A dissociation between perceptual explicit and implicit memory processes

Patient M.S., who underwent right-occipital lobe resection to treat intractable epilepsy, has intact recall and recognition memory for words, but impaired repetition priming in word identification and visual stem-completion tasks. This mirror dissociation to amnesia suggests that explicit recognition and visuoperceptual repetition priming are mediated by distinct neural systems. In prior studies, however, M.S.' recognition memory was tested only with tasks that drew upon his intact verbal knowledge. The present study examined M.S.' recognition memory for nonverbal perceptual information, namely, the modality and font of word presentation and line patterns. M.S.' recognition memory was intact, providing further evidence that perceptual explicit and implicit memory processes are subserved by functionally and neurally independent memory systems.     

Dissociations between familiarity processes in explicit recognition and implicit perceptual memory.

Dual-process theories of recognition posit that a perceptual familiarity process contributes to both explicit recognition and implicit perceptual memory. This putative single familiarity process has been indexed by inclusion–exclusion, remember–know, and repetition priming measures. The present studies examined whether these measures identify a common familiarity process. Familiarity-based explicit recognition (as indexed by the inclusion–exclusion and the independence remember–know procedures) increased with conceptual processing. In contrast, implicit word-identification priming and familiarity-based word-stem completion (as indexed by inclusion–exclusion) increased with study–test perceptual similarity. These dissociations indicate that familiarity-based explicit recognition may be more sensitive to conceptual than to perceptual processing and is functionally distinct from the perceptual familiarity process mediating implicit perceptual memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental differences in implicit and explicit memory performance

Performance of preschool, elementary school, and college students was compared on a series of perceptual and conceptual implicit and explicit memory tasks that followed perceptual or conceptual processing during study. As expected, performance on the conceptual explicit memory task improved across age groups. In contrast, performance on the perceptual explicit memory task as well as that on both types of implicit memory tasks showed no developmental change. Also, perceptual processing during study led to better memory performance than conceptual processing for both the perceptual implicit and perceptual explicit tasks and conceptual processing during study led to better memory performance on the conceptual explicit memory task. Performance on the conceptual implicit memory task, in contrast, was affected equally by both types of study processing. The results are discussed in terms of transfer-appropriate processing (Roediger & Blaxton, 1987b) and unitization and grouping processes (Graf & Schacter, 1989).     

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).     

Transfer-appropriate processing for implicit and explicit memory.

To examine how feature-specific pattern-analyzing processes affect implicit and explicit memory test performance, words were displayed for study and testing in 2 visually distinct formats: upside down vs normal for Exp 1, upside down vs backward for Exp 2, and in Applesoft pudgy vs shadow typeface for Exp 3. Implicit and explicit memory performance were assessed with word identification and recognition tests, respectively. The results showed larger priming effects when the study and test formats were the same rather than different, but only in some experimental conditions. The discussion focuses on how skill and processing strategies contribute to format-specific effects on implicit and explicit memory test performance, and it outlines a theoretical account based on the idea of transfer-appropriate processing. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dual-mode presentation and its effect on implicit and explicit memory

Chronic exposure to methyl tertiary butyl ether (MTBE) altered the rodent tumor incidence of endocrine-sensitive tissues and decreased the incidence of estrogen-dependent uterine cystic hyperplasia in mice. To test the hypothesis that changes in the incidence of tumors in female B6C3F1 mice after MTBE exposure are secondary to endocrine alterations, we exposed female mice to the carcinogenic dose of MTBE vapor (8000 ppm) for 3 or 21 days or 4 or 8 months under conditions similar to a previous 2-year bioassay. MTBE exposure significantly decreased body weight gain and ovary and pituitary weight at 4 and 8 months and uterine weight at all time points. After 8 months of exposure, MTBE significantly increased the length of the estrous cycle by increasing the mean number of days in both the estrus and the nonestrus stages. Histological evaluation of H&E-stained tissues showed a decrease in the number of uterine glands after subchronic MTBE exposure. DNA synthesis, as measured by the incorporation of 5-bromo-2'-deoxyuridine (BrdU), was decreased in uterine glandular and luminal epithelial cells after MTBE exposure for 3 or 21 days or 4 or 8 months. MTBE exposure decreased the number of epithelial layers in the cervix and vagina at all time points. DNA synthesis was decreased in cervical and vaginal epithelium after 21 days of MTBE. Decreased zona reticularis of adrenal glands was found after 4 and 8 months of MTBE exposure without changes in BrdU incorporation. MTBE did not competitively bind to estrogen receptor. MTBE exposure did not alter serum estrogen levels or alter the location or intensity of estrogen receptor immunoreactivity in the uterus, cervix, and vagina. These data indicate that while MTBE exposure causes multiple endocrine-related tissue and cellular responses, these effects are not mediated through the estrogen receptor.     

