Early Event-related Potential Components Research Articles

Perception of static eye gaze direction facilitates subsequent early visual processing.

Using event-related potentials (ERPs), it has been recently shown that a reflexive shift of attention following the observation of a dynamic eye gaze cue enhances and speeds up early visual processing of a target presented at the gazed-at location. Here we investigate whether similar early sensory modulations are also elicited by static gaze cues, or if previously described attentional effects were caused mainly by visual motion cues and not by eye gaze direction per se. Furthermore, we explore if these possible attentional orienting effects reflect facilitation of the processing of cued stimuli, inhibition of the unattended stimuli, or both. Subjects were presented with a face looking to the right or left visual field (VF), or straight away, before the occurrence of a lateralized target to detect. There were 3 conditions in this nonpredictive cueing task: (1) target presented in the VF indicated by the eye gaze direction (congruent); (2) opposite to the eye gaze direction (incongruent); or (3) preceded by a straight gazing face (neutral). Subjects were faster at detecting congruently than incongruently and neutrally cued targets. Facilitation effects were observed on early ERP components: the occipital P1 and occipito-temporal N1 components were speeded up as early as approximately 100 ms following stimulus onset (P1), and enhanced (P1 and N1) in response to congruent trials, particularly in the right hemisphere. Spatial attention triggered by static eye gaze direction produces response facilitations - predominantly lateralized to the right hemisphere - from the early sensory stages of visual processing. This study provides the first evidence of a speeding up and amplification of early visual processing following attention triggered by static eye gaze perception.

Source analysis of event-related cortical activity during visuo-spatial attention.

Recordings of event-related potentials (ERPs) were combined with structural and functional magnetic resonance imaging (fMRI) to study the spatio-temporal patterns of cortical activity that underlie visual-spatial attention. Small checkerboard stimuli were flashed in random order to the four quadrants of the visual field at a rapid rate while subjects attended to stimuli in one quadrant at a time. Attended stimuli elicited enhanced ERP components in the latency range 80-200 ms that were co-localized with fMRI activations in multiple extrastriate cortical regions. The earliest ERP component (C1 at 50-90 ms) was unaffected by attention and was localized by dipole modeling to calcarine cortex. A longer latency deflection in the 150-225 ms range that was accounted for by this same calcarine source, however, did show consistent modulation with attention. This late attention effect, like the C1, inverted in polarity for upper versus lower field stimuli, consistent with a neural generator in primary visual cortex (area V1). These results provide support to current hypotheses that spatial attention in humans is associated with delayed feedback to area V1 from higher extrastriate areas that may have the function of improving the salience of stimuli at attended locations.

The Effect of Food Deprivation on ERP During Identification of Tachistoscopically Presented Food-Related Words

Abstract The present study served to investigate the effects of food deprivation on the identification of subliminally presented food-related words by means of event-related potentials (ERPs). ERPs were recorded in 16 hungry and 16 satiated subjects during repeated tachistoscopic presentation of food-related words (food names) and food-unrelated words (neutral words, sexual words) as controls. ERPs were recorded during each presentation of a word prior to identification and during the first presentation after identification and exhibited N1, P2, and slow-wave components. The number of tachistoscopic presentations until identification was not affected by hunger and satiety. However, ERPs were differentially affected by hunger and satiety: the P2 to food-related words was larger in hungry subjects compared to satiated subjects in all presentations. Additionally, the P2 was also larger to sexual words in hungry subjects in all presentations except the one preceding the identification response. The slow wave was not affected by hunger but increased with progressing stimulus identification. Following the identification of the words, all ERP components markedly declined in amplitude. The results indicate that hunger affects the processing of food and sexual stimuli during identification at an early ERP component (P2) even if the stimuli are not fully identified. In contrast, the later slow wave is sensitive to progressing stimulus identification, irrespective of hunger and stimulus meaning.

ERP time course of perceptual and post-perceptual mechanisms of spatial selection

Event-related potentials (ERPs) were recorded from volunteers performing a task requiring simple judgements about the spatial location of a single target that could appear with equal probability to the left or right of fixation. A robust finding in the ERP literature is a dichotomy between attentional selection for spatial and non-spatial features. Visual spatial selection is manifest as a modulation of early components (P1, N1) that reveal exogenous processes, while non-spatial selection is revealed by the presence of longer latency endogenous components (N2). We present an analysis of several conditions that require different degrees of visual analysis to confirm the location of the single target, and show that spatial selection can be manifest at early (N1) or later (N2) stages. Observers identified the location of targets that were more salient (2D line drawings with abrupt onset) or less salient (2D line drawings without abrupt onset or 3D objects embedded in random-dot stereograms). We examined differences in amplitude, latency, and topography of early ERP components (P1, N1, P2, N2), and compared responses measured over the left and right hemispheres in response to left and right targets. The results support the hypothesis that the processes involved in spatial selection can be manifest at early or late stages, dependent on the quality of the incoming data. Moreover, the iterative process by which the percept is established benefits from a change in the visual input that is specific to the target.

