The effect of midazolam on implicit and explicit memory in category exemplar production and category cued recall

Transfer-appropriate processing theory (Roediger, Weldon, & Challis, 1989) proposes that dissociations between performance on explicit and implicit memory tests arise because these tests often rely on different types of information processing (e.g., perceptual processing vs conceptual processing). This perspective predicts that implicit and explicit memory tasks that rely primarily on conceptual processing should show comparable results, not dissociations. Numerous studies have demonstrated such similarities. It is, however, possible that these results arise from explicit memory contamination of performance on implicit memory tasks. To address this issue, an experiment was conducted in which participants were administered the sedative midazolam prior to study. Midazolam is known to create a temporary, but dense, period of anterograde amnesia. The effects of blocking stimulus materials by semantic category at study and generation at study were investigated on category exemplar production and category-cued recall. The results of this study demonstrated a dissociation of the effects of midazolam on category exemplar production and category-cued recall. Specifically, midazolam reduced the effect of blocking stimulus materials in category-cued recall, but not in category exemplar production. The differential effect of midazolam on explicit and implicit memory is at odds with transfer-appropriate processing theory and suggests that theories of memory must distinguish the roles of different types of conceptual processing on implicit and explicit memory tests.     

The effect of midazolam on implicit and explicit memory in category exemplar production and category cued recall

Transfer‐appropriate processing theory (Roediger, Weldon, & Challis, 1989) proposes that dissociations between performance on explicit and implicit memory tests arise because these tests often rely on different types of information processing (e.g., perceptual processing vs conceptual processing). This perspective predicts that implicit and explicit memory tasks that rely primarily on conceptual processing should show comparable results, not dissociations. Numerous studies have demonstrated such similarities. It is, however, possible that these results arise from explicit memory contamination of performance on implicit memory tasks. To address this issue, an experiment was conducted in which participants were administered the sedative midazolam prior to study. Midazolam is known to create a temporary, but dense, period of anterograde amnesia. The effects of blocking stimulus materials by semantic category at study and generation at study were investigated on category exemplar production and category‐cued recall. The results of this study demonstrated a dissociation of the effects of midazolam on category exemplar production and category‐cued recall. Specifically, midazolam reduced the effect of blocking stimulus materials in category‐cued recall, but not in category exemplar production. The differential effect of midazolam on explicit and implicit memory is at odds with transfer‐appropriate processing theory and suggests that theories of memory must distinguish the roles of different types of conceptual processing on implicit and explicit memory tests.     

Direct comparison of auditory implicit memory tests

In this experiment, we examined the degree to which four implicit tests and two explicit tests, all involving auditory presentation, were sensitive to the perceptual characteristics of the stimuli presented during study. Presenting stimuli visually decreased priming in all the implicit memory tests, relative to auditory presentation. However, changing voice between study and test decreased priming only in the implicit memory tests requiring identification of words degraded by noise or by low-pass filtering, but not in those tests requiring generation from word portions (stems and fragments). Modality effects without voice effects were observed in cued recall, but the opposite pattern of results (voice effects without modality effects) was obtained in recognition. The primary new finding is the demonstration that auditory memory tests, both explicit and implicit, differ in their sensitivity to the perceptual information encoded during study.     

Elaboration effects in implicit and explicit memory tests

Dissociation effects in explicit and implicit tests of memory were examined in two experiments. In Experiment 1 serial-position effects were studied. Results showed that the standard primacy effect found in free recall is absent in an implicit word-stem completion test. In Experiment 2 a dissociation was found for the effect of high- and low-frequency words in free recall and word-stem completion tests. Both findings are explained in terms of a modified and extended version of the activation-elaboration learning account, which was inspired by attempts to simulate dissociation effects in connectionist models. The relationship between this account and two other leading accounts of dissociation effects in implicit and explicit memory is discussed, and a model to integrate aspects of all three accounts is suggested.     

