Differential effects of bilateral hippocampal CA3 damage on the implicit learning and recognition of complex event sequences.

Learning regularities in the environment is a fundament of human cognition, which is supported by a network of brain regions that include the hippocampus. In two experiments, we assessed the effects of selective bilateral damage to human hippocampal subregion CA3, which was associated with autobiographical episodic amnesia extending ~50 years prior to the damage, on the ability to recognize complex, deterministic event sequences presented either in a spatial or a non-spatial configuration. In contrast to findings from related paradigms, modalities, and homologue species, hippocampal damage did not preclude recognition memory for an event sequence studied and tested at four spatial locations, whereas recognition memory for an event sequence presented at a single location was at chance. In two additional experiments, recognition memory for novel single-items was intact, whereas the ability to recognize novel single-items in a different location from that presented at study was at chance. The results are at variance with a general role of the hippocampus in the learning and recognition of complex event sequences based on non-adjacent spatial and temporal dependencies. We discuss the impact of the results on established theoretical accounts of the hippocampal contributions to implicit sequence learning and episodic memory.

Lower constraint testing enhances the testing effect for some contextual details but not others.

INTRODUCTION: Retrieval practice has been shown to be an effective means of learning new information, a memory phenomenon known as the testing effect or the retrieval practice effect. Some work suggests that the magnitude of the testing effect can be enhanced when the test used for retrieval practice uses fewer cues to retrieve previously studied information. It is unclear, however, whether such testing benefits extend to peripheral contextual details associated with studied materials (e.g., location where stimuli appear, font color in which items are presented, etc.). In this experiment, we examine both item memory (i.e., memory for the studied items) and context memory under conditions where the intervening test offers fewer cues (i.e., lower constraint) compared to more cues (higher constraint) to better understand item and context memory testing effects. METHODS: Participants first studied word pairs presented in one of eight locations as well as in either red or green font color. Then, in the re-exposure phase, participants processed materials in two types of intervening tests (lower constraint and a higher constraint test) as well as in a restudy condition, before a final memory test. RESULTS: For item memory, results showed that memory was better in the lower constraint testing condition compared to both the higher constraint testing condition as well as the restudy (control) condition. For context memory, results indicated improved memory for location context under lower constraint testing compared to both higher constraint testing and restudy conditions. There was no difference in memory, however, for color context across all conditions. CONCLUSION: Overall, these findings suggest that providing fewer cues to aid retrieval in the intervening test can induce better memory for both items as well as some contextual details.

Did I text you? The influence of the mode of transmission on destination memory.

In a society where people often communicate through digital technology, it is crucial to investigate whether the transmission mode influences destination memory performance (our capacity to remember to whom we transmitted certain information). In Experiment 1, we asked young adults (N = 31) to share of a set of familiar proverbs only by typing and the rest by both typing and saying them aloud. Better destination memory was observed when the information was transmitted by the two means (aloud and typing). Did this better performance occur because participants shared the information aloud or because the information was transmitted by two means? In Experiment 2, young adults (N = 34) shared familiar proverbs aloud, by typing, or simultaneously aloud and by typing. Results showed that transmission aloud led to a better destination memory than typing, and no further improvement occurred when the transmission was both aloud and by typing. Additionally, no differences were observed regarding item memory, supporting the idea that item and destination memories are two different types of memory.

Not so different after all? An event-related potential study on item and source memory for object-scene pairs in German and Chinese young adults.

In recent years, several cross-cultural studies reported that Westerners focus more on central aspects of a scene (e.g., an object) relative to peripheral aspects (e.g., the background), whereas Easterners more evenly allocate attention to central and peripheral aspects. In memory tasks, Easterners exhibit worse recognition for the central object when peripheral aspects are changed, whereas Westerners are less affected by peripheral changes. However, most of these studies rely on hit rates without correcting for response bias, whereas studies accounting for response bias failed to replicate cultural differences in memory tasks. In this event-related potential (ERP) study, we investigated item and source memory for semantically unrelated object-scene pairs in German and Chinese young adults using memory measures corrected for response bias (i.e., the discrimination index Pr). Both groups completed study-test cycles with either item memory tests or source memory tests. In item memory blocks, participants completed an old/new recognition test for the central object. Source memory blocks entailed an associative recognition test for the association between object and background. Item and source memory were better for intact than for recombined pairs. However, as verified with frequentist and Bayesian analyzes, this context effect was not modulated by culture. The ERP results revealed an old/new effect for the item memory task in both groups which was again not modulated by culture. Our findings suggest that cultural differences in young adults do not manifest in intentional memory tasks probing memory for object-scene pairs without semantic relations when using bias-corrected memory measures.

