Electrophysiological evidence for the modulation of retrieval orientation by depth of study processing

Effect of familiarity and recollection during constrained retrieval on incidental encoding for new “foil” information

Behavioral studies have demonstrated differences in the effect of constrained retrieval of semantic vs. non-semantic information on the encoding of foils. However, the impact of recognition on foils between semantic and non-semantic trials remains unclear. This study thus examines the roles of recognition—familiarity and recollection—in constrained retrieval for foils. We applied the event-related brain potentials (ERPs) data of new/old effects to elucidate the neural mechanisms underlying the “foil effect.” Participants encoded semantic and non-semantic tasks (Phase 1), were tested in a blocked memory task with new words presented as foils (Phase 2), and performed a surprise recognition task involving foils and completely new words (Phase 3). Behavioral results showed better recognition performance regarding reaction times and accuracy by hit and correct reject for semantic vs. non-semantic trials in Phase 2. Conversely, inferior recognition performance in reaction times and accuracy by hit and correct reject was noted for semantic vs. non-semantic foils in Phase 3. ERP results showed more positive Frontal N400 (FN400) for hit in non-semantic trials, more positive late positive component (LPC) for correct rejects in semantic trials in Phase 2, and more positive LPC for hits in both semantic and non-semantic trials only in Phase 3. Through dual-processing theory, we prove that different task types in constrained retrieval depend on different retrieval processes. Particularly, familiarity may be applied more often in non-semantic trials, and recollection in semantic trials. The difference in processes between semantic and non-semantic trials during constrained retrieval affects incidental encoding of foils.

The role of temporal distance of the events on the spatiotemporal dynamics of mental time travel to one's personal past and future

Mental time travel to personal past and future events shows remarkable cognitive and neural similarities. Both temporalities seem to rely on the same core network involving episodic binding and monitoring processes. However, it is still unclear in what way the temporal distance of the simulated events modulates the recruitment of this network when mental time-travelling to the past and the future. The present study explored the electrophysiological correlates of remembering and imagining personal events at two temporal distances from the present moment (near and far). Temporal distance modulated the late parietal component (LPC) and the late frontal effect (LFE), respectively involved in episodic and monitoring processes. Interestingly, temporal distance modulations differed in the past and future event simulation, suggesting greater episodic processing for near as opposed to far future situations (with no differences on near and far past), and the implementation of greater post-simulation monitoring processes for near past as compared to far past events (with high demands on both near and far future). These findings show that both past and future event simulations are affected by the temporal distance of the events, although not exactly in a mirrored way. They are discussed according to the increasing role of semantic memory in episodic mental time travel to farther temporal distances from the present.

Does testing enhance new learning because it insulates against proactive interference?

Taking a test on previously learned material can enhance new learning. One explanation for this forward testing effect is that retrieval inoculates learners from proactive interference (PI). Although this release-from-PI account has received considerable empirical support, most extant evidence is correlational rather than causal. We tested this account by manipulating the level of PI that participants experience as they studied several lists while receiving interpolated tests or not. In Experiments 1 and 2, we found that testing benefited new learning similarly regardless of PI level. These results contradict those from Nunes and Weinstein (Memory, 20(2), 138-154, 2012), who found no forward testing effect when encoding conditions minimized PI. In Experiments 3 and 4, we failed to replicate their results. Together, our data indicate that reduced PI might be a byproduct, rather than a causal factor, of the forward testing effect.

Study of differences between patients with schizophrenia and healthy people in semantic processing

Semantic processing is important in language comprehension and production, and context can facilitate understanding and accelerate processing speed by pre-activating semantically related words. There are many studies suggesting that patients with schizophrenia have inferior language ability. This study was aimed to examine the differences between patients with schizophrenia and healthy people in semantic processing with Chinese classifier-noun pairs rating tasks. Participants were required to finish rating tasks to judge acceptability of classifier-noun pairs. Also, the Positive and Negative Syndrome Scale (PANSS) was conducted in the schizophrenia group. According to results of variance analysis, schizophrenic patients' accuracy of judgment on the acceptability of classifier-noun pairs differed from the control group (F = 4.13, p < .05), and the contextual effect of classifier constraint could be observed in healthy people (F(1, 31) = 5.38, p < .05) but not in patients with schizophrenia (F(1, 25) = 3.55, p = .07), indicating that they failed to use the contextual information to facilitate language comprehension as healthy people. Stepwise linear regression analysis found that hostility, poor impulse control and suspiciousness/persecution and preoccupation in the PANSS may have contributed to the reduced sensitivity in the rating in patients (t = -2.38-3.80, p < .05).

Retrieval orientation for memories encoded in emotional contexts: An ERP study

Retrieval orientation, which is involved in recognition cue processing, optimizes goal-directed memory retrieval. However, whether the emotionality of encoding context affects subsequent retrieval orientation remains unclear. To clarify this, neutral objects were paired with either emotional or neutral background scenes during the study phase. During recognition test, only neutral objects were presented. The ERP analysis on the correctly rejected new items indicated that at least two processes were modulated by the emotionality of memory: 1) the arousal-modulated effect on the right-frontal scalp, and 2) the posterior-distributed effect, which was found to differentiate between memories with positive and negative valence. Furthermore, the magnitude of posterior-distributed effect was correlated with affective rating. The topographical distribution indicated that retrieval orientation for positive memories involves at least partially different neural circuitries from neutral or negative memories. Our results suggest that the emotionality of encoding context affects subsequent retrieval orientation.