Dissociation of the neural correlates of implicit and explicit memory

One presentation of a word to a subject is enough to change the way in which the word is processed subsequently, even when there is no conscious (explicit) memory of the original presentation. This phenomenon is known as implicit memory. The neural correlates of implicit memory have been studied previously, but they have never been compared with the correlates of explicit memory while holding task conditions constant or while using a procedure that ensured that the neural correlates were not 'contaminated' by explicit memory. Here we use scalp-recorded event-related brain potentials to identify neural activity associated with implicit and explicit memory during the performance of a recognition memory task. Relative to new words, recently studied words produced activity in three neuroanatomically and functionally dissociable neural populations. One of these populations was activated whether or not the word was consciously recognized, and its activity therefore represents a neural correlate of implicit memory. Thus, when task and memory contamination effects are eliminated, the neural correlates of explicit and implicit memory differ qualitatively.     

Dissociations in infant memory: Rethinking the development of implicit and explicit memory.

Extending the Jacksonian principle of the hierarchical development and dissolution of function to the development and dissolution of memory, researchers have concluded that implicit (procedural) memory is a primitive system, functional shortly after birth, that processes information automatically, whereas explicit (declarative) memory matures late in the 1st year and mediates the conscious recollection of a prior event. Support for a developmental hierarchy has only been inferred from the memory performance of adults with amnesia on priming and recognition-recall tests in response to manipulations of different independent variables. This article reviews evidence that very young infants exhibit memory dissociations like those exhibited by adults with normal memory on analogous memory tests in response to manipulations of the same independent variables. These data demonstrate that implicit and explicit memory follow the same developmental timetable and challenge the utility of conscious recollection as the defining characteristic of explicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Form-specific explicit and implicit memory in the right cerebral hemisphere.

Results from 2 divided visual field (DVF) experiments indicate that in some conditions both explicit and implicit memory are greater when same-letter-case stimuli are presented directly to the right cerebral hemisphere (in the left visual field) than when they are presented directly to the left (in the right visual field). Explicit memory was measured with word-stem cued recall, and implicit memory was measured with word-stem completion priming. Words were presented centrally during encoding, and word stems were presented directly to the right hemisphere or to the left hemisphere during testing. Results for explicit memory contrast with findings from a previous DVF study that used a different procedure, those for implicit memory replicate previous DVF findings, and both results corroborate positron emission tomography findings. It is suggested that a form-specific system in the right hemisphere may contribute to both explicit and implicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age differences in explicit and implicit memory for pictures.

In the present study, the authors examined age effects in memory for nonverbal material. A picture fragment completion task was used to test explicit and implicit memory in a younger and an older group. Explicit memory was indexed by free recall of pictures, whereas implicit memory was indexed by perceptual learning (priming). Both free recall and perceptual learning performance were found to be impaired in the older group. A measure of executive functioning was found to be predictive of both explicit and implicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluating the relationship between explicit and implicit knowledge in a sequential reaction time task.

Can knowledge underlying a simple perceptual-motor skill be unconscious? Three experiments with college students (a) trained Ss on a 4-choice reaction time (RT) task in which the stimulus on each trial was determined by a repeating 12-element sequence and (b) studied the extent to which participants' knowledge of this sequence was implicit, that is, unavailable for conscious access. Participants proved via an indirect test to have acquired knowledge of the sequence, because their RTs increased when the sequence was changed. To evaluate whether this knowledge was consciously accessible, participants were asked to perform an "objective" free-generation or recognition test of sequence knowledge. Results show that sequence knowledge is fully accessible on these objective tests. Moreover, it is demonstrated in this procedure that old-new recognition cannot be explained by unconscious attribution of perceptual-motor fluency. The question is raised whether distinct implicit (procedural) and explicit (declarative) forms of knowledge are acquired when participants learn a perceptual motor skill. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

TAP, implicit and explicit memory, and adult memory development.

This paper proposes a view of memory based on the notion of transfer appropriate processing (TAP) of Morris, Bransford, and Franks (1977). The author makes three specific assumptions to explain the disassociation between implicit and explicit memory. First, the author distinguishes between two memory organizing processes--integration and elaboration. Second, the author assumes that every kind of study task engages a combination of integrative and elaborative processing, but that some tasks focus primarily on integrative processing, and others focus more heavily on elaborative processing. Third, the author also assumes that every kind of test engages a combination of integrative and elaborative processing, but that implicit memory tests depend primarily on integrative processing, whereas explicit tests focus more heavily on elaborative processing. The long term goal of several on-going experiments is to learn more about the specific stimulus attributes that serve as cues for initialing/guiding integrative versus elaborative processing, and how these cues change across the life-span. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of color and pattern on implicit and explicit picture memory.

