Event-related potentials differentiates the processes involved in the effects of sleep on recognition memory

This study examined the role of sleep on event-related potential (ERP) indicators of memory following sleep and wake. We expected a larger ERP effect due to a facilitory effect of sleep on memory. During the study session, subjects memorized a series of stimuli (faces). At test, after a retention interval characterized by either sleep or by normal waking activities, subjects were asked to recognize old items intermixed with new. Results revealed differences in the old/new effect whereby the amplitude between old/new items was larger after sleep versus wake, suggesting a role of sleep in consolidation. Retention over sleep versus wake was associated with modified early and late frontal and posterior components possibly manifesting reduced interference inhibition, increased contextual processing, and facilitation of episodic memory. These findings suggest that ERP indices are differentially affected by sleep, reflecting differences in memory processing.     

Relatedness proportion effects on masked associative priming: an ERP study

Abstract The effect of relatedness proportion (the percentage of related words in a list) on associative priming was investigated in two masked priming experiments. In Experiment 1, subjects were randomly assigned to either a high (80%) or low (20%) relatedness proportion condition and performed a lexical decision task. Semantically related and unrelated primes were briefly flashed (50 ms) before the targets and were preceded by a mask that prevented their overt identification. In Experiment 2, subjects were tested in both relatedness proportion conditions in a categorization task; the N400, an electrophysiological index of lexical and semantic priming, was measured in trials that did not require a button press. Behavioral and electrophysiological priming effects were observed in both high and low relatedness proportion conditions. The observed priming effects were not modulated by relatedness proportion. The results are discussed in terms of current theories of associative priming.     

Interfacing mind and brain: a neurocognitive model of recognition memory

A variety of processes contribute to successful recognition memory, some of which can be associated with spatiotemporally distinct event-related potential old/new effects. An early frontal and a subsequent parietal old/new effect are correlated with the familiarity and recollection subcomponents of recognition memory, respectively, whereas a late, postretrieval old/new effect seems to reflect an ensemble of evaluation processes that are set by the task context in which retrieval occurs. Both the early frontal and the parietal old/new effects are differentially modulated by the informational content (e.g., object forms and spatial locations) of recognition and seem to rely on brain systems damaged in amnesia. The late frontal effect appears to reflect prefrontal cortex activation. A neurophysiologically based model of recognition memory retrieval is presented and it is shown that coupling recognition memory subprocesses with distinct old/new effects allow examination of the time course of the processes that contribute to correct and to illusory memories. In conjunction with event-related functional magnetic resonance imaging activation patterns the brain systems recruited by various aspects of episodic memory retrieval can be identified.     

Neural correlates of source memory retrieval in young, middle-aged and elderly adults

Event-related potentials (ERPs) were recorded in young (21-27 years old), middle-aged (50-57 years old) and older adults (70-77 years old) to determine whether the decline in source memory that occurs with advancing age coincides with contemporaneous neurophysiological changes. Source memory for the spatial location (quadrant on the screen) of images presented during encoding was examined. The images were shown in the center of the screen during the retrieval task. Retrieval success for source information was characterized by different scalp topographies at frontal electrode sites in young adults relative to middle-aged and older adults. The right frontal effect during unsuccessful retrieval attempts showed amplitude and latency differences across age groups and was related to the ability to discriminate between old and new images only in young adults. These results suggest that the neural correlates of the retrieval success and attempt were affected by age and these effects were present by middle-age.     

Processing sentence context in women with schizotypal personality disorder: an ERP study

Accumulating evidence suggests that schizophrenic patients do not use context efficiently. Also, studies suggest similarities in clinical and cognitive profiles between schizophrenic and schizotypal personality disorder (SPD) individuals, and epidemiological studies point to a genetic link between the two disorders. This study examined electrophysiological correlates of processing sentence context in a group of SPD women in a classical N400 sentence paradigm. The study assessed if the dysfunction in context use found previously in schizophrenia and male SPD also exists in female SPD. We tested 17 SPD and 16 matched normal control women. The results suggest the presence of abnormality in context use in female SPD similar to that previously reported for male schizophrenic and SPD individuals, but of lesser degree of severity. In SPD women, relative to their comparison group, a more negative N400 was found only to auditory congruent sentences.     

