The bizarreness effect: Dissociation between item and source memory

The present study investigated the relationship between memory for particular items (nouns embedded in sentences) varying in bizarreness and the spatial location in which they were learned. Consistent with earlier findings, the items embedded in bizarre sentences were better recalled than those embedded in common sentences. This mnemonic advantage for bizarre sentences did not extend to memory for source (spatial location), which did not reliably vary as a function of bizarreness. This pattern is inconsistent with several existing theoretical formulations of the relation between item and source encoding and related findings. We propose a theoretical possibility for integrating these varied findings. Finally, the expectation-violation explanation of the bizarreness effect was not supported by the absence of a relation between recall of the items and memory for context.     

Monitoring item and source information: Evidence for a negative generation effect in source memory

Item memory and source memory were assessed in a task that simulated a social conversation. Participants generated answers to questions or read statements presented by one of three sources (faces on a computer screen). Positive generation effects were observed for item memory. That is, participants remembered topics of conversation better if they were asked questions about the topics than if they simply read statements about topics. However, a negative generation effect occurred for source memory. That is, remembering the source of some information was disrupted if participants were required to answer questions pertaining to that information. These findings support the notion that item and source memory are mediated, as least in part, by different processes during encoding.     

The generation effect: dissociating enhanced item memory and disrupted order memory

Generating stimuli at encoding typically improves memory for occurrence (item memory) but might disrupt memory for order. In three experiments, the relationship between generation and order memory was examined by using familiar stimuli, which give rise to the standard generation advantage in item memory, and unfamiliar stimuli, which do not. The participants generated or read words and non-words in Experiments 1 and 2 and familiar and unfamiliar word compounds in Experiment 3. For the familiar stimuli, generation enhanced item memory (as measured by recognition) but disrupted performance on the order-reconstruction test. For the unfamiliar stimuli, generation produced no recognition advantage and yet persisted in disrupting order reconstruction. Thus, the positive effects of generation on item memory were dissociated from its negative impact on order memory.     

Negative effects of item repetition on source memory

In the present study, we explored how item repetition affects source memory for new item-feature associations (picture-location or picture-color). We presented line drawings varying numbers of times in Phase 1. In Phase 2, each drawing was presented once with a critical new feature. In Phase 3, we tested memory for the new source feature of each item from Phase 2. Experiments 1 and 2 demonstrated and replicated the negative effects of item repetition on incidental source memory. Prior item repetition also had a negative effect on source memory when different source dimensions were used in Phases 1 and 2 (Experiment 3) and when participants were explicitly instructed to learn source information in Phase 2 (Experiments 4 and 5). Importantly, when the order between Phases 1 and 2 was reversed, such that item repetition occurred after the encoding of critical item-source combinations, item repetition no longer affected source memory (Experiment 6). Overall, our findings did not support predictions based on item predifferentiation, within-dimension source interference, or general interference from multiple traces of an item. Rather, the findings were consistent with the idea that prior item repetition reduces attention to subsequent presentations of the item, decreasing the likelihood that critical item-source associations will be encoded.     

Adult age differences in memory for distinctive information: Evidence from the bizarreness effect

Two experiments examined age-related differences in memory for bizarre and common pictures. In Experiment 1, a facilitative effect of bizarreness was obtained for young adults and one of the older groups, but not for the oldest group (over age 70). However, the bizarreness effect was found for even the oldest group when predominantly common lists were used in Experiment 2. It is concluded that older adults suffer from deficits in distinctive processing, but those deficits can be reduced by providing a more uniformly common context in which differences can be processed.     

Differential effects of cue dependency on item and source memory

The authors investigated the cue dependency of source and item memory. Individuals listened to words spoken by a man or a woman and later determined whether a test word was previously presented by a man or by a woman, or whether it was a new word. Cue dependent effects were assessed by presenting test words with (a) the same voice (match condition) that originally presented the word, (b) a different but familiar voice (mismatch condition), (c) a novel test voice (novel condition), and (d) no test voice (control condition). Compared with the control condition, source recollection was facilitated in matching-context conditions, disrupted in mismatching-context conditions, and not affected in novel test conditions. By contrast, item recognition was not affected by the match-mismatch manipulation but was significantly worse in novel test voice conditions. The authors propose an associative source interference view to account for the voice match-mismatch effects observed in source recollection.     

