Competitive Semantic Memory Retrieval: Temporal Dynamics Revealed by Event-Related Potentials

Counterfactual imagination impairs memory for true actions: EEG and behavioural evidence

Imagined events can be misremembered as experienced, leading to memory distortions. However, less is known regarding how imagining counterfactual versions of past events can impair existing memories. We addressed this issue, and used EEG to investigate the neurocognitive processes involved when retrieving memories of true events that are associated with a competing imagined event. Participants first performed simple actions with everyday objects (e.g., rolling dice). A week later, they were shown pictures of some of the objects and either imagined the same action they had originally performed, or imagined a counterfactual action (e.g., stacking the dice). Subsequent tests showed that memory for performed actions was reduced after counterfactual imagination when compared to both veridical imagination and a baseline condition that had not been imagined at all, providing novel evidence that counterfactual imagination impairs true memories beyond simple forgetting over time. ERPs and EEG oscillations showed evidence of separate processes associated with memory retrieval versus post-retrieval processes that were recruited to support recall of memories that were challenging to access. The findings show that counterfactual imagination can cause impairments to sensorimotor-rich event memories, and provide new evidence regarding the neurocognitive mechanisms that are recruited when people need to distinguish memories of imagined versus true events.

Neurocognitive effects of binge drinking on verbal episodic memory. An ERP study in university students

Background: Verbal memory may be affected by engagement in alcohol binge drinking during youth, according to the findings of neuropsychological studies. However, little is known about the dynamics of the neural activity underlying this cognitive process in young, heavy drinkers. Aims: To investigate brain event-related potentials associated with cued recall from episodic memory in binge drinkers and controls. Methods: Seventy first-year university students were classified as binge drinkers (32: 17 female) or controls (38: 18 female). The participants completed a verbal paired associates learning task during electroencephalogram (EEG) recording. ERPs elicited by old and new word pairs were extracted from the cued-recall phase of the task by using Principal Component Analysis. Subjects also performed a standardized neuropsychological verbal learning test. Results: Two of the three event-related potentials components indicating old/new memory effects provided evidence for anomalies associated with binge drinking. The old/new effects were absent in the binge drinkers in the two subsequent posterior components, identified with the late parietal component and the late posterior negativity The late frontal component revealed similar old/new effects in both groups. Binge drinkers showed similar behavioural performance to controls in the verbal paired associates task, but performed poorly in the more demanding short-term cued-recall trial of a neuropsychological standardized test. Conclusion: Event-related potentials elicited during a verbal cued-recall task revealed differences in brain functioning between young binge drinkers and controls that may underlie emergent deficits in episodic memory linked to alcohol abuse. The brain activity of binge drinkers suggests alterations in the hippocampal - posterior parietal cortex circuitry subserving recognition and recollection of the cue context and generation of the solution, in relation to verbal information shallowly memorised.

An event-related potential study of the testing effect: Electrophysiological evidence for context-dependent processes changing throughout repeated practice

The testing effect refers to a special form of performance improvement following practice. Specifically, repeated retrieval attempts improve long-term memory. In the present study we examined the underlying mechanisms of the testing effect as a function of time by investigating the electrophysiological correlates of repeated retrieval practice. We additionally investigated the ERP waveforms of the repeated practice phase as a function of the accuracy on the final test in a "difference due to memory" (Dm) analysis. We found a parietally distributed, increased positive amplitude between 500-700 ms, and a more positive parietal wave between 700 and 1000 ms in the later relative to the early phases of retrieval practice. We found parietal Dm effects in the same two time windows in the retrieval practice condition with a more positive amplitude predicting retrieval success on the final test. We interpret the earlier waveform as a component associated with episodic recollection and the later ERP as a component related to post-retrieval evaluation processes. Our results demonstrate the important role of these retrieval-related processes in the facilitating effect of retrieval practice on later retrieval, and show that the involvement of these processes changes throughout practice.

