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In this article, we report on two experiments that aimed to shed light on the memorability effect that derives from varying the uniqueness of contextual cues presented at encoding and retrieval. We sought to understand the locus of the recognition advantage for studying and testing words with nominally irrelevant features that are rarely shared with other words ('low-fan' features) as compared with features that are studied with more words ('high-fan' features). Each word was studied with one high-fan feature and one low-fan feature, but only one of the two features was reinstated at test. Recognition judgments were more accurate when the low-fan feature was reinstated than when the high-fan feature was reinstated. The data suggest that encoding cues that suffer from contextual interference negatively affect retrieval and do so by hindering recollection-based processing. [ABSTRACT FROM AUTHOR]

Research on the list strength effect (LSE) has shown that learning some words on a list more strongly than others impairs memory for the weakly learned words when tested with a recall task. Norman (2002) demonstrated that the LSE also occurs within the recollection process of a recognition test. In this study, a mechanistic dual-process account of the LSE was tested that simultaneously makes predictions concerning additional sources of context in interference effects. In two experiments, we attempted to replicate Norman's (2002) findings and provide the basis for our modeling efforts. We found evidence for a recollection LSE in raw measures of responding, with memory performance also benefiting from reinstatement of perceptual characteristics at test. However, large differences in the hits between the lists were accompanied by small differences in false alarms, such that when d' is calculated, differences between the lists are not significant. We propose an account of the LSE whereby the actual effect of competition between items on the list is small, although present, and difficult to distinguish from large effects of bias due to the strength manipulations. We argue that our findings provide support for a mechanistic explanation of LSE that is based on competition of source activation and changes in the thresholds for responses. [ABSTRACT FROM AUTHOR]

Using the false memory paradigm (Deese, 1959), recently revived by Roediger and McDermott (1995), we examined the effect on true and false recognition of presenting study items in unusual looking fonts. In one condition, each font was associated with a single study item. In a second condition, each font was presented 12 times per study list, randomly distributed across several themes. In a third condition, each font was presented 12 times in the study list, and was associated with a particular study theme. False recognition levels were lowest when there was a unique association between each font and a single study item, whereas false recognition levels were highest when all items from a theme were presented in the same font. Further, the effects of font condition on false recognition of lures maintained when font condition was manipulated within participants and lists. These results, taken together, are inconsistent with theories proposing that false recognition reduction is the product of global shifts in response strategies across conditions (e.g., Schacter, Israel, & Racine, 1999). However, perspectives highlighting the effects of memory based processes on true and false recognition provide an adequate account. Copyright © 2003 by Elsevier Science (USA). [ABSTRACT FROM AUTHOR]

To further the understanding of the mechanisms of strategy choice, in three experiments, we investigate the role of explicit awareness and working memory in strategy adaptivity. Experiment 1 provided correlational evidence that individual differences in strategy adaptivity to changing base rates are related to individual differences in awareness of those changes but appear not to be related to individual differences in working memory capacity. Experiment 2 replicated the role of awareness, and the results suggest that awareness at the time of the base-rate change, rather than afterwards, is related to increased strategy adaptivity. Experiment 3 measured working memory capacity using a different procedure and manipulated working memory load with a dual-task procedure; again, no apparent role of working memory capacity in strategy adaptivity was found. This juxtaposition of findings presents a challenge for existing models of strategy choice. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of experimentally delivered acute pain on memory. Twenty-five participants participated in experimental sessions on consecutive days. The first session involved a categorization task to encourage memory encoding. There were two conditions, presented in randomized order, in which participants listened to a series of words, which were repeated three times. In one condition, one-third of the word items were immediately followed by a painful electrical shock. This word-shock pairing was consistent across repetition and the pain-paired items were presented unpredictably. In the other condition, all word items were not associated with pain. Response times over these repeated presentations were assessed for differences. Explicit memory was tested the following day, employing a Remember-Know assessment of word recognition, with no shocks employed. We found evidence that recollection may be reduced for pain-paired words, as the proportion of correct Remember responses (out of total correct responses) was significantly lower. There were no significant reductions in memory for non-pain items that followed painful stimulation after a period of several seconds. Consistent with the experience of pain consuming working memory resources, we theorize that painful shocks interrupt memory encoding for the immediately preceding experimental items, due to a shift in attention away from the word item., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Normative word frequency has played a key role in the study of human memory, but there is little agreement as to the mechanism responsible for its effects. To determine whether word frequency affects binding probability or memory precision, we used a continuous reproduction task to examine working memory for spatial positions of words. In three experiments, after studying a list of five words, participants had to report the spatial location of one of them on a circle. Across experiments we varied word frequency, presentation rate, and the proportion of low-frequency words on each trial. A mixture model dissociated memory precision, binding failure, and guessing rate parameters from the continuous distribution of errors. On trials that contained only low- or only high-frequency words, low-frequency words led to a greater degree of error in recalling the associated location. This was due to a higher word-location binding failure and not due to differences in memory precision or guessing rates. Slowing down the presentation rate eliminated the word frequency effect by reducing binding failures for low-frequency words. Mixing frequencies in a single trial hurt high-frequency and helped low-frequency words. These findings support the idea that word frequency can lead to both positive and negative mnemonic effects depending on a trade-off between an HF encoding advantage and a LF retrieval cue advantage. We suggest that (1) low-frequency words require more resources for binding, (2) that these resources recover gradually over time, and that (3) binding fails when these resources are insufficient. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Background: Despite the well-known clinical effects of midazolam and ketamine, including sedation and memory impairment, the neural mechanisms of these distinct drugs in humans are incompletely understood. The authors hypothesized that both drugs would decrease recollection memory, task-related brain activity, and long-range connectivity between components of the brain systems for memory encoding, pain processing, and fear learning., Methods: In this randomized within-subject crossover study of 26 healthy adults, the authors used behavioral measures and functional magnetic resonance imaging to study these two anesthetics, at sedative doses, in an experimental memory paradigm using periodic pain. The primary outcome, recollection memory performance, was quantified with d' (a difference of z scores between successful recognition versus false identifications). Secondary outcomes were familiarity memory performance, serial task response times, task-related brain responses, and underlying brain connectivity from 17 preselected anatomical seed regions. All measures were determined under saline and steady-state concentrations of the drugs., Results: Recollection memory was reduced under midazolam (median [95% CI], d' = 0.73 [0.43 to 1.02]) compared with saline (d' = 1.78 [1.61 to 1.96]) and ketamine (d' = 1.55 [1.12 to 1.97]; P < 0.0001). Task-related brain activity was detected under saline in areas involved in memory, pain, and fear, particularly the hippocampus, insula, and amygdala. Compared with saline, midazolam increased functional connectivity to 20 brain areas and decreased to 8, from seed regions in the precuneus, posterior cingulate, and left insula. Compared with saline, ketamine decreased connectivity to 17 brain areas and increased to 2, from 8 seed regions including the hippocampus, parahippocampus, amygdala, and anterior and primary somatosensory cortex., Conclusions: Painful stimulation during light sedation with midazolam, but not ketamine, can be accompanied by increased coherence in brain connectivity, even though details are less likely to be recollected as explicit memories., (Copyright © 2021, the American Society of Anesthesiologists. All Rights Reserved.)

