An electrophysiological investigation of factors facilitating strategic recollection

Episodic memory is thought to be mediated by executive processes that facilitate the retrieval of task-relevant information at the expense of irrelevant information. The exclusion task [A process dissociation framework: Separating automatic from intentional uses of memory.Journal of Memory and Language, 30, 513-541, 1991] can be used to explore these processes. In this task, studied items from one source (“targets”) are endorsed on one response key, whereas new and studied items from another source (“nontargets”) are rejected on another key. Herron and Rugg [Strategic influences on recollection in the exclusion task: Electrophysiological evidence.Psychonomic Bulletin and Review, 10, 703-710, 2003] reported that nontargets elicited the ERP correlate of recollection (the “left parietal old/new effect”) when target accuracy was low, but not when it was high. Their explanation for this was that participants only focused exclusively on the recollection of target information when the likelihood of target recollection was high, as under these conditions this strategy is one that that will give rise to accurate task performance. The fact, however, that targets were encoded in different tasks in the high-and low-accuracy groups means that the results can also be explained in terms of the encoding operations performed at study rather than in terms of target accuracy. This study was designed to distinguish between these competing accounts. All targets were encoded elaboratively. Target accuracy was reduced in one condition with a 40-min study-test interval. Nontargets elicited no left parietal effect in either condition, suggesting that target-specific strategic retrieval is facilitated by certain classes of encoding operations rather than simply high target accuracy per se

Working memory capacity is related to variations in the magnitude of an electrophysiological marker of recollection

he links between the resources available for cognitive control and the ability to recover and maintain episodic content were investigated by contrasting an ERP index of recollection (the left-parietal ERP old/new effect) with a measure of working memory capacity (WMC). Participants were given the O-Span measure of WMC and completed a retrieval task in which they had to make responses on one key to previously studied words (targets) and responses on a second key to words that were presented at retrieval on either one or two occasions (new words and non-targets, respectively). The size of the ERP index of recollection associated with correct responses to targets was correlated with WMC, a finding consistent with the view that this ERP effect is linked to operations associated with maintaining information on-line in service of task goals. In addition, the degree to which left-parietal ERP old/new effects for targets were larger than for non-targets increased as WMC increased. Larger left-parietal ERP old/new effects for targets than for non-targets have been interpreted as evidence of successful prioritisation of recollection of target information. The link with WMC reported here is consistent this view, in so far as WMC indexes the availability of resources that are necessary to exert cognitive control over memory retrieval

Brain Potentials Reflect Behavioral Differences in True and False Recognition

People often falsely recognize nonstudied lures that are semantically similar to previously studied words. Behavioral research suggests that such false recognition is based on high semantic overlap between studied items and lures that yield a feeling of familiarity, whereas true recognition is more often associated with the recollection of details. Despite this behavioral evidence for differences between true and false recognition, research measuring brain activity (PET, fMRI, ERP) has not clearly differentiated corresponding differences in brain activity. A median split was used to separate subjects into Good and Poor performers based on their discrimination of studied targets from similar lures. Only Good performers showed late (1000-1500 msec), right frontal event-related brain potentials (ERPs) that were more positive for targets and lures compared with new items. The right frontal differences are interpreted as reflecting postretrieval evaluation processes that were more likely to be engaged by Good than Poor performers. Both Good and Poor performers showed a parietal ERP old/new effect (400-800 msec), but only Poor performers showed a parietal old/lure difference. These results are consistent with the view that the parietal and frontal ERP old/new effects reflect dissociable processes related to recollection.Psycholog

Continued effects of context reinstatement in recognition

The context reinstatement effect refers to the enhanced memory performance found when the context information paired with a target item at study is re-­‐presented at test. Here we investigated the consequences of the way context information is processed in such a setting that gives rise to its beneficial effect on item recognition memory. Specifically, we assessed whether reinstating context in a recognition test facilitates subsequent memory for this context beyond facilitation conferred by presentation of the same context with a different study item. Reinstating study context at test led to better accuracy in 2-­‐alternative forced choice recognition for target faces than did re-­‐pairing those faces with another context encountered during the study phase. The advantage for reinstated over re-­‐paired conditions occurred for both within (Experiment 1) and between subjects (Experiment 2) manipulations. Critically, in a subsequent recognition test for the contexts themselves, contexts serving previously in the reinstated condition were recognized better than contexts serving previously in the re-­‐paired context condition. This constitutes the first demonstration of continuous effects of context reinstatement for memory for context

