Implicit and explicit memory in young and older adults.

In three experiments, young and older adults were compared on both implicit and explicit memory tasks. The size of repetition priming effects in word completion and in perceptual identification tasks did not differ reliably across ages. However, age-related decrements in performance were obtained in free recall, cued recall, and recognition. These results, similar to those observed in amnesics, suggest that older adults are impaired on tasks which require conscious recollection but that memory which depends on automatic activation processes is relatively unaffected by age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age Differences in Implicit Memory: Conceptual, Perceptual, or Methodological?

The authors examined age differences in conceptual and perceptual implicit memory via word-fragment completion, word-stem completion, category exemplar generation, picture-fragment identification, and picture naming. Young, middle-aged, and older participants (N=60) named pictures and words at study. Limited test exposure minimized explicit memory contamination, yielding no reliable age differences and equivalent cross-format effects. In contrast, explicit memory and neuropsychological measures produced significant age differences. In a follow-up experiment, 24 young adults were informed a priori about implicit testing. Their priming was equivalent to the main experiment, showing that test trial time restrictions limit explicit memory strategies. The authors concluded that most implicit memory processes remain stable across adulthood and suggest that explicit contamination be rigorously monitored in aging studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 task 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociative effect of massed repetition on implicit and explicit measures of memory.

Ss saw or heard words presented once, or repeated 4 or 16 times in massed fashion, and then received an implicit or explicit memory test. Massed repetition did not increase priming on word fragment completion beyond that obtained from a single presentation but did enhance performance on various explicit tests (free recall, recognition, question cued recall, and word fragment cued recall) and an implicit general knowledge test. Modality of presentation affected implicit and explicit word fragment cued tests but did not affect performance on any of the other tests. Levels of processing affected performance on implicit and explicit question cued tests. These results are consistent with a transfer appropriate processing account of dissociations among memory measures and imply that massed repetition promotes conceptual processing but does not entail a repetition of perceptual-based processes responsible for priming on word fragment completion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative priming in word fragment completion: a dissociation between explicit and implicit retrieval processes

Three experiments investigated associative priming in word fragment completion. In associative priming, the study word that acts as a prime is semantically related in some way to the response word that the subject must produce or respond to at test. For example, a prime might be semantically related to the solution to its paired word fragment (e.g. study "VANILLA", solve fragment "-H-C--A-E" at test, solution is "CHOCOLATE"). Associative priming therefore differs from both repetition and conceptual priming, in which the studied primes are themselves the words that must be produced or responded to at test. In Experiment 1, associative primes were found to influence word fragment completion performance on an explicit test, but not on an implicit test. Experiment 2 demonstrated that the effects of associative primes on explicitly instructed fragment completion cannot be attributed to the specific information about cue-prime relationships that is included in the explicit instructions. Experiment 3 demonstrated that a manipulation of modality, a variable known to disrupt implicit retrieval processes, disrupts repetition priming on an explicit test, but not associative priming. The results of these three experiments suggest that whereas repetition primes are retrieved from memory by both explicit and implicit retrieval processes, associative primes are retrieved by only explicit processes. These data suggest that implicit retrieval processes are cue-dependent processes which automatically retrieve memory information that provides a good match to retrieval cues. Explicit retrieval processes are cue-independent, functioning as an intentional retrieval set to access particular categories or types of memory information.     

Correlation between frontal lobe functions and explicit and implicit stem completion in health elderly.

Investigated the relationship between performance on neuropsychological tests, which were sensitive to medial-temporal and frontal lobe (FL) function, and implicit and explicit stem completion (SC) in a group of healthy elderly Ss (mean age 77.3 yrs). Several SC conditions varying in the size of the search space and the specificity of the cues were included. Across conditions, performance on a FL sensitive test (word fluency) and on medial-temporal tests (California Verbal Learning Test; delayed recall) correlated with explicit SC. The correlations between frontal and medial–temporal test performance and implicit SC were weaker. A relationship was observed between FL functioning and SC when the search space was large and the cues were constrained and when the search space was limited and the cues were relatively unconstrained. The role of the FLs in implicit SC seems to be to detect bias resulting from prior study. This involvement can only be revealed when the interaction between the size of the search space and the retrieval cues (a) makes bias detection necessary and (b) allows it to play a role. The stronger involvement of the FLs in explicit SC likely reflects strategic retrieval processes, and the medial-temporal lobe involvement may be related to verification processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of aging and Alzheimer's disease on conceptual implicit and explicit memory.