Chinese character unitization enhances item memory in addition to associative memory: Evidence from ERP and TFR.

While the effect of unitization on associative memory has been established, its effect on item memory remains debated. This study aimed to investigate the influence of unitization on item memory using Chinese characters to manipulate unitization and recording scalp EEG to elucidate the underlying neural mechanisms. In the learning phase, participants were asked to determine whether the character pairs presented could form a Chinese compound character. In the subsequent testing phase, participants performed item recognition and associative recognition tasks. Behavioral results revealed that unitization not only improved associative memory but also facilitated item memory. Event-related potential analysis indicated there were FN400 effect (related to familiarity) and LPC effect (related to recollection) during associative recognition after unitization, however, only the LPC effect was observed for the item recognition. More importantly, time-frequency analysis demonstrated stronger θ oscillations (associated with recollection) in the unitized condition compared to the non-unitized condition, which further partially mediated the reduction in RT during the item recognition. These results suggest that unitization enhances item memory through recollection, thereby leading to more confident recognition judgments, and that unitization does not impair item processing within an association but rather enables more precise and accurate processing.

Does Expecting Matter? The Impact of Experimentally Established Expectations on Subsequent Memory Retrieval of Emotional Words.

Previous studies have confirmed that different degrees of expectation, including the bipolarity of the expected and unexpected, as well as an intermediate level (no expectation), can affect memory. However, only a few investigations have manipulated expectation through experimentally established schema, with no consideration of how expectation impacts both item and source memory. Furthermore, stimulus emotionality may also impact memory. Therefore, we conducted a study to investigate the effects of three levels of expectation on item and source memory while considering the impact of stimulus emotionality. The experiment began with a phase dedicated to learning the rules. In the subsequent study phase, negative and neutral words were manipulated as expected, no expectation, and unexpected, based on these rules. This was followed by tasks focused on item and source memory. The study found that there was a "U-shape" relationship between expectation and item memory. Additionally, the study revealed the distinct impacts of expectation on item and source memory. When it came to item memory, both expected and unexpected words were better remembered than those with no expectations. In source memory, expected words showed memory inferiority for expectation-irrelevant source information, but an advantage for expectation-relevant source information. Stimulus emotionality modulated the effect of expectation on both item and source memory. Our findings provide behavioral evidence for the schema-linked interactions between medial prefrontal and medial temporal regions (SLIMM) theory, which proposes that congruent and incongruent events enhance memory through different brain regions. The different patterns between item and source memory also support dual-process models. Moreover, we speculate that processing events with varying levels of emotionality may undermine the impact of expectation, as implied by other neural investigations.

The temporal development of memory processes in source monitoring: An investigation with mouse tracking.

The present study investigated whether we first remember an item (e.g., a word itself) and then its source (e.g., position on the screen) or whether the retrieval of item and source information can (partially) overlap. Participants were tested on the source either in immediate sequence to item recognition (as standard in source-monitoring research) or following as a separate block after full completion of the item recognition test to separate these processes in time, providing a baseline. Using the mouse-tracking procedure during the item and source tests, we analyzed how item and source decisions unfolded qualitatively over time. Despite no significant difference in the aggregated trajectory curvatures, more thorough analyses based on the individual trajectories revealed differences across the test formats. In the standard format, trajectories were less curved in the source than in the item test. In contrast, in the blocked format, this difference was in the other direction with source showing more curved trajectories than item. Alternative interpretations of mouse-trajectory curvatures on the source-monitoring paradigm and what their difference may imply for item and source processing are discussed.

Pre-associative item encoding influences associative memory: Behavioral and ERP evidence.

