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.     

Dissociation of implicit and explicit memory tests: Effect of age and divided attention on category exemplar generation and cued recall

In this article, we report an experiment that provides further evidence concerning the differences between explicit and implicit measures of memory. The effects of age and divided attention on the implicit conceptual test of category exemplar generation (CEG) were compared with their effects on the explicit test of cued recall, where the category names served as cues in both tasks. Four age groups (20–35, 40–55, 60–75, and 76–90) were compared. Half of the subjects were also required to carry out a secondary letter-detection task during the learning phase. Cued recall performance was significantly impaired by increased age and imposition of the secondary task. In contrast, the CEG task was unaffected by these two factors. These results suggest that implicit conceptual tasks and explicit memory tasks are mediated by different processes. This conclusion opposes those of previous studies that showed that experimental manipulations (level of processing, generation, organization) influenced these two kinds of memory tests in a similar way.     

The effects of levels-of-processing and organization on conceptual implicit memory in the category exemplar production test

The distinction between item-specific and relational information (Hunt & Einstein, 1981) may be relevant to accounts of conceptual priming in the category exemplar production task. In three experiments, the implications of this hypothesis were tested by examining the effects of organization and levels-of-processing (LOP) on this implicit test. Consistent with the hypothesis, the effects of LOP were greater when study lists were organized by category than when they were presented randomly. Furthermore, when subjects claiming test awareness or intentional retrieval were excluded from the analysis, the LOP effect was reduced (and, in fact, eliminated) in the random list condition but remained robust in the categorized condition. Finally, the experimental design of the LOP manipulation (i.e., mixed-list within, blocked-list within, or between subjects) did not moderate the effects of LOP on this priming task.     

The effect of midazolam on implicit memory tests

Substantial empirical evidence exists suggesting that there are distinct forms of explicit and implicit memory. However, methodological problems have hampered attempts to identify the nature of the information processing underlying these forms of memory. These problems include the contamination of performance on implicit memory tests by explicit memory processes, as well as a host of difficulties inherent in correlational approaches that involve amnesiac subjects. In this paper we attempt to explore whether midazolam, a benzodiazepine used in surgical anesthesia, might be useful for studying implicit memory. Specifically, we attempt to determine whether midazolam produces selective effects on explicit, as opposed to implicit, memory. We focus on midazolam because of prior studies demonstrating that benzodiazepines do not affect implicit memory and because its rapid pharmacokinetics ensure that sedative effects are minimized when testing occurs at relatively short retention intervals. The results of an experiment using free recall, fragment completion and perceptual identification tests suggest that midazolam diminishes memory in implicit and explicit memory tests, although the diminution is proportionally larger in explicit memory. These results constrain the inferences that may be drawn when midazolam is used to explore implicit memory.     

Collaboration in implicit memory: evidence from word-fragment completion and category exemplar generation

Psychological Research - Recent studies have begun to investigate the effects of collaboration on explicit tests such as free recall, cued recall, and recognition. In contrast, little is known...     

Age differences in implicit memory: fragmented object identification and category exemplar generation.

In a cross-sectional study of 164 participants aged 21 to 91, the authors examined age differences on two implicit tests, fragmented object identification (FOI) and category exemplar generation (CEG), and on tests of explicit memory, attention, and verbal fluency. FOI results revealed impaired perceptual skill learning in those over 60 and a decrease in perceptual priming across young, middle-aged, and older groups. CEG priming was impaired in those over 80. Regression analysis revealed explicit contamination of priming on both the FOI and CEG tests. Across the three implicit measures, age accounted for 4 to 13% of the variance when explicit memory was controlled. Semantic fluency predicted CEG priming, suggesting possible frontal lobe involvement on the test. Altogether, results indicate that age has a small but reliable influence on implicit memory.     

Working memory capacity and the spacing effect in cued recall

Spacing repetitions typically improves memory (the spacing effect). In three cued recall experiments, we explored the relationship between working memory capacity and the spacing effect. People with higher working memory capacity are more accurate on memory tasks that require retrieval relative to people with lower working memory capacity. The experiments used different retention intervals and lags between repetitions, but were otherwise similar. Working memory capacity and spacing of repetitions both improved memory in most of conditions, but they did not interact, suggesting additive effects. The results are consistent with the ACT-R model’s predictions, and with a study-phase recognition process underpinning the spacing effect in cued recall.     

