The effect of immediate and delayed word repetition on event-related potential in a continuous recognition task

The impact of brand longevity on consumers' purchase intention: An ERP study

This study aims to investigate the neural correlates of brand longevity on consumers' purchase intention by applying the event-related potentials (ERP) method. Behaviorally, in contrast to the short longevity condition, participants in the long longevity condition showed a high purchase rate and a shorter reaction time (RT). In addition, at the neural level, the long longevity condition elicited a decreased N400 and an increased LPP compared to the short longevity condition. This study demonstrated that brand longevity has a positive impact on consumers' purchase intention. The results of this study extend research on brand heritage.

Disentangling Effects of Memory Storage and Inter-articulator Coordination on Generalization in Speech Motor Sequence Learning

Generalization in motor control is the extent to which motor learning affects movements in situations different than those in which it originally occurred. Recent data on orofacial speech movements indicates that motor sequence learning generalizes to novel syllable sequences containing phonotactically illegal, but previously practiced, consonant clusters. Practicing an entire syllable, however, results in even larger performance gains compared to practicing just its clusters. These patterns of generalization could reflect language-general changes in phonological memory storage and/or inter-articulator coordination during motor sequence learning. To disentangle these factors, we conducted two experiments in which talkers intensively practiced producing novel syllables containing illegal onset and coda clusters over two consecutive days. During the practice phases of both experiments, we observed that, through repetition, talkers gradually produced the syllables with fewer errors, indicative of learning. After learning, talkers were tested for generalization to single syllables (Experiment 1) or syllable pairs (Experiment 2) that overlapped to varying degrees with the practiced syllables. Across both experiments, we found that performance improvements from practicing syllables with illegal clusters partially generalized to novel syllables that contained those clusters, but performance was more error prone if the clusters occurred in a different syllable position (onset versus coda) as in practice, demonstrating that inter-articulator coordination is contextually sensitive. Furthermore, changing the position of a cluster was found to be more deleterious to motor performance during the production of the second syllables in syllable pairs, which required talkers to store more phonological material in memory prior to articulation, compared to single syllables. This interaction effect reveals a complex interplay between memory storage and inter-articulator coordination on generalization in speech motor sequence learning.

Does unitization really function like items? The role of interference on item and associative memory processes

Associative memory declines as we age, while item memory remains relatively stable. Previous work has shown that, in both younger and older adults, while item recognition declines linearly across time and interference, associative recognition declines only with longer delays and more interference. Unitization is a memory process found to support associative memory by allowing pairs to presumably be processed like single items. Research has found that unitization can benefit memory in aging by boosting associative memory to be on par with that of younger adults. Yet it remains unclear exactly the mechanism responsible for this enhancement in memory. The current studies aimed to determine whether unitized pairs show similar memory to that of items or associations with increasing time and interference, and determine how physically similar unitized pairs must be to perform like items and examine the effect of age on unitization in a continuous recognition paradigm. The results show that while unitized pairs exhibit higher corrected recognition compared with associative pairs at all lags, unitized pairs are not remembered to the degree that items are. It is critical that unitization boosts accurate recognition of pairs in both age groups across all early and middle lags compared with associative pairs. The results suggest that unitization may promote a more efficient associative link than unrelated associations over increasing time and interference, but the benefit does not reach that of item memory. These results demonstrate that while unitization benefits corrected recognition with earlier interference, its effect may not hold with later interference.

Evidence of the Spacing Effect and Influences on Perceptions of Learning and Science Curricula

The conventional science curricula generally favour educational practices that yield high scores on immediate examination, though it may not accurately predict students’ long-term academic achievement. In view of the pre-exam cramming phenomenon, this article shows the evidence of spacing effect in science education and probes into its theoretical mechanisms, effectiveness in experimental settings, and current applications in science learning. In brief, spacing works by repeatedly presenting the learning material across various temporal intervals. This paper suggests that spacing could significantly result in greater memory strength by alleviating multiple neurocognitive and behavioural properties of learning that are hampered by cramming. Together with the analysis of its relevance in science education, the spacing effect may further provide leverages for promoting long-term conceptual understanding and reflective skill development. However, there are many reasons that students and teachers may not be aware of or fully appreciate its benefits. Finally, this article discusses systemic barriers to why spaced repetition is underutilized in science curricula.