It is unknown whether the manner with which an item is encoded in isolation, immediately before it is encoded into an inter-inter association, influences associative memory. We therefore presented the items of to-be-encoded associative pairings sequentially and manipulated how each first item of a pair was encoded (before associative encoding could begin). Furthermore, we recorded ERPs during memory encoding to investigate the neurocognitive processes that might relate pre-associative item encoding to subsequent associative memory performance. Behaviorally, we found that pre-associative item elaboration (vs. no elaboration) led to a memory tradeoff-enhanced item memory relative to impaired associative memory. This tradeoff likely reflected that item elaboration reduced cognitive resources for ensuing associative encoding, indexed by a reduced P300 and frontal slow wave at the time of associative encoding. However, frontal slow wave subsequent memory effects measured during pre-associative item encoding revealed that, for a given item, greater semantic elaboration was related to better item and associative memory while greater visual elaboration was related to better item and worse associative memory. Thus, there are likely two opposing ways in which pre-associative item encoding can influence associative memory: (1) by depleting encoding resources to impair associative memory and (2) by scaffolding inter-item associations to enhance associative memory. When item encoding occurs immediately before associative encoding, it appears that the temporary depletion of encoding resources is more important in determining later memory performance. Future research should compare the independent effects of resource depletion and encoding strategy during pre-associative item encoding.

Impaired cognitive performance in older adults is associated with deficits in item memory and memory for object features.

Amnestic mild cognitive impairment (aMCI) is associated with damage to the perirhinal/entorhinal cortex, and consequently, deficits in item/object memory. However, cognitive assessments commonly used to identify individuals with aMCI require a clinician to administer and interpret the test. We developed a novel self-administered global cognitive assessment, called the Cognitive Assessment via Keyboard (CAKe). To assess the relationship between CAKe performance and perirhinal/entorhinal cortex-dependent memory function, participants completed the CAKe, a feature source memory task, and a context memory task. During the memory tasks, participants studied line drawings with either a green or orange internal color (feature memory runs) or external color (context memory runs) and then classified each item as old and previously presented with a "green" or "orange" color, or "new". CAKe scores were correlated with item memory accuracies and source memory accuracies on both tasks. Participants with 'impaired' CAKe performance had worse item memory and worse feature source memory accuracies than those with 'normal' CAKe performance. These results demonstrate specific deficits in item memory and feature source memory and suggest that our assessments may be a valid predictor of aMCI memory deficits.

Effect of retrieval reward on episodic recognition with different difficulty: ERP evidence.

Previous studies found that the reward effect is stronger in more difficult retrieval tasks of item memory. However, it remains unclear whether the effect of reward is influenced by the memory task difficulty level in the source memory. We investigated the effects and neural mechanisms of the processing depth during encoding and rewards at retrieval on the item and source memory using event-related potentials (ERPs). Participants were required to carry out the congruity-judgment (deep processing) and size-judgment (shallow processing) tasks during encoding, and they completed separate object and background tests (half presented with reward) immediately after encoding. The results revealed that congruity-judgment (compare to size-judgment) task had longer response time in encoding phase, and evoked significantly greater reward differences at Prs (the hit rate minus the false alarm rate) in item retrieval, and the reward (relative to no reward) significantly improved recognition accuracy in source retrieval. ERP results also showed that congruity-judgment (compare to size-judgment) task evoked the larger N170, P3a, LPP and a decreased P3b of the stimuli in encoding phase, and elicited the wider distribution of LPC and LPN reward effects (i.e., the average amplitudes under the reward condition were significantly more positive than under the non-reward condition) in item retrieval, and the reward effects at FN400, LPC, and LPN were found only in the congruity-judged items with optimal difficulty in source retrieval. The results suggest that reward at retrieval evoked a greater boost in the congruity-judged stimuli, whether in item or source retrieval, which maybe be related to their optimal retrieval difficulty (Pr is closer to medium 0.50). This meant that the reward is more effective in memory retrieval with optimal difficulty.

Affective Enhancement of Episodic Memory Is Associated With Widespread Patterns of Intrinsic Functional Connectivity in the Brain Across the Adult Lifespan.