Effects of implicit memory on explicit recall: Set size and word-frequency effects

PIER was designed to explain findings related to tasks involving an encoding phase and a testing phase in which retrieval cues prime the recovery of what has been encoded. The model assumes that retrieval cues initiate the sampling of associated memories linked to the encoded information and that sampled memories are subjected to a recognition check to determine whether they meet criteria specified by the purpose of the retrieval. The model explains how the number of implicitly activated associates linked to a studied word affects its later recovery and predicts that words infrequently experienced will be recovered with greater likelihood than words frequently experienced. This prediction was tested and confirmed in two experiments in which the associative set size and the frequency of the studied words were manipulated. Implications for the study of implicit memory are considered.     

Development of implicit and explicit category learning

We present two studies that examined developmental differences in the implicit and explicit acquisition of category knowledge. College-attending adults consistently outperformed school-age children on two separate information-integration paradigms due to children’s more frequent use of an explicit rule-based strategy. Accuracy rates were also higher for adults on a unidimensional rule-based task due to children’s more frequent use of the irrelevant dimension to guide their behavior. Results across these two studies suggest that the ability to learn categorization structures may be dependent on a child’s ability to inhibit output from the explicit system.     

Prior knowledge and cued recall: category size and dominance

Previous work indicates that our ability to recall a recently experienced word is reduced by the number of related concepts that it activates in permanent memory. The purpose of this research was to evaluate the possibility that dominance of primary associates, and not category size, is responsible for this observation. The results of three experiments involving manipulations of target and cue set size, as well as meaning and rhyme, indicate that category size effects are independent of dominance. In fact, the advantage of smaller categories and fewer activated items is substantially reduced for words having very dominant primary associates. The findings are discussed in relation to the Sensory-Semantic model.     

The role of enactment in implicit and explicit memory

Enactment during the encoding of simple imperatives has been found to improve substantially performance on conceptually driven explicit-memory tests. In two experiments the effect of this manipulation on a conceptually driven implicit test (category association) was studied. A conceptually driven explicit test (free recall) was also included. In Experiment one three different study conditions (enactment with real objects, reading, and generation) were considered. In Experiment two there were two study conditions (enactment with imaginary objects and reading). Compared to reading, generation was found to improve the performance on both free recall and category association, whereas enactment affected free recall only. In a final experiment subjects imagined that they performed the tasks, and this manipulation was found to improve the memory performance on both tests. Taken together, this pattern of results is interpreted as suggesting that free recall and category association have a process in common that is sensitive to semantic processing at study (promoted by generation and imagery, but not by enactment), and that free recall involves a retrieval process in addition that is facilitated by a rich encoding environment (provided by enactment).     

Retrieval processes in perceptual recognition and cued recall: The influence of category size

The purpose of these experiments was to determine whether nonsemantic category size and other variables would influence perceptual recognition as they influence cued recall. Procedures developed by Jacoby and his associates were replicated with words belonging to either small or large nonsemantic categories and with recognition tested under bright-target/patterned-mask conditions. The results indicated that words belonging to larger nonsemantic sets were more difficult to identify. This finding and the results of other manipulations are discussed in relation to the interactive activation model and to the proposal that perceptual recognition performance is dependent on a retrieval process similar to that involved in recall prompted by nonsemantic cues.     

The effect of articulatory suppression on implicit and explicit false memory in the DRM paradigm

Several studies have shown that reliable implicit false memory can be obtained in the DRM paradigm. There has been considerable debate, however, about whether or not conscious activation of critical lures during study is a necessary condition for this. Recent findings have revealed that articulatory suppression prevents subsequent false priming in an anagram task (Lovden & Johansson, 2003). The present experiment sought to replicate and extend these findings to an implicit word stem completion task, and to additionally investigate the effect of articulatory suppression on explicit false memory. Results showed an inhibitory effect of articulatory suppression on veridical memory, as well as on implicit false memory, whereas the level of explicit false memory was heightened. This suggests that articulatory suppression did not merely eliminate conscious lure activation, but had a more general capacity-delimiting effect. The drop in veridical memory can be attributed to diminished encoding of item-specific information. Superficial encoding also limited the spreading of semantic activation during study, which inhibited later false priming. In addition, the lack of item-specific and phenomenological details caused impaired source monitoring at test, resulting in heightened explicit false memory.     