Feigning memory impairment in a forced-choice task: Evidence from event-related potentials

Strategies of malingering detection have brought about a wealth of neuropsychological studies in the last decades. However, the investigation of physiological measures to reliably differentiate between authentic and manipulated symptom presentations is still in its infancy. The present study examined event-related potentials (ERP) to identify feigned memory impairment. We tested instructed malingerers (n = 25) and control participants (n = 22) with a recognition task similar to the Test of Memory Malingering. No differences between groups were found for P1 (70-110 ms) but for N1 (120-170 ms) and P300 components, with lower amplitudes for instructed malingerers. Behavioral data showed a typical pattern of unrealistically high errors in a forced-choice recognition task and less overall recalled stimuli in instructed malingerers. We also found study-phase repetition and old/new effects in the P300, but no interactions with groups (control vs. malingering). Post-hoc analyses revealed that the P300 effect is greater when participants reported an attention-based faking strategy, as opposed to response-based malingerers and controls. The employment of physiological measures can yield additional information on the validity of test data without the need to perform additional tests.

Specifying the neural basis of the spacing effect with multivariate ERP

The spacing effect refers to the finding that, given a fixed amount of study time, a longer interval between study repetitions improves long-term retention (e.g., Cepeda et al., 2006; Ebbinghaus, 1885/1967; Melton, 1970). Although the spacing effect is a robust and reliable finding in the memory literature, its cognitive and neural mechanisms remain unclear. We used event-related potentials (ERPs) to investigate the neural correlates of the spacing effect in the context of the study-phase retrieval hypothesis, which posits that repeated exposure of an item serves as a reminder of one's previous experience with the item, thereby promoting long-term retention. ERPs were recorded from 30 healthy young adults as they studied pairs of words under three levels of lag, corresponding to 0, 4, or 12 intervening pairs between the first and second occurrences of a target pair. We used two study-phase tasks that differed in the degree of retrieval that was required. During the test phase, participants were tested on paired-associate recall. The results demonstrated a significant effect of spacing on memory performance. However, the effect of encoding task and the interaction between encoding task and spacing were not significant. The results of the partial least squares analyses, which are not constrained by time window or electrode selection, revealed a spacing effect on the ERP data for both study-phase tasks; this effect occurred late in the epoch and was most salient over the centro-parietal scalp region. The results add to the literature on the neural correlates of the spacing effect by providing a more comprehensive account compared to past ERP findings that were focused on testing specific ERP components. They also call for further investigation on the various theoretical accounts of the spacing effect.

Effects of modality and repetition in a continuous recognition memory task: Repetition has no effect on auditory recognition memory

Previous research has shown that auditory recognition memory is poorer compared to visual and cross-modal (visual and auditory) recognition memory. The effect of repetition on memory has been robust in showing improved performance. It is not clear, however, how auditory recognition memory compares to visual and cross-modal recognition memory following repetition. Participants performed a recognition memory task, making old/new discriminations to new stimuli, stimuli repeated for the first time after 4-7 intervening items (R1), or repeated for the second time after 36-39 intervening items (R2). Depending on the condition, participants were either exposed to visual stimuli (2D line drawings), auditory stimuli (spoken words), or cross-modal stimuli (pairs of images and associated spoken words). Results showed that unlike participants in the visual and cross-modal conditions, participants in the auditory recognition did not show improvements in performance on R2 trials compared to R1 trials. These findings have implications for pedagogical techniques in education, as well as for interventions and exercises aimed at boosting memory performance.