Interactions of Emotion and Self-reference in Source Memory: An ERP Study

The way emotional information is encoded (e.g., deciding whether it is self-related or not) has been found to affect source memory. However, few studies have addressed how the emotional quality and self-referential properties of a stimulus interactively modulate brain responses during stimulus encoding and source memory recognition. In the current study, 22 participants completed five study-test cycles with negative, neutral, and positive words encoded in self-referential versus non-self-referential conditions, while event-related potentials of the electroencephalogram were recorded. An advantage of self-referential processing in source memory performance, reflected in increased recognition accuracy, was shown for neutral and positive words. At the electrophysiological level, self-referential words elicited increased amplitudes in later processing stages during encoding (700-1,200 ms) and were associated with the emergence of old/new effects in the 300-500 ms latency window linked to familiarity effects. In the 500-800 ms latency window, old/new effects emerged for all valence conditions except for negative words studied in the non-self-referential condition. Negative self-referential words also elicited a greater mobilization of post-retrieval monitoring processes, reflected in an enhanced mean amplitude in the 800-1,200 ms latency window. Together, the current findings suggest that valence and self-reference interactively modulate source memory. Specifically, negative self-related information is more likely to interfere with the recollection of source memory features.

Reward anticipation selectively boosts encoding of gist for visual objects

Reward anticipation at encoding enhances later recognition, but it is unknown to what extent different levels of processing at encoding (gist vs. detail) can benefit from reward-related memory enhancement. In the current study, participants (N = 50) performed an incidental encoding task in which they made gist-related or detail-related judgments about pairs of visual objects while in anticipation of high or low reward. Results of a subsequent old/new recognition test revealed a reward-related memory benefit that was specific to objects from pairs encoded in the attention-to-gist condition. These findings are consistent with the theory of long-axis specialization along the human hippocampus, which localizes gist-based memory processes to the anterior hippocampus, a region highly interconnected with the dopaminergic reward network.

Neurocognitive mechanisms underlying working memory encoding and retrieval in Attention-Deficit/Hyperactivity Disorder

Working memory (WM) impairments in ADHD have been consistently reported along with deficits in attentional control. Yet, it is not clear which specific WM processes are affected in this condition. A deficient coupling between attention and WM has been reported. Nevertheless, most studies focus on the capacity to retain information rather than on the attention-dependent stages of encoding and retrieval. The current study uses a visual short-term memory binding task, measuring both behavioral and electrophysiological responses to characterize WM encoding, binding and retrieval comparing ADHD and non-ADHD matched adolescents. ADHD exhibited poorer accuracy and larger reaction times than non-ADHD on all conditions but especially when a change across encoding and test displays occurred. Binding manipulation affected equally both groups. Encoding P3 was larger in the non-ADHD group. Retrieval P3 discriminated change only in the non-ADHD group. Binding-dependent ERP modulations did not reveal group differences. Encoding and retrieval P3 were significantly correlated only in non-ADHD. These results suggest that while binding processes seem to be intact in ADHD, attention-related encoding and retrieval processes are compromised, resulting in a failure in the prioritization of relevant information. This new evidence can also inform recent theories of binding in visual WM.

An ERP investigation of item-scene incongruity at encoding on subsequent recognition

The aim of the present study was to investigate how item-scene incongruity at encoding influences subsequent item recognition and the associated event-related potential (ERP) old/new effects. Participants (N = 26) studied pictures showing an item in a scene, either in a congruent condition (e.g., a tent in a field) or an incongruent condition (e.g., a shower cabin in a field). Items were presented alone at test. Behavioral data revealed a benefit of incongruent information, with greater source memory performance but no significant effect on old/new recognition judgments. Longer response times for old compared to new items showed that participants not only evaluated the old-new status of objects during recognition, but also worked already on the scene context decision relative to the source memory judgment. An ERP incongruity effect was found at study, with greater N400 amplitude in the incongruent condition than the congruent condition. During recognition, the results provide evidence that item-scene incongruity at study increases the amplitude of ERP old/new effects. A mid-frontal N400 old/new effect was found in the early time window (300-500 ms), and a right frontal sub-component was modulated by item-scene incongruity at encoding. The modulation observed in the later time window (500-800 ms) confirmed previous studies showing that the parietal old/new effect reflects the retrieval of episodic contextual details. The present study shows that the magnitude of ERP old/new effects is sensitive to item-scene incongruity at encoding from the early time window in the right frontal region to the later retrieval processes.

Downstream Behavioral and Electrophysiological Consequences of Word Prediction on Recognition Memory

When people process language, they can use context to predict upcoming information, influencing processing and comprehension as seen in both behavioral and neural measures. Although numerous studies have shown immediate facilitative effects of confirmed predictions, the downstream consequences of prediction have been less explored. In the current study, we examined those consequences by probing participants' recognition memory for words after they read sets of sentences. Participants read strongly and weakly constraining sentences with expected or unexpected endings ("I added my name to the list/basket"), and later were tested on their memory for the sentence endings while EEG was recorded. Critically, the memory test contained words that were predictable ("list") but were never read (participants saw "basket"). Behaviorally, participants showed successful discrimination between old and new items, but false alarmed to the expected-item lures more often than to new items, showing that predicted words or concepts can linger, even when predictions are disconfirmed. Although false alarm rates did not differ by constraint, event-related potentials (ERPs) differed between false alarms to strongly and weakly predictable words. Additionally, previously unexpected (compared to previously expected) endings that appeared on the memory test elicited larger N1 and LPC amplitudes, suggesting greater attention and episodic recollection. In contrast, highly predictable sentence endings that had been read elicited reduced LPC amplitudes during the memory test. Thus, prediction can facilitate processing in the moment, but can also lead to false memory and reduced recollection for predictable information.

