Recognition memory with and without retrieval of context: studies with event-related potentials

In six experiments event-related potentials (ERPs) were recorded while subjects performed modified recognition memory tests. All experiments consisted of an initial study phase in which subjects studied words which were presented in one of two contexts. In a subsequent test phase subjects discriminated between old and new items, and between old items which had been presented in one of the two contexts at study. The design of these experiments permitted a comparison of three critical classes of ERPs: those to words correctly judged new, and those to words correctly judged old which were either correctly or incorrectly assigned to study context. All six experiments revealed reliable differences between the ERPs to correctly identified old and new words. In experiments 3-6 the analyses of the differences between the ERPs to correctly identified old and new words revealed two topographically and temporally dissociable modulations. The first of these was maximal at parietal sites over the 500-900 msec time window, and was larger over the left hemisphere than over the right. The second modulation was more temporally extended, maximal at frontal scalp locations, and displayed a right-greater than-left hemisphere asymmetry. Both of these modulations were of greater magnitude for words which were correctly assigned to study context. These findings are consistent with the view that multiple neural systems contribute to memory for context. The experimental findings are discussed in relation to theories of the relationship between memory for prior occurrences, and memory for contextual details of those occurrences

Direct real-time neural evidence for task-set inertia

One influential explanation for the costs incurred when switching between tasks is that they reflect interference arising from completing the previous task—known as task set inertia. We report a novel approach for assessing task-set inertia in a memory experiment using event related potentials (ERPs). After a study phase participants completed a test block in which they switched between a memory task (retrieving information from the study phase) and a perceptual task. These tasks alternated every two trials. An ERP index of the retrieval of study information was evident in the memory task. It was also present on the first trial of the perceptual task but was markedly attenuated on the second. Moreover, this task-irrelevant ERP activity was positively correlated with a behavioral cost associated with switching between tasks. This real-time measure of neural activity thus provides direct evidence of task-set inertia, its duration, and the functional role it plays in switch costs

Retrieval processes supporting judgments of recency.

Abstract & The circumstances under which different retrieval processes can support judgments about how long ago events occurred remain a matter of debate, as do the ways in which retrieved information can be employed in support of such judgments. In order to contribute to an understanding of the nature and number of distinct retrieval processes that support time judgments, event-related potentials (ERPs) were acquired during a continuous verbal memory task, where the lag between presentation and re-presentation of words was varied. Participants made judgments of recency ( JORs), indicating the number of words that had intervened between presentation and re-presentation. Two spatially and temporally separable ERP effects predicted JORs, and the two effects bore correspondences with ERP modulations that have been linked to the processes of recollection and familiarity, suggesting that both of these processes contributed to JORs. The two effects predicting recency judgments also did so in the same way, with larger effects uniformly predicting shorter lag judgments. In so far as the sizes of the effects index memory strength, these findings are consistent with theoretical accounts of JORs where strength is employed heuristically: The more information recovered, the more recently the event occurred. &amp

On the sensitivity of event-related fields to recollection and familiarity

The sensitivity of event-related potentials (ERPs) to the processes of recollection and familiarity has been explored extensively, and ERPs have been used subsequently to infer the contributions these processes make to memory judgments under a range of different circumstances. It has also been shown that event-related fields (ERFs, the magnetic counterparts of ERPs) are sensitive to memory retrieval processes. The links between ERFs, recollection and familiarity are, however, established only weakly. In this experiment, the sensitivity of ERFs to these processes was investigated in a paradigm used previously with ERPs. An early frontally distributed modulation varied with memory confidence in a way that aligns it with the process of familiarity, while a later parietally distributed modulation tracked subjective claims of recollection in a way that aligns it with this process. These data points strengthen the argument for employing ERFs to assess the contributions these processes can make to memory judgments, as well as for investigating the nature of the processes themselves

Separating content-specific retrieval from post-retrieval processing

According to cortical reinstatement accounts, neural processes engaged at the time of encoding are re-engaged at the time of memory retrieval. The temporal precision of event-related potentials (ERPs) has been exploited to assess this possibility, and in this study ERPs were acquired while people made memory judgments to visually presented words encoded in two different ways. There were reliable differences between the scalp distributions of the signatures of successful retrieval of different contents from 300 to 1100 ms after stimulus presentation. Moreover, the scalp distributions of these content-sensitive effects changed during this period. These findings are, to our knowledge, the first demonstration in one study that ERPs reflect content-specific processing in two separable ways: first, via reinstatement, and second, via downstream processes that operate on recovered information in the service of memory judgments

Metamemory or just memory? : searching for the neural correlates of judgments of learning

