Binding neutral information to emotional contexts: Brain dynamics of long-term recognition memory

There is abundant evidence in memory research that emotional stimuli are better remembered than neutral stimuli. However, effects of an emotionally charged context on memory for associated neutral elements is also important, particularly in trauma and stress-related disorders, where strong memories are often activated by neutral cues due to their emotional associations. In the present study, we used event-related potentials (ERPs) to investigate long-term recognition memory (1-week delay) for neutral objects that had been paired with emotionally arousing or neutral scenes during encoding. Context effects were clearly evident in the ERPs: An early frontal ERP old/new difference (300–500 ms) was enhanced for objects encoded in unpleasant compared to pleasant and neutral contexts; and a late central-parietal old/new difference (400–700 ms) was observed for objects paired with both pleasant and unpleasant contexts but not for items paired with neutral backgrounds. Interestingly, objects encoded in emotional contexts (and novel objects) also prompted an enhanced frontal early (180–220 ms) positivity compared to objects paired with neutral scenes indicating early perceptual significance. The present data suggest that emotional—particularly unpleasant—backgrounds strengthen memory for items encountered within these contexts and engage automatic and explicit recognition processes. These results could help in understanding binding mechanisms involved in the activation of trauma-related memories by neutral cues.     

The effects of age on the neural correlates of successful episodic retrieval: An ERP study

The neural correlates of successful episodic retrieval (recollection), as reflected in event-related potentials (ERPs), were investigated in young (ca. 20 years; n=18) and older (ca. 70 years; n=16) healthy individuals. Subjects classified a series of pictures according to whether each item was new or had been encountered at study in the context of an animacy or a size judgment task. By manipulating the number of times items were presented for study, subsets of test items were formed for which source accuracy did not differ according to age. Relative to ERPs elicited by unstudied pictures, ERPs elicited by items attracting equivalent levels of source accuracy showed marked age-related differences. Those from younger subjects demonstrated the positive-going left parietal and right frontal old/new effects described in several previous studies of source memory. By contrast, analogous ERPs from older subjects contained a large left-lateralized negative effect that overshadowed the positive-going effects evident in the young. No age-related differences in either parietal or frontal ERP old/new effects were detected at electrode sites overlying the right hemisphere. It is possible that the age-related ERP differences observed in this task primarily reflect the use of different kinds of information as a basis for source judgments.     

Incidental retrieval of emotional contexts in post-traumatic stress disorder and depression: an fMRI study

In the present study, we used fMRI to assess patients suffering from post-traumatic stress disorder (PTSD) or depression, and trauma-exposed controls, during an episodic memory retrieval task that included non-trauma-related emotional information. In the study phase of the task neutral pictures were presented in emotional or neutral contexts. Participants were scanned during the test phase, when they were presented with old and new neutral images in a yes/no recognition memory task. fMRI results for the contrast between old and new items revealed activation in a predominantly left-sided network of cortical regions including the left middle temporal, bilateral posterior cingulate, and left prefrontal cortices. Activity common to all three groups when correctly judging pictures encoded in emotional contexts was much more limited. Relative to the control and depressed groups the PTSD group exhibited greater sensitivity to correctly recognised stimuli in the left amygdala/ventral striatum and right occipital cortex, and more specific sensitivity to items encoded in emotional contexts in the right precuneus, left superior frontal gyrus, and bilateral insula. These results are consistent with a substantially intact neural system supporting episodic retrieval in patients suffering from PTSD. Moreover, there was little indication that PTSD is associated with a marked change in the way negatively valenced information, not of personal significance, is processed.     

An Event-Related Potential Study of Item Recognition Memory in Children and Adults

The purpose of this study was to contrast children's event-related potentials (ERPs) with those of adults in an item recognition memory task. Four-year-old children and adults were presented with pictorial images, one half of which had been previously shown, and were asked to indicate whether each picture had been seen before. In both samples, an old-new effect was found in the ERP, namely that responses to correctly recognized old pictures elicited more positive-going ERPs than responses to correctly rejected new pictures. However, there were differences between adults' and children's ERPs with respect to the asymmetric scalp distribution and the time course of the old-new difference. In adults, the ERP differences between old and new pictures were bilateral, whereas in children the differences had a tendency to be stronger over the right hemisphere. In addition, children's ERP effects for correct discrimination between old and new pictures began around 400 to 500 msec later than it did in adults. The similarities and differences between the child and adult findings are discussed in terms of developmental changes in cognitive abilities that may be mirrored through corresponding changes in ERPs.     