Effects of emotion-induced self-focused attention on item and source memory

Motivation and Emotion - Affective states are closely linked to attention to internal aspects of the self (i.e., self-focused attention). We investigated how self-focused attention induced by...     

Time-limited effects of emotional arousal on item and source memory

Two experiments investigated the time-limited effects of emotional arousal on consolidation of item and source memory. In Experiment 1, participants memorized words (items) and the corresponding speakers (sources) and then took an immediate free recall test. Then they watched a neutral, positive, or negative video 5, 35, or 50?min after learning, and 24 hours later they took surprise memory tests. Experiment 2 was similar to Experiment 1 except that (a) a reality monitoring task was used; (b) elicitation delays of 5, 30, and 45?min were used; and (c) delayed memory tests were given 60?min after learning. Both experiments showed that, regardless of elicitation delay, emotional arousal did not enhance item recall memory. Second, both experiments showed that negative arousal enhanced delayed item recognition memory only at the medium elicitation delay, but not in the shorter or longer delays. Positive arousal enhanced performance only in Experiment 1. Third, regardless of elicitation delay, emotional arousal had little effect on source memory. These findings have implications for theories of emotion and memory, suggesting that emotion effects are contingent upon the nature of the memory task and elicitation delay.     

The extralist-feature effect: evidence against item matching in short-term recognition memory

The authors varied the similarity between negative probes and study items in a short-term item-recognition task. Current models treat similarity as a function of the number of occurrences of the probe's features in the study set, a factor that is often confounded with the number of the probe's features occurring in the study set. Unconfounded comparisons showed that performance reflected only the latter factor, with response time a linear function of the number of probe features in the study set. The effect was obtained for both stimuli with manipulated features (colored shapes) and words. Number of presented features is a global property of the study list, but existing global models calculate familiarity by averaging across item matches and cannot readily accommodate the data. The authors proposed that the probe's features are compared with a global representation of the study set's features.     

Metacognitive inferences in source memory judgements: The role of perceived differences in item recognition

This research investigated the hypothesis that metacognitive inferences in source memory judgements are based on the recognition or nonrecognition of an event together with perceived or expected differences in the recognizability of events from different sources. The hypothesis was tested with a multinomial source-monitoring model that allowed separation of source-guessing tendencies for recognized and unrecognized items. Experiments 1A and 1B manipulated the number of item presentations as relevant source information and revealed differential guessing tendencies for recognized and unrecognized items, with a bias to attribute unrecognized items to the source associated with poor item recognition. Experiments 2A and 2B replicated the findings with a manipulation of presentation time and extended the analysis to subjective differences in item recognition. Experiments 3A and 3B used more natural source information by varying type of acoustic signal and demonstrated that subjective theories about differences in item recognition are sufficient to elicit differential source-guessing biases for recognized and unrecognized items. Together the findings provide new insights into the cognitive processes underlying source memory decisions, which involve episodic memory and reconstructive tendencies based on metacognitive beliefs and general world knowledge.     

The bizarreness effect and individual differences in imaging ability

The bizarreness effect refers to the superior performance in recall of bizarre sentences as compared to common sentences. The subjects studied each target word and in Exp. 1 rated its congruity with its sentence frame. In Exp. 2 they rated the vividness of the image for each sentence frame in which it was included. Four types of sentence frames were provided: bizarre image sentences, bizarre nonimage sentences, common image sentences, and common nonimage sentences. Good imagers and poor imagers were assessed on the Questionnaire Upon Mental Imagery. Both experiments showed that good imagers recalled target words in bizarre image sentences better than target words in common image sentences. A difference between the two sentence types was not observed for poor imagers. The differences between bizarre nonimage sentences and common nonimage sentences were not found for both type of imagers. The results were interpreted as showing that a difference in imaging ability was critical for the occurrence of a bizarreness effect.     