Elaborately rehearsed information can be forgotten: A new paradigm to investigate directed forgetting

In previous item-method directed forgetting (DF) studies, forgetting may have occurred when the maintenance rehearsal of memory items was performed. In this study, a modified item-method DF paradigm was adopted to investigate whether forgetting instruction could produce a positive effect on forgetting the items that were elaborately rehearsed. During the study phase, a to-be-forgotten (TBF) word was followed by a forgetting cue. If no cue followed, the word was a to-be-remembered (TBR) item. Participants were required to intentionally memorize the word when it appeared. During the test phase, a yes/no recognition (Experiment 1) or a remember/know procedure (Experiment 2) was adopted. The behavioural results revealed that both the hit rate (Experiment 1) and remembering rate (Experiment 2) were higher for TBR relative to TBF words. For correctly identified old words, reaction times were consistently shorter for TBR compared to TBF words. These results revealed superior memory retention for TBR than for TBF words. The event-related potential (ERP) results revealed that, during both FN400 and late-positive complex (LPC) time windows, the remembered TBR words evoked more positive ERPs than the remembered TBF words and correctly rejected (CR) words (i.e., FN400 and LPC old/new effects). However, more negative ERPs were evoked for both remembered and forgotten TBF words than for CR words during the LPC time window (i.e., reversed LPC old/new effect). These results demonstrated that TBF words were associated with lower level of familiarity and recollection process than TBR words. The memory representation of TBF information might be inhibited.

Feasibility of using auditory event-related potentials to investigate learning and memory in nonverbal individuals with Angelman syndrome

The combination of intellectual, communicative, and motor deficits limit the use of standardized behavioral assessments of cognition in individuals with Angelman syndrome (AS). The current study is the first to objectively evaluate learning and memory in AS using auditory event-related potentials (ERP) during passive exposure to spoken stimuli. Fifteen nonverbal individuals with the deletion subtype of AS (age 4-45 years) completed the auditory incidental memory paradigm. Auditory ERPs were recorded in response to a sequence of unfamiliar nonwords, in which one randomly selected stimulus was repeated multiple times and the rest were presented once. Larger parietal responses within 200-500 ms for the repeated nonword compared to novel distracters were associated with caregiver reports of more adaptive communication skills. These findings demonstrate good tolerability of ERP procedures (94% success rate) and indicate that persons with AS can acquire new information following repeated auditory exposure, even in the absence of explicit memorization instructions. Strong associations between the caregiver reports of adaptive functioning and neural indices of auditory learning and memory support the utility of brain-based measures for objectively evaluating higher-order information processing in nonverbal persons with neurodevelopmental disorders.

Incidental memory for faces in children with different genetic subtypes of Prader-Willi syndrome

The present study examined the effects of genetic subtype on social memory in children (7–16 years) with Prader–Willi syndrome (PWS). Visual event-related potentials (ERPs) during a passive viewing task were used to compare incidental memory traces for repeated vs single presentations of previously unfamiliar social (faces) and nonsocial (houses) images in 15 children with the deletion subtype and 13 children with maternal uniparental disomy (mUPD). While all participants perceived faces as different from houses (N170 responses), repeated faces elicited more positive ERP amplitudes (‘old/new’ effect, 250–500ms) only in children with the deletion subtype. Conversely, the mUPD group demonstrated reduced amplitudes suggestive of habituation to the repeated faces. ERP responses to repeated vs single house images did not differ in either group. The results suggest that faces hold different motivational value for individuals with the deletion vs mUPD subtype of PWS and could contribute to the explanation of subtype differences in the psychiatric symptoms, including autism symptomatology.

Direct electrophysiological evidence for the maintenance of retrieval orientations and the role of cognitive control

Retrieval orientations are memory states that bias retrieval towards specific memory contents. Many neuroimaging studies have examined the influence of retrieval orientations on stimulus processing, but very little direct evidence exists regarding the ongoing maintenance of orientations themselves. Participants completed two memory tasks with different retrieval goals. ERPs were time-locked to a pre-stimulus fixation asterisk and contrasted according to retrieval goals. Pre-stimulus ERPs elicited during the two retrieval tasks diverged at frontal electrode sites. These differences onset early and were sustained throughout the fixation-stimulus interval. The functional and spatiotemporal characteristics of this ERP effect comprise the first direct electrophysiological evidence of the ongoing maintenance of retrieval orientations throughout a task. Moreover, this effect was eliminated in participants who performed a stroop task prior to the memory tests, indicating that reserves of cognitive control play an important role in the maintenance of retrieval orientations throughout memory tasks.

•

Pre-stimulus fixation-locked ERPs differed during recognition according to retrieval goal.

•

It is proposed that this preparatory effect is a correlate of retrieval orientation maintenance.

•

The preparatory effect was eliminated in participants who first completed a stroop task.

•

Cognitive control reserves therefore appear to influence retrieval orientation maintenance.

•

Elimination of the preparatory effect was associated with enhanced post-retrieval monitoring.

FN400 and LPC memory effects for concrete and abstract words

According to dual-process models, recognition memory depends on two neurocognitive mechanisms: familiarity, which has been linked to the frontal N400 (FN400) effect in studies using ERPs, and recollection, which is reflected by changes in the late positive complex (LPC). Recently, there has been some debate over the relationship between FN400 familiarity effects and N400 semantic effects. According to one view, these effects are one and the same. Proponents of this view have suggested that the frontal distribution of the FN400 could be due to stimulus concreteness: recognition memory experiments commonly use highly imageable or concrete words (or pictures), which elicit semantic ERPs with a frontal distribution. In the present study, we tested this claim using a recognition memory paradigm in which subjects memorized concrete and abstract nouns; half of the words changed font color between study and test. FN400 and LPC old/new effects were observed for abstract as well as concrete words, and were stronger over right hemisphere electrodes for concrete words. However, there was no difference in anteriority of the FN400 effect for the two word types. These findings challenge the notion that the frontal distribution of the FN400 old/new effect is fully explained by stimulus concreteness.