Subjectively arousing experiences tend to be better remembered than neutral ones. While numerous task-related neuroimaging studies have revealed the neural mechanisms associated with this phenomenon, it remains unclear how variability in the extent to which individuals show superior memory for subjectively arousing stimuli is associated with the intrinsic functional organization of their brains. Here, we addressed this issue using functional magnetic resonance imaging data collected at rest from a sample drawn from the Cambridge Centre for Ageing and Neuroscience cohort (N = 269, 18-86 years). Specifically, we performed multi-voxel pattern analysis of intrinsic functional connectivity, an unbiased, data-driven approach to examine whole-brain voxel-wise connectivity patterns. This technique allowed us to reveal the most important features from the high-dimensional, whole-brain connectivity structure without a priori hypotheses about the topography and direction of functional connectivity differences. Behaviorally, both item and associative memory accuracy were enhanced for trials with affectively arousing (positive or negative) stimuli than those with neutral ones. Whole-brain multi-voxel pattern analysis of functional connectivity revealed that the affective enhancement of memory was associated with intrinsic connectivity patterns of spatially distributed brain regions belonging to several functional networks in the cerebral cortex. Post hoc seed-based brain-behavior regression analysis and principal component analysis of the resulting correlation maps showed that these connectivity patterns were in turn primarily characterized by the involvement of heteromodal association and paralimbic (dorsal attention, salience, and default mode) networks of the cerebral cortex as well as select subcortical structures (striatum, thalamus, and cerebellum). Collectively, these findings suggest that the affective enhancement of episodic memory may be characterized as a whole-brain phenomenon, possibly supported by intrinsic functional interactions across several networks and structures in the brain.

The attentional boost effect facilitates the encoding of contextual details: New evidence with verbal materials and a modified recognition task.

In the attentional boost effect (ABE), words or images encoded with to-be-responded targets are later recalled better than words or images encoded with to-be-ignored distractors. The ABE has been repeatedly demonstrated to improve item memory, whereas evidence concerning contextual memory is mixed, with studies showing both significant and null results. The present three experiments investigated whether the ABE could enhance contextual memory when using a recognition task that allowed participants to reinstate the original study context, by simultaneously manipulating the nature of the instructions provided at encoding. Participants studied a sequence of colored words paired with target (gray circles) or distractor (gray squares) stimuli, under the instructions to remember either the words and their colors (Exps. 1-2) or only the words (Exp. 3) and simultaneously press the space bar whenever a gray circle appeared on the screen. Then, after a brief interval, they were administered a modified recognition task involving two successive stages. First, participants were presented with two different words and had to decide which word was originally encoded; second, they were presented with five colored versions of the (correct) old words and had to remember the color in which they were studied. Results converged in showing that the ABE enhanced contextual memory, although the effect was more robust with intentional encoding instructions.

You won't guess that: On the limited benefits of guessing when learning a foreign language.

Guessing the meaning of a foreign word before being presented with the right answer benefits recognition performance for the translation compared to reading the full translation outright. However, guessing does not increase memory for the foreign-word-to-translation associations, which is crucial for language acquisition. In this study, we aimed to investigate whether this disadvantage of guessing for performance in cued-recall tests would be eliminated if a restudy phase was added. In Experiments 1-3, we consistently demonstrated that guessing resulted in lower cued-recall performance compared to reading, both before and after restudy. Even for items for which participants successfully recalled their initial guesses on the cued-recall test, accuracy levels did not exceed those from the reading condition. In Experiment 4, we aimed to generalize our findings concerning restudy to a different set of materials - weakly associated word pairs. Even though this time guessing led to better performance than reading, consistent with previous studies, this guessing benefit was not moderated by adding a restudy phase. Our results thus underscore the importance of the initial learning phase for future learning and retention, while undermining the usefulness of the learning-through-guessing strategy for acquiring foreign language vocabulary.

Interactions between the hippocampus and fronto-parietal regions during memory encoding in early childhood.