Emotional learning retroactively enhances item memory but distorts source attribution

An adaptive memory system should prioritize information surrounding a powerful learning event that may prove useful for predicting future meaningful events. The behavioral tagging hypothesis provides a mechanistic framework to interpret how weak experiences persist as durable memories through temporal association with a strong experience. Memories are composed of multiple elements, and different mnemonic aspects of the same experience may be uniquely affected by mechanisms that retroactively modulate a weakly encoded memory. Here, we investigated how emotional learning affects item and source memory for related events encoded close in time. Participants encoded trial-unique category exemplars before, during, and after Pavlovian fear conditioning. Selective retroactive enhancements in 24-h item memory were accompanied by a bias to misattribute items to the temporal context of fear conditioning. The strength of this source memory bias correlated with participants’ retroactive item memory enhancement, and source misattribution to the emotional context predicted whether items were remembered overall. In the framework of behavioral tagging: Memory attribution was biased to the temporal context of the stronger event that provided the putative source of memory stabilization for the weaker event. We additionally found that fear conditioning selectively and retroactively enhanced stimulus typicality ratings for related items, and that stimulus typicality also predicted overall item memory. Collectively, these results provide new evidence that items related to emotional learning are misattributed to the temporal context of the emotional event and judged to be more representative of their semantic category. Both processes may facilitate memory retrieval for related events encoded close in time.

Emotional experiences gain privileged access to the neurobehavioral mechanisms of long-term memory (LaBar and Cabeza 2006; Kensinger 2009; McGaugh 2015; Yonelinas and Ritchey 2015; Mather et al. 2016). Importantly, this emotional enhancement of memory can spread to seemingly mundane details encoded close in time to the emotional experience. Through this temporal association, affectively neutral information retroactively acquires the capacity to predict emotional events, allowing us to better avoid or seek out those outcomes. However, what aspects of memory are modulated via temporal proximity to an emotional event? Episodic memories, for instance, are composed of stimulus information (e.g., item memory) embedded with contextual details (e.g., source memory) (Johnson et al. 1993; Tulving 2002). Emotion enhances item memory (Sharot and Phelps 2004; LaBar and Cabeza 2006; Mather 2007) but has inconsistent effects on contextual details associated with emotional stimuli (Yonelinas and Ritchey 2015). While there is evidence that episodic memory is selectively prioritized for related information encoded before (Dunsmoor et al. 2015) and after (Dunsmoor et al. 2015, 2018; Tambini et al. 2017; Keller and Dunsmoor 2020) an emotional experience, retroactive and proactive effects of emotional learning on source memory for this same information is unknown. Here, we investigated how temporal proximity to an emotional learning event influences both item memory and contextual details for related information.Enhancement in memory via a temporal association between mundane and salient events is consistent with neurobiological models of long-term memory. For example, the behavioral tagging hypothesis (derived from the synaptic tagging hypothesis; Frey and Morris 1997) proposes that weak learning is strengthened in memory if it is encoded within a critical time window of a more salient event and if the two events share overlapping neural ensembles (Moncada and Viola 2007; Ballarini et al. 2009; Wang et al. 2010; Takeuchi et al. 2016). As emotion is a powerful learning event, information encoded within temporal proximity may be strengthened in memory via a mechanism of behavioral tagging. The behavioral tagging hypothesis has been translated to humans using novelty (Fenker et al. 2008; Ballarini et al. 2013; Ramirez Butavand et al. 2020), threat (Dunsmoor et al. 2015), and reward (Patil et al. 2017) to induce memory enhancements for weakly encoded information encoded close in time. However, it is unclear whether and how this mechanism may affect memory for the contextual details associated with the weak event.Emotion can sometimes improve memory accuracy for information directly associated with an emotional stimulus, such as the spatial and temporal context in which the emotional stimulus was encoded (Kensinger and Schacter 2006; Schmidt et al. 2011; Rimmele et al. 2012; Talmi et al. 2019). Therefore, one possibility is that emotional learning improves both item and source memory for information in temporal proximity to an emotional event. In this case, we might expect item memory to be accompanied by source memory accuracy, such that items are appropriately organized in time relative to the emotional event. Alternatively, emotional learning might have no effect (Sharot and Yonelinas 2008; Wang and Fu 2010) or even impair memory for contextual information. Indeed, it may be simpler to remember a trivial item by virtue of associating the item with the salient context (Takashima et al. 2016). It is therefore plausible that linking weak and strong events by temporal proximity might improve item memory at the cost of source memory. Consequently, we may expect a relationship between the strength of item memory for related events encoded close in time and the strength of a misallocation bias to source the item to the more salient temporal context. This might suggest that retroactive memory enhancement for weakly encoded items relies in part on misattribution to the more salient emotional context.In addition to our exploration of how emotional learning impacts item and source memory for proximal events, we tested a parallel hypothesis that emotional learning alters abstract stimulus properties that may indirectly facilitate memory retrieval for those items as well. Previous work demonstrates that emotional learning is sensitive to how well an item represents its broader category; that is, typicality (Dunsmoor and Murphy 2014, 2015; Dunsmoor et al. 2014; Struyf et al. 2018; Lei et al. 2019). Whether emotional learning has the power to alter an abstract stimulus property such as subjective typicality is unknown, but stimulus memorability may be an underappreciated factor contributing to item memory (Bainbridge 2019). For instance, the hippocampus plays a role in both episodic memory and concept representations (Quiroga 2012; Davis and Poldrack 2014; Mack et al. 2016). Moreover, typical category members used as conditioned stimuli in Pavlovian fear conditioning preferentially engage the hippocampus and hippocampal-amygdala functional connectivity (Dunsmoor et al. 2014), which is a substrate for emotional memory enhancement (Murty et al. 2010).In the present study participants underwent a 2-d Pavlovian fear conditioning task that included trial-unique (i.e., nonrepeating) pictures of animals and tools as conditioned stimuli (CSs), based on the protocol from Dunsmoor et al. (2015). Items were encoded before, during, and after Pavlovian fear conditioning. We predicted that emotional learning would have divergent effects on 24-h episodic memory accuracy for CS items and the encoding temporal context. Specifically, we predicted that CSs semantically related to the fear conditioned category would be selectively remembered regardless of their temporal context (Dunsmoor et al. 2015), but that participants would have a bias to attribute these related CSs to the temporal context of fear conditioning. We also investigated whether emotional learning enhances subjective typicality for CS category members related to the fear conditioning category, and whether long-term memory would be influenced by how strongly an item was deemed to represent its superordinate category. Such findings might indicate that weak memories formed in temporal proximity to an emotional experience our bound to the more salient temporal context, and that emotional learning can alter abstract stimulus properties of weakly encoded information to make this information more memorable.     