Electrophysiological evidence for strategically orienting retrieval toward the specific age of a memory

For over a century, memory researchers have extensively studied the differences between retrieving memories that were encoded in the remote past as opposed to recently. Although this work has largely focused on the changes that these memory traces undergo over time, an unexplored issue is whether retrieval attempts and other strategic processes might be differentially oriented in order to effectively access memories of different ages. The current study addressed this issue by instructing participants to retrieve words that were encoded either one week (remote) or about 30 minutes earlier (recent). To maximize the possibility that participants adopted distinct retrieval orientations, separate blocks of the memory test employed exclusion task procedures in which the words from only one encoding period were targeted at a given time, in the face of distractors from the other period. Event-related potentials (ERPs) elicited by correctly-rejected new items were contrasted to minimize confounding effects of retrieval success. The new-item ERPs revealed differences according to the targeted week, such that the ERPs over posterior scalp were more positive-going for the recent compared to remote blocks. Furthermore, using multiple methods, these ERP effects were dissociated from differences in difficulty across the two conditions. The findings provide novel evidence that knowledge about when a memory was initially encoded leads to differences in the adoption of retrieval processing strategies.

Face repetition detection and social interest: An ERP study in adults with and without Williams syndrome

The present study examined possible neural mechanisms underlying increased social interest in persons with Williams syndrome (WS). Visual event-related potentials (ERPs) during passive viewing were used to compare incidental memory traces for repeated vs. single presentations of previously unfamiliar social (faces) and nonsocial (houses) images in 26 adults with WS and 26 typical adults. Results indicated that participants with WS developed familiarity with the repeated faces and houses (frontal N400 response), but only typical adults evidenced the parietal old/new effect (previously associated with stimulus recollection) for the repeated faces. There was also no evidence of exceptional salience of social information in WS, as ERP markers of memory for repeated faces vs. houses were not significantly different. Thus, while persons with WS exhibit behavioral evidence of increased social interest, their processing of social information in the absence of specific instructions may be relatively superficial. The ERP evidence of face repetition detection in WS was independent of IQ and the earlier perceptual differentiation of social vs. nonsocial stimuli. Large individual differences in ERPs of participants with WS may provide valuable information for understanding the WS phenotype and have relevance for educational and treatment purposes.

Genetic variation in the serotonin transporter gene influences ERP old/new effects during recognition memory

Recognition memory is defined as the ability to recognize a previously encountered stimulus and has been associated with spatially and temporally distinct event-related potentials (ERPs). Allelic variations of the serotonin transporter gene (SLC6A4) have recently been shown to impact memory performance. Common variants of the serotonin transporter-linked polymorphic region (5HTTLPR) of the SLC6A4 gene result in long (l) and short (s) allelic variants with carriers of the s allele having lowered transcriptional efficiency. Thus, the current study examines the effects polymorphisms of the SLC6A4 gene have on performance and ERP amplitudes commonly associated with recognition memory. Electroencephalogram (EEG), genetic, and behavioral data were collected from sixty participants as they performed an item and source memory recognition task. In both tasks, participants studied and encoded 200 words, which were then mixed with 200 new words during retrieval. Participants were monitored with EEG during the retrieval portion of each memory task. EEG electrodes were grouped into four ROIs, left anterior superior, right anterior superior, left posterior superior, and right posterior superior. ERP mean amplitudes during hits in the item and source memory task were compared to correctly recognizing new items (correct rejections). Results show that s-carriers have decreased mean hit amplitudes in both the right anterior superior ROI 1000-1500ms post stimulus during the source memory task and the left anterior superior ROI 300-500ms post stimulus during the item memory task. These results suggest that individual differences due to genetic variation of the serotonin transporter gene influences recognition memory.

Age-related effects on perceptual and semantic encoding in memory

This study examined the age-related subsequent memory effect (SME) in perceptual and semantic encoding using event-related potentials (ERPs). Seventeen younger adults and 17 older adults studied a series of Chinese characters either perceptually (by inspecting orthographic components) or semantically (by determining whether the depicted object makes sounds). The two tasks had similar levels of difficulty. The participants made studied or unstudied judgments during the recognition phase. Younger adults performed better in both conditions, with significant SMEs detected in the time windows of P2, N3, P550, and late positive component (LPC). In the older group, SMEs were observed in the P2 and N3 latencies in both conditions but were only detected in the P550 in the semantic condition. Between-group analyses showed larger frontal and central SMEs in the younger sample in the LPC latency regardless of encoding type. Aging effect appears to be stronger on influencing perceptual than semantic encoding processes. The effects seem to be associated with a decline in updating and maintaining representations during perceptual encoding. The age-related decline in the encoding function may be due in part to changes in frontal lobe function.

Event-related potential index of age-related differences in memory processes in adults with Down syndrome

A major goal of aging research is to identify early markers of age-related cognitive decline. Persons with Down syndrome (DS) experience accelerated aging and high risks for dementia, making them a valuable albeit understudied model for testing such markers. This study examined event-related potential (ERP) indices of visual memory in younger (19-25 years) and older (35-40 years) adults with DS using a passive viewing paradigm that did not require memorization or behavioral responses. ERPs were recorded in response to unfamiliar urban and nature scenes, with some images presented once and others repeated multiple times. Within 600 to 900 milliseconds after stimulus onset, repeated stimuli elicited more positive amplitudes in younger participants, indicating stimilus recognition. ERPs of older adults did not show such increases, suggesting reduced memory functioning. ERP indices were unrelated to participants' intellectual functioning, but did correlate with age and caregiver-reported lethargy/withdrawal behaviors. Passive ERP measures of memory processes are sensitive to early stages of cognitive decline in DS and are promising markers of cognitive risk for future aging studies.