High-complexity stimuli are thought to place extra demands on working memory when processing and manipulating such stimuli; however, operational definitions of complexity are not well established, nor are the measures that would demonstrate such effects. Here, we argue that complexity is a relative quantity that is affected by preexisting experience. Experiment 1 compared cued-recall performance for Chinese and English speakers when the stimuli involved Chinese features that varied in the number of strokes or involved Ethiopic features unfamiliar to both groups. Chinese pseudocharacters (two radicals) had half the strokes of Chinese pseudowords (two characters). The response terms were English words familiar to both groups. English speakers performed equivalently with the Ethiopic and pseudocharacters, but much worse on the pseudowords. In contrast, Chinese speakers performed equivalently with pseudowords or pseudocharacters, but worse with Ethiopic cues. Experiment 2 showed that the lack of a complexity effect for Chinese speakers was not due to greater ease of rehearsal of pseudowords compared with pseudocharacters. Experiment 3 ruled out that Chinese speakers are just better at learning paired associates involving Mandarin by demonstrating that while complexity did not affect them, other features of the stimuli did. Taken together, it appears that complexity is not an absolute property based on the number of visual elements, but rather a relative property affected by one's prior knowledge.

Despite the conventional wisdom that it is more difficult to find a target among similar distractors, this study demonstrates that this disadvantage is short-lived, and that high target-to-distractor (TD) similarity during visual search training can have beneficial effects for learning. Participants with no prior knowledge of Chinese performed 12 hour-long sessions over 4 weeks, where they had to find a briefly presented target character among a set of distractors. At the beginning of the experiment, high TD similarity hurt performance, but the effect reversed during the first session and remained positive throughout the remaining sessions. This effect was due primarily to reducing false alarms on trials in which the target was absent from the search display. In addition, making an error on a trial with a specific character was associated with slower visual search response times on the subsequent repetition of the character, suggesting that participants paid more attention in encoding the characters after false alarms. Finally, the benefit of high TD similarity during visual search training transferred to a subsequent N-back working-memory task. These results suggest that greater discrimination difficulty likely induces stronger and more distinct representations of each character.

We present a review of frequency effects in memory, accompanied by a theory of memory, according to which the storage of new information in long-term memory (LTM) depletes a limited pool of working memory (WM) resources as an inverse function of item strength. We support the theory by showing that items with stronger representations in LTM (e.g., high frequency items) are easier to store, bind to context, and bind to one another; that WM resources are involved in storage and retrieval from LTM; that WM performance is better for stronger, more familiar stimuli. We present a novel analysis of preceding item strength, in which we show from nine existing studies that memory for an item is higher if during study it was preceded by a stronger item (e.g., a high frequency word). This effect is cumulative (the more prior items are of high frequency, the better), continuous (memory proportional to word frequency of preceding item), interacts with current item strength (larger for weaker items), and interacts with lag (decreases as the lag between the current and prior study item increases). A computational model that implements the theory is presented, which accounts for these effects. We discuss related phenomena that the model/theory can explain. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

In the present study, we used an item-method directed-forgetting paradigm to test whether instructions to forget or remember one item affect memory for subsequently studied items. In two experiments ( N s = 138 and 33, respectively), recall was higher when a word pair was preceded during study by a to-be-forgotten word pair. This effect was cumulative: Performance increased when more preceding study items were to be forgotten. The effect decreased when memory was conditioned on instructions for items appearing farther back in the study list. Experiment 2 used a dual-task paradigm that suppressed, during encoding, verbal rehearsal or attentional refreshing. Neither task removed the effect, ruling out that rehearsal or attentional borrowing is responsible for the advantage conferred from previous to-be-forgotten items. We propose that memory formation depletes a limited resource that recovers over time and that to-be-forgotten items consume fewer resources, leaving more resources available for storing subsequent items. A computational model implementing the theory provided excellent fits to the data.

