Conceptual priming in perceptual identification for patients with Alzheimer's disease and a patient with right occipital lobectomy.

Two experiments examined explicit recognition memory and perceptual and conceptual contributions to implicit perceptual-identification repetition priming for patients with Alzheimer's disease (AD) and Patient M.S. with right-occipital lobectomy. Participants read words (perceptual encoding) and generated words (conceptual encoding) from a definition and letter cue (e.g., "a vehicle for moving the injured—a"). AD patients demonstrated impaired explicit and intact implicit memory for both perceptually and conceptually encoded words. M.S. demonstrated the opposite pattern: intact explicit and impaired implicit memory in both encoding conditions. The double dissociation between AD and M.S. on implicit and explicit memory tasks is discussed in terms of a putative visual memory mechanism in the right-occipital cortex that interacts with lexical mechanisms to yield perceptual-identification priming after perceptual and conceptual encoding. (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)     

Level-of-processing effects in conceptually driven implicit tasks.

Level of processing (LOP) has often been shown to affect performance on explicit memory tasks, but not on implicit memory tasks. These findings have been explained by the processing framework (H. J. Roediger et al, 1989): Study–test transfer depends on the overlap between the type of processing at study and at test. This framework predicts that conceptually driven implicit (CDI) memory tasks should be affected by an LOP manipulation because the study and test tasks share common conceptual processes. This prediction was investigated with 2 CDI tasks: general knowledge retrieval and category exemplar generation. LOP effects were found in both tasks, thus supporting the processing framework. Category exemplar priming declined rapidly over a 90-min interval, and elaborative study conditions enhanced the duration of priming relative to physical conditions. (PsycINFO Database Record (c) 2011 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)     

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)     

Effects of divided attention on implicit and explicit memory performance following severe closed head injury.

This study investigated the relation between attentional limitations and memory impairments in patients with closed head injuries (CHI). Twenty-seven CHI participants ( > 1 year postinjury) and 27 matched controls rated their liking of target words under conditions of full and divided attention. Participants then completed an implicit test of tachistoscopic identification (TI) and an explicit test of recognition for the target words As expected, the results revealed impaired explicit memory but preserved perceptually driven implicit memory performance following a CHI. Contrary to what was hypothesized, a reduction in attention available at encoding did not disproportionately impair the recognition performance of the CHI patients. Finally, unlike controls, the CHI participants' priming scores on the TI task were significantly affected by dividing attention at encoding. However, this finding interacted with CHI participants perceptual processing rates, suggesting that nonmemory cognitive factors may influence measured performances on implicit memory tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is striatal dopaminergic receptor imbalance responsible for levodopa-induced dyskinesia?

Amnesic patients often exhibit spared priming effects on implicit memory tests despite poor explicit memory. In previous research, we found normal auditory priming in amnesic patients on a task in which the magnitude of priming in control subjects was independent of whether speaker's voice was same or different at study and test, and found impaired voice-specific priming on a task in which priming in control subjects is higher when speaker's voice is the same at study and test than when it is different. The present experiments provide further evidence of spared auditory priming in amnesia, demonstrate that normal priming effects are not an artifact of low levels of baseline performance, and provide suggestive evidence that amnesic patients can exhibit voice-specific priming when experimental conditions do not require them to interactively bind together word and voice information.     

Impaired priming on the general knowledge task in amnesia.

The status of priming on the general knowledge test was examined in amnesia. Twenty amnesic and 20 control participants studied words (e.g., CHEETAH) under semantic and nonsemantic encoding conditions and attempted to answer general knowledge questions (e.g., "What is the fastest animal on earth"?) under implicit and explicit retrieval instructions. The measure of memory was how many more test questions participants answered correctly using studied than nonstudied words. Amnesic patients showed impaired memory under implicit and explicit retrieval instructions. Control participants showed equal memory under implicit and explicit retrieval instructions, a result indicating that they engaged in explicit retrieval in both instruction conditions. General-knowledge priming appears to involve explicit retrieval that depends on medial-temporal and diencephalic regions damaged in amnesia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Explicit contamination in "implicit" memory for new associations

In one view of implicit memory, priming arises from modification of preexisting representations; however, the role of such representations is currently in doubt following findings of implicit memory for newly formed associations. Closer consideration of studies reporting this effect, and of others that have failed to obtain it, suggests that such priming might results from the employment of explicit memory strategies. With measures designed to permit exclusion of such strategies, three experiments using lexical decision and stem-completion tasks found no evidence of truly implicit memory for unrelated pairs. Instead, priming was found only in those subjects (50% of the total in one experiment) who reported using explicit memory in stem completion. Contrary to previous conclusions, the results indicate a role for established representations in explaining implicit memory.     

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)     

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)     

Spared priming despite impaired comprehension: Implicit memory in a case of word-meaning deafness.

Previous research has established that direct priming effects on implicit memory tests can be dissociated from explicit remembering. Evidence from studies of college students suggests that priming on various implicit tests can be characterized as a presemantic phenomenon: Priming can occur at full strength following nonsemantic encoding tasks that typically produce low levels of explicit memory. To provide a strong test of this idea, auditory priming in a case of word-meaning deafness was examined. Despite the patient's impaired auditory comprehension abilities, he showed normal priming on auditory identification tests after study-list exposure to spoken words. Results support the idea that priming depends on perceptual systems that operate at a presemantic level. (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.     

