Event-related potentials in an auditory semantic oddball task in humans

Whenever rare target stimuli are presented interspersed by frequent irrelevant stimuli (standards), the targets elicit a late parieto-central positive wave called P3. Usually standards and targets differ by a simple physical feature (e.g. tone pitch). Less consistent are the data obtained in semantic tasks, in which standards and targets are represented by different word classes. Given an equal number of words in the target and standard categories, each individual standard is more frequent than each target, that is, the frequency of the category is confounded with that of individual stimuli. In the present study participants were presented five semantic classes each being represented by 15 words. Words belonging to one particular class should be counted. Thus targets were rare (20%), although the frequencies of each word and of each semantic class were equal. A highly significant P3 was recorded. Its latency was longer, and the amplitude was smaller, than when standards and targets were two tones. These data indicate that brain waves recorded in semantic tasks are not necessarily manifestations of specific semantic processing.     

Event-related potentials and monoamines in autistic children on a clinical trial of fenfluramine

In a double blind, crossover study of the response of autistic subjects to fenfluramine, event-related potentials (ERPs) were recorded from 7 subjects on an attention-demanding auditory choice reaction time task (ACRT). ACRT, IQ and biochemical measures were taken after 5 months placebo and 5 months fenfluramine treatment. After fenfluramine treatment blood serotonin levels fell, urinary catecholamine levels fell and the HVA/DA ratio rose. IQ and ACRT performance improved. On the ACRT subjects were asked to press a button to a rare target (500 Hz, P = 0.14) and to ignore higher pitched rare (2,000 Hz, P = 0.14) and frequent non-targets (1,000 Hz). After fenfluramine treatment N1 latencies increased. The scalp distribution of ERP maxima changes slightly with treatment. P3 maxima elicited by rare non-targets were recorded more rostrally after fenfluramine treatment. After rare non-targets N1 amplitudes at Fz decreased but P3 amplitudes at Pz increased. Early negativity after the rare non-target (particularly on the right side) was negatively correlated with the HVA/DA ratio. Subtraction of the P3 component elicited in a passive condition where no response was required from the active condition showed that P3 positivity to targets was halved with treatment. (In contrast Nd increased on fenfluramine treatment). Overall, N1 and P3 components showed greatest responsiveness to rare non-targets on fenfluramine. N1 but not P3 changes may represent slight improvement of attention-related function with treatment. Small changes in ERP latency and distribution, associated with the neuroleptic action of fenfluramine may be partly responsible for a mild improvement of IQ and ACRT performance on medication.     

Event-related potentials during an emotional Stroop task.

Emotional Stroop tasks have gained wide interest in scientific literature in the last two decades. Although no direct measure of attention is employed, these studies infer the presence of preferential processing of threatening information based on reaction time (RT) impairment in a competing task. Because event-related potential (ERP) measures are sensitive to both the extent (amplitude) and speed (latency) of cerebral processing, they are valuable tools with which to examine more directly the claim that threatening stimuli are associated with enhanced attention. Twenty-two students rated a pool of words to identify those that were personally disturbing. Two word types (threat and neutral) were then compared in two tasks (color relevant, in which the color ink of words was identified, and word relevant in which words were classified as threatening or not). No emotional Stroop effect was observed in terms of longer RTs to identify the colors of threat words. ERP results provided valuable information about threat processing which was not observed with behavioral measures. Threat content was associated with larger P2 amplitude in the right than left hemisphere, and larger P3 amplitude, across tasks. The results indicate strong evidence for enhanced processing of threat-related stimuli in healthy individuals. It is concluded that ERPs are a sensitive measure of processes underlying emotional Stroop performance, which can be used to elucidate attentional biases in healthy and clinical populations.     

