Age differences in implicit memory: more apparent than real

Age differences in priming as a function of processing at encoding

It is unclear whether implicit memory (priming) is affected by aging. Some studies have reported no difference between young and older adults, while others have uncovered reliable reductions. An important factor that may explain these discrepancies is the manner of encoding. Processing requirements (perceptual/conceptual) have varied considerably between studies, yet processing abilities are not equally affected by aging. This study examined whether processing during encoding moderates age effects on priming. Young and older participants studied object-word pairs and made natural/manufactured (conceptual) and left/right rotation (perceptual) judgements in relation to the word or object. Objects served as targets on a subsequent continuous identification with recognition task to assess priming and recognition. Priming and recognition were greater in young than older adults for attended items, with a larger effect size in the conceptual than the perceptual condition. Findings suggest that age differences in priming may be a function of processing at encoding.

Age and processing effects on perceptual and conceptual priming

Explicit (declarative) memory declines with age, but age effects on implicit (nondeclarative) memory are debated. Some studies have reported null changes in implicit memory (e.g., priming in word-fragment completion, perceptual identification, category exemplar generation) with age, while others have uncovered declines. One factor that may account for these discrepancies is processing. Evidence suggests that conceptual and perceptual processes are not equally affected by ageing, yet processing requirements have varied greatly between studies. Processing may moderate age effects on priming, but no study has systematically examined this issue. This registered report presents an experiment to manipulate processing (conceptual / perceptual) during incidental encoding of words, prior to measures of perceptual (perceptual identification) and conceptual (category verification) priming. The perceptual and conceptual priming tasks were matched on all characteristics except processing, making them highly comparable. The four orthogonal conditions (perceptual encoding, perceptual test [PP]; conceptual encoding, perceptual test [CP]; perceptual encoding, conceptual test [PC]; conceptual encoding, conceptual test [CC]) were designed to clarify situations in which age effects on implicit memory emerge, which holds important practical and theoretical implications. Significant effects of Age, Test, and an Age × Processing interaction emerged. Priming was greater in young than older adults and on the perceptual than the conceptual test, but in contrast to the predictions, the age difference was only significant when prior encoding was perceptual (i.e., in the PP and CP conditions).

Aging Predicts Decline in Explicit and Implicit Memory: A Life-Span Study

Explicit memory declines with age, but age effects on implicit memory are debated. This issue is important because if implicit memory is age invariant, it may support effective interventions in individuals experiencing memory decline. In this study, we overcame several methodological issues in past research to clarify age effects on implicit memory (priming) and their relationship to explicit memory (recognition, source memory). We (a) recruited a large life-span sample of participants (N = 1,072) during a residency at the Science Museum in London, (b) employed an implicit task that was unaffected by explicit contamination, and (c) systematically manipulated attention and depth of processing to assess their contribution to age effects. Participants witnessed a succession of overlapping colored objects, attending to one color stream and ignoring the other, and identified masked objects at test before judging whether they were previously attended, unattended, or new. Age significantly predicted decline in both explicit and implicit memory for attended items.

Preserved memory-based orienting of attention with impaired explicit memory in healthy ageing

It is increasingly recognised that spatial contextual long-term memory (LTM) prepares neural activity for guiding visuo-spatial attention in a proactive manner. In the current study, we investigated whether the decline in explicit memory observed in healthy ageing would compromise this mechanism. We compared the behavioural performance of younger and older participants on learning new contextual memories, on orienting visual attention based on these learnt contextual associations, and on explicit recall of contextual memories. We found a striking dissociation between older versus younger participants in the relationship between the ability to retrieve contextual memories versus the ability to use these to guide attention to enhance performance on a target-detection task. Older participants showed significant deficits in the explicit retrieval task, but their behavioural benefits from memory-based orienting of attention were equivalent to those in young participants. Furthermore, memory-based orienting correlated significantly with explicit contextual LTM in younger adults but not in older adults. These results suggest that explicit memory deficits in ageing might not compromise initial perception and encoding of events. Importantly, the results also shed light on the mechanisms of memory-guided attention, suggesting that explicit contextual memories are not necessary.