The effects of aging and Alzheimer's disease (AD) on conceptual explicit and implicit memory were examined. Three groups of participants patients with AD; age-matched, older control participants; and younger control participants made deep (semantic) or shallow (nonsemantic) judgments about low-dominant category exemplars. Explicit memory was measured by category cued recall and implicit memory was measured by priming on a category-exemplar generation task. Younger participants had enhanced cued recall and priming following deep, relative to shallow, encoding; this indicated that both memory measures were conceptually driven. Aging reduced explicit, but not implicit, test performance, and it did not reduce conceptually driven processes for either test. In contrast, AD reduced explicit and implicit test performance, and it impaired conceptually driven memory processes for both tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Direct comparison of two implicit memory tests: Word fragment and word stem completion.

In 3 experiments, the implicit memory tests of word fragment and word stem completion showed comparable effects over several variables: Study of words produced more priming than did study of pictures; no levels-of-processing effect occurred for words; more priming was obtained from pictures when Ss imaged the pictures' names than when they rated them for pleasantness; and forgetting rates were generally similar for the tests. A different pattern of results for the first 3 variables occurred under explicit test conditions with the same word fragments or word stems as cues. It is concluded that the 2 implicit tests are measuring a similar form of perceptual memory. Furthermore, it is argued that both tests are truly implicit because they meet the D. L. Schacter et al (1989) retrieval intentionality criterion: Levels of processing of words have a powerful effect on explicit versions of the tests but no effect on implicit versions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lexical priming deficits as a function of age.

The effects of age on implicit memory were assessed in elderly and young adults using 2 priming procedures. Subjects also completed the Wechsler Adult Intelligence Scale—Revised (WAIS—R), 3 tests to assess frontal lobe function, and 2 recall and 2 recognition tests of explicit memory. In Experiment 1, subjects were exposed to the low-frequency member of a homophone pair in a test purported to assess general knowledge. Subsequently, subjects completed a spelling test that contained the previously presented homophones to assess priming. Young subjects demonstrated priming (p?p?p?     

A role for the hippocampal formation in implicit memory: a 3-D PET study

The apparent preservation of word priming effects in amnesia has been interpreted as supporting the view that implicit memory depends on brain systems that are independent of mesial temporal lobe structures which are in part responsible for explicit memory disorders. Nevertheless, a number of studies have demonstrated word priming deficits in amnesic patients relatively to normal subjects, suggesting that such structures may also be involved in implicit memory. To determine whether one such structure, the hippocampal formation, is a component of the brain system subserving word priming, a 3-D PET study was carried out in 13 normal individuals. Encoding was carried out using the brief multiple presentation technique, a procedure that allows one to effectively circumvent contamination of implicit memory tasks by explicit memory strategies. Results revealed that word priming was indeed associated with an activation of the right hippocampal formation. This finding of an hippocampal involvement in word priming calls into question the notion of absolute dissociability between the brain systems underlying performance on various explicit and implicit memory tasks.     

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)     

Conceptual implicit memory performance in Alzheimer's disease.

Alzheimer's disease (AD) patients often exhibit deficits on conceptual implicit memory tests such as category exemplar generation and word association. However, these tests rely on word production abilities, which are known to be disrupted by AD. The current study assessed conceptual implicit memory performance in AD patients and elderly control participants using a conceptual priming task that did not require word production (i.e., semantic decision). Memory performance was also examined using a category exemplar generation test (i.e., a conceptual priming task that required word production) and a recognition memory test. AD patients exhibited deficits on the semantic decision task, the category exemplar generation task, and the recognition memory task. The results indicate that the conceptual memory deficits observed in AD patients cannot be attributed completely to word production difficulties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Adult Age Differences in the Implicit and Explicit Components of Top-Down Attentional Guidance During Visual Search.