Effects of aging on event-related brain potentials and reaction times in an auditory oddball task

Auditory event-related potentials (ERPs) were recorded from 71 healthy individuals between 18 and 82 years of age during performance of a disjunctive reaction time task in an auditory oddball paradigm. The effects of aging on reaction times and on the latencies, amplitudes, and distributions of each of the main ERP components were examined. No significant slowing of the reaction times of the elderly subjects was observed in relation to the younger ones. The peak latencies of both the N1 and P2 components elicited by standard tones were slightly but significantly slowed with age. In the ERPs of target tones, the later, endogenous components (N2, P3, and SW) showed linear increases in latency as a function of age; the later the component, the longer the age-related delay. In general, aging was associated with less negativity (both N2 and SW) and more positivity (P3) over the anterior scalp, together with a smaller P3 and a more pronounced N2 over posterior scalp areas. Most of the effects observed in target ERPs were also evident in the difference waves derived from subtraction of the standard from the target ERPs, although the slope of the age-related latency increase of N2 was shallower and that of the P3 was steeper in the difference ERPs. These findings are discussed in relation to previous accounts of ERP changes with aging.     

Event-related potential evidence of semantic mismatch in a 'same-different' reaction time task

In a 'same-different' reaction time (RT) task, suit (spades and/or hearts) target stimuli, and irrelevant suits (distractors) or plus signs (indifferent elements) were presented. The 'same' RT was shorter than the 'different' RT. This 'fast same' effect was independent of the RT increase caused by the distractor stimuli. Event-related potentials (ERPs) in trials with distractor elements were more negative in the 350-600 ms latency range than the ERPs of trials with different irrelevant elements.     

Event-related potentials before saccades and antisaccades and their relation to reaction time

In the present study, reaction time (RT) was measured in 12 healthy subjects in a saccade and antisaccade task while recording electroencephalographic activity (EEG) from 62 electrodes on the scalp. Event-related potentials averaged both on target appearance and on saccade onset were larger in amplitude (increased negativity) for the antisaccade task compared to the saccade task. The relation of RT variability to EEG amplitude was studied by averaging stimulus-aligned and movement-aligned individual trials for each subject into four RT quartile groups. The analysis showed a relation of EEG amplitude to RT for both saccades and antisaccades. More specifically, the ERP negativity at 100–120 ms after stimulus onset in the saccade task and at 160–200 ms after stimulus onset in the antisaccade task for stimulus-aligned ERPs decreased monotonically with increasing RT as would be expected if this signal would be related to the eye movement preparation processes. This was much more pronounced and wide spread for the antisaccades than for visually triggered saccades. The peak negativity before movement onset for movement-aligned ERPs also covaried with RT suggesting no relation of this activity to movement preparation processes. This study then confirmed that only a particular ERP signal variation was related to the saccadic eye movement preparatory processes while other components of the ERP have no specific relation to the movement preparation. This particular signal was more prominent for antisaccades compared to visually triggered saccades supporting previous evidence for the cortical involvement in the preparation of these voluntary eye movements. In conclusion, this study validates the use of ERPs in the study of the planning and execution of saccadic eye movements.     

Event-related potentials elicited by non-target tones in an auditory oddball paradigm in schizophrenia.

It has been reported that in event-related potentials (ERPs) elicited by non-target tones in oddball paradigms, the superimposition of a negative component on the descending slope of N100 depends on subjects' attention to the task. We tested the possibility that this attention-related change is abnormal for patients with schizophrenia. ERPs induced by non-target, frequent tones were measured for 52 patients and 31 healthy controls under two oddball conditions: a passive condition where the subjects were told to disregard the tones, and an active condition where they were instructed to respond to infrequent tones. For both groups, a negative component was superimposed from the descending slope of N100 to the end of P150 (latency, 120-200 ms) for the active condition. The peak latency of this attention-related negative component was longer for the patients than for the controls, while the amplitude showed no group difference. In addition, the active P150 for the patients was more enlarged than that for the controls. Furthermore, the active P150 amplitude for the patients correlated positively with the score for the negative symptom factor of the Positive and Negative Syndrome Scale. These findings suggest that the enlargement of non-target P150 observed in conjunction with the latency prolongation of the attention-related negative component may be a biological marker for the severity of the negative symptoms in schizophrenia.     

Event-related potentials to auditory and visual selective attention in schizophrenia.