Automatic Processing of Emotional Words in the Absence of Awareness: The Critical Role of P2

It has been long debated to what extent emotional words can be processed in the absence of awareness. Behavioral studies have shown that the meaning of emotional words can be accessed even without any awareness. However, functional magnetic resonance imaging studies have revealed that emotional words that are unconsciously presented do not activate the brain regions involved in semantic or emotional processing. To clarify this point, we used continuous flash suppression (CFS) and event-related potential (ERP) techniques to distinguish between semantic and emotional processing. In CFS, we successively flashed some Mondrian-style images into one participant's eye steadily, which suppressed the images projected to the other eye. Negative, neutral, and scrambled words were presented to 16 healthy participants for 500 ms. Whenever the participants saw the stimuli—in both visible and invisible conditions—they pressed specific keyboard buttons. Behavioral data revealed that there was no difference in reaction time to negative words and to neutral words in the invisible condition, although negative words were processed faster than neutral words in the visible condition. The ERP results showed that negative words elicited a larger P2 amplitude in the invisible condition than in the visible condition. The P2 component was enhanced for the neutral words compared with the scrambled words in the visible condition; however, the scrambled words elicited larger P2 amplitudes than the neutral words in the invisible condition. These results suggest that the emotional processing of words is more sensitive than semantic processing in the conscious condition. Semantic processing was found to be attenuated in the absence of awareness. Our findings indicate that P2 plays an important role in the unconscious processing of emotional words, which highlights the fact that emotional processing may be automatic and prioritized compared with semantic processing in the absence of awareness.

Rapid memory stabilization by transient theta coherence in the human medial temporal lobe

Presenting stimuli again after presentation of intervening stimuli improves their retention, an effect known as the spacing effect. However, using event-related potentials (ERPs), we had observed that immediate, in comparison to spaced, repetition of pictures induced a positive frontal potential at 200-300 ms. This potential appeared to emanate from the left medial temporal lobe (MTL), a structure critical for memory consolidation. In this study, we tested the behavioral relevance of this signal and explored functional connectivity changes during picture repetition. We obtained high-density electroencephalographic recordings from 14 healthy subjects performing a continuous recognition task where pictures were either repeated immediately or after 9 intervening items. Conventional ERP analysis replicated the positive frontal potential emanating from the left MTL at 250-350 ms in response to immediately repeated stimuli. Connectivity analysis showed that this ERP was associated with increased coherence in the MTL region--left more that right--in the theta-band (3.5-7 Hz) 200-400 ms following immediate, but not spaced, repetition. This increase was stronger in subjects who better recognized immediately repeated stimuli after 30 min. These findings indicate that transient theta-band synchronization between the MTL and the rest of the brain at 200-400 ms reflects a memory stabilizing signal.

Neural mechanisms of the spacing effect in episodic memory: A parallel EEG and fMRI study

Although behavioral studies have consistently reported the spacing effect in learning, its cognitive and neural mechanisms are still not clearly elucidated. According to the storage/retrieval strength framework proposed by Bjork (1999; Bjork & Bjork, 1992), which was built on the study-phase retrieval hypothesis and the deficient processing hypothesis, the spacing effect is achieved by reducing memomtary retrieval strength during subsequent repetitions and thus enhancing storage strength. The present study tested this hypothesis with parallel fMRI and EEG. Participants were asked to study 180 words that were repeated three times, with half of the words having an inter-repetition-lag of 1-3 words (i.e., massed learning) and the other half an inter-repetition-lag of 25-35 words (i.e., spaced learning). An unexpected recognition test was administered 24 h after learning. Consistent with Bjork's hypothesis, the EEG data suggested that spaced learning was associated with weaker retrieval strength, as indicated by a reduced familiarity effect in frontal N400. Meanwhile, spaced learning effectively enhanced the encoding process and thus led to stronger storage strength, as indicated by greater fMRI responses during learning in brain regions whose activities were associated with subsequent memory. Interestingly, no direct association was found between repetition priming and episodic memory. These results furthered our understanding of the neural mechanisms underlying the spacing effect.