Does implicit memory extend to legal and illegal nonwords?

In 4 experiments, implicit and explicit memory for words and nonwords were compared. In Exps 1–2 memory for words and legal nonwords (e.g., kers) was assessed with an identification (implicit) and a recognition (explicit) memory task: Robust priming was obtained for both words and nonwords, and the priming effects dissociated from explicit memory following a levels-of-processing manipulation (Exp 1) and following a study-test modality shift (Exp 2). In Exp 3, priming for legal and illegal nonwords (e.g., xyks) was observed on an identification task, and the effects dissociated from explicit memory following a levels-of-processing manipulation. Finally, in Exp 4, significant inhibitory priming for legal nonwords was observed when a lexical-decision task was used. Results suggest that implicit memory can extend to legal and illegal nonwords. Implications for theories of implicit memory are discussed. (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)     

Priming and baseline perceptual identification performance in amnesia: A comment on Hamann, Squire, and Schacter.

There is evidence that stimulus processing deficits, some of which may be due to striatal damage, are prevalent in memory-impaired patients. The deficits often result in impaired baseline performance in implicit memory tasks, which in turn is associated with increased priming effects. When priming scores were corrected for such processing deficits, the authors found a relationship between priming and both recognition memory and mesial temporal lobe damage. On the basis of 4 tachistoscopic word identification experiments, S. B. Hamann et al (see record 1995-14158-001) challenged the notion that either processing deficits or striatal damage is prevalent in amnesia patients. They claim that both priming and baseline word identification are normal in amnesia patients, except that patients with Korsakoff amnesia show deficits under certain restricted circumstances. The authors argue that the results of the Hamann et al study are entirely consistent with their previous reports. When Hamann et al did not find differences between amnesia patients and controls in word identification, the results were contaminated by ceiling effects, and there was poor control over the effective exposure duration of the stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nondeclarative memory--neuropsychological findings and neuroanatomic principles

The contents of long-term memory will influence behaviour, even if the acquired knowledge or the original learning episode are not remembered. These phenomena have been termed "non-declarative" or "implicit" memory, and they are contrasted with "declarative" or "explicit" memory which is characterised by conscious search and retrieval procedures. Non-declarative memory encompasses non-associative learning, simple conditioning, priming effects as well as motor, perceptual and cognitive skill acquisition. The dissociation of both forms of memory is documented by studies in health subjects which indicated that experimental manipulations or drugs may differentially affect declarative and non-declarative memory processes. Damage to the medial temporal or the medial thalamic regions is known to result in declarative memory deficits whereas non-declarative memory is largely unaffected by such lesions. Animal research and clinical findings indicate that several components of non-declarative memory such as motor and cognitive skill acquisition or certain types of classical conditioning are dependent upon the integrity of the basal ganglia or the cerebellum. These issues are therefore of increasing importance for the understanding of extrapyramidal and cerebellar diseases. This paper presents recent neuropsychological findings and neuroanatomical data relating to the issue of non-declarative memory.     

Implicit and Explicit Memory in Children With Congenital and Acquired Brain Disorder.

Implicit and explicit memory were examined in 8- to 15-year-old children with myelomeningocele and shunted hydrocephalus, severe traumatic brain injuries, or orthopedic injuries. Each group included between 22 and 29 children. Children completed a fragmented picture identification task to assess perceptual priming and a semantic decision-making task to assess conceptual priming. Each task also assessed procedural learning as well as explicit recall and recognition. All 3 groups showed significant perceptual and semantic priming of similar magnitude. In contrast, both brain-disordered groups displayed poorer explicit memory than did the comparison group. No group showed significant procedural learning on either task. Age and IQ were stronger predictors of explicit recall than of implicit memory. The findings indicate that implicit memory is relatively intact in many children with congenital and acquired brain disorders, despite deficits in explicit memory, and support the existence of separate memory systems in children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Confidence level and feeling of knowing for episodic and semantic memory: an investigation of lorazepam effects on metamemory

The effects of lorazepam (0.026 or 0.038 mg/kg), a benzodiazepine, and of a placebo on metamemory, i.e. knowledge about one's own memory capabilities, were investigated in 36 healthy volunteers. Accuracy of confidence levels (CL) in the correctness of recalled answers and accuracy of feeling of knowing (FOK) the answers when recall fails were measured using a sentence memory task assessing episodic memory and a task consisting of general information questions and assessing semantic memory. Lorazepam impaired episodic memory. Unexpectedly, it also impaired performance in both the recall and recognition phases of the task assessing semantic memory, suggesting that it decreased the ability to distinguish between correct and incorrect information. In episodic memory, lorazepam 0.038 mg/kg-treated subjects exhibited an impaired CL accuracy, compared to placebo-treated subjects, and their FOK accuracy was at chance. In semantic memory, their overall CL and FOK accuracy was apparently spared. However, these subjects selectively overestimated their CL judgements for incorrect answers; moreover, secondary analyses showed that FOK accuracy for a subset of low-accuracy items was virtually nil. These results suggest that lorazepam impairs metamemory for both episodic and semantic memory.