Comparing arithmetic and semantic fact retrieval: Effects of problem size and sentence constraint on event-related brain potentials

Event-related potentials were recorded with 61 electrodes from 16 students who verified either the correctness of single-digit multiplication problems or the semantic congruency of sentences. Multiplication problems varied in size and sentence fragments in constraint. Both semantic and arithmetic incongruencies evoked a typical N400 with a clear parieto-central maximum. In addition, numerically larger problems (8×7), in comparison to smaller problems (3×2), evoked a negativity starting at about 360 ms whose maximum was located over the right temporal-parietal scalp. These results indicate that the arithmetic incongruency and the problem-size effect are functionally distinct. It is suggested that the arithmetic and the semantic incongruency effects are both functionally related to a context-dependent spread of activation in specialized associative networks, whereas the arithmetic problem-size effect is due to rechecking routines that go beyond basic fact retrieval.     

Comparing arithmetic and semantic fact retrieval: effects of problem size and sentence constraint on event-related brain potentials

Event-related potentials were recorded with 61 electrodes from 16 students who verified either the correctness of single-digit multiplication problems or the semantic congruency of sentences. Multiplication problems varied in size and sentence fragments in constraint. Both semantic and arithmetic incongruencies evoked a typical N400 with a clear parieto-central maximum. In addition, numerically larger problems (8x7), in comparison to smaller problems (3x2), evoked a negativity starting at about 360 ms whose maximum was located over the right temporal-parietal scalp. These results indicate that the arithmetic incongruency and the problem-size effect are functionally distinct. It is suggested that the arithmetic and the semantic incongruency effects are both functionally related to a context-dependent spread of activation in specialized associative networks, whereas the arithmetic problem-size effect is due to rechecking routines that go beyond basic fact retrieval.     

The operand-order effect in single-digit multiplication: an ERP study of Chinese adults

Unlike those used in the West, a typical Chinese multiplication table includes only smaller-operand-first entries (e.g., 3 x 7=21, but not 7 x 3=21). Due to this unique feature, multiplication for Chinese subjects has been found to show an operand-order effect. The present study aims to investigate the neural bases of the operand-order effect. Subjects were 20 Mainland Chinese subjects who learned as children the half multiplication table (i.e., smaller-operand-first entries only) and 20 Hong Kong and Macao Chinese subjects who learned as children the whole multiplication table (i.e., both smaller- and larger-operand-first entries) under the British and Portuguese educational systems, respectively. ERP data showed that, for those who learned the half table (Mainland Chinese), but not for those who learned the whole table (Hong Kong and Macao Chinese), the larger-operand-first problems elicited greater negative potentials across representative electrodes of the whole scalp, emerging at about 120 ms after the onset of the second operand and lasting until around 750 ms. These results suggest that the particular experience of acquiring multiplication facts had pronounced impact on their representations in the brain.     

Modality shift effects mimic multisensory interactions: an event-related potential study

A frequent approach to study interactions of the auditory and the visual system is to measure event-related potentials (ERPs) to auditory, visual, and auditory-visual stimuli (A, V, AV). A nonzero result of the AV ? (A + V) comparison indicates that the sensory systems interact at a specific processing stage. Two possible biases weaken the conclusions drawn by this approach: first, subtracting two ERPs from one requires that A, V, and AV do not share any common activity. We have shown before (Gondan and Röder in Brain Res 1073–1074:389–397, 2006) that the problem of common activity can be avoided using an additional tactile stimulus (T) and evaluating the ERP difference (T + TAV) ? (TA + TV). A second possible confound is the modality shift effect (MSE): for example, the auditory N1 is increased if an auditory stimulus follows a visual stimulus, whereas it is smaller if the modality is unchanged (ipsimodal stimulus). Bimodal stimuli might be affected less by MSEs because at least one component always matches the preceding trial. Consequently, an apparent amplitude modulation of the N1 would be observed in AV. We tested the influence of MSEs on auditory-visual interactions by comparing the results of AV ? (A + V) using (a) all stimuli and using (b) only ipsimodal stimuli. (a) and (b) differed around 150 ms, this indicates that AV ? (A + V) is indeed affected by the MSE. We then formally and empirically demonstrate that (T + TAV) ? (TA + TV) is robust against possible biases due to the MSE.     