The eyewitness suggestibility effect and memory for source

We examined the possibility that eyewitness suggestibility reflects failures of the processes by which people normally discriminate between memories derived from different sources. To test this hypothesis, misled and control subjects were tested either with a yes/no recognition test or with a "source monitoring" test designed to orient subjects to attend to information about the sources of their memories. The results demonstrate that suggestibility effects obtained with a recognition test can be eliminated by orienting subjects toward thinking about the sources of their memories while taking the test. Our findings indicate that although misled subjects are capable of identifying the source of their memories of misleading suggestions, they nonetheless sometimes misidentify them as memories derived from the original event. The extent to which such errors reflect genuine memory confusions (produced, for example, by lax judgment criteria) or conscious misattributions (perhaps due to demand characteristics) remains to be specified.     

The relation between source memory and aging.

Previous research has shown that elderly adults have difficulty recalling the source of recently acquired facts but does not indicate whether source memory is more impaired than fact memory. This study examined old and young subjects' memory for novel facts that had been read to them by 1 of 2 experimental sources either in a random order or in a blocked order. When fact memory was equated in young and old at different levels of performance, the elderly exhibited disproportionate source memory deficits in the blocked condition but not in the random condition. Results suggest that the relation between fact and source memory in the elderly varies across experimental conditions.     