Neural Correlate of Anterograde Amnesia in Wernicke-Korsakoff Syndrome

The neural correlate of anterograde amnesia in Wernicke-Korsakoff syndrome (WKS) is still debated. While the capacity to learn new information has been associated with integrity of the medial temporal lobe (MTL), previous studies indicated that the WKS is associated with diencephalic lesions, mainly in the mammillary bodies and anterior or dorsomedial thalamic nuclei. The present study tested the hypothesis that amnesia in WKS is associated with a disrupted neural circuit between diencephalic and hippocampal structures. High-density evoked potentials were recorded in four severely amnesic patients with chronic WKS, in five patients with chronic alcoholism without WKS, and in ten age matched controls. Participants performed a continuous recognition task of pictures previously shown to induce a left medial temporal lobe dependent positive potential between 250 and 350 ms. In addition, the integrity of the fornix was assessed using diffusion tensor imaging (DTI). WKS, but not alcoholic patients without WKS, showed absence of the early, left MTL dependent positive potential following immediate picture repetitions. DTI indicated disruption of the fornix, which connects diencephalic and hippocampal structures. The findings support an interpretation of anterograde amnesia in WKS as a consequence of a disconnection between diencephalic and MTL structures with deficient contribution of the MTL to rapid consolidation.

Electrophysiological correlates of object-repetition effects: sLORETA imaging with 64-channel EEG and individual MRI

BACKGROUND

We investigated the electrophysiological correlates of object-repetition effects using an object categorization task, standardized low-resolution electromagnetic tomography (sLORETA), and individual magnetic resonance imaging. Sixteen healthy adults participated, and a total of 396 line drawings of living and non-living objects were used as stimuli. Of these stimuli, 274 were presented only once, and 122 were repeated after one to five intervening pictures. Participants were asked to categorize the objects as living or non-living things by pressing one of two buttons.

RESULTS

The old/new effect (i.e., a faster response time and more positive potentials in response to repeated stimuli than to stimuli initially presented) was observed at 350-550 ms post-stimulus. The distributions of cortical sources for the old and new stimuli were very similar at 250-650 ms after stimulus-onset. Activation in the right middle occipital gyrus/cuneus, right fusiform gyrus, left superior temporal gyrus, and right inferior frontal gyrus was significantly reduced in response to old compared with new stimuli at 250-350, 350-450, 450-550, and 550-650 ms after stimulus-onset, respectively. Priming in response time was correlated with the electrophysiological priming at left parietal area and repetition suppression at left superior temporal gyrus in 450-550 ms.

CONCLUSIONS

These results suggest processing of repeated objects is facilitated by sharpening perceptual representation and by efficient detection or attentional control of repeated objects.

Event related potentials to digit learning: tracking neurophysiologic changes accompanying recall performance

The aim of this study was to track recall performance and event-related potentials (ERPs) across multiple trials in a digit-learning task. When a sequence is practiced by repetition, the number of errors typically decreases and a learning curve emerges. Until now, almost all ERP learning and memory research has focused on effects after a single presentation and, therefore, fails to capture the dynamic changes that characterize a learning process. However, the current study used a free-recall task in which a sequence of ten auditory digits was presented repeatedly. Auditory sequences of ten digits were presented in a logical order (control sequences) or in a random order (experimental sequences). Each sequence was presented six times. Participants had to reproduce the sequence after each presentation. EEG recordings were made at the time of the digit presentations. Recall performance for the control sequences was close to asymptote right after the first learning trial, whereas performance for the experimental sequences initially displayed primacy and recency effects. However, these latter effects gradually disappeared over the six repetitions, resulting in near-asymptotic recall performance for all digits. The performance improvement for the middle items of the list was accompanied by an increase in P300 amplitude, implying a close correspondence between this ERP component and the behavioral data. These results, which were discussed in the framework of theories on the functional significance of the P300 amplitude, add to the scarce empirical data on the dynamics of ERP responses in the process of intentional learning.