Judgments of Learning (JOLs) are judgments of the likelihood of remembering recently studied material on a future test. Although JOLs have been extensively studied, particularly due to their important applications in education, relatively little is known about the cognitive and neural processes supporting JOLs and how these processes relate to actual memory processing. Direct access theories describe JOLs as outputs following direct readings of memory traces and hence predict that JOLs cannot be distinguished from objective memory encoding operations. Inferential theories, by contrast, claim JOLs are products of the evaluation of a number of cues, perceived by learners to carry predictive value. This alternative account argues that JOLs are made on the basis of multiple underlying processes, which do not necessarily overlap with memory encoding. In this thesis, the neural and cognitive bases of JOLs were examined in a series of four ERP experiments. Across experiments the study phase ERP data showed that JOLs produce neural activity that is partly overlapping with, but also partly distinct from, the activity that predicts successful memory encoding. Furthermore, the neural correlates of successful memory encoding appear sensitive to the requirements to make a JOL, emphasising the close interaction between subjective and objective measures of memory encoding. Finally, the neural correlates of both JOLs and successful memory encoding were found to vary depending on the nature of the stimulus materials, suggesting that both phenomena are supported by multiple cognitive and neural systems. Although the primary focus was on the study phase ERP data, the thesis also contains two additional chapters reporting the ERP data acquired during the test phases of three of the original experiments. These data, which examined the relative engagements of retrieval processes for low and high JOL items, suggest that encoding processes specifically resulting in later recollection (as opposed to familiarity) form one reliable basis for making JOLs. Overall, the evidence collected in this series of ERP experiments suggests that JOLs are not pure products of objective memory processes, as suggested by direct access theories, but are supported by neural systems that are at least partly distinct from those supporting successful memory encoding. These observations are compatible with inferential theories claiming that JOLs are supported by multiple processes that can be differentially engaged across stimulus contents.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Behavioral/Systems/Cognitive A Role for Perirhinal Cortex in Memory for Novel Object-Context Associations

It is debated whether functional divisions between structures in the medial temporal lobe (MTL) , ). In the latter theory, complex object representations in PrC are capable of supporting memory for objects as well as for object-context associations, particularly when there is a demand to discriminate between highly visually similar objects (Cowell et al., 2010). To adjudicate between these accounts, human participants were scanned while making two different judgments about visually presented objects (is the object common or uncommon, or does the object have more edges or curves). In a subsequent, unscanned, retrieval phase, participants made item (old/new) followed by context (encoding task) judgments about previously seen and novel objects. Neural activity at encoding was separated according to the accuracy of the retrieval judgments. PrC activity predicted successful item-context judgments, a result that remained when itemmemory strength was equated across objects for which the context was remembered or forgotten. These data imply that the function of PrC goes beyond processing item-based memory information, contributing additionally to memory for item-context associations when the stimuli are object

On the antecedents of an electrophysiological signature of retrieval mode

It has been proposed that people employ a common set of sustained operations (retrieval mode) when preparing to remember different kinds of episodic information. In two experiments, however, there was no evidence for the pattern of brain activity commonly assumed to index these operations. In both experiments event-related potentials (ERPs) were recorded time-locked to alternating preparatory cues signalling that participants should prepare for different retrieval tasks. One cue signalled episodic retrieval: remember the location where the object was presented in a prior study phase. The other signalled semantic retrieval: identify the location where the object is most commonly found (Experiment 1) or identify the typical size of the object (Experiment 2). In both experiments, only two trials of the same task were completed in succession. This enabled ERP contrasts between 'repeat' trials (the cue on the preceding trial signalled the same retrieval task), and `switch' trials (the cue differed from the preceding trial). There were differences between the ERPs elicited by the preparatory task cues in Experiment 1 only: these were evident only on switch trials and comprised more positive-going activity over right-frontal scalp for the semantic than for the episodic task. These findings diverge from previous outcomes where the activity differentiating cues signalling preparation for episodic or semantic retrieval has been restricted to rightfrontal scalp sites, comprising more positive-going activity for the episodic than for the semantic task. While these findings are consistent with the view that there is not a common set of operations engaged when people prepare to remember different kinds of episodic information, an alternative account is offered here, which is that these outcomes are a consequence of structural and temporal components of the experiment designs

Electrophysiological evidence for flexible goal-directed cue processing during episodic retrieval

A widely held assumption is that memory retrieval is aided by cognitive control processes that are engaged flexibly in service of memory retrieval and memory decisions. While there is some empirical support for this view, a notable exception is the absence of evidence for the flexible use of retrieval control in functional neuroimaging experiments requiring frequent switches between tasks with different cognitive demands. This absence is troublesome in so far as frequent switches between tasks mimic some of the challenges that are typically placed on memory outside the laboratory. In this experiment we instructed participants to alternate frequently between three episodic memory tasks requiring item recognition or retrieval of one of two different kinds of contextual information encoded in a prior study phase (screen location or encoding task). Event-related potentials (ERPs) elicited by unstudied items in the two tasks requiring retrieval of study context were reliably different, demonstrating for the first time that ERPs index task-specific processing of retrieval cues when retrieval goals change frequently. The inclusion of the item recognition task was a novel and important addition in this study, because only the ERPs elicited by unstudied items in one of the two context conditions diverged from those in the item recognition condition. This outcome constrains functional interpretations of the differences that emerged between the two context conditions and emphasises the utility of this baseline in functional imaging studies of retrieval processing operations