Source memory in the absence of successful cued recall

Five experiments were conducted to address the question of whether source information could be accessed in the absence of being able to recall an item. The authors used a paired-associate learning paradigm in which cue-target word pairs were studied, and target recall was requested in the presence of the cue. When target recall failed, participants were asked to make a source judgment of whether a man or woman spoke the unrecalled item. In 3 of the 5 experiments, source accuracy was at or very close to chance. By contrast, if cue-target pairs were studied multiple times or participants knew in advance of learning that a predictive judgment would be required, then predictive source accuracy was well above chance. These data are suggestive that context information may not play a very large role in metacognitive judgments such as feeling-of-knowing ratings or putting one into a tip-of-the-tongue state without strong and specific encoding procedures. These same results also highlight the important role that item memory plays in retrieving information about the context in which an item was experienced.     

The role of colour in implicit and explicit memory performance

We present two experiments that examine the effects of colour transformation between study and test (from black and white to colour and vice versa, or from incorrectly coloured to correctly coloured and vice versa) on implicit and explicit measures of memory for diagnostically coloured natural objects (e.g., yellow banana). For naming and coloured-object decision (i.e., deciding whether an object is correctly coloured), there were shorter response times to correctly coloured-objects than to black-and-white and incorrectly coloured-objects. Repetition priming was equivalent for the different stimulus types. Colour transformation did not influence priming of picture naming, but for coloured-object decision priming was evident only for objects remaining the same from study to test. This was the case for both naming and coloured-object decision as study tasks. When participants were asked to consciously recognize objects that they had named or made coloured-object decisions to previously, whilst ignoring their colour, colour transformation reduced recognition efficiency. We discuss these results in terms of the flexibility of object representations that mediate priming and recognition.     

Effect of divided attention on explicit and implicit aspects of recall

If subjects have to form word images before spelling a word from the image, results of a repetition of the spelling test reveal a reliable priming effect: Old words can be spelled faster than comparable control words, reflecting a form of implicit memory. We investigated whether this kind of repetition priming remains stable under conditions of divided attention in the study phase. The subjects had to spell meaningful words, meaningless non-words, and non-words that were meaningful with a backward spelling direction (troper, for example). In the testing stage, recognition judgments as a form of explicit memory were required, too. Divided attention in the study phase had a negative effect on explicit memory, as revealed by performance on the recognition task, but had little effect on implicit memory, as revealed by performance on the repetition of the spelling test. A further dissociation between implicit and explicit memory showed up as meaningful words were recognized much better than non-words, whereas implicit memory was uninfluenced by the meaningfulness variable. The disadvantage of backward spellings was not reduced with non-words (like troper) spelled backwards. Finally, we analyzed the relations between spelling times and recognition judgments and found a pattern of dependency for non-words only. Generally, the results are discussed within processing-oriented approaches to implicit memory with a special emphasis on controversial findings concerning the role of attention in different expressions of memory.     

Context-dependence of implicit and explicit memory characteristics

The present experiments explore whether repetition priming in a word-stem completion task is context-dependent. In the first experiment, the environmental context was changed or remained constant at the testing stage. Implicit memory performance did not reveal any effects of environmental context. When tested by free recall, however, the same subjects showed an environmental congruency effect. On the other hand, effects of a change in presentation modality were restricted to implicit memory measures. In the second experiment, self-awareness was manipulated to create congruent or incongruent internal contexts at the testing stage. Performance on the word-stem completion task was seen to be influenced by internal contextual information. This pattern of results corroborates a processing account of implicit memory phenomena. Implicit and explicit expressions of memory utilize episodic information, but in a different way.