Two experiments investigated adult age differences in the explicit (knowledge-based) and implicit (repetition priming) components of top-down attentional guidance during discrimination of a target singleton. Experiment 1 demonstrated an additional contribution of explicit top-down attention, relative to the implicit effect of repetition priming, which was similar in magnitude for younger and older adults. Experiment 2 examined repetition priming of target activation and distractor inhibition independently. The additional contribution of explicit top-down attention, relative to the repetition priming of distractor inhibition, was greater for older adults than for younger adults. The results suggest that some forms of top-down attentional control are preserved as a function of adult age and may operate in a compensatory manner. (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)     

Intact and impaired conceptual memory processes in amnesia.

To examine the status of conceptual memory processes in amnesia, a conceptual memory task with implicit or explicit task instructions was given to amnesic and control groups. After studying a list of category exemplars, participants saw category labels and were asked to generate as many exemplars as possible (an implicit memory task) or to generate exemplars that had been in the prior study list (an explicit memory task). After incidental deep or shallow encoding of exemplars, amnesic patients showed normal implicit memory performance (priming), a normal levels-of-processing effect on priming, and impaired explicit memory performance. After intentional encoding of exemplars, amnesic patients showed impaired implicit and explicit memory performance. Results suggest that although amnesic patients can show impairments on implicit and explicit conceptual memory tasks, their deficit does not generalize to all conceptual memory tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Direct and indirect tests of memory for category exemplars in young and older adults.

Young and older adults were compared on direct (cued recall) and indirect (exemplar generation) tests of memory for category members. Because category names served as cues in both tasks, amount of retrieval support was constant across tasks. Although older adults produced fewer category members in cued recall, priming of category exemplars in the generation task did not vary with age. These results suggest that age constancy in priming tasks does not depend on physical similarity between study materials and retrieval cues provided at test and point to the importance of deliberate recollection as a factor in determining the extent of age differences in memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Semantic priming in young and older adults: Evidence for age constancy in automatic and attentional processes.

Automatic and attentional components of semantic priming and the relation of each to episodic memory were evaluated in young and older adults. Category names served as prime words, and the relatedness of the prime to a subsequent lexical decision target was varied orthogonally with whether the target category was expected or unexpected. At a prime-target stimulus-onset asynchrony (SOA) of 410 ms, target words in the same category had faster lexical decision latencies than did different category targets. This effect was not significant at a 1,550-ms SOA and was attributed to automatic processes. Expected category targets had faster latencies than unexpected category targets at the 410-ms SOA, and the magnitude of the effect increased at the 1,550-ms SOA. This effect was attributed to attentional processes. These patterns of priming were obtained for both age groups, but in a surprise memory test older adults had poorer recall of primes and targets. We discuss the implications of these results for the hypothesis that older adults suffer deficits in selective attention and for the related hypothesis that attentional deficits impair semantic processing, which causes memory decrements in old age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conceptual and perceptual implicit memory in Huntington's disease.

The aims of this study were to examine and compare perceptual and conceptual implicit memory (CIM) in Huntington's disease (HD) and to characterize the relationship between tests of frontal lobe functioning and CIM. Sixteen HD patients and 16 normal controls completed structurally parallel tests of perceptual implicit memory and CIM (i.e., rhyme and category exemplar generation), tests of explicit memory, and verbal fluency. HID patients showed intact implicit memory for both rhyme and category exemplars, despite evidence of frontal dysfunction on other tests. An unexpected finding was that patients showed a deficit in cued rhyme generation that correlated with severity of neurological impairment. The authors replicated findings in controls of a correlation between letter fluency and CIM but found no relationship in patients. Frontal dysfunction in HID may lessen the influence of generative strategies on tests of CIM without compromising performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)