ERP correlates of target-distracter differentiation in repeated runs of a continuous recognition task with emotional and neutral faces

The emotional salience of faces has previously been shown to induce memory distortions in recognition memory tasks. This event-related potential (ERP) study used repeated runs of a continuous recognition task with emotional and neutral faces to investigate emotion-induced memory distortions. In the second and third runs, participants made more false alarms to distracters (repeated from previous runs). Emotion did not modulate the amount of errors, but the extent to which recollection was employed to maximise performance as reflected in the putative ERP correlate of recollection; the parietal old-new effect. Targets from all stimulus classes (positive, negative, neutral) were associated with parietal ERP memory effects, but this was also the case for correctly rejected negative distracters. This suggests that recollection was strategically used to correctly reject negative distracters (recall-to-reject). This finding is consistent with the view that facilitated recollection of negative stimuli may be used to decrease the susceptibility to memory errors induced by emotional salience.

Why the white bear is still there: electrophysiological evidence for ironic semantic activation during thought suppression

Much research has focused on the paradoxical effects of thought suppression, leading to the viewpoint that increases in unwanted thoughts are due to an ironic monitoring process that increases the activation of the very thoughts one is trying to rid from consciousness. However, it remains unclear from behavioral findings whether suppressed thoughts become more accessible during the act of suppression. In the current study, event-related potentials were recorded while participants suppressed or expressed thoughts of a focus word during a simple lexical decision task. Modulations in the N400 component reported here demonstrate the paradoxical effects occurring at the semantic level during suppression, as well as some evidence for the rebound effect after suppression periods. Interestingly, semantic activation was greater for focus words during suppression than expression, despite differences in the N1 window suggesting that expression elicited greater perceptual processing than suppression. Results provide electrophysiological evidence for the Ironic Process model and support recent claims of asymmetric network activation during thought suppression.

Neural transition from short- to long-term memory and the medial temporal lobe: a human evoked-potential study

Recent studies indicated that the human medial temporal lobe (MTL) may not only be important for long-term memory consolidation but also for certain forms of short-term memory. In this study, we explored the interplay between short- and long-term memory using high-density event-related potentials. We found that pictures immediately repeated after an unfilled interval were better recognized than pictures repeated after intervening items. After 30 min, however, the immediately repeated pictures were significantly less well recognized than pictures repeated after intervening items. This processing advantage at immediate repetition but disadvantage for long-term storage had an electrophysiological correlate: spatiotemporal analysis showed that immediate repetition induced a strikingly different electrocortical response after 200-300 ms, with inversed polarity, than new stimuli and delayed repetitions. Inverse solutions indicated that this difference reflected transient activity in the MTL. The findings demonstrate behavioral and electrophysiological dissociation between recognition during active maintenance and recognition after intervening items. Processing of novel information seems to immediately initiate a consolidation process, which remains vulnerable during active maintenance and increases its effectiveness during off-line processing.

Visual statistical learning of shape sequences: an ERP study

Behavioral experiments have found that infants and adults learn statistically defined patterns presented in auditory and visual input sequences in the same manner regardless of whether the input was linguistic (syllables) or nonlinguistic (tones and shapes). In order do determine the time course and neural processes involved in online word segmentation and statistical learning of visual sequence, we recorded event-related potentials (ERPs) while participants were exposed to continuous sequences with elements organized into shape-words randomly connected to each other. After viewing three 6.6min sessions of sequences, the participants performed a behavioral choice test. The participants were divided into two groups (high and low learners) based on their behavioral performance. The overall mean performance was 72.2%, indicating that the shape sequence was segmented and that the participants learned the shape-triplets statistically. Grand-averaged ERPs showed that triplet-onset (the initial shapes of shape-words) elicited larger N400 amplitudes than did middle and final shapes embedded in continuous streams during the early learning sessions of high learners, but no triplet-onset effect was found among low learners. The results suggested that the N400 effect indicated online segmentation of the visual sequence and the degree of statistical learning. Our results also imply that statistical learning represents a common learning device.

