Temporal isolation does not facilitate forward serial recall—or does it?

In numerous recent studies in short-term memory, it has been established that forward serial recall is unaffected by the temporal isolation of to-be-remembered items. These findings contradict the temporal distinctiveness view of memory, which expects items that are temporally isolated from their neighbors to be more distinct and hence remembered better. To date, isolation effects have only been found with tests that do not constrain output order, such as free recall. This article reports two experiments that, for the first time, report a temporal isolation effect with forward serial recall, using a running memory task in which the end of the list is unpredictable. The results suggest that people are able to encode and use temporal information in situations in which positional information is of little value. We conclude that the overall pattern of findings concerning temporal isolation supports models of short-term memory that postulate multidimensional representations of items.     

The Isolation, Primacy, and Recency Effects Predicted by an Adaptive LTD/LTP Threshold in Postsynaptic Cells

An item that stands out (is isolated) from its context is better remembered than an item consistent with the context. This isolation effect cannot be accounted for by increased attention, because it occurs when the isolated item is presented as the first item, or by impoverished memory of nonisolated items, because the isolated item is better remembered than a control list consisting of equally different items. The isolation effect is seldom experimentally or theoretically related to the primacy or the recency effects—that is, the improved performance on the first few and last items, respectively, on the serial position curve. The primacy effect cannot easily be accounted for by rehearsal in short-term memory because it occurs when rehearsal is eliminated. This article suggests that the primacy, the recency, and the isolation effects can be accounted for by experience-dependent synaptic plasticity in neural cells. Neurological empirical data suggest that the threshold that determines whether cells will show long-term potentiation (LTP) or long-term depression (LTD) varies as a function of recent postsynaptic activity and that synaptic plasticity is bounded. By implementing an adaptive LTP-LTD threshold in an artificial neural network, the various aspects of the isolation, the primacy, and the recency effects are accounted for, whereas none of these phenomena are accounted for if the threshold is constant. This theory suggests a possible link between the cognitive and the neurological levels.     

Is the enhancement of memory due to reward driven by value or salience?

Past research using two levels of reward has shown that the higher-value items are remembered better than lower-value items and this enhancement is assumed to be driven by an effect of reward value. In the present study, multiple levels of reward were used to test the influence of reward salience on memory. Using a value-learning procedure, words were associated with reward values, and then memory for these words was later tested with free recall. Critically, multiple reward levels were used, allowing us to test two specific hypotheses whereby rewards can influence memory: (a) higher value items are remembered better than lower value items (reward value hypothesis), and (b) highest and lowest value items are remembered best and intermediate-value items are remembered worst (following a U-shaped relationship between value and memory; reward salience hypothesis). In two experiments we observed a U-shaped relationship between reward value and memory, supporting the notion that memory is enhanced due to reward salience, and not purely through reward value.     

What causes the isolation effect?

Events that are incongruent with their prevailing context are usually very well remembered. This fact often is described as the distinctiveness effect in memory, an effect that has served as explanation not only of memory phenomena but also of various other phenomena, including social judgment. The core laboratory paradigm for studying distinctiveness in memory research has long been the isolation paradigm. This paradigm, sometimes attributed to H. von Restorff, yields better memory for an item categorically isolated from surrounding items than for the surrounding items and a proper control item. The authors offer an interpretation of the isolation effect based on the analysis of the processing of similarities and differences among the items. Two experiments provide evidence for this interpretation. The results are discussed in the context of current theories of distinctiveness effects in memory. An appeal is made for a different conceptualization of distinctiveness effects, one that treats distinctiveness as a discriminative process in memory that requires processing of both similarities and differences among items.     