Age effects on explicit and implicit memory

It is well-documented that explicit memory (e.g., recognition) declines with age. In contrast, many argue that implicit memory (e.g., priming) is preserved in healthy aging. For example, priming on tasks such as perceptual identification is often not statistically different in groups of young and older adults. Such observations are commonly taken as evidence for distinct explicit and implicit learning/memory systems. In this article we discuss several lines of evidence that challenge this view. We describe how patterns of differential age-related decline may arise from differences in the ways in which the two forms of memory are commonly measured, and review recent research suggesting that under improved measurement methods, implicit memory is not age-invariant. Formal computational models are of considerable utility in revealing the nature of underlying systems. We report the results of applying single and multiple-systems models to data on age effects in implicit and explicit memory. Model comparison clearly favors the single-system view. Implications for the memory systems debate are discussed.

Lexical Priming in Alzheimer's Disease and Aphasia

Lexical priming was examined in patients with Alzheimer's disease and in aphasic patients. Control participants were divided into young and elderly [cf. Arroyo-Anlló et al.: Eur J Cogn Psychol 2004;16:535-553]. For lexical priming, a word-stem completion task was used. Normal elderly participants had lexical priming scores that were significantly lower than those of young individuals. Analysis of covariance with age and educational level as covariates showed that the control participants, aphasic and Alzheimer patients did not differ significantly on the lexical priming task. Our results suggest that performance in the lexical priming task diminishes with physiological aging, but is not significantly affected by mild or moderate Alzheimer's disease or by fluent or non-fluent aphasia.

The relationship between divided attention and implicit memory: a meta-analysis

This article reports a meta-analysis comparing the size of repetition priming in full and divided-attention (DA) conditions. The main analysis included 38 effect sizes (ES) extracted from 21 empirical studies, for a total of 2074 (full-attention) and 2148 (divided-attention) participants. The mean weighted ES was 0.357 (95% CI=0.278-0.435), indicating that divided attention produced a small, but significant, negative effect on implicit memory. Overall, the distinction between identification and production priming provided the best fit to empirical data (with the effect of DA being greater for production tests), whereas there was no significant difference between perceptual and conceptual priming. A series of focused contrasts suggested that word-stem completion might be influenced by lexical-conceptual processes, and that perceptual identification might involve a productive component. Implications for current theories of implicit memory are discussed.

Aging and implicit memory: examining the contribution of test awareness

The study examined whether test awareness contributes to age effects in priming. Younger and older adults were given two priming tests (word-stem completion and category production). Awareness was assessed using both a standard post-test questionnaire and an on-line measure. Results from the on-line awareness condition showed that, relative to older adults, younger adults showed higher levels of priming and awareness, and a stronger relationship between the two, suggesting that awareness could account for age differences in priming. In contrast, in the post-test questionnaire condition, there was no age effect in word-stem completion or category production priming, despite the fact that awareness was greater in younger than older adults in the word-stem completion test and that category production priming was dependent on awareness in both age groups. These results suggest that awareness may mediate age effects in priming, but only under conditions of relatively high levels of awareness.

Examining the response competition hypothesis of age effects in implicit memory

Age reductions in priming have been explained by differences in processing demands across implicit memory tests. According to one hypothesis, older adults show reduced priming relative to younger adults on implicit tests that require production of a response because these tests typically allow for response competition. In contrast, older adults do not show reductions in priming on identification tests that contain little response competition. The following experiments tested the specific role of response competition in mediating age effects in implicit memory. In Experiment 1, younger and older adults studied a list of words and were then given an implicit test of word stem completion. They studied a second list of words and were given an implicit test of general knowledge. Each implicit test contained items with unique solutions (the low response competition condition) and items with multiple solutions (the high response competition condition). In Experiment 2, younger and older adults were given explicit versions of the word stem completion and the general knowledge tests. Results showed an effect of age on explicit memory (Experiment 2), but no effect of age or response competition on priming (Experiment 1). Results are inconsistent with the theory that response competition leads to age effects on production tests of implicit memory.

Memory systems do not divide on consciousness: Reinterpreting memory in terms of activation and binding

There is a popular hypothesis that performance on implicit and explicit memory tasks reflects 2 distinct memory systems. Explicit memory is said to store those experiences that can be consciously recollected, and implicit memory is said to store experiences and affect subsequent behavior but to be unavailable to conscious awareness. Although this division based on awareness is a useful taxonomy for memory tasks, the authors review the evidence that the unconscious character of implicit memory does not necessitate that it be treated as a separate system of human memory. They also argue that some implicit and explicit memory tasks share the same memory representations and that the important distinction is whether the task (implicit or explicit) requires the formation of a new association. The authors review and critique dissociations from the behavioral, amnesia, and neuroimaging literatures that have been advanced in support of separate explicit and implicit memory systems by highlighting contradictory evidence and by illustrating how the data can be accounted for using a simple computational memory model that assumes the same memory representation for those disparate tasks.