In this study, we sought to examine the effect of experimentally induced somatic pain on memory. Subjects heard a series of words and made categorization decisions in two different conditions. One condition included painful shocks administered just after presentation of some of the words; the other condition involved no shocks. For the condition that included painful stimulations, every other word was followed by a shock, and subjects were informed to expect this pattern. Word lists were repeated three times within each condition in randomized order, with different category judgments but consistent pain-word pairings. After a brief delay, recognition memory was assessed. Non-pain words from the pain condition were less strongly encoded than non-pain words from the completely pain-free condition. Recognition of pain-paired words was not significantly different than either subgroup of non-pain words. An important accompanying finding is that response times to repeated experimental items were slower for non-pain words from the pain condition, compared to non-pain words from the completely pain-free condition. This demonstrates that the effect of pain on memory may generalize to non-pain items experienced in the same experimental context.

Theoretical explanations of the testing effect (why people learn better from a test than a re-study) have largely focused on either the benefit of attempting to retrieve the answer or on the benefit of re-encoding the queried information after a successful retrieval. While a less parsimonious account, prior neuroimaging evidence has led us to postulate that both of these processes contribute to the benefit of testing over re-study. To provide further empirical support for our position, we recorded ERPs while subjects attempted to recall the second word of a pair when cued with the first. These ERPs were analyzed based on the current response accuracy and as a function of accuracy on the subsequent test, yielding three groups: the first and second tests were correct, the first was correct and the second was not, both were incorrect. Mean amplitude waveforms during the first test showed different patterns depending on the outcome patterns: Between 400 and 700 ms the amplitudes were most positive when both tests were correct and least positive when both were incorrect; mean amplitudes between 700 and 1000 ms only differed as a function of subsequent memory. They were more positive when the second test was correct. Importantly, the later component only predicted subsequent memory when the answers were not overlearned, i.e. only correctly recalled once previously. We interpret the 400-700 ms time window as a component reflecting a retrieval attempt process, which differs as a function of both current and subsequent accuracy, and the later time window as a component reflecting a re-encoding process, which only involves learning from tests, both of which are involved in the testing effect., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Do the processing and online manipulation of stimuli that are less familiar require more working memory (WM) resources? Is it more difficult to solve demanding problems when the symbols involved are less rather than more familiar? We explored these questions with a dual-task paradigm in which subjects had to solve algebra problems of different complexities while simultaneously holding novel symbol-digit associations in WM. The symbols were previously unknown Chinese characters, whose familiarity was manipulated by differential training frequency with a visual search task for nine hour-long sessions over 3 weeks. Subsequently, subjects solved equations that required one or two transformations. Before each trial, two different integers were assigned to two different Chinese characters of the same training frequency. Half of the time, those characters were present as variables in the equation and had to be substituted for the corresponding digits. After attempting to solve the equation, subjects had to recognize which two characters were shown immediately before that trial and to recall the integer associated with each. Solution accuracy and response times were better when the problems required one transformation only; variable substitution was not required; or the Chinese characters were high frequency. The effects of stimulus familiarity increased as the WM demands of the equation increased. Character-digit associations were also recalled less well with low-frequency characters. These results provide strong support that WM capacity depends not only on the number of chunks of information one is attempting to process but also on their strength or familiarity.

We examined the neurobiological basis of temporal resetting, an aspect of temporal order memory, using a version of the delayed-match-to-multiple-sample task. While in an fMRI scanner, participants evaluated whether an item was novel or whether it had appeared before or after a reset event that signified the start of a new block of trials. Participants responded "old" to items that were repeated within the current block and "new" to both novel items and items that had last appeared before the reset event (pseudonew items). Medial-temporal, prefrontal, and occipital regions responded to absolute novelty of the stimulus-they differentiated between novel items and previously seen items, but not between old and pseudonew items. Activation for pseudonew items in the frontopolar and parietal regions, in contrast, was intermediate between old and new items. The posterior cingulate cortex extending to precuneus was the only region that showed complete temporal resetting, and its activation reflected whether an item was new or old according to the task instructions regardless of its familiarity. There was also a significant Condition (old/pseudonew) × Familiarity (second/third presentations) interaction effect on behavioral and neural measures. For pseudonew items, greater familiarity decreased response accuracy, increased RTs, increased ACC activation, and increased functional connectivity between ACC and the left frontal pole. The reverse was observed for old items. On the basis of these results, we propose a theoretical framework in which temporal resetting relies on an episodic retrieval network that is modulated by cognitive control and conflict resolution.