BACKGROUND: Prior studies have shown a consistent reduction of the auditory P300 in schizophrenia, while the visual attention findings have been mixed. Both the auditory and visual N2b, an earlier, modality-specific attention index, are reduced in schizophrenia, sometimes despite sparing of the visual P300. Thus there may be a dissociation between the N2b and P300 attention effects in auditory and visual modalities in schizophrenia. METHODS: Thirteen patients and thirteen controls observed symbols appearing on a screen, paired with simultaneous tones. In some blocks subjects responded to one of the symbols, in others to one of the tones. The N2b was predicted to be reduced in the patient group in both auditory and visual attention but the P300 reduced only while attending to tones. RESULTS: Results showed a reduction of the N1 component in the patient group in the auditory condition but not in the visual. There was a reduction of the N2b target-minus-non-target difference wave in the patients in both auditory and visual target conditions. The P300 component was larger overall in the control group in both modalities, but did not show the usual enhancement to auditory targets in the control group. CONCLUSIONS: These findings suggest that the ability to selectively attend to a target in one modality while ignoring the other is compromised in patients with schizophrenia. Perceptual processing appears to be impacted in the auditory modality while remaining intact in the visual. The N2b appears more vulnerable than the P300 in both auditory and visual attention in schizophrenia.     

Event-related potentials indicate information extraction in a comparative judgement task

Event-related potentials (ERPs) were recorded from normal subjects in a serial paired-comparison task with the spoken digits one to five. For each digit, the subject decided whether it was smaller or larger than the preceding one. We examined to what extent ERP components are associated with the probability information each digit provides with respect to the subsequent response. Shortest reaction time (RT) and highest accuracy was obtained for the two end terms one and five. The N1 and P2 components of the ERP were attenuated for the two end terms. Three late positivities were found: early P3, P3b, and slow wave. P3b increased in amplitude the more information the eliciting digit provided with respect to the response to the subsequent digit. Moreover, a negative correlation was found between the P3b amplitude associated with information extraction and the RTs to the subsequent digit. During comparative judgement, subjects process the relative position of a stimulus within a stimulus set to extract information about the probability of a forthcoming response, and this process is reflected in P3b amplitude.     

大学生心理理论错误信念任务的事件相关电位特点

目的:研究心理理论错误信念任务中信念推理和现实推理的脑电特点,对心理理论的脑机制进行初步探讨。方法:在天津师范大学方便选取23名大学生,采用NeuroScan公司64导脑电系统记录其执行图片错误信念任务时的事件相关电位(event-related potentials,ERP)和行为学结果,对被试在执行错误信念任务时分别进行的现实推理和信念推理的ERP结果进行分析,最终有效被试18名。结果:从刺激呈现后约300ms,信念推理和现实推理两种实验条件引起的事件相关脑电开始出现差异,600~900ms时间段内,在AF7[(2.34±2.71)vs.(1.32±2.97)]、FPz[(2.83±3.03)vs.(2.08±2.56)]、AF8[(3.75±2.64)vs.(2.76±2.34)]、T7[(1.31±2.77)vs.(0.68±3.54)]、Cz[(5.11±5.42)vs.(4.52±5.66)]、T8[(2.35±2.24)vs.(2.03±2.00)]及POz[(2.48±2.16)vs.(2.18±2.53)]电极上均表现为信念推理波幅正向大于现实推理波幅(P=0.065),此种差异接近有统计学意义,且主要分布于额叶电极。结论:对心理状态进行推理的神经机制与对现实进行推理的神经机制存在差别,心理理论能力与大脑额叶存在较为密切的关系。     

Event-related potentials and serial position effects in a visual probe recognition task

In two experiments, we explored the utility of using event-related brain potentials (ERPs) evoked during picture recognition to examine the cognitive and neural processes underlying primacy and recency effects. Each experiment consisted of 210 trials in which a recognition probe followed a 12-picture sequence (105 match and 105 nonmatch trials). The 105 match-probe trials consisted of 35 trials in which the probe matched a prime memory set item (Positions 1–3), 35 in which the probe matched a middle memory set item (Positions 6–8), and 35 in which the probe matched a recent memory set item (Positions 10–12). Behavioral results revealed recency but not primacy effects in both experiments. Recent probes, compared with prime and middle probes, evoked ERPs that were more positive from approximately 300 to 400 ms; this enhanced positivity occurred in a positive component peaking around 315 ms and a negative component peaking around 365 ms. These findings fit more closely with the notion of short-term memory as an activation of elements in long-term memory than as a distinct memory store (or stores) separate from long-term memory.     