On-line Assessment of Statistical Learning by Event-related Potentials

We investigated the neural processes involved in on-line statistical learning and word segmentation. Auditory event-related potentials (ERPs) were recorded while participants were exposed to continuous, nonlinguistic auditory sequences, the elements of which were organized into “tritone words” that were sequenced in random order, with no silent spaces between them. After listening to three 6.6-min sessions of sequences, the participants performed a behavioral choice test, in which they were instructed to indicate the most familiar tone sequence in each test trial by pressing buttons. The participants were divided into three groups (high, middle, and low learners) based on their behavioral performance. The overall mean performance was 74.4%, indicating that the tone sequence was segmented and that the participants learned the tone words statistically. Grand-averaged ERPs showed that word onset (initial tone) elicited the largest N100 and N400 in the early learning session of high learners, but in middle learners, the word-onset effect was elicited in a later session, and there was no effect in low learners. The N400 amplitudes significantly differed between the three learning sessions in the high- and middle-learner groups. The results suggest that the N400 effect indicates not only on-line word segmentation but also the degree of statistical learning. This study provides insight into the neural mechanisms underlying on-line statistical learning processes.

Electrophysiological correlates of behavioral response inhibition in patients with obsessive-compulsive disorder

In this study, we have attempted to determine the electrophysiological correlates of behavioral response inhibition in patients with obsessive-compulsive disorder (OCD). To evaluate response inhibition ability, we have used the Go/NoGo task and measured N2 and P3 event-related potential (ERP) components. Both the OCD and control groups exhibited greater and more frontally distributed N2 and P3 amplitudes in the NoGo condition compared to what we observed in the Go condition. However, the patients with OCD also manifested reduced NoGo-N2 and Go-N2 amplitudes at the frontocentral electrode sites compared to the controls. In addition, the NoGo-N2 amplitudes were more posteriorly distributed in patients with OCD than in controls. The NoGo-N2 amplitudes and latencies measured at the central sites were also negatively correlated with the obsession score on the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). The OCD and control groups were comparable with regard to Go-P3 and NoGo-P3 amplitude and latencies. Our findings suggest dysfunctions in frontal regions mediating response inhibition in OCD, consistent with the involvement of response inhibition in the pathophysiology of this disorder. In addition, NoGo-N2 seems to result in more accurate response inhibition measurements in patients with OCD than does NoGo-P3.

N170 ERPs could represent a logographic processing strategy in visual word recognition

BACKGROUND

Occipito-temporal N170 component represents the first step where face, object and word processing are discriminated along the ventral stream of the brain. N170 leftward asymmetry observed during reading has been often associated to prelexical orthographic visual word form activation. However, some studies reported a lexical frequency effect for this component particularly during word repetition that appears in contradiction with this prelexical orthographic step. Here, we tested the hypothesis that under word repetition condition, discrimination between words would be operated on visual rather than orthographic basis. In this case, N170 activity may correspond to a logographic processing where a word is processed as a whole.

METHODS

To test such an assumption, frequent words, infrequent words and pseudowords were presented to the subjects that had to complete a visual lexical decision task. Different repetition conditions were defined 1--weak repetition, 2--massive repetition and 3--massive repetition with font alternation. This last condition was designed to change visual word shape during repetition and therefore to interfere with a possible visual strategy during word recognition.

RESULTS

Behavioral data showed an important frequency effect for the weak repetition condition, a lower but significant frequency effect for massive repetition, and no frequency effect for the changing font repetition. Moreover alternating font repetitions slowed subject's responses in comparison to "simple" massive repetition.ERPs results evidenced larger N170 amplitude in the left hemisphere for frequent than both infrequent words and pseudowords during massive repetition. Moreover, when words were repeated with different fonts this N170 effect was not present, suggesting a visual locus for such a N170 frequency effect.

CONCLUSION

N170 represents an important step in visual word recognition, consisting probably in a prelexical orthographic processing. But during the reading of very frequent words or after a massive repetition of a word, it could represent a more holistic process where words are processed as a global visual pattern.

