Capturing conceptual implicit memory: The time it takes to produce an association

Conceptual implicit memory is demonstrated when, in the absence of explicit retrieval, performance on a task requiring conceptual processing benefits more from prior conceptual encoding than from prior nonconceptual encoding. In the present study, we sought to provide an improved measure of conceptual implicit memory by minimizing contamination from explicit retrieval. On a modified word association test, participants free-associated to the actually studied items, with response time to produce any associate serving as the dependent measure. Experiment 1 varied whether words were read or generated at study and showed that generated words were associated to more quickly than were read words. Experiment 2 varied level of processing at study and showed that words processed semantically were associated to more quickly than were words processed nonsemantically. With modifications to ensure its implicit nature, a conceptual implicit test can be consistently affected by the same encoding manipulations as those that affect conceptual explicit memory tests.     

Electrophysiological correlates of exemplar-specific processes in implicit and explicit memory

The present ERP study investigated the retrieval of task-irrelevant exemplar-specific information under implicit and explicit memory conditions. Subjects completed either an indirect memory test (a natural/artificial judgment) or a direct recognition memory test. Both test groups were presented with new items, identical repetitions, and perceptually different but conceptually similar exemplars of previously seen study objects. Implicit and explicit memory retrieval elicited clearly dissociable ERP components that were differentially affected by exemplar changes from study to test. In the indirect test, identical repetitions, but not different exemplars, elicited a significant ERP repetition priming effect. In contrast, both types of repeated objects gave rise to a reliable old/new effect in the direct test. The results corroborate that implicit and explicit memory fall back on distinct cognitive representation and, more importantly, indicate that these representations differ in the type of stimulus information stored. Implicit retrieval entailed obligatory access to exemplar-specific perceptual information, despite its being task irrelevant. In contrast, explicit retrieval proved to be more flexible with conceptual and perceptual information accessed according to task demands.     

Correlational analyses of explicit and implicit memory performance

Sixty-four subjects were administered two tests of explicit memory (selective recall and recognition) and four tests of implicit memory (identification in a perceptual clarification procedure, word-fragment completion, tachistoscopic identification, and anagram solution). Each test drew on a different subset of a long list of previously displayed words. Although the four implicit memory tests showed sizable priming effects, correlational and factor analyses showed striking dissociations. On the one hand, performance on the perceptual clarification procedure and word-completion tests were related to one another, as well as to recall and recognition. On the other hand, performance on tachistoscopic identification and anagram solution were related to one another, but not to the measures for the other tasks. A framework is proposed to reconcile these new results with current knowledge on the explicit/implicit memory distinction, based in particular on studies of amnesic subjects. It is argued that a small number of tasks, especially tachistoscopic identification, may serve as relatively uncontaminated and ubiquitous indicators of implicit memory. However, explicit remembering could affect performance in so-called implicit memory tasks that allow for a strategy of controlled selection of candidate responses from accumulating cues, in experimental conditions that make the explicit remembering of relevant events possible.     

Recall and stem-completion priming have different electrophysiological correlates and are modified differentially by directed forgetting

The notion that different aspects of memory are assessed by explicit and implicit memory tests was supported by behavioral and electrophysiological results. In a study-test procedure, 24 subjects were instructed to remember some words and to forget other words. Free recall and cued recall were better for words associated with the remember instruction, whereas directed forgetting did not influence stem completion (an implicit memory test). Event-related brain potentials elicited during study differed as a function of subsequent memory performance for free recall and cued recall, but not for stem completion. These results implicate encoding differences in the distinction between the 2 types of memory test. Factors governing whether explicit retrieval affects performance on an implicit memory test, mechanisms that may underlie directed-forgetting effects, and the importance of electrophysiological correlates of memory are also discussed.     

Effects of timbre and tempo change on memory for music

We investigated the effects of different encoding tasks and of manipulations of two supposedly surface parameters of music on implicit and explicit memory for tunes. In two experiments, participants were first asked to either categorize instrument or judge familiarity of 40 unfamiliar short tunes. Subsequently, participants were asked to give explicit and implicit memory ratings for a list of 80 tunes, which included 40 previously heard. Half of the 40 previously heard tunes differed in timbre (Experiment 1) or tempo (Experiment 2) in comparison with the first exposure. A third experiment compared similarity ratings of the tunes that varied in timbre or tempo. Analysis of variance (ANOVA) results suggest first that the encoding task made no difference for either memory mode. Secondly, timbre and tempo change both impaired explicit memory, whereas tempo change additionally made implicit tune recognition worse. Results are discussed in the context of implicit memory for nonsemantic materials and the possible differences in timbre and tempo in musical representations.     