Manipulating letter fluency for words alters electrophysiological correlates of recognition memory

The mechanisms that give rise to familiarity memory have received intense research interest. One current topic of debate concerns the extent to which familiarity is driven by the same fluency sources that give rise to certain implicit memory phenomena. Familiarity may be tied to conceptual fluency, given that familiarity and conceptual implicit memory can exhibit similar neurocognitive properties. However, familiarity can also be driven by perceptual factors, and its neural basis under these circumstances has received less attention. Here we recorded brain potentials during recognition testing using a procedure that has previously been shown to encourage a reliance on letter information when assessing familiarity for words. Studied and unstudied words were derived either from two separate letter pools or a single letter pool ("letter-segregated" and "normal" conditions, respectively) in a within-subjects contrast. As predicted, recognition accuracy was higher in the letter-segregated relative to the normal condition. Electrophysiological analyses revealed parietal old-new effects from 500-700 ms in both conditions. In addition, a topographically dissociable occipital old-new effect from 300-700 ms was present in the letter-segregated condition only. In a second experiment, we found that similar occipital brain potentials were associated with confident false recognition of words that shared letters with studied words but were not themselves studied. These findings indicate that familiarity is a multiply determined phenomenon, and that the stimulus dimensions on which familiarity is based can moderate its neural correlates. Conceptual and perceptual contributions to familiarity vary across testing circumstances, and both must be accounted for in theories of recognition memory and its neural basis.

Neural correlates of familiarity and conceptual fluency in a recognition test with ancient pictographic characters

Familiarity and conceptual priming refer to distinct memory expressions and are subtypes of explicit memory and implicit memory, respectively. Given that the neural events that produce conceptual priming may in some cases promote familiarity, distinguishing between neural signals of these two types of memory may further our understanding of recognition memory mechanisms. Although FN400 event-related potentials observed during recognition tests have often been ascribed to familiarity, much evidence suggests that they should instead be ascribed to conceptual fluency. To help resolve this controversy, we studied potentials elicited by unrecognizable ancient Chinese characters. These stimuli were categorized as high or low in meaningfulness based on subjective ratings. Conceptual priming was produced exclusively by repetition of characters high in meaningfulness. During a recognition test in which recollection was discouraged, FN400 old-new effects were observed, and amplitudes of the FN400 potentials varied inversely with familiarity confidence. However, these effects were absent for old items given low meaningfulness ratings. For both high and low meaningfulness, late positive (LPC) potentials were found in old-new comparisons, and LPC amplitudes were greater when higher familiarity confidence was registered during the recognition test. These findings linked familiarity and conceptual fluency with different brain potentials - LPC and FN400, respectively - and provide additional evidence that explicit memory and implicit memory have distinct neural substrates.

Midazolam-induced amnesia reduces memory for details and affects the ERP correlates of recollection and familiarity

Dual process models suggest that recognition memory is supported by familiarity and recollection processes. Previous research administering amnesic drugs and measuring ERPs during recognition memory have provided evidence for separable neural correlates of familiarity and recollection. This study examined the effect of midazolam-induced amnesia on memory for details and the proposed ERP correlates of recognition. Midazolam or saline was administered while subjects studied oriented pictures of common objects. ERPs were recorded during a recognition test 1 day later. Subjects' discrimination of old and new pictures as well as orientation discrimination was worse when they were given midazolam instead of saline. As predicted, the parietal old/new effect was decreased with the administration of midazolam. However, weaker effects on FN400 old/new effects were also observed. These results provide converging pharmacological and electrophysiological evidence that midazolam primarily affects recollection as indexed by parietal ERP old/new effects and memory for orientation, while also exerting some weaker effects on familiarity as indexed by FN400 old/new effects.

Listening to the sound of silence: disfluent silent pauses in speech have consequences for listeners

Silent pauses are a common form of disfluency in speech yet little attention has been paid to them in the psycholinguistic literature. The present paper investigates the consequences of such silences for listeners, using an Event-Related Potential (ERP) paradigm. Participants heard utterances ending in predictable or unpredictable words, some of which included a disfluent silence before the target. In common with previous findings using er disfluencies, the N400 difference between predictable and unpredictable words was attenuated for the utterances that included silent pauses, suggesting a reduction in the relative processing benefit for predictable words. An earlier relative negativity, topographically distinct from the N400 effect and identifiable as a Phonological Mismatch Negativity (PMN), was found for fluent utterances only. This suggests that only in the fluent condition did participants perceive the phonology of unpredictable words to mismatch with their expectations. By contrast, for disfluent utterances only, unpredictable words gave rise to a late left frontal positivity, an effect previously observed following ers and disfluent repetitions. We suggest that this effect reflects the engagement of working memory processes that occurs when fluent speech is resumed. Using a surprise recognition memory test, we also show that listeners were more likely to recognise words which had been encountered after silent pauses, demonstrating that silence affects not only the process of language comprehension but also its eventual outcome. We argue that, from a listener's perspective, one critical feature of disfluency is the temporal delay which it adds to the speech signal.