Explicit and implicit memory in female college students with schizotypal traits: an event-related potential study

The explicit and implicit memory of nonclinical individuals with schizotypal traits was investigated using event-related potentials. Explicit and implicit memory was measured with continuous recognition and categorization tasks, respectively. On the recognition task, the control group demonstrated a greater old/new effect in response to the old than to the new words during the 250-750 ms post-stimulus period, whereas schizotypal trait group did not exhibit an old/new effect during the 550-650 ms period. The control group demonstrated faster response times to the old than to the new words, whereas the schizotypal group demonstrated longer response times to the old than to the new words. On the categorization task, both groups showed old/new effects during the 250-550 ms after stimulus onset and responded more rapidly and with fewer errors to the old than to the new words. These results suggest that individuals with schizotypal traits have impaired explicit but preserved implicit memory.     

Stimulus- and response-locked neuronal generator patterns of auditory and visual word recognition memory in schizophrenia

Examining visual word recognition memory (WRM) with nose-referenced EEGs, we reported a preserved ERP ‘old-new effect’ (enhanced parietal positivity 300–800 ms to correctly-recognized repeated items) in schizophrenia ([Kayser, J., Bruder, G.E., Friedman, D., Tenke, C.E., Amador, X.F., Clark, S.C., Malaspina, D., Gorman, J.M., 1999. Brain event-related potentials (ERPs) in schizophrenia during a word recognition memory task. Int. J. Psychophysiol. 34(3), 249–265.]). However, patients showed reduced early negative potentials (N1, N2) and poorer WRM. Because group differences in neuronal generator patterns (i.e., sink-source orientation) may be masked by choice of EEG recording reference, the current study combined surface Laplacians and principal components analysis (PCA) to clarify ERP component topography and polarity and to disentangle stimulus- and response-related contributions. To investigate the impact of stimulus modality, 31-channel ERPs were recorded from 20 schizophrenic patients (15 male) and 20 age-, gender-, and handedness-matched healthy adults during parallel visual and auditory continuous WRM tasks. Stimulus- and response-locked reference-free current source densities (spherical splines) were submitted to unrestricted Varimax-PCA to identify and measure neuronal generator patterns underlying ERPs. Poorer (78.2 ± 18.7% vs. 87.8 ± 11.3% correct) and slower (958 ± 226 vs. 773 ± 206 ms) performance in patients was accompanied by reduced stimulus-related left-parietal P3 sources (150 ms pre-response) and vertex N2 sinks (both overall and old/new effects) but modality-specific N1 sinks were not significantly reduced. A distinct mid-frontal sink 50-ms post-response was markedly attenuated in patients. Reductions were more robust for auditory stimuli. However, patients showed increased lateral-frontotemporal sinks (T7 maximum) concurrent with auditory P3 sources. Electrophysiologic correlates of WRM deficits in schizophrenia suggest functional impairments of posterior cortex (stimulus representation) and anterior cingulate (stimulus categorization, response monitoring), primarily affecting memory for spoken words.     

Association and not semantic relationships elicit the N400 effect: electrophysiological evidence from an explicit language comprehension task

Language comprehension studies have identified the N400, an event-related potential (ERP) correlate of the processing of meaning, modulation of which is typically assumed to reflect the activation of semantic information. However, N400 studies of conscious language processing have not clearly distinguished between meaning derived from a semantic relationship and meaning extracted through association. We independently manipulated the presence of associative and semantic relationships while examining the N400 effect. Participants were asked to read and remember visually presented word pairs that shared an association ( traffic – jam ), an association+semantic relationship ( lemon – orange ), a semantic relationship alone ( cereal – bread ), or were unrelated ( beard – tower ). Modulation of the N400 (relative to unrelated word pairs) was observed for association and association+semantic word pairs but not for those that only shared a semantic relationship.     