ERP evidence for the control of emotional memories during strategic retrieval

Neural evidence for the strategic retrieval of task-relevant ‘target’ memories at the expense of less relevant ‘nontarget’ memories has been demonstrated across a wide variety of studies. In ERP studies, this evidence consists of the ERP correlate of recollection (i.e. the ‘left parietal old/new effect’) being evident for targets and attenuated for nontargets. It is not yet known, however, whether this degree of strategic control can be extended to emotionally valenced words, or whether these items instead reactivate associated memories. The present study used a paradigm previously employed to demonstrate the strategic retrieval of neutral words (Herron & Rugg, Psychonomic Bulletin and & Review, 10(3), 703-–710, 2003b) to assess the effects of stimulus valence on behavioural and event-related potential (ERP) measures of strategic retrieval. While response accuracy and reaction times associated with targets were unaffected by valence, negative nontargets and new items were both associated with an elevated false alarm rate and longer RTs than their neutral equivalents. Both neutral and negative targets and nontargets elicited early old/new effects between 300 and 500 ms. Critically, whereas neutral and negative targets elicited robust and statistically equivalent left parietal old/new effects between 500 and 800 ms, these were absent for neutral and negative nontargets. A right frontal positivity associated with postretrieval monitoring was evident for neutral targets versus nontargets, for negative versus neutral nontargets, and for targets versus new items. It can therefore be concluded that the recollection of negatively valenced words is subject to strategic control during retrieval, and that postretrieval monitoring processes are influenced by emotional valence

Preparation breeds success: Brain activity predicts remembering

Successful retrieval of episodic information is thought to involve the adoption of memory states that ensure that stimulus events are treated as episodic memory cues (retrieval mode) and which can bias retrieval toward specific memory contents (retrieval orientation). The neural correlates of these memory states have been identified in many neuroimaging studies, yet critically there is no direct evidence that they facilitate retrieval success. We cued participants before each test item to prepare to complete an episodic (retrieve the encoding task performed on the item at study) or a non-episodic task. Our design allowed us to separate event-related potentials (ERPs) elicited by the preparatory episodic cue according to the accuracy of the subsequent memory judgment. We predicted that a correlate of retrieval orientation should be larger in magnitude preceding correct source judgments than that preceding source errors. This hypothesis was confirmed. Preparatory ERPs at bilateral frontal sites were significantly more positive-going when preceding correct source judgments than when preceding source errors or correct responses in a non-episodic baseline task. Furthermore this effect was not evident prior to recognized items associated with incorrect source judgments. This pattern of results indicates a direct contribution of retrieval orientation to the recovery of task-relevant information and highlights the value of separating preparatory neural activity at retrieval according to subsequent memory accuracy. Moreover, at a more general level this work demonstrates the important role of pre-stimulus processing in ecphory, which has remained largely neglected to date