This study explored how temporal context influences recognition. In an ERP experiment, subjects were asked to judge whether pictures, presented one at a time, had been seen since the previous appearance of a special reset screen. The reset screen separated sequences of successively presented stimuli and signaled a change in temporal context. A "new-repeat" picture was one that had been seen before but was to be called "new" because it had not appeared since the previous reset screen. New-repeat pictures elicited a more negative FN400 component than did "old" pictures even though both had seen before during the experiment. This suggests that familiarity, as indexed by the FN400, is sensitive to temporal context. An earlier frontopolar old/new effect distinguished pictures that were seen for the first time in the experiment from all other pictures. The late positive component (LPC), which is typically greater for old stimuli, was smaller for new-repeat pictures than for pictures seen for the first time in the experiment. Finally, individual differences in task performance were predicted by the differences in amplitude of P3b that was evoked by the onset of the reset screen., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Introduction: The testing effect refers to superior retention when study is followed by a test rather than followed by another study. Most research to date on why the testing effect occurs has been behavioral, but we employed neuroimaging methods in this study in order to shed light on the underlying processes., Methods: Subjects were scanned while studying, restudying, and taking cued-recall tests of word pairs (with no feedback). We analyzed the BOLD responses by back sorting the encoding and test trials based on whether the subsequent test was correct or incorrect. We compared the subsequent memory patterns in initial study, restudy, and test trials., Results: Overall, brain activity during test trials was a better predictor of later performance than brain activity during restudy trials. For test trials, we separately examined brain regions associated with the retrieval attempt process during successful retrieval and regions associated with the re-encoding process during retrieval in terms of prediction of subsequent memory. Regions associated with retrieval attempts were found to always predict subsequent memory success (the greater the activation, the more likely the correct recall); however, the regions associated with re-encoding would sometimes predict subsequent failure, specifically when subjects had correctly recalled the associated word several times already., Conclusions: These results suggest that whether a testing effect advantage is observed depends on both on the retrieval process and the re-encoding process which follows that retrieval.

Despite vast efforts to better understand human learning, some principles have been overlooked; specifically, that less familiar stimuli are more difficult to combine to create new knowledge and that this is because less familiar stimuli consume more working memory resources. Participants previously unfamiliar with Chinese characters were trained to discriminate visually similar characters during a visual search task over the course of a month, during which half of the characters appeared much more frequently. Ability to form associations involving these characters was tested via cued recall for novel associations consisting of two Chinese characters and an English word. Each week performance improved on the cued-recall task. Crucially, however, even though all Chinese character pairs were novel each week, those pairs consisting of more familiar characters were more easily learned. Performance on a working-memory task was better for more familiar stimuli, consistent with the claim that familiar stimuli consume fewer working memory resources. These findings have implications for optimal instruction, including second language learning.

This study examined whether there are neural markers of individual differences in working memory (WM) capacity and whether these differences are only manifest when performing a demanding WM task or at all levels of difficulty. Each subject's WM capacity was estimated using a modified digit span task prior to participation in an N-back task that varied difficulty from 1- to 4-back. While performing the N-back task, subjects wore scalp electrodes that allowed measurement of both event-related potentials (ERP) and event-related synchronization and desynchronization (ERS/ERD). Those subjects classified as low WM were more affected by the higher cognitive demands (many more errors in the 4-back task and generally slower responses) than those classified as high WM. These behavioral differences between the two groups were also apparent in the neural markers. Specifically, low WM subjects, when compared with high WM subjects, produced smaller P300 amplitudes and theta ERS, as well as greater alpha ERD at the most difficult level. Importantly, the observed differences in electrophysiological responses between the two groups were also observed at the lowest difficulty level, not just when the task challenged WM capacity. In addition, P300 amplitudes and alpha ERD responses were found to correlate with individual WM capacities independent of the task difficulty. These results suggest that there are qualitative neural differences among individuals with different WM capacities when approaching cognitive operations. Individuals with high WM capacities may make more efficient use of neural resources to keep their attention focused on the task-relevant information when performing cognitive tasks., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The neural mechanism underlying preparation for tasks that vary in difficulty has not been explored. This functional magnetic resonance imaging study manipulated task difficulty by varying the working memory (WM) load of the n-back task. Each n-back task block was preceded by a preparation period involving a screen that indicated the level of difficulty of the upcoming task. Consistent with previous work, activation in some brain regions depended on WM load in the task. These regions were used as regions of interest for the univariate and multivariate (classification) analyses of preparation periods. The findings were that the patterns of brain activation during task preparation contain information about the upcoming task difficulty. (1) A support vector machine classifier was able to decode the n-back task difficulty from the patterns of brain activation during task preparation. Those individuals whose activation patterns for anticipated 1- versus 2- versus 3-back conditions were classified with higher accuracy showed better behavioral performance on the task, suggesting that task performance depends on task preparation. (2) Left inferior frontal gyrus, intraparietal sulcus, and anterior cingulate cortex parametrically decreased activation as anticipated task difficulty increased. Taken together, these results suggest dynamic involvement of the WM network not only during WM task performance, but also during task preparation., (© The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Recent neuroimaging studies have shown that working memory (WM) task difficulty can be decoded from patterns of brain activation in the WM network during preparation to perform those tasks. The inter-regional connectivity among the WM regions during task preparation has not yet been investigated. We examined this question using the graph modeling methods IMaGES and LOFS, applied to the previously published fMRI data of Manelis and Reder (2013). In that study, subjects performed 1-, 2-, and 3-back tasks. Each block of n-back was preceded by a preparation period and followed by a rest period. The analyses of task-related brain activity identified a network of 18 regions that increased in activation from 1- to 3-back (Increase network) and a network of 17 regions that decreased in activation from 1- to 3-back (Decrease network). The graph analyses revealed two types of connectivity sub-networks within the Increase and Decrease networks: "default" and "preparation-related." The "default" connectivity was present not only during task performance, but also during task preparation and during rest. We propose that this sub-network may serve as a core system that allows one to quickly activate cognitive, perceptual and motor systems in response to the relevant stimuli. The "preparation-related" connectivity was present during task preparation and task performance, but not at rest, and depended on the n-back condition. The role of this sub-network may be to pre-activate a connectivity "road map" in order to establish a top-down and bottom-up regulation of attention prior to performance on WM tasks.