The memory that's right and the memory that's left: event-related potentials reveal hemispheric asymmetries in the encoding and retention of verbal information

We examined the nature and timecourse of hemispheric asymmetries in verbal memory by recording event-related potentials (ERPs) in a continuous recognition task. Participants made overt recognition judgments to test words presented in central vision that were either novel (new words) or had been previously presented in the left or right visual field (old words). An ERP memory effect linked to explicit retrieval revealed no asymmetries for words repeated at short and medium retention intervals, but at longer repetition lags (20-50 intervening words) this 'old/new effect' was more pronounced for words whose study presentation had been biased to the right hemisphere (RH). Additionally, a repetition effect linked to more implicit recognition processes (P2 amplitude changes) was observed at all lags for words preferentially encoded by the RH but was not observed for left hemisphere (LH)-encoded words. These results are consistent with theories that the RH encodes verbal stimuli more veridically whereas the LH encodes in a more abstract manner. The current findings provide a critical link between prior work on memory asymmetries, which has emphasized general LH advantages for verbal material, and on language comprehension, which has pointed to an important role for the RH in language processes that require the retention and integration of verbal information over long time spans.

Frontoparietal network involved in successful retrieval from episodic memory. Spatial and temporal analyses using fMRI and ERP

The neural basis for successful recognition of previously studied items, referred to as "retrieval success," has been investigated using either neuroimaging or brain potentials; however, few studies have used both modalities. Our study combined event-related functional magnetic resonance imaging (fMRI) and event-related potential (ERP) in separate groups of subjects. The neural responses were measured while the subjects performed an old/new recognition task with pictures that had been previously studied in either a deep- or shallow-encoding condition. The fMRI experiment showed that among the frontoparietal regions involved in retrieval success, the inferior frontal gyrus and intraparietal sulcus were crucial to conscious recollection because the activity of these regions was influenced by the depth of memory at encoding. The activity of the right parietal region in response to a repeated item was modulated by the repetition lag, indicating that this area would be critical to familiarity-based judgment. The results of structural equation modeling revealed that the functional connectivity among the regions in the left hemisphere was more significant than that in the right hemisphere. The results of the ERP experiment and independent component analysis paralleled those of the fMRI experiment and demonstrated that the repeated item produced an earlier peak than the hit item by approximately 50 ms.

Emerging Neurophysiological Specialization for Letter Strings

In adult readers, printed words and other letter strings activate specialized visual functions within 200 msec, as evident from neurophysiological recordings of brain activity. These fast, specialized responses to letter strings are thought to develop through plastic changes in the visual system. However, it is unknown whether this specialization emerges only with the onset of word reading, or represents a precursor of literacy. We compared 6-year-old kindergarten children who could not yet read words to adult readers. Both age groups detected immediate repetitions of visually presented words, pseudo-words, symbol strings, and pictures during event-related potential (ERP) mapping. Maps from seven corresponding ERP segments in children and adults were analyzed regarding fast (<250 msec) and slow (>300 msec) specialization for letter strings. Adults reliably differentiated words through increased fast (<150 msec) occipito-temporal N1 activity from symbols. Children showed a later, more mid-occipital N1 with marginal word-symbol differences, which were absent in those children with low letter knowledge. Children with high letter knowledge showed some fast sensitivity to letter strings, which was confined to right occipito-temporal sites, unlike the stronger adult N1 specialization. This suggests that a critical degree of early literacy induces some immature, but fast, specialization for letter strings before word reading becomes possible. Children also differentiated words from symbols in later segments through increased right occipito-temporal negativity for words. This slow specialization for letter strings was not modulated by letter knowledge and was absent in adults, possibly reflecting a visual precursor of literacy due to visual familiarity with letter strings.

Oscillatory EEG correlates of episodic trace decay

Recent studies suggest that human theta oscillations appear to be functionally associated with memory processes. It is less clear, however, to what type of memory sub-processes theta is related. Using a continuous word recognition task with different repetition lags, we investigate whether theta reflects the strength of an episodic memory trace or general processing demands, such as task difficulty. The results favor the episodic trace decay hypothesis and show that during the access of an episodic trace in a time window of approximately 200-400 ms, theta power decreases with increasing lag (between the first and second presentation of an item). LORETA source localization of this early theta lag effect indicates that parietal regions are involved in episodic trace processing, whereas right frontal regions may guide the process of retrieval. We conclude that episodic encoding can be characterized by two different stages: traces are first processed at parietal sites at approximately 300 ms, then further processing takes place in regions of the medial temporal lobe at approximately 500 ms. Only the first stage is related to theta, whereas the second is reflected by a slow wave with a frequency of approximately 2.5 Hz.