From Cue to Recall : The Temporal Dynamics of Long-Term Memory Retrieval

A fundamental function of long-term memory is the ability to retrieve a specific memory when encountering a retrieval cue. The purpose of this dissertation was to further our understanding of such cued recall by investigating the temporal dynamics from the presentation of the retrieval cue until the target memory is recalled. Retrieval cues are often related with several memories. When such a retrieval cue is presented, the associated memories will compete for retrieval and this retrieval competition needs to be handled in order to retrieve the sought after target memory. Study 1 and Study 2 investigated the temporal dynamics of such competitive semantic cued recall. Interestingly, previous research has shown that the ability to retrieve the currently relevant target memory comes with a cost, namely retrieval-induced forgetting of the competing memories. These studies also investigated the role of competitor activation and target retrieval in this forgetting phenomenon. Study 1 investigated the electrophysiological correlates of reactivation of competing currently irrelevant memories and the role of such competitor activation in retrieval-induced forgetting. Competitor activation was related to an FN400 event-related potential (ERP) effect and this effect predicted increased levels of retrieval-induced forgetting, indicating that this forgetting effect is dependent on competitor activation. Study 2 examined processes involved in target retrieval in a similar competitive semantic cued recall task. The main finding in this study was that attempts to retrieve the target memory were related to a late posterior negativity ERP effect. Another important finding was that behavioural and ERP measures of target retrieval were unrelated to retrieval-induced forgetting. Retrieval cues can sometimes elicit involuntary retrieval of unwanted memories. Such memory intrusions are a core symptom of post-traumatic stress disorder. Study 3 investigated the temporal dynamics of such memory intrusions. One of the key findings was that memory intrusions were related to a negative slow wave ERP effect possibly reflecting the activation of the intruding memory in working memory. Taken together the findings in the dissertation indicate that cued recall involves several cognitive processes ranging from early automatic memory reactivation to conscious processes such as working memory activation and recollection. The findings have implications for cognitive theories of memory and have relevance for several clinical conditions including depression and post-traumatic stress disorder

Ageing and Episodic Memory: Combining Neuropsychological and Event-Related Potential Approaches to Investigate Strategic Retrieval

This thesis investigates the effect of normal ageing on the strategies adopted during episodic memory retrieval, using a combination of neuropsychological profiling and neuroimaging data measured during performance on a source memory exclusion task. The exclusion task is a type of source memory task where participants distinguish between targets (studied items from one source e.g. female voice), non-targets (studied items from another source e.g. male voice) and new items. Unlike a source memory task where three separate buttons are pressed for each item at test, in the exclusion task one button is pressed for targets and a second for non-target and new items. As this task is more complex than a normal source memory paradigm and also allows participants to perform the task in more than one way, it places high emphasis on the use of strategies to facilitate retrieval and is therefore ideal for investigating strategic retrieval. Previous source memory studies have shown that while older adults are reasonably good at recognising whether items are old or new, they show marked impairments at remembering the source in which items were presented at study. Dual process theories propose that the age-related decline in source memory occurs because recollection becomes impaired with ageing whereas familiarity remains relatively spared. The results reported in this thesis support dual process theory. Experiment 2a showed that, behaviourally, as expected, the young outperformed the elderly. Event-related potentials (ERPs), recorded while a source memory exclusion test was performed, revealed that both young and older adults showed bilateral frontal and left parietal old/new effects, thought to index familiarity and recollection respectively. Importantly, the magnitude of the left parietal effect was significantly reduced in the older adults. The ERP findings also suggested that dual process theories represent an oversimplification of episodic memory decline with age. In Experiment 1a, three temporally and topographically distinct late frontal old/new effects were present in the younger adults: a bilateral anterior frontal effect (450-900ms post stimulus), a right prefrontal effect (900-1300ms) and a right frontal effect (1300-2000ms). Significant positive correlations between the magnitude of these effects and performance on neuropsychological tests of executive functioning in Experiment 1b, revealed that the bilateral anterior frontal effect was related to working memory, strategy use and planning; the right prefrontal effect was related to working memory and planning while the right frontal effect was related to planning. By contrast, the older adults in Experiment 2a only produced the right frontal effect, which correlated with planning across all three time windows in Experiment 2c. Post-retrieval monitoring in older adults therefore appeared to be qualitatively different than their younger counterparts. Performance on the neuropsychological tests in Experiment 2b, revealed that the older adults’ working memory and strategy use was impaired compared to the young, whereas planning was relatively intact, suggesting that age-related differences in post retrieval processing may be due to reduced executive functioning in older adults. Identifying distinct late frontal effects and demonstrating a relationship between these effects and specific executive functions is a novel finding. The presence of a left parietal target greater than non-target difference in the young adults from Experiment 1a and 2a was interpreted as the young reducing recollection of irrelevant non-target information. The modulation did not differ in magnitude for targets and non-targets in the elderly adults from Experiment 2a, suggesting they were less able to reduce activation of goal irrelevant non-target information. The results in the young adults from Experiment 1a also highlight the importance of considering the context of source information on the processes engaged at retrieval. The bilateral frontal effect was significant for the retrieval of the intrinsic context (source information inherent to the studied item), but not the extrinsic context (source information not inherent to the studied item). This finding was interpreted within a unitisation framework, where the intrinsic context became unitised with the item and enhanced familiarity based remembering. The findings also highlight that in order to fully understand post retrieval processing in both young and old adults, focus should move away from examining quantitative differences in the right frontal effect over long time periods and instead identify qualitatively distinct late frontal effects that may reflect the engagement of various executive functions over time