People learn better when re-study opportunities are replaced with tests. While researchers have begun to speculate on why testing is superior to study, few studies have directly examined the neural underpinnings of this effect. In this fMRI study, participants engaged in a study phase to learn arbitrary word pairs, followed by a cued recall test (recall second half of pair when cued with first word of pair), re-study of each pair, and finally another cycle of cued recall tests. Brain activation patterns during the first test (recall) of the studied pairs predicts performance on the second test. Importantly, while subsequent memory analyses of encoding trials also predict later accuracy, the brain regions involved in predicting later memory success are more extensive for activity during retrieval (testing) than during encoding (study). Those additional regions that predict subsequent memory based on their activation at test but not at encoding may be key to understanding the basis of the testing effect.

Negative priming (NP) refers to a slower response to a target stimulus if it has been previously ignored. To examine theoretical accounts of spatial NP, we recorded behavioral measures and event-related potentials (ERPs) in a target localization task. A target and distractor briefly appeared, and the participant pressed a key corresponding to the target's location. The probability of the distractor appearing in each of four locations varied, whereas the target appeared with equal probabilities in all locations. We found that response times (RTs) were fastest when the prime distractor appeared in its most probable (frequent) location and when the prime target appeared in the location that never contained a distractor. Moreover, NP effects varied as a function of location: They were smallest when targets followed distractors in the frequent distractor location-a finding not predicted by episodic-retrieval or suppression accounts of NP. The ERP results showed that the P2, an ERP component associated with attentional orientation, was smaller in prime displays when the distractor appeared in its frequent location. Moreover, no differences were apparent between negative-prime and control trials in the N2, which is associated with suppression processes, nor in the P3, which is associated with episodic retrieval processes. These results indicate that the spatial NP effect is caused by both short- and long-term adaptation in preferences based on the history of inspecting unsuccessful locations. This article is dedicated to the memory of Edward E. Smith, and we indicate how this study was inspired by his research career.

In two experiments, we provided support for the hypothesis that stimuli with preexisting memory representations (e.g., famous faces) are easier to associate to their encoding context than are stimuli that lack long-term memory representations (e.g., unknown faces). Subjects viewed faces superimposed on different backgrounds (e.g., the Eiffel Tower). Face recognition on a surprise memory test was better when the encoding background was reinstated than when it was swapped with a different background; however, the reinstatement advantage was modulated by how many faces had been seen with a given background, and reinstatement did not improve recognition for unknown faces. The follow-up experiment added a drug intervention that inhibited the ability to form new associations. Context reinstatement did not improve recognition for famous or unknown faces under the influence of the drug. The results suggest that it is easier to associate context to faces that have a preexisting long-term memory representation than to faces that do not.

Using fMRI, this study examined the relationship between repetition-related changes in the medial temporal lobe (MTL) activation during encoding and subsequent memory for similarity of repetitions. During scanning, subjects classified pictures of objects as natural or man-made. Each object-type was judged twice with presentations of either identical pictures or pictures of different exemplars of the same object. After scanning, a surprise recognition test required subjects to decide whether a probe word corresponded to pictures judged previously. When a subject judged the word as "old," a second judgment was made concerning the physical similarity of the two pictures. Repetition related changes in MTL activation varied depending on whether or not subjects could correctly state that pictures were different. Moreover, psychophysiological interactions analyses showed that accuracy in recalling whether the two pictures were different was predicted by repetition-related changes in the functional connectivity of MTL with frontal regions. Specifically, correct recollection was predicted by increased connectivity between the left posterior hippocampus and the right inferior frontal gyrus, and also by decreased connectivity between the left posterior hippocampus and the left precentral gyrus on the second stimulus presentation. The opposite pattern was found for trials that were incorrectly judged on the nature of the repetition. These results suggest that successful encoding is predicted by a combination of increases and decreases in both the MTL activation and functional connectivity, and not merely by increases in activation and connectivity as suggested previously., (Copyright © 2012 Wiley Periodicals, Inc.)

Using a combination of eye tracking and fMRI in a contextual cueing task, we explored the mechanisms underlying the facilitation of visual search for repeated spatial configurations. When configurations of distractors were repeated, greater activation in the right hippocampus corresponded to greater reductions in the number of saccades to locate the target. A psychophysiological interactions analysis for repeated configurations revealed that a strong functional connectivity between this area in the right hippocampus and the left superior parietal lobule early in learning was significantly reduced toward the end of the task. Practice related changes (which we call "procedural learning") in activation in temporo-occipital and parietal brain regions depended on whether or not spatial context was repeated. We conclude that context repetition facilitates visual search through chunk formation that reduces the number of effective distractors that have to be processed during the search. Context repetition influences procedural learning in a way that allows for continuous and effective chunk updating.