Effects of dividing attention during encoding on perceptual priming of unfamiliar visual objects

According to the distractor-selection hypothesis (Mulligan, 2003), dividing attention during encoding reduces perceptual priming when responses to non-critical (i.e., distractor) stimuli are selected frequently and simultaneously with critical stimulus encoding. Because direct support for this hypothesis comes exclusively from studies using familiar word stimuli, the present study tested whether the predictions of the distractor-selection hypothesis extend to perceptual priming of unfamiliar visual objects using the possible/impossible object decision test. Consistent with the distractor-selection hypothesis, Experiments 1 and 2 found no reduction in priming when the non-critical stimuli were presented infrequently and non-synchronously with the critical target stimuli, even though explicit recognition memory was reduced. In Experiment 3, non-critical stimuli were presented frequently and simultaneously during encoding of critical stimuli; however, no decrement in priming was detected, even when encoding time was reduced. These results suggest that priming in the possible/impossible object decision test is relatively immune to reductions in central attention and that not all aspects of the distractor-selection hypothesis generalise to priming of unfamiliar visual objects. Implications for theoretical models of object decision priming are discussed.

The use of indirect and opposition tests to detect simulated amnesia

Two experiments investigated the effect of instruction to simulate memory impairment on performance on a word stem completion task. In addition to the standard control group, a second control group (divided-attention group) studied the target words concurrently with a digit-monitoring task. Experiment 1, using the indirect instruction, did not discriminate clearly between the groups. Experiment 2 used the opposition instruction in which participants were required to complete stems with words they had not seen earlier. It showed that simulators and controls withheld significantly more studied target items than did the divided-attention group. Increasing the number of study list presentations further increased the difference between the performance of the simulating and control groups and the divided-attention group. These results suggest that the opposition method may be useful in detecting feigned memory impairment.

Short- and Long-Term Implicit Memory in Aging and Alzheimer's Disease

Implicit memory processes were investigated via picture naming in healthy young and older adults and in persons with mild Alzheimer's disease (AD). Repetition priming in picture-naming was intact in all groups over the course of a short retention interval (seconds), and only the AD group revealed a deficit over a longer interval (72 hours). In addition, the AD group showed impaired procedural memory, with no benefit of practice on picture-naming. Impaired long-term priming was related to severity of AD. Both theoretical and methodological implications are discussed.

Fragmented pictures revisited: long-term changes in repetition priming, relation to skill learning, and the role of cognitive resources

BACKGROUND

Whereas age-related declines in declarative memory have been demonstrated in multiple cross-sectional and longitudinal studies, the effect of age on non-declarative manifestations of memory, such as repetition priming and perceptual skill learning, are less clear. The common assumption, based on cross-sectional studies, is that these processes are only mildly (if at all) affected by age.

OBJECTIVE

To investigate long-term changes in repetition priming and age-related differences in identification of fragmented pictures in a 5-year longitudinal design.

METHOD

Healthy adults (age 28-82 years) viewed drawings of objects presented in descending order of fragmentation. The identification threshold (IT) was the highest fragmentation level at which the object was correctly named. After a short interval, old pictures were presented again along with a set of similar but novel pictures. Five years later the participants repeated the experiment.

RESULTS

At baseline and 5-year follow-up alike, one repeated exposure improved IT for old (priming) and new (skill acquisition) pictures. However, long-term retention of priming gains was observed only in young adults. Working memory explained a significant proportion of variance in within-occasion priming, long-term priming, and skill learning.

CONCLUSION

Contrary to cross-sectional results, this longitudinal study suggests perceptual repetition priming is not an age-invariant phenomenon and advanced age and reduced availability of cognitive resources may contribute to its decline.

Disappearance of memory fragments in patients with Alzheimer's disease: evidence from a longitudinal study of visual priming

Previous studies suggested that perceptual memory as indexed by visual priming is normal in patients with Alzheimer's disease (AD). However, these studies did not specifically test the long-term effects of visual priming, which may differ significantly between Alzheimer's patients and normal subjects. To test this possibility, we examined long-term visual priming in AD patients, 1 hour, 1 month, and 3 months after training. Our results indicated a significant difference in visual priming between AD patients and normal subjects after 3 months, but not 1 month. For AD patients, there was a strong positive correlation between the 3-month priming effect and the Mini-Mental State Examination (MMSE) scores-severely demented patients were less likely to exhibit priming after 3 months. It appears that severe cortical degeneration may render AD patients unable to consolidate their perceptual memories. Our results suggest that lack of visual priming in AD patients is linked to the inability to maintain fragmented perceptual memories.

