in a context study, the matching condition, expected to produce superior explicit memory, could produce greater priming, producing the appearance of an context-match effect on the implicit measure. A common technique for assessing explicit contamination is the post-test questionnaire (Bowers & Schacter, 1990). Following the implicit test, the participant is asked a series of increasingly specific questions to determine if the participant was aware of the connection between the study and test phases of the experiment (and also to determine if the participant engaged in intentional retrieval). These questionnaires have demonstrated reliability and validity (e.g., Barnhardt and Geraci, 2008 and Mulligan et al., 1999). Furthermore, the categorization of participants based on the questionnaire (e.g., as test-aware vs. test-unaware) is often related to the amount of priming and its pattern across other variables (e.g., Bowers and Schacter, 1990, Kinoshita, 2001, Mace, 2003, McKone and Slee, 1997 and Mulligan et al., 1999). The present study examined the effects of environmental context on conceptual implicit and explicit tests matched in terms of memory cues and response requirements. The implicit test is the category production task, the most commonly-used measure of conceptual implicit memory. Its explicit counterpart is category-cued recall, in which the same category cues are paired with explicit retrieval instructions. Different groups of participants were given the implicit or explicit test to eliminate the possibility that the effects of one test might influence performance on subsequent tests (cf. Parker et al., 1999 and Smith et al., 1990). Environmental context was manipulated across different experimental rooms designed to be quite distinct from one another. Participants received their test in either the same or different context than their study session. The implicit test was followed with a post-test questionnaire to assess the extent of explicit contamination. In particular, participants were classified as test-aware or test-unaware based on their answers. If changing context generally reduces conceptual priming (Parker et al., 1999), then an effect should be found regardless of test awareness. In contrast, if explicit contamination produced the appearance of disrupted conceptual priming in prior research, the test-unaware participants should exhibit no context effect whereas the test-aware should produce more priming in the same than different-context condition. Recently, Parker et al. (2007) investigated the issue using a different technique to address explicit contamination. These researchers varied context across two experimental rooms that differed in appearance, odor, and music cue. The participants given the implicit test were informed that some of their answers might be the same as items presented on the study list. Regardless, participants were asked to simply produce the first answers that came to mind without intentionally retrieving items from the earlier portion of the experiment. The researchers found under these circumstances that a change in context reduced explicit recall but not conceptual priming. The study by Parker et al. (2007) is an important step in evaluating the explicit-contamination hypothesis but there are a number of limitations in this and prior research that the present study addresses. An important issue is Parker et al.’s approach to limiting explicit contamination. Implicit memory is commonly defined as unconscious or unintentional manifestation of memory. Parker et al.’s technique modified the typical instructions given on an implicit test, explicitly informing the participants about the study–test relationship but instructing the participants to forego explicit retrieval. Ideally, this yields unintentional memory despite an awareness of the study–test relationship (see MacLeod, 2008, for a discussion of approaches to the problem of explicit contamination). The more common alternative, the post-test questionnaire as used in the present experiment, has several advantages in the present case. First, it yields a group of participants who are test-unaware, corresponding to the more stringent definition of implicit memory as unconscious memory and yielding an important converging technique for assessing explicit contamination. Second, the explicit-contamination hypothesis proposes that, under typical implicit testing conditions, participants producing explicit contamination will exhibit the context effect whereas those unaffected by explicit contamination will not. Parker et al.’s study allows us to evaluate only the second half of the prediction and then only for participants given non-standard implicit instructions (that is, participants made aware of the relationship between study and test). With the use of post-test questionnaires, and the allocation of participants into test-aware and test-unaware groups, both aspects of the hypothesis may be assessed. Third, Smith et al. (1990; see also Smith & Vela, 2001) raise a possibility that can only be assessed with test-unaware participants. Specifically, Smith et al. argue that explicit retrieval instructions can cause participants to mentally reinstate the encoding context, thus reducing (or potentially eliminating) the negative effect of being in a different context during retrieval. Smith et al. proposed that implicit tests may actually be more sensitive to environmental-context effects than explicit tests specifically because the participant is unaware that memory is being tested, and so will be unlikely to mentally reinstate the learning environment. In this case, the original context will be represented only for those who are still actually present in that context (the same context condition) but not for those who are tested in a new context. Under this hypothesis, test-unaware participants should be most likely to exhibit context effects, as these effects will not be countermanded by mental reinstatement strategies. In Parker et al.’s (2007) study, participants in the implicit condition were made aware of the study–test connection which may have induced some amount of context reinstatement. A more stringent test of the mental-reinstatement hypothesis (as it applies to implicit memory) requires implicit participants who lack such an awareness. Note that the mental-reinstatement and explicit-contamination hypotheses make opposing predictions regarding context effects and test awareness. Specifically, the mental-reinstatement hypothesis predicts that context effects are more likely with test-unaware than test-aware participants whereas the explicit-contamination hypothesis predicts the opposite. These contrasting predictions cannot be assessed with extant data (e.g., Parker et al., 2007). Consideration of research by Eich, 1995 and Eich, 2008 on mood and memory raises another issue relevant to the assessment of context effects in implicit memory. Eich, 1995 and Eich, 2008 has argued for a mood-mediation account, which proposes that apparent effects of context change in explicit memory may actually stem from mood-dependency rather than dependency on environmental context, per se. Eich, 1995 and Eich, 2008 demonstrated that changes in place can induce changes in mood. To the extent that one place (e.g., outdoors in a park-like setting) consistently induces a different mood than another place (e.g., an indoor room), the apparent finding of place-dependent memory may actually reflect mood-dependent memory. Eich (1995) demonstrated just such place effects on mood, rendering plausible the role of mood as a mediator of context effects in explicit memory. In a complementary finding, Eich (1995) showed that inducing different moods across study and test, while holding environmental context constant, also reduced explicit recall. Research on environmental context and implicit memory has often used manipulations that may inadvertently affect mood, such as varying indoor vs. outdoor locations (e.g., McKone and French, 2001 and Parker et al., 1999) or varying music and odor along with place (e.g., Parker et al., 2007). In both cases, prior research has shown that these changes (indoor vs. outdoor locations, different selections of music) have the power to induce different moods (Eich, 1995). This raises two related concerns. First, if explicit memory is more sensitive to mood changes than implicit memory, a dissociation in which context-change affects explicit recall but not priming may reflect mood-dependency differences rather than differences in sensitivity to environmental context. Second, to the extent that conceptual priming is more sensitive to mood changes than is perceptual priming (which appears to be the case, Eich, 2008), studies showing context effects on conceptual but not perceptual priming (e.g., Parker et al., 1999) may reflect the former’s greater mood-dependency rather than differences in context-dependency, per se. Although mood dependency may not provide a complete explanation of all the findings, it cannot be ruled out as contributing to at least some of the results in the literature on environmental context and implicit memory. In light of this issue, two design features were implemented in the present experiment to render a clearer assessment of context effects in implicit memory. First, attempts were made to manipulate environmental context without additionally manipulating mood (e.g., by not manipulated context between indoor and outdoor locations, or with music and odor cues). Second, measures of mood were taken during both encoding and retrieval to determine if this attempt was successful.