Implicit memory and depression: An analysis of perceptual and conceptual processes

A small number of studies have reported impaired explicit memory and intact implicit memory performance in participants classified as depressed. In the present study we examined this finding taking account of the distinction between datadriven and conceptually driven processing. The performance of participants diagnosed with depression was examined on implicit and explicit memory tasks which were designed to tap either predominantly perceptual or conceptual processes. Depressed participants demonstrated performance deficits on both the implicit and explicit conceptual tasks (category association and free recall, respectively) but showed intact performance in the implicit perceptual task (word-fragment completion). These results suggest that people with severe depression show deficits in conceptual processing and that this deficit occurs under both explicit and implicit task instructions.     

Implicit memory and depression: preserved conceptual priming in subclinical depression

Depression impairs explicit memory but research on implicit memory is equivocal. Initial studies indicated preserved implicit memory, implying a depressive deficit in intentional but not unintentional forms of memory. Subsequent research indicated that conceptual priming is reduced in depression, implying a deficit in conceptual memory processes be they implicit or explicit. However, the findings with conceptual priming may be compromised by explicit contamination. The present study compared subclinically depressed and non-depressed participants on matched conceptual tests of explicit memory (category-cued recall) and implicit memory (category production). The implicit test was followed by a post-test questionnaire used to categorise participants as test-aware or test-unaware. On the explicit test, the subclinically depressed participants recalled less than the non-depressed participants. The results on the implicit test depended on test-awareness. Among test-unaware participants, conceptual priming was equivalent across the two groups, whereas for the test-aware, non-depressed participants produced significantly more priming than the subclinically depressed. This indicates that when explicit contamination is controlled, depression does not impair conceptual priming. The depressive dissociation between implicit and explicit memory is better accounted for by the difference between intentional and unintentional forms of memory rather than by the difference between conceptual and perceptual memory processes.     

The role of chronic physical exercise and selective attention at encoding on implicit and explicit memory

Despite the evidence revealing benefits of chronic cardiovascular exercise on executive functions, little research has been conducted on long-term memory. We aimed to investigate the effect of physical exercise on implicit and explicit memory when attention was modulated at encoding in two groups of active and sedentary participants. With this purpose, attention was manipulated in a similar way in the implicit and explicit memory tasks by presenting picture outlines of two familiar objects, one in blue and the other in green, and participants were asked to pay attention only to one of them. Implicit memory was assessed through conceptual priming and explicit memory through a free recall task followed by recognition. The results did not reveal significant differences between groups in conceptual priming or free recall. However, in recognition, while both groups had similar discrimination for attended stimuli, active participants showed lower discrimination between unattended and new stimuli. These results suggested that exercise may have effects on specific cognitive processes, that is, that active participants may suppress non-relevant information better than sedentary participants, making the discrimination between unattended and new items more difficult.     

Input- and output-monitoring in implicit and explicit memory

Previous experiments have shown that the procedure of questioning subjects retrospectively about the input and output status of information (input and output monitoring) is a useful method for assessing the awareness states of subjects during implicit and explicit memory tasks. The main purpose of the present study was to investigate whether the previous findings could be extended to other implicit and explicit memory tasks. We were especially interested in whether differences in input- and output-monitoring performance can be observed when both the implicit and explicit memory tasks are conceptual ones. In a final test phase, the target items from the study phase and new distractor items were presented. In a recognition-like situation, subjects had to decide whether an item had been presented in the study phase (input status), as well as whether they had produced the item in the memory-test phase (output status). In all three experiments judgments about the input status - but only for those items that had been produced in the implicit or in the explicit memory test - were more precise after explicit than after implicit memory testings. This finding was not influenced by the distinction between perceptual and conceptual-memory tasks (Exp. 1), and was obtained under conditions in which the implicit and the explicit memory tasks were both conceptual and differed only in test instructions (Exps. 2 and 3). These results suggest that not only subjects performing a perceptual test of implicit memory, but also subjects in a conceptual implicit test were less aware of using information from a previous study episode than subjects who received memory instructions. It is concluded that requiring judgments about the input status of information is a good method for assessing subjects test awareness and is preferable to the use of a questionnaire (Exp. 3). In contrast, in all three experiments no differences were found with the output-monitoring measure between implicit and explicit test conditions.     