A test of the frontal lobe functioning hypothesis of age deficits in production priming

Older adults have been hypothesized to show reduced priming relative to younger adults on implicit memory tests that require production of a response because these tasks place high demands on attentional processes associated with frontal lobe function, which are often reduced with age (see D. A. Fleischman & J. D. E. Gabrieli, 1998). The current study directly tested this frontal lobe hypothesis of age effects in production priming. Younger adults and older adults who differed in their attentional abilities as measured by a battery of neuropsychological tests were given two production priming tasks, word stem completion and category production, followed by explicit free recall tests. Results showed that explicit memory performance was reduced by age and older adults' frontal functioning. Age and frontal functioning influenced category production priming but not word stem completion priming. Results failed to support the frontal account of age reductions in production priming. Instead, results implicate the influence of other processes often involved in production priming tasks, such as explicit memory strategies and response competition, as critical for understanding age effects in implicit memory performance.

Emotional enhancement of perceptual priming is preserved in aging and early-stage Alzheimer's disease

Perceptual priming for emotionally-negative and neutral scenes was tested in early-stage Alzheimer's disease (AD) patients and healthy younger, middle-aged and older adults. In the study phase, participants rated the scenes for their arousal properties. In the test phase, studied and novel scenes were initially presented subliminally, and the exposure duration was gradually increased until a valence categorization was made. The difference in exposure duration required to categorize novel versus studied items was the dependent measure of priming. Aversive content increased the magnitude of priming, an effect that was preserved in healthy aging and AD. Results from an immediate recognition memory test showed that the priming effects could not be attributable to enhanced explicit memory for the aversive scenes. These findings implicate a dissociation between the modulatory effect of emotion across implicit and explicit forms of memory in aging and early-stage AD.

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.

Executive function across the life span

The development and determinants of executive function (EF) were studied in children (mean age=8.8 years), young adults ( M= 22.3 years), and elderly adults (M = 71.1 years). EF was indexed by perseverative responding on two bidimensional sorting tasks (Visually Cued Color-Shape task and Auditorily Cued Number-Numeral task), and age-related changes in EF were considered in relation to estimates of conscious vs. unconscious memory that were obtained using the process dissociation procedure (PDP). Results revealed the rise and fall of EF across the life span, with significant quadratic trends found for performance on both sorting tasks and for the conscious recollection component (C) of the PDP task. Regression analyses indicated that PDP estimates of conscious memory accounted for variation in performance on the visual sorting task, but not on the auditory sorting task. The findings are discussed in terms of their implications for hierarchical models of EF and its development.

A Quantitative Model-Based Approach to Examining Aging Effects on Information-Integration Category Learning

Information-integration category learning was examined in older and younger adults. Accuracy results indicated that older participants learned less well than younger participants in both linear and nonlinear conditions. Model-based analyses indicated that both groups in the linear condition tended to use information integration but that later in training younger participants were more likely to do so. In contrast, the 2 groups in the nonlinear condition were equally likely to use information integration. Further analysis indicated that younger adults were more accurate than older adults when an information-integration approach was adopted, whereas fewer age-related differences were observed when a rule-based approach was used, suggesting that age can have a negative impact on information-integration category learning processes but less impact on rule-based learning.

Automatic vigilance for task-related information: perseverance after failure and inhibition after success

In three experiments, the influence of failure and success on persistent automatic vigilance task-related information was investigated. Participants first had to work on a series of synonym selection problems for which negative and positive feedback was given independently of their performance. In the second part of the experiments, words from the synonym selection problems were presented as distractors in a dual task with speeded responses. Interference effects of the distractors served as a measure of automatic vigilance for the previous synonym selection problems that was unbiased by strategic processes. Interference effects were stronger for words from failure tasks than for words from success tasks. Comparing the success and failure conditions against a neutral baseline suggested that this difference was due to both a perseverance of automatic vigilance for failure tasks and an inhibition of cognitive accessibility after success.

