Effects of Inter-Item Lag on Word Repetition: An Event-Related Potential Study

Prior exposure to a word can greatly facilitate performance to subsequent presentations of that word. ERP studies have shown that this facilitation is associated with an attenuation of a negative peak normally occurring around 400 ms poststimulus. Recent studies have interpreted this repetition effect as reflecting either lexical access or episodic memory mechanisms. However, there is now increasing evidence that neither of the above mechanisms alone can fully account for repetition effects. The present experiment recorded ERPs to immediate and delayed word repetition during a lexical decision task in order to investigate the time-course of ERP repetition effects. Immediate repetition was found to produce greater response facilitation than delayed repetition. The ERP waveforms of both immediate and delayed word repetition diverged from that of initial word presentation at approximately 300 ms poststimulus. The waveforms for repeated words separated around 400 ms poststimulus with immediate repetition showing a more rapid resolution of negativity and earlier late positivity than delayed repetition. It is suggested that the negativity may reflect processes involved in the overall activation contributing to word recognition, whereas the late positivity may be related to the repetition of stimulus categorization and decision processes.     

Unnoticed regularity violation elicits change-related brain activity

Event-related brain electric activity (ERP) was investigated to unnoticed visual changes. The orientation of grid elements (vertical or horizontal) changed after the presentation of 10–15 identical stimuli. The grid patterns were task irrelevant, and were presented in the background of a shape discrimination task. During the first half of the session, participants were unaware of the stimulus change. However, in comparison to the ERPs to the fifth identical stimuli, stimulus change elicited posterior negativities in the 270–375 ms range (visual mismatch negativity, vMMN). With participants instructed on the stimulus change, negativities emerged with earlier onset and with wider distribution. When stimulus change was preceded by only two identical stimuli, there were no such ERP effects. As the results show, a longer sequence of identical unattended stimuli may establish the memory representation of stimulus regularity, and violation of regularity is indicated by posterior negative ERP components (vMMN).     

Attention modulates emotional expression processing

To investigate the time course of emotional expression processing, we recorded ERPs to facial stimuli. The first task was to discriminate emotional expressions. Enhanced negativity of the face-specific N170 was elicited by emotional as opposed to neutral faces, followed by the occipital negativity (240-340 ms poststimulus). The second task was to classify face gender. Here, N170 was unaffected by the emotional expression. However, emotional expression effect was expressed in the anterior positivity (160-250 ms poststimulus) and subsequent occipital negativity (240-340 ms poststimulus). Results support the thesis that structural encoding relevant to gender recognition and simultaneous expression analysis are independent processes. Attention modulates facial emotion processing 140-185 ms poststimulus. Involuntary differentiation of facial expression was observed later (160-340 ms poststimulus), suggesting unintentional attention capture.     

ERPs and deviance detection: visual mismatch negativity to repeated visual stimuli

Previous studies showed a visual analogue of the mismatch negativity (MMN) event-related potential (ERP), which is elicited by violating some sensory regularity. Separating physical change from violating a regularity, here we show that the visual MMN (vMMN) is elicited by regularity violations that do not involve physical stimulus change. Adult participants were presented with a series of red-black and green-black checkerboard patterns delivered regularly in an RRGGRRGG ... order. Infrequently (p=0.1) this regularity was broken by repeating a stimulus one additional time (e.g. RRGGRRR). ERPs elicited by irregular stimulus repetitions were negatively displaced compared to those elicited both by regular repetition and regular change in two latency ranges: 100-140 ms and 220-260 ms. Whereas the first of these two negative ERP differences appears to be sensitive to stimulus repetition per se, the second difference can be identified as a vMMN response to violating the sequential regularity. Thus, similarly to its auditory counterpart, vMMN reflects deviance-(regularity-violation) rather than change-detection processes.     