Fearful expressions enhance recognition memory: electrophysiological evidence

Facial expressions play a key role in affective and social behavior. However, the temporal dynamics of the brain responses to emotional faces remain still unclear, in particular an open question is at what stage of face processing expressions might influence encoding and recognition memory. To try and answer this question we recorded the event-related potentials (ERPs) elicited in an old/new recognition task. A novel aspect of the present design was that whereas faces were presented during the study phase with either a happy, fearful or neutral expression, they were always neutral during the memory retrieval task. The ERP results showed three main findings: An enhanced early fronto-central positivity for faces encoded as fearful, both during the study and the retrieval phase. During encoding subsequent memory (Dm effect) was influenced by emotion. At retrieval the early components P100 and N170 were modulated by the emotional expression of the face at the encoding phase. Finally, the later ERP components related to recognition memory were modulated by the previously encoded facial expressions. Overall, these results suggest that face recognition is modulated by top-down influences from brain areas associated with emotional memory, enhancing encoding and retrieval in particular for fearful emotional expressions.     

不同情绪背景下来源记忆的ERPs研究*

使用事件相关电位(ERP)技术和测试来源记忆的多键范式,探讨不同情绪效价背景下来源提取的认知神经机制。学习阶段,同时呈现汉字和3种效价情绪图片(重叠);测验阶段,只呈现汉字,要求被试进行四键判断：旧字且背景为中性,旧字且背景为正性,旧字且背景为负性,新字。结果发现：在提取阶段,刺激呈现后300~500 ms,3种情绪背景下来源判断正确项目和来源判断错误项目都比新项目诱发了更正的ERPs(即都存在新旧效应),这一结果反映出刺激呈现后300~500 ms 是一个早期的项目提取阶段,它独立于来源提取。并且,在中性背景下,两种新旧效应没有差别;而在正性和负性背景下,来源判断正确项目的新旧效应显著大于来源判断错误项目。说明相比于中性背景,情绪背景下被试可能更早对来源信息产生熟悉感。在500~650 ms,3种情绪背景下都存在来源判断正确项目的新旧效应,在来源判断错误项目和新项目之间没有显著差异,来源正确与来源错误有显著的新旧效应差异,但二者在头皮分布上是类似的,这反映了晚期的来源提取过程。同时来源正确的新旧效应在这两个时段有显著不同的头皮分布,表明这两个时段有不同加工过程。另外,在500~650 ms,存在显著的情绪效应,正性背景下正确判断来源诱发的ERPs比中性和负性背景下的更正,而且来源判断错误条件下没有情绪效应。综上所述,来源正确和来源错误可能仅仅反映了大脑激活在量上的不同,并不能推断两者存在质的差异;大脑神经活动的早期不仅反映了对记忆项目的熟悉性,而且也受情绪效应的影响,500 ms之后大脑神经活动反映的是对记忆项目回想的过程,这一回想过程也与情绪效应有关,受到情绪效应的调节。     

Emotional information in body and background hampers recognition memory for faces

Emotional influences on memory for events have long been documented yet surprisingly little is known about how emotional signals conveyed by contextual cues influence memory for face identity. This study investigated how positively and negatively valenced contextual emotion cues conveyed by body expressions or background scenes influence face memory. The results provide evidence of emotional context influence on face recognition memory and show that faces encoded in emotional (either fearful or happy) contexts (either the body or background scene) are less well recognized than faces encoded in neutral contexts and this effect is larger for body context than for scene context. The findings are compatible with the hypothesis that emotional signals in visual scenes trigger orienting responses which may lead to a less elaborate processing of featural details like the identity of a face, in turn resulting in a decreased facial recognition memory.     

Memory errors on emotional lures: Is it possible to mistake a positive stimulus for a negative one?

This study examined whether it is possible for people to mistakenly recognise a stimulus of one emotional valence through exposure to stimuli with another emotional valence that share orthographical relatedness. Across three experiments, the recognition error rates for emotionally distinctive lures were lower than for nondistinctive ones. The reduction in memory errors generalises to different types of emotional distinctiveness: emotional lures from neutral words, neutral lures from emotional words, and lures that have opposite valence from the studied ones. However, emotionally distinctive lures were still prone to memory errors. Repeated exposure to orthographically related items resulted in higher recognition error rates than lures without such exposure. Implications for everyday memory are discussed.     