While our previous work suggests that the midazolam-induced memory impairment results from the inhibition of new association formation, little is known about the neural correlates underlying these effects beyond the effects of GABA agonists on the brain. We used arterial spin-labeling perfusion MRI to measure cerebral blood flow changes associated with the effects of midazolam on ability to learn arbitrary word-pairs. Using a double-blind, within-subject cross-over design, subjects studied word-pairs for a later cued-recall test while they were scanned. Lists of different word-pairs were studied both before and after an injection of either saline or midazolam. As expected, recall was severely impaired under midazolam. The contrast of MRI signal before and after midazolam administration revealed a decrease in CBF in the left dorsolateral prefrontal cortex (DLPFC), left cingulate gyrus and left posterior cingulate gyrus/precuneus. These effects were observed even after controlling for any effect of injection. A strong correlation between the midazolam-induced changes in neural activity and memory performance was found in the left DLPFC. These findings provide converging evidence that this region plays a critical role in the formation of new associations and that low functioning of this region is associated with anterograde amnesia., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

The role of the medial temporal lobe (MTL) in associative memory encoding has been the focus of many memory experiments. However, there has been surprisingly little investigation of whether the contributions of different MTL subregions (amygdala, hippocampus [HPC], parahippocampal [PHc], perirhinal cortex [PRc], and temporal polar cortex [TPc]) shift across multiple presentations during associative encoding. We examined this issue using event-related functional magnetic resonance imaging and a multivoxel pattern classification analysis. Subjects performed a visual search task, becoming faster with practice to locate objects whose locations were held constant across trials. The classification analysis implicated right HPC and amygdala early in the task when the speed-up from trial to trial was greatest. The same analysis implicated right PRc and TPc late in learning when speed-up was minimal. These results suggest that associative encoding relies on complex patterns of neural activity in MTL that cannot be expressed by simple increases or decreases of blood oxygenation level-dependent signal during learning. Involvement of MTL subregions during encoding of object-location associations depends on the nature of the learning phase. Right HPC and amygdala support active integration of object and location information, while right PRc and TPc are involved when object and spatial representations become unitized into a single representation.

The present neuroimaging study examines how repetition-related neural attenuation effects differ as a function of the perceptual similarity of the repetition and subsequent memory. One previous study (Turk-Browne et al., 2006) reported greater attenuation effects for subsequent hits than for misses. Another study (Wagner et al., 2000) found that neural attenuation is negatively correlated with subsequent memory. These opposing results suggest that repetition-related neural attenuation for subsequent hits and misses may be driven by different factors. In order to investigate the factors that affect the degree of neural attenuation, we varied perceptual similarity between repetitions in a scanned encoding phase that was followed by a subsequent memory test outside the scanner. We demonstrated that the degree of neural attenuation in the object processing regions depends on the interaction between perceptual similarity across repeated presentations and the quality their encodings. Specifically, the same areas that decreased neural signal for repetitions of same exemplars that were subsequently recognized with confidence that the repetitions were identical showed a decrease in neural signal for different-exemplar misses but not for the corresponding subsequently recognized hits. Our results imply that repetition-related neural attenuation should be related to the more efficient processing of perceptual properties of the stimuli only if subjects are able to subsequently remember the stimuli. Otherwise, the cause of attenuation may be in the failure to encode the stimuli on the second presentation as shown by the pattern of neural attenuation for the different-exemplar misses., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Young and older adults studied word pairs and later discriminated studied pairs from various types of foils including recombined word-pairs and foil pairs containing one or two previously unstudied words. We manipulated how many times a specific word pair was repeated (1 or 5) and how many different words were associated with a given word (1 or 5) to tease apart the effects of item familiarity from recollection of the association. Rather than making simple old/new judgments, subjects chose one of five responses: (a) Old-Old (original), (b) Old-Old (rearranged), (c) Old-New, (d) New-Old, (e) New-New. Veridical recollection was impaired in old age in all memory conditions. There was evidence for a higher rate of false recollection of rearranged pairs following exact repetition of study pairs in older but not younger adults. In contrast, older adults were not more susceptible to interference than young adults when one or both words of the pair had multiple competing associates. Older adults were just as able as young adults to use item familiarity to recognize which word of a foil was old. This pattern suggests that recollection problems in advanced age are because of a deficit in older adults' formation or retrieval of new associations in memory. A modeling simulation provided good fits to these data and offers a mechanistic explanation based on an age-related reduction of working memory., ((c) 2011 APA, all rights reserved.)