Automatic word form processing in masked priming: an ERP study

Five prime types (unrelated words, pronounceable nonwords, illegal strings of letters, false fonts, or neutral strings of Xs) preceded word and nonword targets in a masked priming study designed to investigate word form processing as indexed by event-related potentials (ERPs). Participants performed a lexical decision task on targets. In the 150-250-ms epoch at fronto-central, central, and temporo-parietal sites ERPs were smallest to targets preceded by words and nonwords, followed by letter strings, false fonts, and finally neutral primes. This refractory pattern sensitive to orthography supports the view that ERPs in the 150-250-ms epoch index activation of neural systems involved in word form processing and suggests that such activation may be graded, being maximal with word-like stimuli and relatively reduced with alphabet-like stimuli. Further, these results from a masked priming paradigm confirm the automatic nature of word form processing.     

The case of letter rhyming: an ERP study

Previous visual event-related potential (ERP) studies using prime-target pairs of word and pseudoword stimuli have reported a robust rhyming effect such that nonrhyming targets elicit a larger N450 than rhyming targets. However, results of similar studies using simpler linguistic stimuli-single letters-are equivocal. We used lowercase and uppercase letter pairs in a simple ERP prime-target rhyming paradigm to further investigate whether single letters could elicit the typical rhyming effect and, if so, whether the rhyming effect was sensitive to physical orthography (which differed between the case conditions). The typical N450 rhyming effect was observed in both the lowercase and uppercase letter pair conditions, with similar amplitude and latency between conditions. This pattern of results suggests that the N450 rhyming effect is not sensitive to physical (case) orthography and likely primarily indexes phonological processing related to the rhyme task.     

汉词再认过程中回忆及熟悉感判别机制的ERPs研究

目的：采用汉语双字词对再认过程中额区新旧效应与熟悉感判别有关、顶区新旧效应与回忆有关的“ERP熟悉感，回忆假说”进行检验。方法：40名大学生参与汉词再认测验，同时记录EEG，离线处理后对旧词、类似词(错判为“旧”)、类似词(正确判为“新”)、及新词诱发出的4类ERPs的主要成分进行了比较。结果：旧词与错判为“旧”的类似词在额区诱发的N300峰值均显著大于新词，而旧词与错判为“旧”的类似词之间无显著性差异。此外，旧词所诱发的LPC波幅显著大于新词与错判为“旧”的类似词，而新词与错判为“旧”的类似词比较未发现显著差异。结论：汉词再认的ERP新旧效应包括额区新旧效应及顶区新旧效应两种成分，其中额区新旧效应与熟悉感判别过程有关。顶叶新旧效应与回忆过程有关。汉词再认的额区新旧效应呈负走向，可能与采用的汉语双字词材料性质有关。     

ERP/CSD indices of impaired verbal working memory subprocesses in schizophrenia

To disentangle subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (>10 s) were recorded from 13 patients and 17 healthy adults during a visual word serial position test. ERP generator patterns were summarized by temporal PCA from reference-free current source density (CSD) waveforms to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source. Build-up of mid-frontal negative slow wave (SW) in controls during item encoding, integration, and active maintenance was absent in patients, whereas a sustained mid-frontal SW sink during the retention interval was comparable across groups. Mid-frontal SW sinks (encoding and retention periods) and posterior SW sinks and sources (encoding only) were related to performance in controls only. Data suggest disturbed processes in a frontal-parietotemporal network in schizophrenia, affecting encoding and early item storage.     

