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

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

Electrophysiological indices of strategic episodic retrieval processing

Event-related potentials (ERPs) were acquired during test phases of a recognition memory exclusion task, in order to contribute to current understanding of the processes responsible for the ways in which memory retrieval can be controlled strategically. Participants were asked to endorse old words from one study task (targets) and to reject new test words as well as those from a second study task (non-targets). The study task designated as the target category varied across test phases. The left-parietal ERP old/new effect – the electrophysiological signature of recollection – was reliable for targets only in all test phases, consistent with the view that participants control recollection strategically in service of task demands. The contrast between the ERPs evoked by new test words separated according to target designation revealed reliable differences at midline, anterior and right-hemisphere locations. These differences likely reflect processes that form part of a retrieval attempt and are interpreted here as indices of processes that are important for the strategic regulation of episodic retrieval

Electrophysiological correlates of processes supporting memory for faces

The retrieval processes supporting recognition memory for faces were investigated using event-related potentials (ERPs). The focus for analyses was ERP old/new effects, which are the differences between neural activities associated with correct judgments to old (studied) and new (unstudied) test stimuli. In two experiments it was possible to identify three old/new effects that behaved as neural indices of the process of recollection. In both experiments there was one old/new effect that behaved as an index of the process of familiarity. These outcomes are relevant to the ongoing debate about the functional significance of ERP old/new effects and the implications that scalp-recorded electrophysiological data have for theories of the processes supporting long-term memory judgments

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

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

Recollection and familiarity make independent contributions to recognition memory

Recognition memory can be supported by the processes of recollection and familiarity. Recollection is recovery of qualitative information about a prior event. Familiarity is a scalar strength signal that permits judgments of prior occurrence. There is vigorous debate about how these processes are conceptualized, how they contribute to memory judgments, and which brain regions support them. One popular method for investigating these questions is the Remember/Know procedure, where subjects give a Remember response to studied stimuli for which they can recover contextual details of the study encounter, and a Know response when details are not recovered but subjects nevertheless believe that a stimulus was studied. According to one model, Remember responses are strong memories that are typically associated with relatively high levels of recollection and familiarity. Know responses are weaker memories and are typically associated with lower levels of both processes. Data inconsistent with this account were obtained in this experiment, where magnetoencephalographic (MEG) measures of neural activity were acquired in the test phase of a verbal memory task where healthy human volunteers made Remember, Know, or New judgments to studied and unstudied words. An MEG index of the process of recollection was larger for Remember than Know judgments, whereas the reverse was true for a MEG index of familiarity. Critically, this result is predicted by a model where recollection and familiarity make independent contributions to Remember and Know judgments, and provides a powerful constraint when mapping memory processes onto their neural substrates