Face repetition effects in direct and indirect tasks: an event-related brain potentials study

We investigated immediate repetition effects on event-related potentials (ERPs) during direct and indirect tasks for sequentially presented face pairs. The first face (F1) was presented masked or unmasked, and at different stimulus onset asynchronies (SOAs, 67 vs. 1000 ms) preceding the second face (F2). Experiment I (indirect task) required a semantic classification of F2, with F1 identity being irrelevant. Experiment II (direct task) used the same stimulus sequence but required a physical identity matching of F1 and F2. Whereas no masked repetition effects in behaviour or ERPs were seen, such effects were clearly shown for unmasked F1 faces. For short SOAs, an early-onset ( approximately 100 ms) occipital repetition effect, an inferior temporal N250r (200-300 ms) and a central-parietal N400 modulation (300-500 ms) were seen in both tasks, whereas a parietal P600 effect (500-800 ms) was only present in the indirect task. For long SOAs, the early occipital effect disappeared, suggesting that it reflects a fast decaying iconic memory trace. Clear task differences were seen for N250r, N400, and P600 modulations: P600 was larger for the indirect task, and may be a correlate of semantic analysis required by this task. By contrast, N250r and N400 were larger for the direct task, suggesting that these components are sensitive to task relevance and/or attentional focus to F1, and thus do not reflect purely automatic facilitation in processing. This suggests an influence of strategic processing on the activation of both perceptual representations of faces and semantic representations of people.

Impairment of recognition memory in schizophrenia: event-related potential study using a continuous recognition task

Recognition memory and the dissociation of immediate and delayed repetition in schizophrenic patients were investigated using event-related potential (ERP) and a continuous word recognition task. In total, 14 schizophrenic patients and 14 age and gender-matched control subjects, were recruited. Among 240 stimulus words used, 40 words were not repeated, 100 were repeated immediately, and 100 were repeated after five intervening words. Both schizophrenic and control groups responded faster to words repeated immediately than to words repeated after a delay and to new words. However, schizophrenic patients responded less accurately to words repeated immediately and to words repeated after a delay than the controls. In terms of ERP, schizophrenic patients showed significantly reduced N200, late positive component (LPC), and N400 amplitudes, and a more frontally-distributed N200 topography than the controls. For controls, immediate repetition was associated with a large LPC amplitude and the absence of N400, while delayed repetition was associated with a small LPC amplitude and the presence of N400. However, this dissociation between immediate and delayed repetition was not observed in schizophrenic patients. All of these results suggest that schizophrenic patients have recognition memory impairment, the cause of which may range from early encoding, and memory search to late retrieval.

Electrical neuroimaging reveals early generator modulation to emotional words

Functional electrical neuroimaging investigated incidental emotional word processing. Previous research suggests that the brain may differentially respond to the emotional content of linguistic stimuli pre-lexically (i.e., before distinguishing that these stimuli are words). We investigated the spatiotemporal brain mechanisms of this apparent paradox and in particular whether the initial differentiation of emotional stimuli is marked by different brain generator configurations using high-density, event-related potentials. Such would support the existence of specific cerebral resources dedicated to emotional word processing. A related issue concerns the possibility of right-hemispheric specialization in the processing of emotional stimuli. Thirteen healthy men performed a go/no-go lexical decision task with bilateral word/non-word or non-word/non-word stimulus pairs. Words included equal numbers of neutral and emotional stimuli, but subjects made no explicit discrimination along this dimension. Emotional words appearing in the right visual field (ERVF) yielded the best overall performance, although the difference between emotional and neutral words was larger for left than for right visual field presentations. Electrophysiologically, ERVF presentations were distinguished from all other conditions over the 100-140 ms period by a distinct scalp topography, indicative of different intracranial generator configurations. A distributed linear source estimation (LAURA) of this distinct scalp potential field revealed bilateral lateral-occipital sources with a right hemisphere current density maximum. These data support the existence of a specialized brain network triggered by the emotional connotation of words at a very early processing stage.