Retrospective attention enhances visual working memory in the young but not the old: An ERP study

Behavioral evidence from the young suggests spatial cues that orient attention toward task‐relevant items in visual working memory (VWM) enhance memory capacity. Whether older adults can also use retrospective cues (“retro‐cues”) to enhance VWM capacity is unknown. In the current event‐related potential (ERP) study, young and old adults performed a VWM task in which spatially informative retro‐cues were presented during maintenance. Young but not older adults' VWM capacity benefited from retro‐cueing. The contralateral delay activity (CDA) ERP index of VWM maintenance was attenuated after the retro‐cue, which effectively reduced the impact of memory load. CDA amplitudes were reduced prior to retro‐cue onset in the old only. Despite a preserved ability to delete items from VWM, older adults may be less able to use retrospective attention to enhance memory capacity when expectancy of impending spatial cues disrupts effective VWM maintenance.     

Enhanced long-term recollection for emotional pictures: Evidence from high-density ERPs

The present study used behavioral and electrophysiological measures to investigate the processes mediating long-term recognition memory for emotional and neutral pictures. The results show enhanced memory recollection for emotional arousing pictures compared to neutral low arousing pictures. In accordance with the behavioral data, we observed enhanced old/new effects in the ERPs for emotionally arousing pictures in the recollection-sensitive old/new component at centro-parietal sites (500–800 ms). Moreover, early old/new effects were present over frontal and parietal sites (300–500 ms) irrespective of picture contents. Analysis of the subjective awareness, indexed by the confidence ratings, showed that the late parietal old/new effect was increased for high confidence responses whereas the early component (300–500 ms) was mainly driven by low confidence responses, an indication for familiarity based recognition processes.     

Identifying deliberate attempts to fake memory impairment through the combined use of reaction time and event-related potential measures

The central aim of this study was to evaluate the value of reaction time (RT) measures and event-related potentials (ERPs) for the assessment of simulated memory impairment. In two identical experiments (N = 24), healthy volunteers carried out an adapted version of the Amsterdam Short-Term Memory (ASTM) test. In half of the cases participants were instructed to perform to their best of abilities (control condition) while in the other half participants were asked to feign a believable memory deficit (simulation condition). Compared to controls, simulating participants were found to produce longer and more variable RTs. In addition, they took longer to respond to new words than to old words, while control participants showed the opposite pattern. Both early (300–500 ms) and late (500–800 ms) ERP old/new effects were similar in magnitude and scalp distribution for both groups of participants, regardless of the fact that simulating participants had significantly lower recognition accuracy than controls. The ERP old/new effect was assumed to reflect unaffected retrieval mechanisms and thus the discrepancy between this measure and recognition performance was interpreted as evidence for intentional underperformance. Results are discussed in relation to clinical observations and deception detection studies. It was concluded that the combined use of RT and ERP measures could be useful to detect and evaluate simulation of memory impairment but that future studies should include patient groups to test some of our assumptions.     

Event-related potential (ERP) asymmetries to emotional stimuli in a visual half-field paradigm

To investigate the hypothesis of a right hemispheric superiority in negative emotional processing, event-related potentials (ERPs) were recorded from 17 sites (Fz, Cz, Pz, F3/4, F7/8, C3/4, T7/8, P3/4, P7/8, O1/2) in a visual half-field paradigm. While maintaining fixation, right-handed women viewed pictures of patients with dermatological diseases before (negative) and after (neutral) cosmetic surgery. A principal components analysis with Varimax rotation performed on ERPs revealed factors identified as N1, N2, early P3, late P3, late P3, and slow wave. Repeated measures analyses of variance performed on factor scores revealed a significant effect of emotional content for all factors except for N1. However, asymmetries in emotional processing were restricted to N2 and early P3, with maximal effects over the right parietal region. N2–P3 amplitude was augmented for negative and reduced for neutral stimuli over right hemisphere regions. Visual field presentation interacted with these asymmetries in enhancing amplitudes contralaterally for early but ipsilaterally for late ERP components. Overall, findings for N2 and P3 support theories of an asymmetry in emotional processing.