The role of retrieval mode and retrieval orientation in retrieval practice: insights from comparing recognition memory testing formats and restudying

The effectiveness of retrieval practice for aiding long-term memory, referred to as the testing effect, has been widely demonstrated. However, the specific neurocognitive mechanisms underlying this phenomenon remain unclear. In the present study, we sought to explore the role of pre-retrieval processes at initial testing on later recognition performance by using event-related potentials (ERPs). Subjects studied two lists of words (Chinese characters) and then performed a recognition task or a source memory task, or restudied the word lists. At the end of the experiment, subjects received a final recognition test based on the remember–know paradigm. Behaviorally, initial testing (active retrieval) enhanced memory retention relative to restudying (passive retrieval). The retrieval mode at initial testing was indexed by more positive-going ERPs for unstudied items in the active-retrieval tasks than in passive retrieval from 300 to 900 ms. Follow-up analyses showed that the magnitude of the early ERP retrieval mode effect (300–500 ms) was predictive of the behavioral testing effect later on. In addition, the ERPs for correctly rejected new items during initial testing differed between the two active-retrieval tasks from 500 to 900 ms, and this ERP retrieval orientation effect predicted differential behavioral testing gains between the two active-retrieval conditions. Our findings confirm that initial testing promotes later retrieval relative to restudying, and they further suggest that adopting pre-retrieval processing in the forms of retrieval mode and retrieval orientation might contribute to these memory enhancements.     

Mine to remember: The impact of ownership on recollective experience

Evaluating information with reference to self is associated with enhanced memory, the “self-reference effect”. The effect is found in recognition accompanied by recollective experience (remembering), but not in recognition based on a feeling of knowing. The current research employed an ownership procedure to investigate whether less evaluative forms of self-referential cognition produce similar enhancement of recollective experience. Participants were asked to sort items into baskets that belonged to themselves or a fictitious other. A subsequent remember–know recognition test showed that items encoded in the context of self-ownership were more likely to be correctly recognized than other-owned items. This ownership effect was found in remember, but not know, responses. This finding suggests that creating a self-referential encoding context leads to elaborative representations in episodic memory, even in the absence of explicit self-evaluation.     

Electrophysiological dissociation of retrieval orientation and retrieval effort

The neural correlates of retrieval orientation-the differential processing of retrieval cues according to the form of the sought-for information-and retrieval effort were investigated in a factorial design. ERPs elicited by test words were recorded during four recognition memory tests. Orientation was manipulated by varying study material: The study phases preceding two of the tests employed pictures, whereas the study phases preceding the other two tests employed words. Effort was manipulated by varying difficulty, using a combination of the variables of length of study list and study-test interval. ERPs elicited by correctly classified new test words were sensitive to both the study material and, to a much lesser extent, the difficulty of manipulations. Whereas difficulty effects onset early and were short-lived, the effects of study material onset later, extended for several hundred milliseconds, and did not vary according to difficulty. It was concluded that retrieval orientation exerts a major influence on the processing of recognition memory test items.     

负性情绪对不同语义、空间关系联结记忆的影响

以负性项目-中性场景以及中性项目-中性场景组成的图片对为材料,通过操控项目-场景之间的语义联系和空间距离,考察了负性情绪对不同语义、空间关系联结记忆的影响。结果显示,当项目-场景空间距离较近时,无论项目-场景之间的语义是否相关,负性情绪始终不会影响项目-场景联结记忆;当项目-场景空间距离较远且语义不相关时,负性情绪会削弱项目-场景联结记忆;而当项目-场景空间距离较远且语义相关时,负性情绪会促进项目-场景联结记忆。结果表明,负性情绪对项目-场景联结记忆的影响会受到项目与场景之间语义关系和空间关系的调节,且语义关系在项目-场景空间距离较远时的作用更为突出。     

Neutral details associated with emotional events are encoded: evidence from a cued recall paradigm

Enhanced emotional memory often comes at the cost of memory for surrounding background information. Narrowed-encoding theories suggest that this is due to narrowed attention for emotional information at encoding, leading to impaired encoding of background information. Recent work has suggested that an encoding-based theory may be insufficient. Here, we examined whether cued recall—instead of previously used recognition memory tasks—would reveal evidence that non-emotional information associated with emotional information was effectively encoded. Participants encoded positive, negative, or neutral objects on neutral backgrounds. At retrieval, they were given either the item or the background as a memory cue and were asked to recall the associated scene element. Counter to narrowed-encoding theories, emotional items were more likely than neutral items to trigger recall of the associated background. This finding suggests that there is a memory trace of this contextual information and that emotional cues may facilitate retrieval of this information.     

Memory with and without awareness: performance and electrophysiological evidence of savings.