The neural mechanisms underlying memory encoding have received much attention in the literature. Research in adults and school-age children suggest that the hippocampus and cortical regions in both frontal and parietal areas are involved in successful formation of memories. Overall, the hippocampus has been shown to interact with fronto-parietal regions to collaboratively support successful memory encoding for both individual items as well as item details (such as the source or color in which the item was originally encountered). To date, only one study has investigated neural regions engaged during memory encoding in children younger than 8 years of age, which is unfortunate since early childhood is a period of dramatic improvement in memory. This previous study indicated that both the hippocampus and cortical regions are involved during the encoding of subsequently remembered item details (i.e., sources). However, this study reported few interactions between these regions, and it did not explore item memory at a more general level. To fill these gaps, this article reanalyzed data from the previous report, aiming to examine the neural correlates of item memory during encoding in early childhood (4-8 years) and interactions between the hippocampus and fronto-parietal regions during encoding. Consistent with research in older individuals, both the hippocampus and fronto-parietal regions were found to participate in item memory encoding. Additionally, functional connectivity between hippocampus and fronto-parietal regions was significantly related to both subsequent item memory and subsequent source memory. Taken together, these findings suggest that not only the activation of individual brain regions (hippocampus and fronto-parietal regions) but also the functional connections between these regions are important for memory encoding. These data add to the growing literature providing insight into how the hippocampus and cortical regions interact to support memory during development.

Examining the influence of brain stimulation to the medial prefrontal cortex on the self-reference effect in memory.

Past work shows that processing information in relation to the self improves memory which is known as the self-reference effect in memory. Other work suggests that transcranial direct current stimulation (tDCS) can also improve memory. Given recent research on self-reference context memory effects (improved memory for contextual episodic details associated with self-referential processing), we were interested in examining the extent stimulation might increase the magnitude of the self-reference context memory effect. In this investigation, participants studied objects superimposed on different background scenes in either a self-reference or other-reference condition while receiving either active or sham stimulation to the dorsal medial prefrontal cortex (dmPFC), a cortical region known to support self-reference context memory effects. Participants then completed a memory test that assessed item memory (have you seen this object before?) and context memory (with which background scene was this object paired?). Results showed a self-reference context memory effect driven by enhanced memory for stimuli processed in the self-reference compared to the other-reference condition across all participants (regardless of stimulation condition). tDCS, however, had no effect on memory. Specifically, stimulation did not increase the magnitude of the self-reference context memory effect under active compared to sham stimulation. These results suggest that stimulation of the dmPFC at encoding may not add to the memory benefits induced by self-referential processing suggesting a boundary condition to tDCS effects on memory.

STOP SHOUTING AT ME: The Influence of Case and Self-Referencing on Explicit and Implicit Memory.

Evidence suggests that physical changes in word appearance, such as those written in all capital letters, and the use of effective encoding strategies, such as self-referential processing, improves memory. In this study we examined the extent both physical changes in word appearance (case) and encoding strategies engaged at study influence memory as measured by both explicit and implicit memory measures. Participants studied words written in upper and lower case under three encoding conditions (self-reference, semantic control, case judgment), which was followed by an implicit (word stem completion) and then an explicit (item and context) memory test. There were two primary results. First, analyses indicated a case enhancement effect for item memory where words written in upper case were better remembered than lower case, but only when participants were prompted to attend to the case of the word. Importantly, this case enhancement effect came at a cost to context memory for words written in upper case. Second, self-referencing increased explicit memory performance relative to control, but there was no effect on implicit memory. Overall, results suggest an item-context memory trade-off for words written in upper case, highlighting a potential downside to writing in all capital letters, and further, that both physical changes to the appearance of words and differing encoding strategies have a strong influence on explicit, but not implicit memory.

Professional discrepancies of doctors and lawyers in episodic memory: Modulations of professional morality and warning.