Interrupted actions affect output monitoring and event-related potentials (ERPs)

Memory for performed and interrupted actions was measured on source recognition and source recall tests in order to investigate output monitoring (i.e., memory for actions). Event-related potentials (ERPs) were recorded during the source recognition test to provide insight into the neural basis of output monitoring (OM). Source identification and recall of performed actions was greater than interrupted actions, thereby replicating the enactment effect. Examination of memory errors revealed that interrupted actions were more often mistaken as performed actions. The ERP data indicated that brain activity elicited by performed actions differed from interrupted and new actions. A clear difference in temporal onset of two ERP effects (i.e., a central-parietal and a frontal ERP difference) was observed, and it supports the previous hypothesis that two distinct processes support OM and source monitoring judgements. The pattern of frontal ERP differences suggested that interrupted actions prompted people to use more systematic decision processes overall to make OM judgements. Central-parietal ERP effects suggested that sensori-motor information was not recollected for interrupted actions--rather OM judgements were based on cognitive operations in this case.

Word learning: An ERP investigation of word experience effects on recognition and word processing

Adults of varying reading comprehension skill learned a set of previously unknown rare English words (e.g., gloaming) in three different learning conditions in which the type of word knowledge was manipulated. The words were presented in one of three conditions: (1) orthography-to-meaning (no phonology); (2) orthography-to-phonology (no meaning); and (3) phonology-to-meaning (no orthography). Following learning, participants made meaning judgments on the learned words, familiar known words, and unpresented (unlearned) rare words while their ERPs were recorded. The behavioral results showed no significant effects of comprehension skill on meaning judgment performance. Contrastingly, the ERP results indicated comprehension skill differences in P600 amplitude; high-skilled readers showed stronger familiarity effects for learned words, whereas less-skilled readers did not distinguish between learned words, familiar words, and unlearned words. Evidence from the P600 and N400 illustrated superior learning of meaning when meaning information was coupled with orthography rather than phonology. These results suggest that the availability of word knowledge (orthography, phonology, and meaning) at learning affects subsequent word identification processes when the words are encountered in a new context.

Picture superiority doubly dissociates the ERP correlates of recollection and familiarity

Two experiments investigated the processes underlying the picture superiority effect on recognition memory. Studied pictures were associated with higher accuracy than studied words, regardless of whether test stimuli were words (Experiment 1) or pictures (Experiment 2). Event-related brain potentials (ERPs) recorded during test suggested that the 300-500 msec FN400 old/new effect, hypothesized to be related to familiarity-based recognition, benefited from study/test congruity, such that it was larger when study and test format remained constant than when they differed. The 500-800 msec parietal old/new effect, hypothesized to be related to recollection, benefited from studying pictures, regardless of test format. The parallel between the accuracy and parietal ERP results suggests that picture superiority may arise from encoding the distinctive attributes of pictures in a manner that enhances their later recollection. Furthermore, when words were tested, opposite effects of studying words versus studying pictures were observed on the FN400 (word > picture) versus parietal (picture > word) old/new effects--providing strong evidence for a crossover interaction between these components that is consistent with a dual-process perspective.

Response bias for picture recognition in patients with Alzheimer disease

OBJECTIVE

To investigate whether changing recognition stimuli from words to pictures would alter response bias in patients with Alzheimer disease (AD).

BACKGROUND

Response bias is an important aspect of memory performance in patients with AD, as they show an abnormally liberal response bias compared with healthy older adults. We have previously found that despite changes in discrimination produced by varying the study and test list length, response bias remained remarkably stable in both patients with AD and older adult controls.

METHODS

Patients with mild AD and healthy older adults underwent two separate study-test sessions of pictures and words. For both pictures and words, increasing study-test list lengths were used to determine whether bias changed as a factor of discrimination or task difficulty.

RESULTS

Consistent with apriori hypotheses, healthy older adults showed increased discrimination and shifted to a more liberal response bias for pictures compared with words. In contrast, despite their higher level of discrimination for pictures, patients with AD showed a similar response bias for both pictures and words. Bias was consistent across varying study-test lengths for both groups.

CONCLUSIONS

These results suggest that response bias is a relatively invariant factor of an individual with AD that remains liberal regardless of discrimination or stimulus type.

Wave-ering: An ERP study of syntactic and semantic context effects on ambiguity resolution for noun/verb homographs

Two event-related potential experiments investigated the effects of syntactic and semantic context information on the processing of noun/verb (NV) homographs (e.g., park). Experiment 1 embedded NV-homographs and matched unambiguous words in contexts that provided only syntactic cues or both syntactic and semantic constraints. Replicating prior work, when only syntactic information was available NV-homographs elicited sustained frontal negativity relative to unambiguous words. Semantic constraints eliminated this frontal ambiguity effect. Semantic constraints also reduced N400 amplitudes, but less so for homographs than unambiguous words. Experiment 2 showed that this reduced N400 facilitation was limited to cases in which the semantic context picks out a nondominant meaning, likely reflecting the semantic mismatch between the context and residual, automatic activation of the contextually-inappropriate dominant sense. Overall, the findings suggest that ambiguity resolution in context involves the interplay between multiple neural networks, some involving more automatic semantic processing mechanisms and others involving top-down control mechanisms.

Not all disfluencies are are equal: The effects of disfluent repetitions on language comprehension

Disfluencies can affect language comprehension, but to date, most studies have focused on disfluent pauses such as er. We investigated whether disfluent repetitions in speech have discernible effects on listeners during language comprehension, and whether repetitions affect the linguistic processing of subsequent words in speech in ways which have been previously observed withers. We used event-related potentials (ERPs) to measure participants' neural responses to disfluent repetitions of words relative to acoustically identical words in fluent contexts, as well as to unpredictable and predictable words that occurred immediately post-disfluency and in fluent utterances. We additionally measured participants' recognition memories for the predictable and unpredictable words. Repetitions elicited an early onsetting relative positivity (100-400 ms post-stimulus), clearly demonstrating listeners' sensitivity to the presence of disfluent repetitions. Unpredictable words elicited an N400 effect. Importantly, there was no evidence that this effect, thought to reflect the difficulty of semantically integrating unpredictable compared to predictable words, differed quantitatively between fluent and disfluent utterances. Furthermore there was no evidence that the memorability of words was affected by the presence of a preceding repetition. These findings contrast with previous research which demonstrated an N400 attenuation of, and an increase in memorability for, words that were preceded by an er. However, in a later (600-900 ms) time window, unpredictable words following a repetition elicited a relative positivity. Reanalysis of previous data confirmed the presence of a similar effect following an er. The effect may reflect difficulties in resuming linguistic processing following any disruption to speech.