Effects of cross-modal and intramodal division of attention on perceptual implicit memory

Extant results motivate 3 hypotheses on the role of attention in perceptual implicit memory. The first proposes that only intramodal manipulations of attention reduce perceptual priming. The second attributes reduced priming to the effects of distractor selection operating in a central bottleneck process. The third proposes that manipulations of attention only affect priming via disrupted stimulus identification. In Experiment 1, a standard cross-modal manipulation did not disrupt priming in perceptual identification. However, when study words and distractors were presented synchronously, cross-modal and intramodal distraction reduced priming. Increasing response frequency in the distractor task produced effects of attention regardless of target-distractor synchrony. These effects generalized to a different category of distractors arguing against domain-specific interference. The results support the distractor-selection hypothesis.

Dissociations between implicit and explicit memory in children: the role of strategic processing and the knowledge base

A review of the literature shows that explicit memory develops substantially from three years of age to adulthood, while implicit memory remains stable across this age range. Previously, this developmental dissociation has been attributed to different memory systems, or to confounds with perceptual vs. conceptual processing. Prompted by an alternative developmental framework, the experiments reported here provide evidence against both interpretations. Instead, it will be argued that (a) the implicit-explicit developmental dissociation reflects differences in strategic processing (strategy use and metamemory) across childhood and (b) that implicit memory can show development if a child's knowledge base in the tested domain is developing with age.

Consequences of violating the assumption of independence in the process dissociation procedure: a word fragment completion study

In three experiments that used levels of processing and study time manipulations as independent variables in a word fragment completion task, the validity of the assumption of independence between recollection and automatic influences of memory was assessed. This assumption underlies the use of the process dissociation procedure (Jacoby, 1991), a tool suggested for distinguishing the different contributions of recollection and automatic influences of memory. Overall, it appeared that semantic processing, as compared with physical processing at study, positively affected recollection but negatively affected automatic influences of memory in word fragment completion. This negative effect on the automatic influences was reduced when the available study time decreased. The incompatibility of these results with the assumption of independence between recollection and automatic influences of memory and their impact on the applicability of the process dissociation procedure are discussed.

Direct and indirect memory measures of temporal order: younger versus older adults

The memory changes associated with age are attributed to the deterioration of the frontal lobes, as well as to the middle temporal structures. Therefore, in addition to a decline in memory for facts and events, as found impaired in amnesics, a memory decline associated with age is predicted for tasks typically found impaired in frontal lobe patients (i.e., temporal order judgment). There are conflicting findings concerning whether indirect measures of memory for facts and events are associated with age. However, there are no studies that address this issue with regard to temporal order judgment. Thirty younger and thirty older adults were tested on a list of words which was repeated five times in fixed or varying order. The number of words recalled, as well as their temporal judgments, were the direct measure of memory. The effect of consistency of order of presentation on the number of words recalled was the indirect measure of memory for temporal order. Results suggest that direct, but not the indirect measures of memory were related to age.

Age-related differences in pictorial implicit memory: role of perceptual and conceptual processes

This study examined the effects of perceptual and conceptual encoding processes on younger and older adults' implicit and explicit memory for pictures. During acquisition, participants studied simple line drawings under varying encoding task conditions. Half of the participants judged the orientation of the central object, a perceptual encoding task. The other half indicated the taxonomic category to which the object belonged, a conceptual encoding task. Implicit memory measures were priming in picture-fragment and word-fragment completion. Explicit measures were free recall and recognition. Results showed that the magnitude of age differences in primed picture completion varied across encoding task conditions. Age deficits occurred on both explicit tasks. Implications of these results for current views on implicit memory aging are discussed.

Full versus divided attention and implicit memory performance

Effects of full and divided attention during study on explicit and implicit memory performance were investigated in two experiments. Study time was manipulated in a third experiment. Experiment 1 showed that both similar and dissociative effects can be found in the two kinds of memory test, depending on the difficulty of the concurrent tasks used in the divided-attention condition. In this experiment, however, standard implicit memory tests were used and contamination by explicit memory influences cannot be ruled out. Therefore, in Experiments 2 and 3 the process dissociation procedure was applied. Manipulations of attention during study and of study time clearly affected the controlled (explicit) memory component, but had no effect on the automatic (implicit) memory component. Theoretical implications of these findings 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-attention-demanding) 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.