An Event-Related Potential Study of Older Children With an Early History of Failure to Thrive

Elementary and junior high school children (n = 13), who were diagnosed with nonorganic failure to thrive (FTT) as infants and toddlers, were compared with a normal control group (n = 14) on visual event-related potentials (ERPs) elicited during a primed lexical decision task. Positive stimuli were real words that were identical to the priming stimuli; negative stimuli were nonpronounceable letter strings. Although the groups did not differ in word-list reading level, the former FTT group had slower reaction (decision) times and did not show ERP evidence of priming in the N400 epoch. Anterior sites yielded better separation of the real words and letter strings than posterior sites. A late anterior component between 500 msec to 650 msec poststimulus onset showed the largest condition effect for both groups. The control group had a larger negative going late anterior component to words than the FTT group. The combined reaction time and ERP findings point to less automatized word recognition in the FTT group.     

An event-related potential study of older children with an early history of failure to thrive

Elementary and junior high school children (n = 13), who were diagnosed with nonorganic failure to thrive (FTT) as infants and toddlers, were compared with a normal control group (n = 14) on visual event-related potentials (ERPs) elicited during a primed lexical decision task. Positive stimuli were real words that were identical to the priming stimuli; negative stimuli were nonpronounceable letter strings. Although the groups did not differ in word-list reading level, the former FTT group had slower reaction (decision) times and did not show ERP evidence of priming in the N400 epoch. Anterior sites yielded better separation of the real words and letter strings than posterior sites. A late anterior component between 500 msec to 650 msec poststimulus onset showed the largest condition effect for both groups. The control group had a larger negative going late anterior component to words than the FTT group. The combined reaction time and ERP findings point to less automatized word recognition in the FTT group.     

The independency of the Bereitschaftspotential from previous stimulus‐locked P3 in visuomotor response tasks

The Bereitschaftspotential (BP) and the P3 are well‐known ERPs usually observed during self‐paced and externally triggered tasks. Recently, the BP was also detected in externally triggered tasks before stimulus onset. However, doubts have been raised about the authenticity of the BP in these tasks due to possible overlaps with the previous trial P3 (hereinafter s‐1 P3). Here, we aim to test the authenticity of the BP in externally triggered tasks by comparing ERPs obtained during two visuomotor response tasks with different interstimulus intervals (ISIs) allowing (short‐ISI; 1,000–2,000 ms) or not (long‐ISI; 2,000–4,000 ms) P3‐BP overlaps. In line with previous research, we hypothesize that BP and the s‐1 P3 contribute independently to the scalp‐detected activities during these tasks. ERPs were recorded from 14 healthy participants during the short‐ISI and long‐ISI visuomotor response tasks. Amplitudes and latencies of pre‐ (BP and pN) and poststimulus ERP components (P1, pN1, pP1, N1, pP2, dpP2, N2, P3) were compared between conditions. No effect of ISI was found on the amplitude of any pre‐ and poststimulus components. In contrast, longer ISI is associated with earlier onsets of the BP and pN components. In visuomotor response tasks, the BP is independent from the P3 elicited by the previous trial (s‐1 P3), even using relatively short ISI. Since the different ISIs did not affect the amplitude of the BP and the P3 components, we conclude that also a short ISI can be adopted safely and conveniently to keep a reasonable duration of the overall experiment.     

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.     

ERPs during continuous recognition memory for words

Event-related brain potentials (ERPs) were recorded from 10 young adults during a version of the continuous recognition memory paradigm. Words were presented after lags of either 2, 8 or 32 intervening items (equiprobable) following their first presentation, and subjects were required on each trial to make a choice: new (never presented previously) or old (previously presented) response. To assess the effect of probability of new to old items, words were presented in separate blocks with ratios of new to old of 2:1 and 1:1. Reaction time increased and successful recognition decreased systematically as the lag between first and second presentations of an item increased, supporting the distinction between primary (immediate memory) and secondary memory for verbal material. However, there were no systematic effects of item lag on the ERP components. ERPs to new items were characterized by larger N300 and smaller P300 amplitudes (from about 250 to 700 ms) than those to old items. These amplitude differences between old and new ERPs were interpreted as primarily reflecting repetition as opposed to semantic priming effects. These old/new effects did not interact with probability, suggesting that frequency of occurrence is not a major determinant the ERP old/new difference. Old items elicited a late negativity following the behavioral response that was interpreted as due to the presence of a "positive slow wave," with a frontally oriented distribution to new words that was absent in the ERPs to old words. Similarly, subtraction of ERPs elicited by new items that were subsequently unrecognized from those subsequently recognized, showed that underlying the ERP subsequent "memory effect" was a "frontal positive slow wave," dissociable from P300 on the basis of differences in scalp distribution. Since positive slow wave has been interpreted as reflecting "further processing," the data suggest that such processing, possibly similar to elaboration (Graf & Mandler, 1984), enhanced the probability of subsequent recognition.     