Effects of color on perceptual and conceptual tests of implicit memory

Two experiments are reported that explore why recent investigations of implicit memory failed to find any effects of color information on test performance. In the first experiment, participants studied colored pictures as well as words printed in colored ink without any memory instructions. During the test phase, a verbal and a pictorial version of a color-choice task (a conceptual priming test) were compared to two perceptual tests (word-stem completion and picture-fragment identification). Similar and significant amounts of priming to color occurred in both color-choice tasks. The perceptual tests were found to be sensitive to changes in the stimulus-presentation mode from study to test, but stimuli remaining the same color and those changed to black-and-white did not differ in the priming scores. In the second experiment, a mild division of attention was introduced in the study phase. Once again, priming to color was observed only in the verbal version of a color-choice test and not in the word-stem completion test. Dividing attention did not decrease performance on both implicit tests, whereas an explicit test of color recall for studied pictures suffered from dividing attention at encoding. It is concluded that a perceptual attribute such as color may be represented and coded by conceptual processing. Furthermore, automatic (or not attention-demanding) encoding processes may suffice for later conceptual tests of implicit memory. Previous failures to find any effects of color information on implicit performance are attributed to the use of perceptual priming tests. Received: 30 June 1997 / Accepted: 20 April 1998     

Retrieval-induced forgetting in implicit memory tests: The role of test awareness

Retrieval practice with particular items in memory may result in decreased recall of different, semantically related, items. This retrieval-induced forgetting effect has been demonstrated in studies using explicit memory tests. Anderson and Spellman (1995) have attributed retrieval-induced forgetting to inhibitory mechanisms. This hypothesis predicts similar effects in implicit memory tasks. In our first experiment, using Anderson and Spellman’s original paradigm, retrieval-induced forgetting was found using an explicit memory test with independent extralist retrieval cues. In our second experiment, using the same materials, retrieval-induced forgetting was also found using an implicit memory test with independent extralist retrieval cues, but only for participants who were aware of the relationship between the study and practice phase on the one hand, and the test phase of the experiment on the other. Thus, test awareness seems to mediate retrieval-induced forgetting in implicit memory tasks.     

High-priority event instructions affect implicit and explicit memory tests

Previous work has shown that instructing subjects to give special priority to one target event in a list enhances recall for that event, but impairs recall for the events immediately preceding it (Tulving, 1969). We examined the benefit of high-priority instructions, and the retrograde amnesia for previous items, in three experiments that included two explicit tests of memory (free recall and cued recall with word-stem cues) and an implicit test (word-stem completion). Experiments 1 and 2 revealed a beneficial effect of high-priority instructions on memory for the target events in both free recall and primed word-stem completion. Retrograde amnesia for previous events was either absent (Experiment 1) or modest (Experiment 2) in free recall; however, no evidence for amnesia occurred on the implicit test. In Experiment 3, we asked if the benefit of high-priority instructions on the implicit test was due to contamination from intentional recollection, by employing the logic of the retrieval-intentionality criterion via a levels-of-processing manipulation. The results showed a beneficial effect of high-priority instructions on free recall, word-stem cued recall, and word-stem completion. Level of processing affected the two explicit tests, but not the implicit test, indicating that it induced incidental retrieval. We conclude that the benefit of high-priority instructions occurred on all three tests used in these experiments. In contrast, the phenomenon of retrograde amnesia occurred in free recall, but not in primed word-stem completion.     

Conscious and unconscious forms of memory in different implicit tests

This study investigated how shallow processing (complexity rating), deep processing (pleasantness rating), and semantic generation (translating from English) of Chinese words affects conscious memory (CM) and unconscious memory (UM) of the words with three implicit tests: word association, word identification, and word-stem completion. A metacognition-based dissociation procedure was used to estimate the two forms of memory for each test. Except for the shallow condition preceding the word-association test, all three study conditions produced a positive effect on the estimate of CM. The estimate of UM did not benefit from any of the study conditions in the word-association test, it benefited from the shallow and deep conditions but did not benefit from the generation condition in the stem-completion test, and it benefited from the shallow condition but did not benefit from the deep and generation conditions in the word-identification test. Implications of these results for CM and UM operations are discussed.     

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.     

When memory fails, intuition reigns: midazolam enhances implicit inference in humans

People often make logically sound decisions using explicit reasoning strategies, but sometimes it pays to rely on more implicit "gut-level" intuition. The transitive inference paradigm has been widely used as a test of explicit logical reasoning in animals and humans, but it can also be solved in a more implicit manner. Some researchers have argued that the hippocampus supports relational memories required for making logical inferences. Here we show that the benzodiazepene midazolam, which inactivates the hippocampus, causes profound explicit memory deficits in healthy participants, but enhances their ability in making implicit transitive inferences. These results are consistent with neurocomputational models of the basal ganglia-dopamine system that learn to make decisions through positive and negative reinforcement. We suggest that disengaging the hippocampal explicit memory system can be advantageous for this more implicit form of learning.     