Environmental context effects in conceptual explicit and implicit memory

Previous research has found environmental context effects for both conceptual explicit and conceptual implicit memory (Parker, Gellatly, & Waterman, 1999). The research presented here challenges these findings on methodological grounds. Experiment 1 assessed the effects of context change on category-exemplar generation (conceptual implicit memory test) and category-cued recall (conceptual explicit memory test). Experiment 2 assessed the effects of context change on word association (conceptual implicit memory test) and word associate cued recall (conceptual explicit memory test). In both experiments, study-test changes in environmental context were found to influence performance only on tests of explicit memory. It is concluded that when retrieval cues across explicit and implicit tests are matched, and the probability of explicit contamination is reduced, then only conceptual explicit test performance is reduced by study-test changes in environmental context.     

Conceptual implicit memory and environmental context

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.     

Attention and implicit memory tests: The effects of varying attentional load on conceptual priming

The role of attention during encoding is important to many current accounts of the implicit/explicit memory distinction. Some accounts suggest that implicit memory tests reflect automatic (non-attentiondemanding) encoding processes, whereas other accounts (such as the transfer-appropriate-processing view) suggest that performance on conceptual implicit tests requires attention during encoding. The present study manipulates attention at encoding over several levels (by varying short-term memory load) and examines the effects on the category-exemplar production task (a conceptual implicit memory test) and its explicit counterpart, category-cued recall. Dividing attention decreased performance on both tests, but in different ways. Mild divisions of attention reduced recall but not conceptual priming. Strong divisions of attention reduced performance on both tests and, in addition, eliminated conceptual priming entirely. These findings resolve apparently conflicting results in the literature and help to clarify the relationship between attention and performance on implicit memory tests.     

Familiarity is related to conceptual implicit memory: An examination of individual differences

Explicit memory is thought to be distinct from implicit memory. However, growing evidence has indicated that explicit familiarity-based recognition memory judgments rely on the same process that supports conceptual implicit memory. We tested this hypothesis by examining individual differences using a paradigm wherein we measured both familiarity and conceptual implicit memory within the same participants. In Experiments 1a and 1b, we examined recognition memory confidence ROCs and remember/know responses, respectively, to estimate recollection and familiarity, and used a free association task to measure conceptual implicit memory. The results demonstrated that, across participants, familiarity, but not recollection, was significantly correlated with conceptual priming. In contrast, in Experiment 2, utilizing a similar paradigm, a comparison of recognition memory ROCs and explicit associative cued-recall performance indicated that cued recall was related to both recollection and familiarity. These results are consistent with models assuming that familiarity-based recognition and conceptual implicit memory rely on similar underlying processes.     

Event-related potentials and recognition memory

According to dual-process models, recognition memory is supported by distinct retrieval processes known as familiarity and recollection. Important evidence supporting the dual-process framework has come from studies using event-related brain potentials (ERPs). These studies have identified two topographically distinct ERP correlates of recognition memory--the "parietal" and "mid-frontal" old/new effects--that are dissociated by variables that selectively modulate recollection and familiarity, respectively. We evaluate the extent to which ERP data support dual-process models in light of the proposal that recollection is a continuous rather than a discrete memory process. We also examine the claim that the putative ERP index of familiarity is a reflection of implicit rather than explicit memory. We conclude that ERP findings continue to offer strong support for the dual-process perspective.     