Semantic and perceptual effects on recognition memory: evidence from ERP

The present experiments examined how semantic vs. perceptual encoding and perceptual match affect the processes involved in recognition memory. Experiment 1 examined the effects of encoding task and perceptual match between study and test fonts on recognition discrimination for words. Font fan was used to determine the effect of distinctiveness on perceptual match. The semantic encoding task and perceptual match for distinctive items led to better recognition memory. Event-related brain potentials (ERPs) recorded from the human scalp during recognition memory experiments have revealed differences between old (studied) and new (not studied) items that are thought to reflect the activity of memory-related brain processes. In Experiment 2, the semantic encoding task and perceptual match for distinctive words led to better recognition memory by acting on both familiarity and recollection processes, as purportedly indexed by the FN400 and parietal old/new effects. Combined these results suggest that the semantic encoding task and perceptual match for distinctive items aid recognition memory by acting on both familiarity and recollection processes.

Right dorsolateral prefrontal cortex is engaged during post-retrieval processing of both episodic and semantic information

Post-retrieval processes are engaged when the outcome of a retrieval attempt must be monitored or evaluated. Functional neuroimaging studies have implicated right dorsolateral prefrontal cortex (DLPFC) as playing a role in post-retrieval processing. The present study used fMRI to investigate whether retrieval-related neural activity in DLPFC is associated specifically with monitoring the episodic content of a retrieval attempt. During study, subjects were cued to make one of two semantic judgments on serially presented pictures. One study phase was followed by a source memory task, in which subjects responded 'new' to unstudied pictures, and signaled the semantic judgment made on each studied picture. A separate study phase was followed by a task in which the studied items were subjected to a judgment about their semantic attributes. Both tasks required that retrieved information be evaluated prior to response selection, but only the source memory task required evaluation of retrieved episodic information. In both tasks, activity in a common region of right DLPFC was greater for studied than for unstudied items, and the magnitude of this effect did not differ between the tasks. Together with the results of a parallel event-related potential study [Hayama, H. R., Johnson, J. D., & Rugg, M. D. (2008). The relationship between the right frontal old/new ERP effect and post-retrieval monitoring: Specific or non-specific? Neuropsychologia, 46(5), 1211-1223, doi:S0028-3932(07)00390-9], the present findings indicate that putative right DLPFC correlates of post-retrieval processing are not associated exclusively with monitoring or evaluating episodic content. Rather, the effects likely reflect processing associated with monitoring or decision-making in multiple cognitive domains.

Multivoxel pattern analysis reveals increased memory targeting and reduced use of retrieved details during single-agenda source monitoring

We used multivoxel pattern analysis (MVPA) of functional MRI (fMRI) data to gain insight into how subjects' retrieval agendas influence source memory judgments (was item X studied using source Y?). In Experiment 1, we used a single-agenda test where subjects judged whether items were studied with the targeted source or not. In Experiment 2, we used a multiagenda test where subjects judged whether items were studied using the targeted source, studied using a different source, or nonstudied. To evaluate the differences between single- and multiagenda source monitoring, we trained a classifier to detect source-specific fMRI activity at study, and then we applied the classifier to data from the test phase. We focused on trials where the targeted source and the actual source differed, so we could use MVPA to track neural activity associated with both the targeted source and the actual source. Our results indicate that single-agenda monitoring was associated with increased focus on the targeted source (as evidenced by increased targeted-source activity, relative to baseline) and reduced use of information relating to the actual, nontarget source. In the multiagenda experiment, high levels of actual-source activity were associated with increased correct rejections, suggesting that subjects were using recollection of actual-source information to avoid source memory errors. In the single-agenda experiment, there were comparable levels of actual-source activity (suggesting that recollection was taking place), but the relationship between actual-source activity and behavior was absent (suggesting that subjects were failing to make proper use of this information).

Adapting to changing memory retrieval demands: evidence from event-related potentials

This study investigated preparatory processes involved in adapting to changing episodic memory retrieval demands. Event-related potentials (ERPs) were recorded while participants performed a general old/new recognition task and a specific task that also required retrieval of perceptual details. The relevant task remained either constant or changed (predictably or randomly) across trials. Responses were slowed when participants switched from the specific to the general task but not vice versa. Hence, asymmetrical switch costs were observed, suggesting that retrieval preparation is dependent not only on the current retrieval goal but also influenced by recent retrieval attempts. Consistently, over posterior scalp regions ERPs associated with advance preparation were modulated by the preceding task, reflecting increased attentional selection requirements for the general task, and by the foreknowledge about the task sequence. When retrieval demands remained constant, frontal slow-waves elicited by retrieval-cues were more positive going for the specific task, indicating full implementation of a retrieval orientation that allows more efficient retrieval of perceptual details.