Eliciting false memories on implicit and explicit memory tests after incidental learning

Abstract: In a false memory experiment, lists of semantic associates (e.g., newspaper, letter, book, etc.) were presented to three groups of participants to induce false memories for critical nonpresented (CN) words (e.g., read) in an incidental learning task. The control group simply estimated the frequency rate in everyday Japanese discourse of each word on a list. The imagery instruction group received an additional instruction to imagine a thematically related converging word from the target words on a list. Participants in the imagery plus writing group received the same instructions as those in the imagery instruction group, but were also required to write down the word they imagined for each list. The results from the implicit and explicit memory tests given after the incidental learning episode showed that the level of priming for CN words was equivalent to that for actually presented target words for all three groups on the implicit test, whereas explicit memory results showed that participants explicitly recognized more target words than CN words. The implications for implicit associative response and fuzzy‐trace theories of false memory, as well as implicit priming, are discussed.     

概念内隐记忆中的注意促进效应

Swallow和Jiang (2010)最早发现, 编码时的目标探测会促进同时呈现的背景信息在随后记忆测验中的表现, 并将这一现象称为注意促进效应(Attentional Boost Effect, ABE)。随后研究发现这一现象并不会出现在概念内隐测验中, 由此提出目标探测主要促进的是背景信息的知觉加工, 而非语义加工。本研究通过3个实验, 操纵了对背景信息的编码加工类型(知觉加工或概念加工)。结果发现, 当与目标探测同时进行的是对背景信息的概念加工任务, 则ABE会出现在随后的概念内隐测验中。反之, 当对背景信息进行的是知觉加工任务时, 则ABE会出现在随后的知觉内隐测验而不是概念内隐测验中。这些结果表明, 目标探测既可能促进背景信息的知觉加工, 也可能促进背景信息的语义加工, 但只有在目标探测下背景信息的编码加工与随后内隐测验中所依赖的提取加工具有一致性, 才会产生ABE。     

Priming on perceptual implicit memory tests can be achieved through presentation of associates

Roediger and McDermott (1995) presented lists of semantic associates (e.g.,door, glass, pane, shade, ledge) to induce false recall of related, nonpresented words (e.g.,window). This study procedure was used in an attempt to determine whether associative activation of target words would be sufficient to produce priming on perceptual implicit memory tests. Priming of the nonpresented items occurred on both word stem completion and word fragment completion, but the level of priming was generally lower than for items that had been studied. Priming of the related, nonpresented words occurred on a conceptual implicit test of word association; further, the level of priming was equivalent to that of presented words.     

The effects of attention on perceptual implicit memory

Reports on the effects of dividing attention at study on subsequent perceptual priming suggest that perceptual priming is generally unaffected by attentional manipulations as long as word identity is processed. We tested this hypothesis in three experiments by using the implicit word fragment completion and word stem completion tasks. Division of attention was instantiated with the Stroop task in order to ensure the processing of word identity even when the participant's attention was directed to a stimulus attribute other than the word itself. Under these conditions, we found that even though perceptual priming was significant, it was significantly reduced in magnitude. A stem cued recall test in Experiment 2 confirmed a more deleterious effect of divided attention on explicit memory. Taken together, our findings delineate the relative contributions of perceptual analysis and attentional processes in mediating perceptual priming on two ubiquitously used tasks of word fragment completion and word stem completion.     

The effects of generation on auditory implicit memory

The generation manipulation produces the classic functional dissociation between explicit and implicit memory. This dissociation has been explained by the transfer-appropriate processing (TAP) framework, which emphasizes the overlap in cognitive processes operative at encoding and at retrieval. However, the vast majority of implicit memory studies have been conducted in the visual modality; in the auditory modality, the effects of generation have never been investigated. In four experiments, we examined the effects of generating from semantic and nonsemantic cues on auditory implicit tests. Generating from antonyms produced a reversed generation effect on priming in auditory perceptual identification and word stem completion, while producing the traditional positive effect on explicit recognition. Generating from definitions, as well as from rhymes, also produced a reversed generation effect on auditory priming. These results are critical for more fully characterizing auditory priming and are consistent with an extended TAP analysis.     