Electrophysiological signature of suppression of competitors during interference resolution

The electrophysiological evidence for suppression to date primarily draws upon traditional retrieval-induced forgetting and Think/No-Think paradigms, which involve strategic and intentional restriction of thought. Here event-related potential (ERP) signatures of suppression were examined using a novel task, which unlike traditional paradigms, does not include an initial priming step or intentional thought restraint. Participants were instructed to verbally generate semantically related responses to cue words (e.g., "PIZZA"), and unrelated responses to others. According to an inhibitory account of interference resolution, semantic competition from automatically activated target words must be resolved in order to generate an unrelated response, whereas no resolution is required for generating related responses. In a subsequent phase, accessibility for target words (e.g., "PEPPERONI") that required suppression, words that did not require suppression, as well as new control words was measured using a lexical decision task. We observed a sustained late positivity for unrelated responses in the generation task, and early negative amplitudes of suppressed items in the lexical decision task. These findings are consistent with inhibitory mechanisms operating at retrieval to suppress competitors and show that such processes operate on automatically activated items that are not presented in the context of an experiment, representative of retrieval situations that occur in everyday life.

Bridging the Gap Between Second Language Acquisition Research and Memory Science: The Case of Foreign Language Attrition

The field of second language acquisition (SLA) is by nature of its subject a highly interdisciplinary area of research. Learning a (foreign) language, for example, involves encoding new words, consolidating and committing them to long-term memory, and later retrieving them. All of these processes have direct parallels in the domain of human memory and have been thoroughly studied by researchers in that field. Yet, despite these clear links, the two fields have largely developed in parallel and in isolation from one another. The present article aims to promote more cross-talk between SLA and memory science. We focus on foreign language (FL) attrition as an example of a research topic in SLA where the parallels with memory science are especially apparent. We discuss evidence that suggests that competition between languages is one of the mechanisms of FL attrition, paralleling the interference process thought to underlie forgetting in other domains of human memory. Backed up by concrete suggestions, we advocate the use of paradigms from the memory literature to study these interference effects in the language domain. In doing so, we hope to facilitate future cross-talk between the two fields and to further our understanding of FL attrition as a memory phenomenon.

Retrieval and Monitoring Processes during Visual Working Memory: An ERP Study of the Benefit of Visual Semantics

In this study, we examined electrophysiological indices of episodic remembering whilst participants recalled novel shapes, with and without semantic content, within a visual working memory paradigm. The components of interest were the parietal episodic (PE; 400-800 ms) and late posterior negativity (LPN; 500-900 ms), as these have previously been identified as reliable markers of recollection and post-retrieval monitoring, respectively. Fifteen young adults completed a visual matrix patterns task, assessing memory for low and high semantic visual representations. Matrices with either low semantic or high semantic content (containing familiar visual forms) were briefly presented to participants for study (1500 ms), followed by a retention interval (6000 ms) and finally a same/different recognition phase. The event-related potentials of interest were tracked from the onset of the recognition test stimuli. Analyses revealed equivalent amplitude for the earlier PE effect for the processing of both low and high semantic stimulus types. However, the LPN was more negative-going for the processing of the low semantic stimuli. These data are discussed in terms of relatively 'pure' and complete retrieval of high semantic items, where support can readily be recruited from semantic memory. However, for the low semantic items additional executive resources, as indexed by the LPN, are recruited when memory monitoring and uncertainty exist in order to recall previously studied items more effectively.

Tracking the intrusion of unwanted memories into awareness with event-related potentials

Involuntary retrieval of unwanted memories is a common symptom in several clinical disorders, including post-traumatic stress disorder. With an aim to track the temporal dynamics of such memory intrusions, we recorded electrophysiological measures of brain activity while participants engaged in a Think/No-Think task. We presented the left hand word (the cue) of previously encoded word pairs in green or red font. We asked participants to think of the associated right hand word (the associate) when the cue appeared in green (Think condition) and to avoid thinking of the associate when the cue appeared in red (No-Think condition). To isolate cases when participants experienced an intrusive memory, at the end of each trial, participants judged whether the response had come to mind; we classified memories that came to mind during No-Think trials, despite efforts to stop retrieval, as intrusions. In an event-related potential (ERP) analysis, we observed a negative going slow wave (NSW) effect that indexed the duration of a trace in mnemonic awareness; whereas voluntary retrieval and maintenance of the associate was related to a sustained NSW that lasted throughout the 3-s recording epoch, memory intrusions generated short-lived NSWs that were rapidly truncated. Based on these findings, we hypothesize that the intrusion-NSW reflects the associate briefly penetrating working memory. More broadly, these findings exploit the high temporal resolution of ERPs to track the online dynamics of memory intrusions.