ERP correlates of item recognition memory: effects of age and performance

Decline in episodic memory is a common feature of healthy aging. Event-related potential (ERP) studies in young adults have consistently reported several modulations thought to index memory retrieval processes, but relatively limited work has explored the impact of aging on them. Further, work with functional imaging has demonstrated differential neural recruitment in elderly subjects depending on their level of cognitive performance which may reflect compensatory or, alternatively, inefficient processing. In the present study we examined the effect of aging and level of performance on both early (FN400, LPC) and later [late frontal effect (LFE)] ERP indices of recognition memory. We found that the FN400 and LPC were absent or attenuated in the older group relative to young adults, but that the LFE was actually increased, analogous to findings in the functional imaging literature. Additionally, the latter effect was most prominent in the poorer performing older participants. These findings suggest that weak memory retrieval supported by earlier ERP modulations, may lead to an enhanced LFE in the service of additional retrieval attempts.

Effects of age on the neural correlates of retrieval cue processing are modulated by task demands

The electrophysiological correlates of retrieval orientation--the differential processing of retrieval cues according to the nature of the sought-for information--were investigated in healthy young (18-20 years old) and older (63-77 years old) adults. In one pair of study-test cycles, subjects studied either words or pictures presented in one of two visually distinct contexts, and then performed a yes/no recognition task with words as test items. In another pair of study-test cycles, subjects again made recognition judgments, but were required, in addition, to signal the study context for each item judged "old." Young subjects' event-related potentials (ERPs) for new (unstudied) test items were more negative-going when the study material was pictures rather than words, and this effect varied little between the two retrieval tasks. Replicating a previous report [Morcom, A. M., & Rugg, M. D. Effects of age on retrieval cue processing as revealed by ERPs. Neuropsychologia, 42, 1525-1542, 2004], the effects of study material on the ERPs of the older subjects were attenuated and statistically nonsignificant in the recognition task. In the source retrieval task, however, material effects in the older group were comparable in both onset latency and magnitude with those of the young subjects. Thus, the failure of older adults to demonstrate differential cue processing in tests of recognition memory likely reflects the adoption of a specific retrieval strategy rather than the incapacity to process retrieval cues in a goal-directed manner.

Event-related potentials and the study of memory retrieval: A critical review

Memory retrieval has been extensively investigated by a variety of techniques and methodological approaches. The present article reports a critical review on the research investigating this subject by means of event-related potentials (ERP). The main goal is to elucidate the key contributions of this technique regarding episodic memory retrieval, as well as to perform a critical analysis taking into account its major advantages and limitations in the framework of current cognitive neuroscience. Considerations concerning its theoretical contributions and implementation in national universities are also discussed.

Brain potentials distinguish new and studied objects during working memory

We investigated brain responses to matching versus nonmatching objects in working memory (WM) with a modified delayed match-to-sample task using event-related potentials (ERPs). In addition, ERP correlates of new items (new matches/new nonmatches) and previously studied items (studied matches/studied nonmatches) were examined in the WM task. Half of the common visual objects were initially studied until 95% accuracy was attained and half were new. Each memory trial began with the presentation of a sample object followed by nine test objects. Participants indicated whether each test item was the same as the object held in mind (i.e., match) or a nonmatch. Compared to studied matches, new matches evoked activity that was 50 ms earlier and largest at frontal sites. In contrast, P3 activity associated with studied nonmatches was larger than for new nonmatches at mostly posterior sites, which parallels previously reported old-new ERP effects. The ERP source analysis further confirms that the cortical mechanisms underlying matching objects and rejecting irrelevant objects during the task are both temporally and spatially distinct. Moreover, our current findings suggest that prior learning affects brain responses to matching visual items during a WM task.

Neuroimaging techniques for memory detection: scientific, ethical, and legal issues

There is considerable interest in the use of neuroimaging techniques for forensic purposes. Memory detection techniques, including the well-publicized Brain Fingerprinting technique (Brain Fingerprinting Laboratories, Inc., Seattle WA), exploit the fact that the brain responds differently to sensory stimuli to which it has been exposed before. When a stimulus is specifically associated with a crime, the resulting brain activity should differentiate between someone who was present at the crime and someone who was not. This article reviews the scientific literature on three such techniques: priming, old/new, and P300 effects. The forensic potential of these techniques is evaluated based on four criteria: specificity, automaticity, encoding flexibility, and longevity. This article concludes that none of the techniques are devoid of forensic potential, although much research is yet to be done. Ethical issues, including rights to privacy and against self-incrimination, are discussed. A discussion of legal issues concludes that current memory detection techniques do not yet meet United States standards of legal admissibility.

The relationship between the right frontal old/new ERP effect and post-retrieval monitoring: specific or non-specific?

Post-retrieval processes are thought to be engaged when the outcome of an attempt to retrieve information from long-term memory must be monitored or evaluated. Previous research employing event-related potentials (ERPs) has implicated a specific ERP modulation - the 'right frontal old/new effect' - as a correlate of post-retrieval processing. In two experiments we examined whether the right frontal effect is specifically associated with processing of the products of an episodic retrieval attempt. During study, subjects in both experiments made one of two semantic judgments on serially presented pictures. In experiment 1, one study phase was followed by a source memory task, in which subjects responded 'new' to unstudied pictures and signaled the semantic judgment made on each studied picture. A separate study phase was followed by a task in which the studied items required a judgment about their semantic attributes. Robust right frontal effects were elicited by old items in both tasks, indicating that the effects are not selective for the monitoring of the content of information retrieved from episodic memory. In experiment 2, separate study phases were followed by test phases where semantic judgments were made either on old items (as in experiment 1), or on new items. Right frontal effects were elicited by whichever class of items, old or new, required the semantic judgment. Together, these findings indicate that the right frontal old/new effect reflects generic monitoring or decisional processes, rather than processing dedicated to the evaluation of the products of an episodic retrieval attempt.