Extensions of the survival advantage in memory: examining the role of ancestral context and implied social isolation

Recent work (e.g., Nairne & Pandeirada, 2010) has shown that words are remembered better when they have been processed for their survival value in a grasslands context than when processed in other contexts. It has been suggested that this is because human memory systems were shaped by evolution specifically to help humans survive. Thus far, the survival processing advantage has mainly been shown with grasslands contexts, which are thought to be particularly relevant to human evolution. The present study demonstrated the survival processing advantage with other contexts (e.g., lost in a jungle), including with contexts that should not, in and of themselves, be relevant to human evolution (e.g., lost in outer space). We further examined whether implied social isolation plays a critical role in the survival advantage to memory by comparing scenarios in which the person is alone versus with other people present (e.g., lost at sea alone or with others), and whether the perceived source of danger is social isolation or other human attackers. A survival advantage was shown in both the isolation and the group settings, and whether the primary source of danger was isolation or other human attackers did not matter. These findings suggest that the survival advantage in memory is not dependent on evolutionarily relevant physical contexts (e.g., grasslands) or particular sources of perceived danger (social isolation vs. perceived attackers), showing the advantage to be robust and applicable to a variety of scenarios.     

Culture impacts the magnitude of the emotion-induced memory trade-off effect

The present study assessed the extent to which culture impacts the emotion-induced memory trade-off effect. This trade-off effect occurs because emotional items are better remembered than neutral ones, but this advantage comes at the expense of memory for backgrounds such that neutral backgrounds are remembered worse when they occurred with an emotional item than with a neutral one. Cultures differ in their prioritisation of focal object versus contextual background information, with Westerners focusing more on objects and Easterners focusing more on backgrounds. Americans, a Western culture, and Turks, an Eastern-influenced culture, incidentally encoded positive, negative, and neutral items placed against neutral backgrounds, and then completed a surprise memory test with the items and backgrounds tested separately. Results revealed a reduced trade-off for Turks compared to Americans. Although both groups exhibited an emotional enhancement in item memory, Turks did not show a decrement in memory for backgrounds that had been paired with emotional items. These findings complement prior ones showing reductions in trade-off effects as a result of task instructions. Here, we suggest that a contextual-focus at the level of culture can mitigate trade-off effects in emotional memory.     

Emotion's influence on memory for spatial and temporal context

Individuals report remembering emotional items vividly. It is debated whether this report reflects enhanced memory accuracy or a bias to believe emotional memories are vivid. We hypothesised emotion would enhance memory accuracy, improving memory for contextual details. The hallmark of episodic memory is that items are remembered in a spatial and temporal context, so we examined whether an item's valence (positive, negative) or arousal (high, low) would influence its ability to be remembered with those contextual details. Across two experiments, high-arousal items were remembered with spatial and temporal context more often than low-arousal items. Item valence did not influence memory for those details, although positive high-arousal items were recognised or recalled more often than negative items. These data suggest that emotion does not just bias participants to believe they have a vivid memory; rather, the arousal elicited by an event can benefit memory for some types of contextual details.     

Emotion's influence on memory for spatial and temporal context

Individuals report remembering emotional items vividly. It is debated whether this report reflects enhanced memory accuracy or a bias to believe emotional memories are vivid. We hypothesized emotion would enhance memory accuracy, improving memory for contextual details. The hallmark of episodic memory is that items are remembered in a spatial and temporal context, so we examined whether an item's valence (positive, negative) or arousal (high, low) would influence its ability to be remembered with those contextual details. Across two experiments, high-arousal items were remembered with spatial and temporal context more often than low-arousal items. Item valence did not influence memory for those details, although positive high-arousal items were recognized or recalled more often than negative items. These data suggest that emotion does not just bias participants to believe they have a vivid memory; rather, the arousal elicited by an event can benefit memory for some types of contextual details.     

Evidence for time-based models of free recall

Is memory temporally organized? According to temporal distinctiveness models of memory, temporally isolated items should be better remembered than temporally crowded items in free recall tasks. Here, we tested this class of model by varying the temporal isolation of items either predictably (Experiment 1) or unpredictably (Experiment 2) in a free recall task. In both experiments, item recall probability increased as a function of the temporal gaps both before and after the item. The results are taken as support for temporal distinctiveness models of memory, in which items are represented and recalled in terms of their positions along a temporal dimension.     