内隐记忆和外显记忆的脑机制分离：面孔再认的ERP研究

该研究采用“学习-再认”实验范式探讨面孔领域的内隐记忆与外显记忆之间的关系。学习阶段采用选择性注意任务,让被试加工面孔上的字来控制对面孔的加工水平,再认阶段采用新旧判断,分析再认出旧面孔与新面孔(外显记忆),以及未再认旧面孔与新面孔(内隐记忆)的ERPs差异。结果表明,在单一的再认过程中,外显记忆和内隐记忆的脑机制产生了分离,外显记忆从刺激后400ms开始,主要表现在前额区和额区,而内隐记忆主要表现在刺激后300~500ms的中央区和顶区。该结果与以往在词领域研究中得到的结果极为类似,表明两种记忆类型在各个刺激领域之间存在着共同性     

Electrophysiological correlates of processes supporting memory for faces

The retrieval processes supporting recognition memory for faces were investigated using event-related potentials (ERPs). The focus for analyses was ERP old/new effects, which are the differences between neural activities associated with correct judgments to old (studied) and new (unstudied) test stimuli. In two experiments it was possible to identify three old/new effects that behaved as neural indices of the process of recollection. In both experiments there was one old/new effect that behaved as an index of the process of familiarity. These outcomes are relevant to the ongoing debate about the functional significance of ERP old/new effects and the implications that scalp-recorded electrophysiological data have for theories of the processes supporting long-term memory judgments.     

Stimulus exposure time and perceptual memory

The recent explosion of research on implicit memory has facilitated the examination of perceptual and conceptual processes in the encoding of information. Nevertheless, stimulus exposure time—the amount of time that a stimulus is physically available to a perceiver’s scrutiny—has received little attention. In the present paper, we examine the effect of stimulus exposure time on three implicit memory measures (word-fragment completion, perceptual identification, and general knowledge) and two explicit memory measures (graphemic cued recall and semantic cued recall). In Experiment 1, we demonstrated that increases in exposure time lead to increases in implicit perceptual memory, but not to implicit conceptual memory, when the encoding task focuses on perceptual features of the stimulus. We replicated this effect in Experiment 2 and demonstrated that increases in exposure time lead to increases in perceptualand conceptual memory when the measures are explicit. Thus, the current experiments demonstrate that manipulations of exposure time lead to dissociations in implicit, but not explicit, memory.     

Implicit and explicit tests of odor memory reveal different outcomes following interference

Experiencing two odors as a mixture can later increase their perceived similarity when presented separately. Such an increase in similarity can be used as an implicit measure of how well participants remember the mixture. Three experiments tested the resistance to interference of this effect by first giving participants exposure to two 2-odor mixtures and then presenting each odor from one mixture (interfered pair) separately many times. After the latter interference phase, participants rated the similarity of the two odors in each pair. The experiments varied in terms of the number of initial exposures to the mixtures, the number of odor presentations in the interference phase, and the control conditions employed. No difference in similarity ratings for the interfered and non-interfered pair was found in any experiment. In contrast to the lack of interference with this implicit measure, an explicit measure of memory based on participants’ ratings of odor frequency revealed that they could recall to some degree that the interfered odors had been presented alone in the second phase. These results suggest that implicit memory for odor mixtures is highly resistant to interference and is consistent with a configural encoding account of this effect.     

Conceptual implicit memory in subclinical depression

Depression adversely affects explicit memory when implicit memory remains intact unless implicit retrieval requires conceptual processes. The impairment of conceptual implicit memory could be the consequence of the completion of implicit memory tests being contaminated by a voluntary retrieval strategy, hence similar results to those in explicit tests are observed. In this study we adopted a method sensitive to the presence of contamination. Depth-of-study-processing effects were observed for the controls completing the explicit version of a word-association task but were absent for the controls completing the implicit version when compound associates were retrieved. This dissociation indicated the adoption of the designated retrieval strategy in each test with the conceptual implicit memory test being uncontaminated. Subclinically depressed participants showed impairment in the explicit version, while for those completing the implicit version there was evidence that they used a voluntary retrieval strategy. The theoretical implications of the findings are discussed.     

Adult age differences in implicit and explicit memory: time course and encoding effects

Young and older adults were tested at three delays on word-stem completion or cued recall following semantic or structural word judgments. Identical three-letter stems were present at retrieval for both implicit (completion) and explicit (cued recall) tasks; only the intention to recall list words differed. The young adults outperformed the older adults on both implicit and explicit tasks at all test delays. Under some conditions, the older but not the young adults performed more poorly on cued recall than on stem completion, suggesting a possible failure to use implicitly available information to support explicit remembering. These results suggest that some forms of implicit memory decline with normal aging.