When subjects are given the balls-and-boxes problem-solving task (Kotovsky & Simon, 1990), they move rapidly towards the goal after an extended exploratory phase, despite having no awareness of how to solve the task. We investigated possible non-conscious learning mechanisms by giving subjects three runs of the task while recording ERPs. Subjects showed significant differences in their ERP components during the exploratory phase between correct and incorrect moves. Exploratory incorrect moves were associated with a shallower response-locked N1 component and a larger response-locked P3 component compared with exploratory correct moves. Subjects who solved the task more quickly exhibited a trend towards larger N1 and P3 components. These results suggest that the brain processes information about the correctness of a move well before subjects are aware of move correctness. They further suggest that relatively simple attentional and error-monitoring processes play an important role in complex problem-solving., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Subjects performed a rapid feeling-of-knowing task developed by (Reder, L. M., & Ritter, F. (1992). What determines initial feeling of knowing? Familiarity with question terms, not with the answer. Journal of Experimental Psychology: Learning, Memory, and Cognition, 18, 435-451), while event-related potentials (ERPs) were recorded to identify the time course of "feeling-of-knowing" signals. Subjects were shown a series of math problems, some of which were repeated multiple times during the course of the experiment, and subjects had to rapidly decide whether the answer to a given problem could be quickly retrieved from memory (retrieval trials) or had to be calculated on scrap paper (calculate trials). Behavioral results replicated the 1992 study, showing that subjects can estimate whether the answer is known much faster than the answer can be retrieved. ERPs time-locked to the onset of the math problem showed that accurate retrieval trials were associated with greater positivity for an early frontal P2 component (epoched from 180 to 280ms) and a frontal-central P3 component (epoched from 300 to 550ms). Moreover, this feeling-of-knowing signal was not found for subjects who never obtained a successful on-time retrieval. We interpret these findings as suggesting that initial feeling-of-knowing relies on a rapid assessment of the "perceptual fluency" with which the stimulus is processed. If a stimulus is deemed sufficiently familiar, the activation level of an internal problem representation is used to arrive at a decision of whether to search for the answer or to calculate it.

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.

In two experiments, participants studied word pairs and later discriminated old (intact) word pairs from foils, including recombined word pairs and pairs including one or two previously unstudied words. Rather than making old/new memory judgments, they chose one of five responses: (1) Old-Old (original), (2) Old-Old (rearranged), (3) Old-New, (4) New-Old, (5) New-New. To tease apart the effects of item familiarity from those of associative strength, we varied both how many times a specific word-pair was repeated (1 or 5) and how many different word pairs were associated with a given word (1 or 5). Participants could discriminate associative information from item information such that they recognized which word of a foil was new, or whether both were new, as well as discriminating recombined studied words from original pairings. The error and latency data support the view that item and associative information are stored as distinct memory representations and make separate contributions at retrieval.

In a double-blind, placebo-controlled experiment that used midazolam, a benzodiazepine that creates temporary amnesia, we compared acquisition and retention of paired associates of different types. Some word pairs were studied before the injection of saline or midazolam, and two lists of word pairs were studied after the injection. Critical comparisons involved retention of pairs that were practiced on all three lists, pairs studied on only one list, and pairs that involved recombining cue and response terms from one list to the next, as a function of drug condition. Previous research with benzodiazepines had found retrograde facilitation for material acquired prior to injection, compared with the control condition. One explanation for this facilitation is that the anterograde amnesia produced by the benzodiazepine frees up the hippocampus to better consolidate previously learned material (Wixted, 2004, 2005). We accounted for a rich data set using a simple computational model that incorporated interference effects (cue overload) at retrieval for both general (experimental context) interference and specific (stimulus term) interference without the need to postulate a role for consolidation. The computational model as an Excel spreadsheet may be downloaded from www.psychonomic.org/archive.

Recent research and meta-analytic reviews suggest that 1 observed pattern of impaired and intact memory performance with advancing age is a deficit in measures of episodic but not semantic memory. The authors used computational modeling to explore a number of age-related parameters to account for this pattern. A 2-parameter solution based on lifelong experience successfully fit the pattern of results in 5 published studies of the word-frequency mirror effect and paired-associate recognition. Lifelong experience increases the strength (resting level of activation) of concepts in the network but also saturates the network with an increasing number of episodic associations to each concept. More episodic associations to each concept mean that activation spreads more diffusely, making retrieval of any newly established memory trace less likely; however, the greater strength of a concept makes recognition based on familiarity more likely. The simulations provide good quantitative fits to the extant age-related memory literature and support the plausibility of this mechanistic account., (((c) 2007 APA, all rights reserved).)

Rationale: Although there have been many studies examining the effects of benzodiazepines on memory performance, their effects on working memory are equivocal and little is known about whether they affect the efficacy of practice of already learned material., Objectives: The objectives in two experiments were to examine (a) whether midazolam impairs performance on a working memory task designed to minimize mnemonic strategies such as rehearsal or chunking of information to be recalled and (b) the effect of midazolam on repeated practice of paired associates that were learned before drug administration., Materials and Methods: Both experiments involved subcutaneous administration of 0.03 mg of saline or midazolam per kilogram of bodyweight in within-subject, placebo-controlled designs, involving 23 subjects in (a) and 31 in (b)., Results: The drug had no effect on the ability to recall the digits in serial order even though the encoding task prevented the digits from being rehearsed or maintained in an articulatory buffer. Paired associates that were learned before the injection showed a benefit of subsequent practice under saline but not under midazolam., Conclusions: The results suggest that (a) midazolam does not affect the formation of new associations in short-term memory provided that the presentation rate is not too fast to form these associations when sedated, despite the evidence that the drug blocks long-term memory (LTM) retention of associations; and (b) the potential for over-learning with practice of learned associations in LTM is adversely affected by midazolam such that repeated exposures do not strengthen new learning.