ERP evidence for the control of emotional memories during strategic retrieval

Neural evidence for the strategic retrieval of task-relevant ‘target’ memories at the expense of less relevant ‘nontarget’ memories has been demonstrated across a wide variety of studies. In ERP studies, this evidence consists of the ERP correlate of recollection (i.e. the ‘left parietal old/new effect’) being evident for targets and attenuated for nontargets. It is not yet known, however, whether this degree of strategic control can be extended to emotionally valenced words, or whether these items instead reactivate associated memories. The present study used a paradigm previously employed to demonstrate the strategic retrieval of neutral words (Herron & Rugg, Psychonomic Bulletin and & Review, 10(3), 703-–710, 2003b) to assess the effects of stimulus valence on behavioural and event-related potential (ERP) measures of strategic retrieval. While response accuracy and reaction times associated with targets were unaffected by valence, negative nontargets and new items were both associated with an elevated false alarm rate and longer RTs than their neutral equivalents. Both neutral and negative targets and nontargets elicited early old/new effects between 300 and 500 ms. Critically, whereas neutral and negative targets elicited robust and statistically equivalent left parietal old/new effects between 500 and 800 ms, these were absent for neutral and negative nontargets. A right frontal positivity associated with postretrieval monitoring was evident for neutral targets versus nontargets, for negative versus neutral nontargets, and for targets versus new items. It can therefore be concluded that the recollection of negatively valenced words is subject to strategic control during retrieval, and that postretrieval monitoring processes are influenced by emotional valence

Ageing and episodic retrieval: using event-related potentials to compare the neural correlates of item and associative recognition in young and older adults.

Older people commonly report problems with remembering, and behavioural studies have confirmed that memory does decline with age. Age-related deficits are particularly evident in episodic memory; however, the degree of impairment appears to be task-dependent. Compared to young adults, older adults generally perform reasonably well on simple item recognition tasks, but are markedly compromised on more complex tasks, such a s those that require memory for context. Dual process theory suggests that this pattern of ageing deficits results from an age-related decline in recollection, whilst familiarly remains relatively intact. This thesis reports a series of event-related potential (ERP) studies conducted to examine the effect of ageing on the neural correlates of simple item recognition and more complex associative recognition. Behaviourally, as anticipated, the young outperformed the elderly, particularly in associative recognition. Electrophysiologically, the age-related reduction of the left parietal effect in item recognition appeared to support the dual process view that recollection becomes compromised as people grow older. Likewise, an early right frontal component, evident in both item and associative recognition, may reflect the preservation of familiarity in elderly adults. However, the ERP data also suggest that dual process theory may represent an oversimplification of episodic memory age decline. While the presence of a left parietal sam e/rearranged difference in young adults was interpreted as evidence of the adoption of a target-specific recollection strategy in associative recognition, the modulation's absence in older adults suggests that they are unable to similarly inhibit the retrieval of goal-irrelevant information. Moreover, the older participants also demonstrated widespread left-sided negative activations that may represent two components: First, the fronto-central negativities elicited by both tasks may index the compensatory operations recruited by older adults to maximise their performance. Second, a central/posterior negativity in item recognition, which strongly resembled a modulation that had been previously observed in source memory ageing studies, was interpreted as reflecting the task-irrelevant retrieval of contextual information