Long-term effects of testing on the recall of nontested materials

The isolation paradigm is a staple in the study of distinctiveness and memory. Isolated items are better remembered than non-isolated controls, and the standard interpretation of this effect is that subjective experience of salience recruits extraordinary processing to the isolated item. This interpretation is at odds with data showing an isolation effect when the isolate is not perceived as salient (e.g., von Restorff, 1933). All available research on the early isolation effect has tested memory after a relatively short retention interval. Perhaps the effect of salience on memory in the isolation paradigm would be revealed following longer retention intervals. The experiment reported here examines the effect of isolation following a 48-hour retention interval when the isolate evokes an experience of salience compared to when the isolate does not evoke that reaction. The isolation effect was substantial after the 48-hour delay but equally so for early and late isolation. Salience appears to have nothing to do with the memory processes even at the longer retention intervals.     

Non-abstractive global-matching models: A framework for investigating the distinctiveness effect on explicit and implicit memory

One very well-known memory phenomenon is the observation that if a specific item seems to be different or rare in any way from other items present in the same encoding context, this item is likely to be remembered more accurately. This phenomenon, named the von Restorff effect or the isolation effect, has been known since 1933 and been considered today as one of the possible ways to create distinctiveness. The aim of this article is to report that the current debate concerning its non-emergence in implicit memory tasks is directly due to a theoretical disagreement about the nature of human memory. In this paper, we conclude that non-abstractive global-matching models can provide an effective theoretical framework for the study of the distinctiveness effect with isolation both in implicit and explicit memory tasks.     

Revisiting von Restorff’s early isolation effect

An item that is conceptually or physically different from other items in a series is often remembered well. This isolation effect has been found independent of the position of the isolated item in the list, suggesting that special attention to or processing of the isolated item is not a necessary precondition of the effect. Three experiments are reported that challenge this conclusion. In Experiment 1a, we compared memory for conceptually isolated items to memory for the same items in unrelated and homogeneous lists. Under moderately distracting conditions, isolation effects were observed with midlist but not with early isolates. In fact, early isolation impaired memory for the conceptually distinct items relative to the same items in homogeneous lists. Experiment 1b replicated this memory impairment for early conceptual isolates and extended it to nondistracting conditions. In Experiment 2, we focused on early isolation, manipulating the type of isolation and whether or not participants performed judgments of learning (JOLs). An early isolation effect was observed for numbers isolated in lists of words (and vice versa), but not for conceptual isolates. Performing the JOL task reduced the size of the early isolation effect. These results suggest that number/word stimulus contrasts are coded automatically and support an isolation effect independent of list position. However, conceptual contrasts require relational processing and will only support an early isolation effect when such processing occurs. The results of Experiments 1a, 1b, and 2 suggest that attentional resources during list presentation and a favorable retrieval environment combine to support good memory for distinctive events.     

Influence of emotion on memory for temporal information

Contextual information, such as color and spatial location, has been found to be better remembered for emotional than for neutral items. The current study examined whether the influence of emotion extends to memory for another fundamental feature of episodic memory: temporal information. Results from a list-discrimination paradigm showed that (a) item memory was enhanced for both negative and positive pictures compared with neutral ones and was better for negative than for positive pictures and (b) temporal information was better remembered for negative than for positive and neutral pictures, whereas positive and neutral pictures did not differ from each other. These findings are discussed in relation to the processes involved in memory for temporal information.     

Schematic influences on category learning and recognition memory

The results from 3 category learning experiments suggest that items are better remembered when they violate a salient knowledge structure such as a rule. The more salient the knowledge structure, the stronger the memory for deviant items. The effect of learning errors on subsequent recognition appears to be mediated through the imposed knowledge structure. The recognition advantage for deviant items extends to unsupervised learning situations. Exemplar-based and hypothesis-testing models cannot account for these results. The authors propose a clustering account in which deviant items are better remembered because they are differentiated from clusters that capture regularities. The function of clusters is akin to that of schemas. Their results and analyses expose connections among research in category learning, schemas, stereotypes, and analogy.     