Immediate and delayed stimulus repetitions evoke different ERPs in a serial-probe recognition task

In this study we examined whether event-related potentials (ERPs) associated with stimulus repetition and recognition in a serial-probe recognition task were comparable to ERPs in other tasks that are more typically used to investigate old/new ERP effects. The experiment consisted of 320 trials in which a recognition probe followed a four-item memory set; 160 trials consisted of images depicting common objects that were easy to label (EL task), and 160 trials consisted of images depicting abstract patterns that were difficult to label (DL task). Nineteen participants indicated whether a probe that followed each memory set was or was not presented in the memory set. Half of the probes matched, and half did not match, an item in the preceding memory set. ERPs appeared to reflect two processes--one that differentiated between recently presented stimuli and other stimuli and another that distinguished between repeated stimuli and new stimuli. ERPs to recent probes were more positive than ERPs to other probes in the EL and DL tasks. ERPs to match (old) probes were more positive than ERPs to nonmatch (new) probes only in the EL task.     

Neural Correlates of Emotion Processing in Typically Developing Children and Children of Diabetic Mothers

To examine the neurocognitive sequelae of children born to diabetic mothers (CDMs), event-related potentials (ERPs) in response to three facial expressions (happy, fear, anger) were collected from 42 children (18 CDMs, 24 controls), aged 36 and/or 48 months. A linear mixed models approach was used to model individual variation in amplitude and latency. As infants, CDMs in the present study displayed subtle impairments in attention and memory processing, including face recognition, as indexed by ERPs. Findings indicate that these same children, now ages 3–4 years, continue to display ERP patterns that differ from controls in amplitude, latency, and hemispheric asymmetry.     

Chronic stress impairs learning and hippocampal cell proliferation in senescence-accelerated prone mice

The anterior N2 is a component of the event-related brain potential (ERP) elicited by visual novel stimuli. Previous studies have reported that the stimuli that were viewed for longer periods of time elicited a larger anterior N2 than the stimuli viewed for shorter periods of time. To scrutinize this relationship between the ERP and viewing duration in response to visual materials, 18 university students were asked to look at various random polygons one-by-one for as long as they wished. ERPs time-locked to stimulus onset were averaged separately for three levels of complexity (12-, 24-, and 48-sided polygons). We found that the more complex the stimulus, the larger the anterior negativity (N2, 200-300 ms) and the posterior positivity (late positive potential [LPP], 400-800 ms), and the longer the viewing duration. However, when ERPs were calculated separately for the stimuli viewed for longer or shorter than the median viewing time of each participant at each complexity level, no amplitude differences were found in either component. These results suggest that the previously reported correlation between the anterior N2 and visual duration is spurious and produced by a third variable, namely, the perceptual demand of the eliciting stimulus such as complexity.     

Effects of display and memory load on the event-related potentials during visual letter search combined with selection by color]

This study investigated the effects of display and memory load on the event-related potentials (ERPs) in a visual letter search task combined with selection by color. ERPs were recorded from 10 adult subjects, when they were required to judge if test stimuli, which consisted of a horizontal array of five colored alphabets, contained target letters defined by shape and color. The results showed that the increase of display or memory load caused the enlargement of three different negativities. The first and second display load effects were observed in the ERPs at midline central electrode (Cz) between 240-280 ms latency range, and in a posterior-distributed negativity that was the maximum at about 650 ms after the stimulus onset. The third was the anterior-central negativity that was the largest at Cz about 550 ms after the stimulus onset. In contrast to the first two effects, this negativity was enhanced by display or memory load. In discussion, a tentative linkage between these ERP changes and two slave systems of working memory (phonological loop and visuo-spatial sketchpad) was proposed.     