Effects of lorazepam and diazepam on conscious and automatic memory processes

Recent studies exploring benzodiazepine memory effects have used the distinction between explicit and implicit tasks. There is now increasing evidence that implicit tasks can be "contaminated" by conscious uses of memory and that unconscious (automatic) use of memory can contaminate explicit tasks, leading to mistaken estimates of their respective influences on memory performance. The aim of the present double-blind, double-placebo study was to assess the memory effects of diazepam and lorazepam using a process-dissociation procedure in a stem-completion task, this procedure providing uncontaminated estimates of conscious and automatic memory processes. The memory task was administrated to 60 healthy volunteers randomly assigned to one of three parallel groups (placebo, diazepam 0.3 mg/kg, lorazepam 0.038 mg/kg). Lorazepam markedly reduced conscious as well as automatic influences of memory. Diazepam also reduced conscious uses of memory, albeit to a lesser extent than lorazepam, but did not decrease the influence of automatic memory. Secondary analyses showed that when the deleterious effect on conscious uses of memory was equated between a diazepam subgroup and the lorazepam group, only lorazepam impaired the automatic use of memory. This study strongly suggests a qualitative difference in the memory effects of the two benzodiazepines. It has some implications regarding the relationships between states of consciousness and memory processes.

Divided attention and indirect memory tests

Attentional state during acquisition is an important determinant of performance on direct memory tests. In two experiments we investigated the effects of dividing attention during acquisition on conceptually driven and data-driven indirect memory tests. Subjects read a list of words with or without distraction. Memory for the words was later tested with an indirect memory test or a direct memory test that differed only in task instructions. In Experiment 1, the indirect test was category-exemplar production (a conceptually driven task) and the direct test was category-cued recall. In Experiment 2, the indirect test was word-fragment completion (a data-driven task) and the direct test was word-fragment cued recall. Dividing attention at encoding decreased performance on both direct memory tests. Of the indirect tests, category-exemplar production but not word-fragment completion was affected. The results indicate that conceptually driven indirect memory tests, like direct memory tests, are affected by divided attention, whereas data-driven indirect tests are not. These results are interpreted within the transfer-appropriate processing framework.

Conceptual implicit memory: a developmental study

The widely accepted standpoint that implicit memory emerges earlier in development than explicit memory, and is more stable from childhood to adult age, is based on experimental data essentially collected in perceptual tasks. The present study was aimed at investigating whether these findings still hold when a more conceptual task is used. We compared the performance of children at two age levels (2nd and 4th grades) on a category-exemplar generation task. Results showed that performances of the two groups were comparable when the target items were typical of their categories, as in Experiment 2, and for a subset of the items in Experiment 1. However, the older children outperformed the younger children in Experiment 1 when the items selected were atypical of their categories. Interpretations of these findings are discussed.

Lorazepam and diazepam effects on memory acquisition in priming tasks

Unlike diazepam, lorazepam has repeatedly been shown to impair perceptual priming as well as explicit memory. To determine whether this deleterious effect was due to an impairment in acquisition of information, 60 healthy volunteers were randomly assigned to five treatment groups (placebo, lorazepam 0.026 or 0.038 mg/kg, diazepam 0.2 or 0.3 mg/kg) and successively performed perceptual priming tasks and a free-recall task. Priming performance on information learned before or 2 h after drug administration, i.e. at the peak concentration of lorazepam, was assessed under the influence of the drugs, using a picture-fragment and a word-stem completion task. Free-recall performance was altered by both drugs. Lorazepam decreased priming performance when information was acquired after, but not before, drug administration, indicating that the drug alters the acquisition of information. Lorazepam also impaired the ability to identify fragmented pictures, but there was no evidence that this perceptual effect accounts for the priming impairment. Surprisingly, diazepam also decreased priming when information was acquired after drug administration, suggesting that, at least in certain circumstances, the two benzodiazepines may exert similar effects on priming measures.

On the origin of functional differences in recollective experience

Subjects studied target words that were repeated either immediately (lag0) or after six intervening items (lag6). At retention testing, subjects were required to discriminate targets from distractors and, contingent on a 'yes' response, to classify each identified item as one that evoked either a 'remember' (R) response or a 'know' (K) response. An R response indicated recognition based on conscious recollection, and K, recognition without conscious recollection. R responses were significantly greater in lag6 than lag0 whereas the reverse was found for K responses. The data are interpreted as showing that R responses depend on the probability of a target stimulus engaging conscious effortful processing, whereas K responses are increased in the absence of conscious involvement at learning.