Signal onset and task variables in auditory evoked potentials

Two auditory evoked potential studies were run to determine the effects of stimulus rise times on amplitude of N₁P₂ onset and offset potentials. Onset potentials were reduced with increased onset durations. No consistent relationship was found in N₁₂ offset potentials as a function of stimulus rise time. The effects of listening tasks and stimulus duration were also examined.     

Event-related potentials and selective attention to auditory stimuli varying in pitch and localization

Event-related potentials were recorded from subjects performing a discrimination task which required selective attention to one of (or divided attention to both of) two classes of tone pips imaged to arrive over two independent sound sources varying systematically in pitch and spatial localization. In selective attention N1 amplitude was larger and P2 amplitude was inversely smaller to the attended tones than to the unattended tones; P2 latency was prolonged to the attended tones; in divided attention, both N1 and P2 amplitudes and P2 latency were intermediate between selective attention and inattention. These attention effects upon both N1 and P2 components were interpreted to be due to a growth of a negative shift superimposed on those evoked components, rather than a modification of each component itself. This endogenous negativity was also considered to reflect the allocation of attentional capacity for discrimination processing whether tones coming from the attended source were ‘signal’ or not.     

Event-related potentials associated with correct and incorrect responses in a cued antisaccade task

In an antisaccade task, subjects are instructed to inhibit a reflexive saccade towards a peripheral stimulus flash and to generate a saccade in the opposite direction. It has been shown recently that normal subjects will generate a high number of incorrect prosaccades in an antisaccade task if the fixation point is extinguished 200 ms before the stimulus appears and if a valid cue for the subsequent antisaccade is given during this gap period. In the present study we recorded cerebral event-related potentials from 19 scalp electrodes from normal subjects prior to correct and incorrect responses in a cued antisaccade task to investigate the neural processes associated with correct antisaccades and incorrect prosaccades in this task. Correct antisaccades and incorrect prosaccades were associated with a negative potential with a maximal amplitude around stimulus onset over the dorsomedial frontal cortex. This potential was higher prior to correct antisaccades than prior to incorrect prosaccades. The execution of a correct antisaccade was preceded by a shift of a negative potential from the parietal hemisphere contralateral to the visual stimulus towards the parietal hemisphere ipsilateral to the stimulus. These results support the view that the supplementary eye fields participate in the inhibition of incorrect saccades in a cued antisaccade task and show that the parietal cortex participates in generating a neural representation of the visual stimulus in the hemifield ipsilateral to the stimulus before generating a motor response. Received: 20 December 1996 / Accepted: 18 June 1997     

Event-related brain potentials in a varied-set memory search task: A reconsideration

Event-related potentials (ERPs) were recorded in 19 healthy subjects as they completed two Sternberg (1969, American Scientist, 57, 421–457) memory tests. In separate sessions, either single digits (i.e., 0–9) or 10 abstract figures were used as stimuli. In both sessions, memory set sizes were 1 (M1), 2 (M2), or 4 (M4). The amplitude and latency of the parietal P400 and the frontocentral negativity preceding P400 varied significantly with set size, but only between M1 and M2, whereas reaction time increased dramatically from M1 to M2 and from M2 to M4. These findings challenge previous assertions that the ERPs reflect aspects of the exhaustive serial search proposed by Sternberg. A late parietal positivity (P620), which failed to vary with set size, was larger in response to figures than to digits and may represent the search for, or utilization of, semantic traces of the stimuli.     

Cortical potentials in an auditory oddball task reflect individual differences in working memory capacity

This study determined whether auditory cortical responses associated with mechanisms of attention vary with individual differences in working memory capacity (WMC) and perceptual load. The operation span test defined subjects with low versus high WMC, who then discriminated target/nontarget tones while EEG was recorded. Infrequent white noise distracters were presented at midline or ±90° locations, and perceptual load was manipulated by varying nontarget frequency. Amplitude of the N100 to distracters was negatively correlated with WMC. Relative to targets, only high WMC subjects showed attenuated N100 amplitudes to nontargets. In the higher WMC group, increased perceptual load was associated with decreased P3a amplitudes to distracters and longer‐lasting negative slow wave to nontargets. Results show that auditory cortical processing is associated with multiple facets of attention related to WMC and possibly higher‐level cognition.     