Using event-related potentials to study perinatal nutrition and brain development in infants of diabetic mothers

Proper prenatal and postnatal nutrition is essential for optimal brain development and function. The early use of event-related potentials enables neuroscientists to study the development of cognitive function from birth and to evaluate the role of specific nutrients in development. Perinatal iron deficiency occurs in severely affected infants of diabetic mothers. In animal models, severe perinatal iron deficiency targets the explicit memory system of the brain. Cross-sectional ERP studies have shown that infants of diabetic mothers have impairments in recognition memory from birth through 8 months of age. The purpose of this study was to evaluate longitudinal development of recognition memory using ERPs in infants of diabetic mothers compared with control infants. Infants of diabetic mothers were divided into high and low risk status based upon their birth weights and iron status and compared with healthy control infants. Infants were tested in the newborn period for auditory recognition memory, at 6 months for visual recognition memory and at 8 months for cross modal memory. ERPs were evaluated for developmental changes in the slow waves that are thought to reflect memory and the Nc component that is thought to reflect attention. The results of the study showed differences in development between the IDMs and control infants in the development of the slow waves over the left anterior temporal leads and age-related patterns of development in the NC component. These results are consistent with animal models showing that perinatal iron deficiency affects the development of the memory networks of the brain. This study highlights the value of using ERPs to translate basic science information obtained from animal models to the development of the human infant.     

A Topographic Study of ERPs Elicited by Visual Feature Discrimination

The functional properties and topographic distribution of event-related potential (ERP) components elicited by visual discrimination of orientation, spatial frequency, spatial location, and color were investigated. ERPs were recorded from 28 electrode sites from 16 adult subjects. Five ERP components were measured: N1 (peak latency = 160 ms), P2 (250 ms), anterior N2 (260 ms), posterior N2 (280 ms), and P3 (400 ms). N1 and P2 were more negative when a stimulus was a target, showing the selection negativity effect. Feature-specific effects on component amplitude or topography varied by component. N1 and P2 were sensitive to stimulus orientation and location. Anterior or posterior N2 was sensitive to orientation, spatial frequency, and location. P3 varied with orientation, but not with other stimulus features. Cross-task comparisons of ERPs to vertical line segments in the color, orientation, and location discrimination tasks indicated that P2 and N2, but not N1 and P3, were sensitive to changes in task-demand. These data provide topographic evidence that ERP components in the 160-400 ms time domain can be differentiated on the basis to processing of specific visual features, and reflect neurophysiologically distinct visual pathways in the human cortex.     

Using Event-Related Potentials to Study Perinatal Nutrition and Brain Development in Infants of Diabetic Mothers

Proper prenatal and postnatal nutrition is essential for optimal brain development and function. The early use of event-related potentials enables neuroscientists to study the development of cognitive function from birth and to evaluate the role of specific nutrients in development. Perinatal iron deficiency occurs in severely affected infants of diabetic mothers. In animal models, severe perinatal iron deficiency targets the explicit memory system of the brain. Cross-sectional ERP studies have shown that infants of diabetic mothers have impairments in recognition memory from birth through 8 months of age. The purpose of this study was to evaluate longitudinal development of recognition memory using ERPs in infants of diabetic mothers compared with control infants. Infants of diabetic mothers were divided into high and low risk status based upon their birth weights and iron status and compared with healthy control infants. Infants were tested in the newborn period for auditory recognition memory, at 6 months for visual recognition memory and at 8 months for cross modal memory. ERPs were evaluated for developmental changes in the slow waves that are thought to reflect memory and the Nc component that is thought to reflect attention. The results of the study showed differences in development between the IDMs and control infants in the development of the slow waves over the left anterior temporal leads and age-related patterns of development in the NC component. These results are consistent with animal models showing that perinatal iron deficiency affects the development of the memory networks of the brain. This study highlights the value of using ERPs to translate basic science information obtained from animal models to the development of the human infant.     

