A within-subject ERP and fMRI investigation of orientation-specific recognition memory for pictures

Common ERP responses to narrative incoherence in sentence and picture pair comprehension

Understanding the neural processes underlying the comprehension of visual images and sentences remains a major open challenge in cognitive neuroscience. We previously demonstrated with fMRI and DTI that comprehension of visual images and sentences describing human activities recruits a common extended parietal-temporal-frontal semantic system. The current research tests the hypothesis that this common semantic system will display similar ERP profiles during processing in these two modalities, providing further support for the common comprehension system. We recorded EEG from naïve subjects as they saw simple narratives made up of a first visual image depicting a human event, followed by a second image that was either a sequentially coherent narrative follow-up, or not, of the first. Incoherent second stimuli depict the same agents but shifted into a different situation. In separate blocks of trials the same protocol was presented using narrative sentence stimuli. Part of the novelty is the comparison of sentence and visual narrative responses. ERPs revealed common neural profiles for narrative processing across image and sentence modalities in the form of early and late central and frontal positivities in response to narrative incoherence. There was an additional posterior positivity only for sentences in a very late window. These results are discussed in the context of ERP signatures of narrative processing and meaning, and a current model of narrative comprehension.

Neurobiological basis of feeling of knowing in episodic memory

Feeling of knowing (FOK) is a metacognitive process which allows individuals to predict the likelihood that they will be able to remember, in the future, information which they currently cannot recall. Although FOK provides evidence for the mechanisms of metacognitive systems, the neurobiological basis of FOK is still unclear. We investigated the neural correlates of FOK induced by an episodic memory task in 77 younger adult participants. Data were gathered using event-related potentials (ERPs). ERP components during high, low, extremely high and extremely low FOK judgments were analyzed. Stimulus-locked ERP analyses indicated that FOK judgment was associated with greater positivity for P200 component at frontal, central, and parietal electrode zones and greater negativity for the N200 component at parietal electrode zones. Furthermore, results revealed that amplitude of the ERP components for FOK judgments were affected by the level of FOK judgment. Results suggest that ERP components of FOK judgment observed within a 200 ms time window support the perceptual fluency-based model.

Food-related salience processing in healthy subjects during word recognition: Fronto-parietal network activation as revealed by independent component analysis

BACKGROUND

The study aimed to isolate and localize mutually independent cognitive processes evoked during a word recognition task involving food-related and food-neutral words using independent component analysis (ICA) for continuously recorded EEG data. Recognition memory (old/new effect) involves cognitive subcomponents-familiarity and recollection-which may be temporally and spatially dissociated in the brain. Food words may evoke additional attentional salience which may interact with the old/new effect.

METHODS

Sixteen satiated female participants undertook a word recognition task consisting of an encoding phase (learning of presented words, 40 food-related and 40 food neutral) and a test phase (recognition of previously learned words and new words). Simultaneously recorded 64-channel EEG data were decomposed into mutually independent components using the Infomax algorithm in EEGLAB. The components were localized using single dipole fitting using a four-shell BESA head model. The resulting (nonartefactual) components with <15% residual variance were clustered across subjects using the kmeans algorithm resulting in five meaningful clusters localized to fronto-parietal regions. Repeated-measures anova was employed to test main effects (old/new and food relevance) and their interaction on cluster time courses.

RESULTS

Early task-relevant old/new effects were localized to the medial frontal gyrus (MFG) and later old/new effects to the right parietal regions (precuneus). Food-related (nontask-relevant) salience effects were localized to bilateral parietal regions (left precuneus and right postcentral gyrus). Food-related salience interacted with task relevance, the old/new effect in MFG being significant only for food-neutral words highlighting central the role of MFG as the converging site of endogenous and exogenous salience inputs.

CONCLUSION

Our results indicate ICA to be a valid technique to decompose complex neurophysiological signals involving multiple cognitive processes and implicate the fronto-parietal network as an important attentional network for processing salience and task demands.

Aerobic Exercise During Encoding Impairs Hippocampus-Dependent Memory

We investigated how aerobic exercise during encoding affects hippocampus-dependent memory through a source memory task that assessed hippocampus-independent familiarity and hippocampus-dependent recollection processes. Using a within-participants design, young adult participants performed a memory-encoding task while performing a cycling exercise or being seated. The subsequent retrieval phase was conducted while sitting on a chair. We assessed behavioral and event-related brain potential measures of familiarity and recollection processes during the retrieval phase. Results indicated that source accuracy was lower for encoding with exercise than for encoding in the resting condition. Event-related brain potential measures indicated that the parietal old/new effect, which has been linked to recollection processing, was observed in the exercise condition, whereas it was absent in the rest condition, which is indicative of exercise-induced hippocampal activation. These findings suggest that aerobic exercise during encoding impairs hippocampus-dependent memory, which may be attributed to inefficient source encoding during aerobic exercise.

Recollection is delayed under changed viewing conditions: A graded effect on the latency of the late posterior component

Object recognition is a central human ability. In everyday life, the conditions under which objects have to be recognized are usually not perfect. Often, viewing conditions change in between two encounters with an object; typical are changes in illumination or in the object-observer distance. With such changes, object recognition sometimes feels slightly delayed. We examined this phenomenon empirically by measuring the latency of the well-established electrophysiological correlate of recollection, the late posterior component (LPC), in an object-recognition task. Although the cognitive processes underlying successful recognition are well examined, thus far the consequences of changed viewing conditions on the timing of these processes have not been investigated. The ERP technique is well suited for investigating this question, because it allows differentiating between processes contributing to recognition times (in particular, recollection from familiarity as indexed by the FN400 component) and measuring their time course with high temporal precision. In the present study, participants' task was to differentiate previously studied (old) objects from a set of new objects. Viewing conditions for old objects changed slightly, changed strongly, or remained identical between learning and test. We found that the latency of the LPC in response to an old object was delayed whenever viewing conditions changed. Moreover, this delay in LPC latency scaled with the size of the change. These effects were absent for the FN400. This is the first examination of effects of changes in viewing conditions on the latency of recollection and the first dissociation of FN400 and LPC latencies.