Event-related brain potentials evoked by verbs and nouns in a primed lexical decision task

We investigated whether verbs and nouns evoke comparable behavioral and N400 effects in a primed lexical decision task. Twenty-nine students were tested, 13 in a pilot study in which only response times and error rates were collected and 16 in a study in which ERPs were recorded from 124 scalp electrodes. Stimuli were noun-noun and verb-verb pairs with the targets bearing either a strong, a moderate, or no semantic association to the prime or being a pseudoword. Behavioral data revealed comparable priming effects for both word categories. These proved to be independent from the SOA (250 and 800 ms) and they followed the well-known pattern of decreasing response times and error rates with increasing relatedness between target and prime. ERPs revealed pronounced N400 effects for both word categories with a larger amplitude for noun than for verb pairs. A systematic analysis of topographic differences between noun- and verb-evoked ERPs and N400 effects, respectively, gave no convincing support to the hypothesis that the two word categories activate distinct neuronal networks.     

Event-related potentials elicited during a context-free homograph task in normal versus schizophrenic subjects

Thought disorder in schizophrenia may involve abnormal semantic activation or faulty working memory maintenance. Event-related potentials (ERPs) were recorded while sentences reading "THE NOUN WAS ADJECTIVE/VERB" were presented to 34 schizophrenic and 34 control subjects. Some nouns were homographs with dominant and subordinate meanings. Their sentence ending presented information crucial for interpretation (e.g., The bank was [closed, steep]). Greatest N400 activity to subordinate homograph-meaning sentence endings in schizophrenia would reflect a semantic bias to strong associates. N400 to all endings would reflect faulty verbal working memory maintenance. Schizophrenic subjects showed N400 activity to all endings, suggesting problems in contextual maintenance independent of content, but slightly greater N400 activity to subordinate endings that correlated with the severity of psychosis. Future research should help determine whether a semantic activation bias in schizophrenia toward strong associates is reflected in ERP activity or whether this effect is overshadowed by faulty verbal working memory maintenance of context.     

Apolipoprotein E modulates auditory event-related potentials in healthy aging

42 individuals ranging from 47 to 73 years of age underwent an auditory three-stimulus oddball task while their event-related potentials (ERPs) were recorded. Half were APOE ?3 homozygotes and the remaining participants were either ?3/?4 heterozygotes (n = 13), or ?4 homozygotes (n = 8). Analyses of variance showed that the heterozygotes had lower N1 amplitudes than the ?3 homozygotes, consistent with a previous study of participants with mild cognitive impairment (MCI) [I. Reinvang, T. Espeseth, L. Gjerstad, Cognitive ERPs are related to ApoE allelic variation in mildly cognitively impaired patients, Neuroscience Letters 382 (3) (2005) 346–351]. APOE genotype also significantly modulated N2 latency. ?4 homozygotes had longer N2 latencies, and importantly, longer N2 latencies predicted decline in verbal learning after 3.5 years follow up. These findings indicate a potential clinical significance of individual differences in ERP components N1 and N2.     

Event-related potentials to auditory stimuli in female Vietnam nurse veterans with posttraumatic stress disorder

Individuals with posttraumatic stress disorder (PTSD) have been found to show several event-related brain potential (ERP) abnormalities including reduced target P3b amplitude, P50 suppression, and P2 amplitude/intensity slope. Female Vietnam nurse veterans with (n = 29) and without (n = 38) current PTSD completed P50 paired-click, three-tone "oddball" and four-tone stimulus-intensity modulation procedures. Opposite to previous findings, the current PTSD group had larger target P3b amplitudes and increased P2 amplitude/intensity slopes. Reduced P50 suppression was associated with increased severity of general psychopathology, but not with PTSD diagnosis. Findings suggest that target P3b amplitude and P2 amplitude/intensity slope abnormalities reflect different pathophysiological processes. Future research is needed to determine whether the opposite ERP abnormalities observed in this PTSD sample reflect gender-, trauma-, or sample-specific findings.