A comparison of implicit memory tests in schizophrenic patients and normal controls

The objective of the current study was to compare the performance of schizophrenic patients and normal controls on implicit memory tests. Two neuropsychological tasks were administered to 29 patients and normal participant samples. The implicit tests were: Word fragment completion and Word production from semantic categories. The priming score was the variable of interest. Priming effects are obtained in normal subjects and schizophrenia patients, regardless of the implicit test used. However, a dissociation in priming between normal and patient groups was observed, depending on the test used. For word fragment test, priming was identical between the two groups. However, for word production, priming obtained in schizophrenics was lower than priming in normal controls. Results confirm a dissociation effect in implicit memory tests. These results could be explained in the context of the Roediger and Blaxton (1987) distinction between data-driven and conceptually-driven processing. This evidence suggests that a complete neuropsychological assessment of memory in schizophrenia should include different kinds of implicit memory tests (procedural, perceptual, and conceptual tasks).     

A dissociation in the effects of study modality on tests of implicit and explicit memory

Three experiments investigated variables affecting explicit and implicit memory for study modality. Explicit memory for modality was compared with implicit memory for modality (modalityspecific priming) following the study manipulation of modality and level of processing. Explicit recall of modality showed the same pattern of dissociations that has been observed between other measures of episodic memory and priming measures of memory. Manipulations of meaning at study that facilitated recognition and fragment-cued recall increased the accuracy of modality recall, but had no effect on primed fragment-completion performance. In contrast, changing modality between study and test affected fragment-cued performance, but had no effect on recognition or on modality recall. Successive tests of fragment-cued recall and modality recall were found to be highly dependent, whereas successive tests of fragment-completion and modality recall were essentially independent. The results are interpreted as evidence that (1) factors relevant to episodic memory of modality are unrelated to factors that produce modality-specific priming and (2) episodic memory for incidental attributes of an episode, such as modality of study, interacts with and is dependent upon memory for the episode as a whole.     

Further evidence for systematic reliability differences between explicit and implicit memory tests

Meier and Perrig (2000) as well as Buchner and Wippich (2000) have shown that simple dissociations between explicit and implicit memory measures need not reflect functional dissociations of hypothetical underlying memory systems. Instead, such dissociations may also result from the fact that some widely used implicit memory measures are simply less reliable than the explicit measures with which they have been compared. We extend this argument in two ways. First, we show that illusion-based memory measures such as the priming measures derived from fame andpreference judgement tasks are also subject to the reliability problem. Second, we show that yes-no and two-alternative forced-choice paradigms should, and in fact do, yield virtually identical results as far as the reliability of the memory tests is concerned.     

The impact of retrieval suppression on conceptual implicit memory

ABSTRACT

When people suppress retrieval of episodic memories, it can induce forgetting on later direct tests of memory for those events. Recent reports indicate that suppressing retrieval affects less conscious, unintentional retrieval of unwanted memories as well, at least on perceptually-oriented indirect tests. In the current study we examined how suppressing retrieval affects conceptual implicit memory for the suppressed content, using a category verification task. Participants studied cue-target words pairs in which the targets were exemplars of 22 semantic categories, such as vegetables or occupations. They then repeatedly retrieved or suppressed the targets in response to the cues for some of those pairs. Afterwards, they were exposed to the targets intermixed with novel items, one at a time, and asked to verify the membership of each of the words in a semantic category, as quickly as possible. Judgment response times to studied words were faster than to unstudied exemplars, reflecting repetition priming, as has been previously observed. Strikingly, the beneficial effects of prior exposure on response time were eliminated for targets that had been suppressed. Follow-up explicit memory tests also demonstrated that retrieval suppression continued to disrupt episodic recall for the items that had been just been re-exposed on the category verification test. These findings support the contention that the effects of retrieval suppression are not limited to episodic memory, but also affect indirect expressions of those memories on conceptually oriented tests, raising the possibility that underlying semantic representations of suppressed content are affected.     

The influence of implicit motives on memory processes.

Four studies tested the hypothesis that agentic and communal motives act as a channel for new knowledge and are linked to specific ways of organizing information that facilitate its accessibility. In Study 1, agentic and communal participants read an agentic or a communal vignette consisting of differentiated and integrated statements, performed a distraction task, then completed written recall and recognition tasks. Agentics recalled and recognized more differentiation in the agentic story; communals recalled and recognized more integration in the communal story. A computerized replication with randomized recognition items (Study 2) found the same pattern of recognition results. Studies 3 and 4 used implicit motive primes and found similar results in both written and computerized recognition tasks. These ways of organizing information have powerful implications for the encoding of autobiographical knowledge and its long-term organization.