Basic perceptual changes that alter meaning and neural correlates of recognition memory

It is difficult to pinpoint the border between perceptual and conceptual processing, despite their treatment as distinct entities in many studies of recognition memory. For instance, alteration of simple perceptual characteristics of a stimulus can radically change meaning, such as the color of bread changing from white to green. We sought to better understand the role of perceptual and conceptual processing in memory by identifying the effects of changing a basic perceptual feature (color) on behavioral and neural correlates of memory in circumstances when this change would be expected to either change the meaning of a stimulus or to have no effect on meaning (i.e., to influence conceptual processing or not). Abstract visual shapes (“squiggles”) were colorized during study and presented during test in either the same color or a different color. Those squiggles that subjects found to resemble meaningful objects supported behavioral measures of conceptual priming, whereas meaningless squiggles did not. Further, changing color from study to test had a selective effect on behavioral correlates of priming for meaningful squiggles, indicating that color change altered conceptual processing. During a recognition memory test, color change altered event-related brain potential (ERP) correlates of memory for meaningful squiggles but not for meaningless squiggles. Specifically, color change reduced the amplitude of frontally distributed N400 potentials (FN400), implying that these potentials indicated conceptual processing during recognition memory that was sensitive to color change. In contrast, color change had no effect on FN400 correlates of recognition for meaningless squiggles, which were overall smaller in amplitude than for meaningful squiggles (further indicating that these potentials signal conceptual processing during recognition). Thus, merely changing the color of abstract visual shapes can alter their meaning, changing behavioral and neural correlates of memory. These findings are relevant to understanding similarities and distinctions between perceptual and conceptual processing as well as the functional interpretation of neural correlates of recognition memory.

The time course of episodic associative retrieval: electrophysiological correlates of cued recall of unimodal and crossmodal pair-associate learning

Little is known about the time course of processes supporting episodic cued recall. To examine these processes, we recorded event-related scalp electrical potentials during episodic cued recall following pair-associate learning of unimodal object-picture pairs and crossmodal object-picture and sound pairs. Successful cued recall of unimodal associates was characterized by markedly early scalp potential differences over frontal areas, while cued recall of both unimodal and crossmodal associates were reflected by subsequent differences recorded over frontal and parietal areas. Notably, unimodal cued recall success divergences over frontal areas were apparent in a time window generally assumed to reflect the operation of familiarity but not recollection processes, raising the possibility that retrieval success effects in that temporal window may reflect additional mnemonic processes beyond familiarity. Furthermore, parietal scalp potential recall success differences, which did not distinguish between crossmodal and unimodal tasks, seemingly support attentional or buffer accounts of posterior parietal mnemonic function but appear to constrain signal accumulation, expectation, or representational accounts.

Prestige versus citation volume as journal indices in cognitive neuroscience

In recent years, alternative measures of a journal's influence have been developed to those based on citation metrics (such as Impact Factor). This includes the Scimago Journal Rank (SJR) which is adapted from algorithms used to prioritize webpages in search engines. It is considered a measure of "prestige" insofar as it takes into account the importance of links/citations and not just their total number. Taking a sample of 38 journals from within the field of cognitive neuroscience, it is shown that SJR and Impact Factor correlate highly (r = .83) but with a few large discrepancies in rankings. This journal, Cognitive Neuroscience, fares better on the prestige-based measure than might otherwise be expected from its citation-based rank.

Temporal texture of associative encoding modulates recall processes

Binding aspects of an experience that are distributed over time is an important element of episodic memory. In the current study, we examined how the temporal complexity of an experience may govern the processes required for its retrieval. We recorded event-related potentials during episodic cued recall following pair associate learning of concurrently and sequentially presented object-picture pairs. Cued recall success effects over anterior and posterior areas were apparent in several time windows. In anterior locations, these recall success effects were similar for concurrently and sequentially encoded pairs. However, in posterior sites clustered over parietal scalp the effect was larger for the retrieval of sequentially encoded pairs. We suggest that anterior aspects of the mid-latency recall success effects may reflect working-with-memory operations or direct access recall processes, while more posterior aspects reflect recollective processes which are required for retrieval of episodes of greater temporal complexity.

Optimization of contrast detection power with probabilistic behavioral information

Recent progress in the experimental design for event-related fMRI experiments made it possible to find the optimal stimulus sequence for maximum contrast detection power using a genetic algorithm. In this study, a novel algorithm is proposed for optimization of contrast detection power by including probabilistic behavioral information, based on pilot data, in the genetic algorithm. As a particular application, a recognition memory task is studied and the design matrix optimized for contrasts involving the familiarity of individual items (pictures of objects) and the recollection of qualitative information associated with the items (left/right orientation). Optimization of contrast efficiency is a complicated issue whenever subjects' responses are not deterministic but probabilistic. Contrast efficiencies are not predictable unless behavioral responses are included in the design optimization. However, available software for design optimization does not include options for probabilistic behavioral constraints. If the anticipated behavioral responses are included in the optimization algorithm, the design is optimal for the assumed behavioral responses, and the resulting contrast efficiency is greater than what either a block design or a random design can achieve. Furthermore, improvements of contrast detection power depend strongly on the behavioral probabilities, the perceived randomness, and the contrast of interest. The present genetic algorithm can be applied to any case in which fMRI contrasts are dependent on probabilistic responses that can be estimated from pilot data.