Midazolam is a drug that creates temporary anterograde amnesia. In a within-subjects, double-blind experiment, participants studied a list of stimuli after receiving an injection of midazolam in one session and after receiving saline in another session. The lists consisted of three types of stimuli: words, photographs, and abstract pictures. Recognition memory was tested at the end of each session. Memory was reliably poorer in the midazolam condition than the saline condition, but this amnesic effect was significantly smaller for pictorial stimuli than for words and almost nonexistent for abstract pictures. We argue that the less familiar the stimulus, the less likely it is to be associated with an experimental context. These data bolster our claim that unitization increases the chances of episodic binding and that drug-induced amnesia prevents episodic binding regardless of unitization.

Low-frequency words produce more hits and fewer false alarms than high-frequency words in a recognition task. The low-frequency hit rate advantage has sometimes been attributed to processes that operate during the recognition test (e.g., L. M. Reder et al., 2000). When tasks other than recognition, such as recall, cued recall, or associative recognition, are used, the effects seem to contradict a low-frequency advantage in memory. Four experiments are presented to support the claim that in addition to the advantage of low-frequency words at retrieval, there is a low-frequency disadvantage during encoding. That is, low-frequency words require more processing resources to be encoded episodically than high-frequency words. Under encoding conditions in which processing resources are limited, low-frequency words show a larger decrement in recognition than high-frequency words. Also, studying items (pictures and words of varying frequencies) along with low-frequency words reduces performance for those stimuli., (Copyright 2006 APA, all rights reserved.)

The majority of computationally specified models of recognition memory have been based on a single-process interpretation, claiming that familiarity is the only influence on recognition. There is increasing evidence that recognition is, in fact, based on two processes: recollection and familiarity. This article reviews the current state of the evidence for dual-process models, including the usefulness of the remember/know paradigm, and interprets the relevant results in terms of the source of activation confusion (SAC) model of memory. We argue that the evidence from each of the areas we discuss, when combined, presents a strong case that inclusion of a recollection process is necessary. Given this conclusion, we also argue that the dual-process claim that the recollection process is always available is, in fact, more parsimonious than the single-process claim that the recollection process is used only in certain paradigms. The value of a well-specified process model such as the SAC model is discussed with regard to other types of dual-process models.

Previous recognition memory studies have looked for differences in brain activity during recollection- and familiarity-based responding. Although an ERP component correlated with recollection success has been reported, no analogous component related to search initiation has been found. We argue that such a component has not been discovered because studies have compared trials in which participants have made a search attempt and failed (such as Know responses) with those in which the search attempt is successful (such as Remember responses). In the current study, we compared a task that required judgments of lifetime familiarity (differentiating famous from nonfamous names) with one that required judgments of episodic information (deciding whether a name was seen previously in the experiment). By comparing a task on which familiarity judgments were made with no search attempt to a second task in which a search attempt was likely to occur, we identified a component that may reflect the initiation of a memory search. This effect, maximal between 190 and 235 ms, is correlated with Old judgments in the episodic task. Previous ERP findings (e.g., FN400, parietal old/new effect) were also replicated in the present study.

K. J. Malmberg, J. Holden, and R. M. Shiffrin (2004) reported more false alarms for low- than high-frequency words when the foils were similar to the targets. According to the source of activation confusion (SAC) model of memory, that pattern is based on recollection of an underspecified episodic trace rather than the error-prone familiarity process. The authors tested the SAC account by varying whether participants were warned about the nature of similar foils and whether the recognition test required the discrimination. More false alarms for low-frequency similar items occurred only when participants were not warned at study about the subtle features to be discriminated later. The differential false-alarm rate by word frequency corresponded to the pattern of remember responses obtained when the test instructions did not ask for a subtle discrimination, supporting the SAC account that reversed false-alarm rates to similar foils are based on the recollection process.

The notion of multiple memory systems based on conscious accessibility has been supported largely by neuropsychological patient studies. Specifically, it was widely held that amnesic patients have impaired explicit memory performance but spared implicit memory performance. However, recent patient studies have called the implicit/explicit memory distinction into question. In this study, normal participants were tested on a visual search task, once after an injection of midazolam, an anesthetic that induces temporary amnesia, and once after an injection of saline. Under the influence of midazolam, participants did not show facilitation in search times for repeated configurations (contextual cuing), although there was a general speed-up in performance across blocks in both the midazolam and saline conditions. Neither the contextual-cuing effect nor the procedural-learning effect was available to subjective experience, yet only one of these was affected by midazolam-induced amnesia. These data call into question the notion that memory systems divide on the basis of subjective experience of consciousness or reportability. Rather, the findings support the contention that anterograde amnesia affects learning that depends on building novel associations in memory and that this deficit does not hinge upon accessibility to consciousness.

As people study more facts about a concept, it takes longer to retrieve a particular fact about that concept. This fan effect (Anderson, 1974) has been attributed to competition among associations to a concept. Alternatively, the mental-model theory (Radvansky & Zacks, 1991) suggests that the fan effect disappears when the related concepts are organized into a single mental model. In the present study, attentional focus was manipulated to affect the mental model to be constructed. One group of participants focused on the person dimension of person-location pairs, whereas the other group focused on the location dimension. The result showed that the fan effect with the focused dimension was greater than the fan effect with the nonfocused dimension, which is contrary to the mental-model theory. The number of associations with a concept is indeed crucial during retrieval, and the importance of the information seems to be accentuated with attentional focus.