The degree to which repetition priming is perceptually specific is informative about the mechanisms of implicit memory as well as of perceptual processing. In 2 sets of experiments with pictures as stimuli, we tested the effects of color and pattern manipulations between study and test on implicit memory (i.e., naming facilitation) and explicit memory (i.e., 2 forms of recognition). These manipulations did not affect priming. However, participants were able to explicitly detect stimulus changes at above-change levels. changes in color also produced small decrements in participants' ability to judge that repeated stimuli were old on a recognition tests. Experiment 2 showed diminished priming with changes in the stimulus exemplar (i.e., a different picture of the same named object) from study to test, which demonstrated that the picture-naming paradigm is sensitive to changes in physical attributes. The results suggest that physical attributes that are not essential to the formation of a shape representation do not influence repetition priming in a basic identification paradigm. Suggestions for how priming may be mediated are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial position effects in implicit and explicit tests of memory.

The effects of serial position at study on implicit and explicit tests of memory were investigated. Both primacy and recency effects were observed in implicit tests of word-stem completion. These effects, however, were transient. No serial position effects were found in the 2nd half of testing (Exps 1 and 3) or when testing followed a 1-min, filled delay (Exp 2). Serial position effects were also examined on explicit tests of cued recall. When performance on explicit cued recall was below ceiling levels, a primacy effect persisted throughout testing (Exp 3). Similarly, in explicit tests of free recall, primacy effects were consistently observed, both with immediate testing (Exps 1 and 3) and when testing followed a filled delay (Exp 2). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of automatic associative activation on explicit and implicit memory tests.

Ss made either a graphemic or a semantic decision concerning word pairs during a study phase. Pair relatedness effects were observed in behavioral measures for the semantic task only, but a physiological measure (event-related potential) showed relatedness effects for both study tasks. Relatedness at study helped subsequent memory for tests involving word generation (fragment completion and cued recall). These effects were independent of those of the level of processing on memory. The results support P. Graf and G. Mandler's (1984) 2-process model of implicit and explicit remembering and demonstrate that automatically activated associations can have significant effects on both types of remembering. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of forgetting in an implicit and explicit memory task.

Among possible criteria for distinguishing separate memory systems for implicit and explicit memory is that of substantial differences in either the form or rate of forgetting. Prior literature has claimed both differential forgetting and equivalent forgetting for implicit and explicit tasks. Existing experimental data for word-stem completion and explicit control tasks were reviewed and shown to be inconclusive. Our experiments measure forgetting in comparable implicit and explicit memory tasks of stem completion and stem cued recall. The form and the rate of forgetting are essentially the same for these implicit and explicit tasks. Levels of processing and task conditions differ only in the level of initial learning or availability. Thus, either the implicit and explicit task reflect traces in the same memory system or they reflect traces in different systems that have identical forgetting dynamics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Affective valence of words, explicit and implicit memory in clinical depression

Explicit and implicit memory for affectively valenced words (positive, negative or neutral) were investigated in 30 patients suffering from a major depressive episode (DSM-III-R criteria) and 30 normal control subjects. Explicit memory was assessed with a free-recall and a recognition task and implicit memory with a word-stem completion task. Depressed and control subjects recalled more emotional, i.e., positive and negative, words than neutral ones. They recognized less negative than neutral words. In contrast, to recall and recognition performance, word-completion performance was not sensitive to the affective valence of words: depressed and control subjects exhibited equivalent priming of positive, negative and neutral words. These results indicate that, in depressed and normal subjects, the affective valence of words influences memory when conscious, intentional recollection is required but is devoid of effect when such a recollection is not required.     

The role of attention during encoding in implicit and explicit memory.

In 5 experiments, participants read study words under conditions of divided or full attention. Dividing attention reduced performance on the general knowledge test, a conceptual implicit test of memory. Likewise, dividing attention reduced conceptual priming on the word association task, as well as on a matched explicit test, associate-cued recall. In contrast, even very strong division of attention did not reduce perceptual priming on word-fragment completion, although it did reduce recall on the matched explicit test of word-fragment-cued recall. Finally, dividing attention reduced recall on the perceptual explicit tests of graphemic-cued recall and graphemic recognition. The results indicate that perceptual implicit tests rely minimally on attention-demanding encoding processes relative to other types of memory tests. The obtained pattern of dissociations is not readily accommodated by the transfer-appropriate-processing (TAP) account of implicit and explicit memory. Potential extensions of the TAP view are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)