Divided attention selectively impairs memory for self-relevant information

Information that is relevant to oneself tends to be remembered more than information that relates to other people, but the role of attention in eliciting this “self-reference effect” is unclear. In the present study, we assessed the importance of attention in self-referential encoding using an ownership paradigm, which required participants to encode items under conditions of imagined ownership by themselves or by another person. Previous work has established that this paradigm elicits a robust self-reference effect, with more “self-owned” items being remembered than “other-owned” items. Access to attentional resources was manipulated using divided-attention tasks at encoding. A significant self-reference effect emerged under full-attention conditions and was related to an increase in episodic recollection for self-owned items, but dividing attention eliminated this memory advantage. These findings are discussed in relation to the nature of self-referential cognition and the importance of attentional resources at encoding in the manifestation of the self-reference effect in memory.     

Reality monitoring and memory distortion: Effects of negative, arousing content

Although individuals often claim to vividly remember negatively arousing information, few studies have been performed to examine whether this emotional information is remembered more accurately than nonemotional information. In the present study, we investigated whether the emotional content of items modulates the accuracy with which individuals make reality-monitoring decisions. Participants (young adults, 18-35 years of age) distinguished imagined from seen words (Experiments 1 and 3A) or objects (Experiments 2 and 3B). Half of the items studied in each condition (presented and imagined) were negative and arousing, and half were neutral. The participants mistook imagined items for presented ones, but the number of reality-monitoring errors was lower for the arousing items than for the neutral items. Negative, arousing items appear to be remembered with contextual detail more frequently than are neutral items, leading memory for this emotional information to be less prone to distortion than is memory for neutral information. Thus, negative arousal can enhance not only the subjective vividness of a memory, but also a memory's accuracy.     

Looking sharp: Becoming a search template boosts precision and stability in visual working memory

Visual working memory (VWM) plays a central role in visual cognition, and current work suggests that there is a special state in VWM for items that are the goal of visual searches. However, whether the quality of memory for target templates differs from memory for other items in VWM is currently unknown. In this study, we measured the precision and stability of memory for search templates and accessory items to determine whether search templates receive representational priority in VWM. Memory for search templates exhibited increased precision and probability of recall, whereas accessory items were remembered less often. Additionally, while memory for Templates showed benefits when instances of the Template appeared in search, this benefit was not consistently observed for Accessory items when they appeared in search. Our results show that becoming a search template can substantially affect the quality of a representation in VWM.     

Memory advantage for produced words and familiar native accents

Our memory is better for words that we have read aloud than for words that we have read silently or have listened to. The present study tested this memory advantage for words with native accent markers that participants were either highly familiar or less familiar. As in previous studies, produced words were subsequently remembered better than listened-to words. In contrast to previous studies that involved a comparison of global foreign accents with standard native accents, in the present study words with highly familiar accent markers were remembered better than words with less familiar accent markers (Experiment 1). The familiar accent advantage was also found when participants could not hear their own productions during the training phase (Experiment 2). When tested with a week delay, produced words were still remembered better than listened-to words, but the advantage for words with familiar accent markers was no longer found (Experiment 3).     

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.     

The emotional carryover effect in memory for words

Emotional material rarely occurs in isolation; rather it is experienced in the spatial and temporal proximity of less emotional items. Some previous researchers have found that emotional stimuli impair memory for surrounding information, whereas others have reported evidence for memory facilitation. Researchers have not determined which types of emotional items or memory tests produce effects that carry over to surrounding items. Six experiments are reported that measured carryover from emotional words varying in arousal to temporally adjacent neutral words. Taboo, non-taboo emotional, and neutral words were compared using different stimulus onset asynchronies (SOAs), recognition and recall tests, and intentional and incidental memory instructions. Strong emotional memory effects were obtained in all six experiments. However, emotional items influenced memory for temporally adjacent words under limited conditions. Words following taboo words were more poorly remembered than words following neutral words when relatively short SOAs were employed. Words preceding taboo words were affected only when recall tests and relatively short retention intervals were used. These results suggest that increased attention to the emotional items sometimes produces emotional carryover effects; however, retrieval processes also contribute to retrograde amnesia and may extend the conditions under which anterograde amnesia is observed.