Time course of effects of emotion on item memory and source memory for Chinese words

Although many studies have investigated the effect of emotion on memory, it is unclear whether the effect of emotion extends to all aspects of an event. In addition, it is poorly understood how effects of emotion on item memory and source memory change over time. This study examined the time course of effects of emotion on item memory and source memory. Participants learned intentionally a list of neutral, positive, and negative Chinese words, which were presented twice, and then took test of free recall, followed by recognition and source memory tests, at one of eight delayed points of time. The main findings are (within the time frame of 2 weeks): (1) Negative emotion enhances free recall, whereas there is only a trend that positive emotion enhances free recall. In addition, negative and positive emotions have different points of time at which their effects on free recall reach the greatest magnitude. (2) Negative emotion reduces recognition, whereas positive emotion has no effect on recognition. (3) Neither positive nor negative emotion has any effect on source memory. The above findings indicate that effect of emotion does not necessarily extend to all aspects of an event and that valence is a critical modulating factor in effect of emotion on item memory. Furthermore, emotion does not affect the time course of item memory and source memory, at least with a time frame of 2 weeks. This study has implications for establishing the theoretical model regarding the effect of emotion on memory.     

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.     

Effects of emotion on item and source memory in young and older adults

Emotional experiences are easier to remember than neutral ones, but whether memory for all aspects of an experience is improved by emotion remains unclear. Some researchers have argued that the influence of emotion on memory is different for item than for source information, whereas others have argued that emotion affects both similarly. Also, whether item and source memory are affected by emotion in older people in the same way as in young people is currently unclear. We examined item and source memory for emotional and neutral materials in young and older adults. Memory for emotional items was superior to memory for neutral items, whereas there was no difference in source memory. Overall, item and source memory were poorer in older people than in young people, but emotion seemed to have a similar effect on both age groups. Although emotional content was remembered better than neutral content, this benefit did not apply to source memory. However, varying the emotionality of the source (i.e., the voice in Experiment 3) improved memory for the source, and this effect was greater in young than in older people. Tone of voice had no effect on item memory in older people, but the effect was variable in the young and may depend on the extent to which the tone of voice moderates the interpretation of the content.     

Gender differences in the effects of post-learning emotion on consolidation of item memory and source memory

Item memory and source memory are two integral elements of episodic memory. Although many studies have examined the effect of emotion on item memory, little research has simultaneously taken into account item memory and source memory. In addition, in the majority of previous studies, learning stimuli are used as the source of emotion, making it difficult to understand whether emotion has an effect on encoding or on consolidation of episodic memory. Furthermore, although gender differences exist in neurophysiological responses to emotional stimuli, in many studies gender differences were neglected and this leaves the picture incomplete regarding the effect of emotion on episodic memory. In this study, we examined gender differences in the effects of post-learning emotion on consolidation of item memory and source memory. Participants learned neutral Chinese nouns, took a memory pretest, and were then randomly assigned to three conditions, in which they either watched a 3-min negative video clip, or watched a 3-min positive video clip, or remained calm and relaxed for 3 min. Thirty minutes after the initial learning, participants took a memory posttest. We found that: (1) For females, post-learning negative emotion enhanced consolidation of item memory; however, neither negative emotion nor positive emotion had a significant effect on consolidation of source memory; (2) For males, neither negative nor positive emotion after learning had a significant effect on either item memory or source memory. Possible reasons for the gender differences, as well as the theoretical significance and practical implications of this study were discussed.     

The bizarreness effect: evidence for the critical influence of retrieval processes

People show better memory for bizarre sentences relative to common sentences, a finding referred to as the bizarrness effect. Interestingly, this effect is typically only obtained using a mixed-list design, in which participants study common and bizarre sentences in the same list. This bizarreness effect in mixed-list designs has been explained as the result of both enhanced encoding processes and efficient retrieval processes. The present experiment was designed to isolate the unique contributions of the retrieval context to the bizarreness effect. Participants studied common sentences in one room under one set of instructions, and bizarre sentences in another room under another set of instructions. At test, participants recalled the common and bizarre sentences either together or separately. The results showed that the bizarreness effect was only obtained when participants recalled the common and bizarre items together; no bizarreness advantage emerged when participants were required to recall the common and bizarre items separately. These results suggest that differential encoding processes are not necessary for explaining the bizarreness effect in memory. Rather, retrieval of the mixed-list context appears to be critical for obtaining the effect.