Past investigations have consistently demonstrated the robust stereotype-consistent effect in the circumstance of source memory but not always in item memory, including the case of professional stereotype. However, it remains unclear whether the effect still occurs in professional stereotype when considering the attributes of negative (or bad) or positive (or good); besides, it has not been concerned about how does warning work in remembering the professional stereotypical stimuli. The current experiments aimed to address these issues by adopting descriptive sentences as stimuli, which were related or unrelated to doctors and lawyers, and with different professional moral valences (negative, neutral, or positive). Item memory and source memory were tested successively. Experiment 1 without the explicit warning confirmed the reliable stereotype-consistent effect solely in source memory; the modulation of professional morality on memory behaved differently between doctor and lawyer, that is, negativity bias versus positivity bias. When giving an explicit warning (Experiment 2), the stereotype-consistent effect attenuated in the lawyer case, and the occurrence of negativity bias was sensitive to the memory task. Thus, our findings further reinforce the dual-process model; both professional morality and warning work in memory of professional stereotype, depending upon the nature of the profession, the concerned memory task, and also the presence of warning. Implications are made for future research to consider more perspectives.

Sleep deprivation impairs binding of information with its context.

Binding information to its context in long-term memory is critical for many tasks, including memory tasks and decision making. Failure to associate information to its context could be an important aspect of sleep deprivation effects on cognition, but little is known about binding problems from being sleep-deprived at the time of encoding. We studied how sleep deprivation affects binding using a well-established paradigm testing the ability to remember auditorily presented words (items) and their speakers (source context). In a laboratory study, 68 healthy young adults were randomly assigned to total sleep deprivation or a well-rested control condition. Participants completed an affective item and source memory task twice: once after 7-hour awake during baseline and again 24 hours later, after nearly 31 hours awake in the total sleep deprivation condition or 7 hours awake in the control condition. Participants listened to negative, positive, and neutral words presented by a male or female speaker and were immediately tested for recognition of the words and their respective speakers. Recognition of items declined during sleep deprivation, but even when items were recognized accurately, recognition of their associated sources also declined. Negative items were less bound with their sources than positive or neutral items, but sleep deprivation did not significantly affect this pattern. Our findings indicate that learning while sleep-deprived disrupts the binding of information to its context independent of item valence. Such binding failures may contribute to sleep deprivation effects on tasks requiring the ability to bind new information together in memory.

Value-directed memory effects on item and context memory.

The ability to prioritize learning some information over others when that information is considered important or valuable is known as value-directed remembering. In these experiments, we investigate how value influences different aspects of memory, including item memory (memory for the to-be-learned materials) and context memory (memory for peripheral details that occurred when studying items) to get a better understanding of how people prioritize learning information. In this investigation, participants encoded words associated with a range of values (binned into higher, medium, and lower value in Experiment 1, and into higher and lower value in Experiment 2) for a subsequent memory test that measured item memory (Is this item old or new?) as well as both objective context memory (memory for an objectively verifiable contextual detail: In which voice was this item spoken?) and subjective context memory (How many visual, auditory, and extraneous thoughts/feelings can you remember associated with this item?). Results indicated that value influenced item memory but had no effect on objective context memory in both Experiments. In Experiment 2, results showed better subjective context memory for multiple episodic details for higher-value relative to lower-value materials. Overall, these findings suggest that value has a strong influence over some aspects of memory, but not others. This work gives a richer understanding of how people prioritize learning more important over less important information.

Examining the relationship between generation constraint and memory.

Self-generated information is often better remembered than read information (the generation effect). Recent research, however, has shown that generating information under fewer experimental constraints (i.e., fewer limitations on what can be generated) can increase the magnitude of the generation effect. This study systematically varied generation constraint to better understand the effects of constraint on memory. Participants encoded associated cue-target word pairs (above-below) on either the left or right side of a computer monitor. At encoding, generation constraint was manipulated by systematically varying the number of letters given to participants to generate the target word (i.e., above-below; option-choic_; bank-mon__; etc.). At retrieval, participants were given either a recognition, cued recall, or free recall test measuring both item (target word) and context memory (location on the computer monitor). Using mixed-effects logistic regression analyses to control for item-selection effects (e.g., participants producing idiosyncratic targets in some conditions relative to others), results indicated that generation constraint significantly influenced item, but not context (location) memory. The relationship between generation constraint and memory performance, however, differed by the type of memory test administered: Recognition data revealed a curvilinear relationship; cued recall showed a negative, linear relationship; and free recall showed no significant relationship. Overall, these findings provide more evidence that generation constraint has a strong yet complex effect on different aspects of memory, and further delineates some boundary conditions of the influence of generation constraint on memory.