Event-related potential index of age-related differences in memory processes in adults with Down syndrome

A major goal of aging research is to identify early markers of age-related cognitive decline. Persons with Down syndrome (DS) experience accelerated aging and high risks for dementia, making them a valuable albeit understudied model for testing such markers. This study examined event-related potential (ERP) indices of visual memory in younger (19–25 years) and older (35–40 years) adults with DS using a passive viewing paradigm that did not require memorization or behavioral responses. ERPs were recorded in response to unfamiliar urban and nature scenes, with some images presented once and others repeated multiple times. Within 600 to 900 milliseconds after stimulus onset, repeated stimuli elicited more positive amplitudes in younger participants, indicating stimilus recognition. ERPs of older adults did not show such increases, suggesting reduced memory functioning. ERP indices were unrelated to participants' intellectual functioning, but did correlate with age and caregiver-reported lethargy/withdrawal behaviors. Passive ERP measures of memory processes are sensitive to early stages of cognitive decline in DS and are promising markers of cognitive risk for future aging studies.     

The effects of between-source discriminability on attended and unattended auditory ERPs

Event-related potentials (ERPs) for tone pips from attended and unattended sources, which varied on discriminability, were compared with ERPs for the same stimuli recorded during performance of a visual task. This comparison revealed that Nd, the negative shift of attended relative to unattended ERPs, consisted of three components: a negativity in the attended ERP from 100 to 270 ms, a positivity in the unattended ERP from 170 ms to the end of the epoch, and a second negativity in the attended ERP from 270 to 700 ms. In general, the later onset of early Nd with more difficult between-source discriminations could be attributed to the later onset of the positivity in unattended ERPs. A number of hypotheses were advanced for the origin of the unattended positivity: the suppression of the later of two negative components in the 100–220-ms range, an enhanced P2 component, an endogenous positivity, or the resolution of a protracted negativity elicited by preceding attended stimuli.     

Attention‐dependent sound offset‐related brain potentials

When performing sensory tasks, knowing the potentially occurring goal‐relevant and irrelevant stimulus events allows the establishment of selective attention sets, which result in enhanced sensory processing of goal‐relevant events. In the auditory modality, such enhancements are reflected in the increased amplitude of the N1 ERP elicited by the onsets of task‐relevant sounds. It has been recently suggested that ERPs to task‐relevant sound offsets are similarly enhanced in a tone‐focused state in comparison to a distracted one. The goal of the present study was to explore the influence of attention on ERPs elicited by sound offsets. ERPs elicited by tones in a duration‐discrimination task were compared to ERPs elicited by the same tones in not‐tone‐focused attentional setting. Tone offsets elicited a consistent, attention‐dependent biphasic (positive‐negative—P1‐N1) ERP waveform for tone durations ranging from 150 to 450 ms. The evidence, however, did not support the notion that the offset‐related ERPs reflected an offset‐specific attention set: The offset‐related ERPs elicited in a duration‐discrimination condition (in which offsets were task relevant) did not significantly differ from those elicited in a pitch‐discrimination condition (in which the offsets were task irrelevant). Although an N2 reflecting the processing of offsets in task‐related terms contributed to the observed waveform, this contribution was separable from the offset‐related P1 and N1. The results demonstrate that when tones are attended, offset‐related ERPs may substantially overlap endogenous ERP activity in the postoffset interval irrespective of tone duration, and attention differences may cause ERP differences in such postoffset intervals.     

Anterior N2 predicts subsequent viewing time and interest rating for novel drawings

Event-related brain potentials (ERPs) in response to novel pictures and subsequent visual exploration were examined. Eighteen undergraduates viewed 120 novel drawings as long as they wished. ERPs were calculated separately for drawings that were viewed longer or shorter than the median viewing time of each participant. The drawings viewed longer elicited a larger anterior negativity (N2) peaking at 245 ms than the shorter viewed drawings. This effect disappeared and the overall amplitude of the N2 decreased when the same set of drawings was presented again in a subsequent interest-rating session. Drawings rated as more interesting elicited a larger N2 than did drawings rated as less interesting. This study demonstrates a type of anterior N2 that is sensitive to stimulus unfamiliarity or difficulty in encoding, which reflects a conflict between stimulus input and existing knowledge and prompts further recognition processes and visual exploration.