Event-related potentials (ERPs) recorded on the scalp were shown to be sensitive indicators of the strength of a memory trace on both implicit and explicit tests of memory. In explicit recognition tests, the amplitude of a positive potential identified as P300 was larger for "old" than for "new" words regardless of whether the subject categorized the items correctly. This effect, however, was statistically reliable only when the recognition memory (d') was relatively high. In contrast to ERPs, the reaction times in explicit recognition were sensitive to accuracy but not to repetition. In implicit tests, lexical decisions to repeated words were faster than to newly presented words. The magnitude of the repetition effect varied neither with elapsed time since the last repetition nor with the number of previous repetitions. In contrast, the P300 elicited by the same words were sensitive to both lag and recency of repetition, suggesting that they were influenced by the episodic memory strength of the items.     

Event-related potentials of emotional memory: encoding pleasant,unpleasant, and neutral pictures

Emotional events tend to be remembered better than nonemotional events. We investigated this phenomenon by measuring two event-related potential (ERP) effects: the emotion effect (more positive ERPs for pleasant or unpleasant stimuli than for neutral stimuli) and the subsequent memory effect (more positive ERPs for subsequently remembered items than for subsequently forgotten items). ERPs were measured while subjects rated the emotional content of pleasant, unpleasant, and neutral pictures. As was expected, subsequent recall was better for pleasant and unpleasant pictures than for neutral pictures. The emotion effect was sensitive to arousal in parietal electrodes and to both arousal and valence in frontocentral electrodes. The subsequent memory effect at centroparietal electrodes was greater for emotional pictures than for neutral pictures during an early epoch (400-600 msec). This result suggests that emotional information has privileged access to processing resources, possibly leading to better memory formation.     

Post-encoding emotional arousal enhances consolidation of item memory,but not reality-monitoring source memory

The current study examined whether the effect of post-encoding emotional arousal on item memory extends to reality-monitoring source memory and, if so, whether the effect depends on emotionality of learning stimuli and testing format. In Experiment 1, participants encoded neutral words and imagined or viewed their corresponding object pictures. Then they watched a neutral, positive, or negative video. The 24-hour delayed test showed that emotional arousal had little effect on both item memory and reality-monitoring source memory. Experiment 2 was similar except that participants encoded neutral, positive, and negative words and imagined or viewed their corresponding object pictures. The results showed that positive and negative emotional arousal induced after encoding enhanced consolidation of item memory, but not reality-monitoring source memory, regardless of emotionality of learning stimuli. Experiment 3, identical to Experiment 2 except that participants were tested only on source memory for all the encoded items, still showed that post-encoding emotional arousal had little effect on consolidation of reality-monitoring source memory. Taken together, regardless of emotionality of learning stimuli and regardless of testing format of source memory (conjunction test vs. independent test), the facilitatory effect of post-encoding emotional arousal on item memory does not generalize to reality-monitoring source memory.     

记忆机制中再认的事件相关电位

ERP对于记忆的研究有独到之处,在研究方法是有外显的直接范式和内隐的间接范式,分别表现为ERP新旧效应和重复效应,即在刺激200ms以后的正向偏移.对于记忆提取的ERP效应已有一些理论解释,但在听觉记忆、汉字记忆以及记忆的脑内机制等方面还需要进一步的深入研究.     

故事情境下真实记忆与虚假记忆的活动差异

以故事情境为实验材料,采用学习再认实验范式,通过操纵再认靶词与故事情境的关联性考察了情境故事对关联虚假记忆和真实再认神经活动的影响。结果发现：在记忆再认的熟悉性加工和回想性加工阶段,虚假记忆与真实记忆所诱发FN400和LPC成分走向一致;在额叶后提取阶段,虚假再认所诱发的晚慢成分波幅大于真实再认。结果说明：情境性关联虚假记忆与真实记忆表现出相似的熟悉性和回想性加工,但在后期需耗费额外的加工资源进行成功的提取。     

The effects of conformity on recognition judgements for emotional stimuli

Exposure to another’s account of a shared event can influence the content of an individual’s memory report. We examine whether the emotionality of the to-be-remembered information influences the likelihood that socially encountered post-event information is accepted into memory. Participants were exposed to positive, negative or neutral emotional pictures. Subsequently, they had to discriminate these pictures from new pictures in a ‘yes/no’ recognition decision either before or subsequent to a confederate providing misinformation, accurate or no information. Post-event information influenced participants’ responding in the recognition test. Effects were larger for participants viewing neutral items and persisted for these items on a subsequent private source monitoring test. These findings indicate that people rely more on information from others when encountering non-emotional compared to emotional items. We suggest that increased memory strength in conjunction with access to strong retrieval cues in the recognition test serves to shield emotional items from vulnerability to effects of memory conformity.