Crossmodal links in spatial attention between vision, audition, and touch: evidence from event-related brain potentials

Results from event-related potential (ERP) studies are reviewed that investigated crossmodal links in spatial attention between vision, audition and touch to find out which stages in the processing of sensory stimuli are affected by such crossmodal links. ERPs were recorded in response to visual, auditory, and tactile stimuli under conditions where attention was directed to a specific location within one (primary) modality, while stimuli in another (secondary) modality were to be ignored regardless of their position. Systematic ERP effects of spatial attention were observed not only in the primary modality, but also for secondary modality stimuli, thus revealing crossmodal links in spatial attention. These links affected relatively early sensory-specific ERP components between 100 and 200 ms post-stimulus. Beyond 200 ms, ERPs to secondary modality stimuli were little affected by the current focus of attention within another modality. This pattern of results suggests that crossmodal links in spatial attention may affect sensory-perceptual processes within modality-specific cortical regions, but have little impact on later post-perceptual processing stages.

The mode of short-term memory encoding as indicated by event-related potentials in a memory scanning task with distractions

Objective: Auditory event-related potentials (ERPs) were recorded during the performance of a memory scanning task, with and without distracters between the memorized items and the probe. The effect of distracters with different phonological/semantic characteristics was tested, to indicate the encoding mode in short-term memory. Methods: Three types of sets (‘memorized sets’) were presented to the subject before the probe: 4 memorized digits, two memorized digits with two distracter digits and two memorized digits with two noise distracters. Potentials in response to the set items were averaged separately according to stimulus type and position in the set. Potentials in response to the probe were averaged according to the preceding stimulus sequence: 4 memorized digits, two distracter digits or two noise distracters. Results: The early components (N1, P2) differed between distracter items and memorized items, indicating lower attention allocation to distracter items. In contrast, the late components (N2, P3) indicated similar processing of distracters and memorized items. Behavioral measures indicated shorter scanning times of sets with distracters. The early ERP components in response to the probe (P2, N2) indicated differences among probes according to the preceding combinations of memorized items and distracters. The late component (P3) indicated different speeds (latencies) of scanning and comparison for series with compared to without distracters, but similar processing resource allocation (amplitudes). Processing was prolonged when the distracter items were phonological. Conclusions: This study shows that distracters affect both the memorization process and the scanning and comparison in short-term memory. The stronger distraction by stimuli that are phonologically similar to the memorized items supports phonological processing in short-term memory.

The Role of Spatial Selective Attention in Working Memory for Locations: Evidence from Event-Related Potentials

We investigated the hypothesis that the covert focusing of spatial attention mediates the on-line maintenance of location information in spatial working memory. During the delay period of a spatial working-memory task, behaviorally irrelevant probe stimuli were flashed at both memorized and nonmemorized locations. Multichannel recordings of event-related potentials (ERPs) were used to assess visual processing of the probes at the different locations. Consistent with the hypothesis of attention-based rehearsal, early ERP components were enlarged in response to probes that appeared at memorized locations. These visual modulations were similar in latency and topography to those observed after explicit manipulations of spatial selective attention in a parallel experimental condition that employed an identical stimulus display.

Abnormalities of visual search behaviour in ALS patients detected with event-related brain potentials.

A number of recent reports have emphasized neuropyschological symptoms in ALS, including frontal functions, memory and attention. We investigated visual search behaviour of ALS in two types of tasks: a simple, relatively effortless parallel search task and a more complex attention-demanding serial search task. Behavioural parameters and cognitive event-related potentials (ERP) from 19 scalp channels were obtained from 13 ALS patients and 13 matched controls during task performance. ALS patients showed the same target detection rates as controls in the parallel task but were significantly impaired in the serial task. Performance was slower in the patients than in the controls. This slowing could be attributed to cognitive rather than motor impairments, by inspection of the latency of the P3 component, which was delayed by 120 ms in the patients. In addition, the ERPs in the serial task showed a grossly reduced P3 amplitude, indicating disturbed stimulus evaluation in the patients under these conditions. Changes of an early attention-sensitive ERP component suggest an attention deficit underlying the disturbances in search behaviour.

Neuronal firing activity in the dorsal hippocampus during the auditory discrimination oddball task in awake rats: relation to event-related potential generation

In order to investigate the roles of the hippocampus in event-related potential (ERP) generation, extracellular neuronal firings in the dorsal hippocampus were recorded together with the ERPs on the cortical surface and at the hippocampus during the auditory discrimination task in awake rats. The major ERP components on the cortical surface in response to the target tone were the P2, N2, and P3 with the latencies being approximately 100, 200 and 450 ms, respectively. For the non-target tone, the N2 and P3 components were not clearly observed. Local ERP at the hippocampus exhibited similar wave-forms to that on the cortex in response to the target and non-target tones. In the hippocampus, 11 of 21 neuronal firings showed a long-latency sustained activation from 113.6±89.7 ms to 539.1±208.6 ms with the peak being 281.6±167.4 ms after the target tone onset. This increase was not observed after the non-target tone, and was not prominent when the rat did not perform the task. It was not time-locked to lever pressing behavior, and was not affected by the intensity of the tone stimulus. These features in relation to behavioral and paradigm indices were similar to the long-latency ERP components, N2 and P3. Possible involvement of the hippocampus in ERP generation was further suggested by the correlation between the magnitude of the long-latency activation and the amplitudes of N2 and P3 in some hippocampal firings. On the other hand, seven neuronal firings showed a short-latency transient activation with the peak at 36.3±14.4 ms accompanied by the early components of local ERP in the hippocampus both after the target and non-target tones. This response was more conspicuous when the rat did not perform the task and its amplitude was positively affected by the stimulus intensity. These findings imply that there are two types of hippocampal neuronal activation during the auditory discrimination oddball task. One is the short-latency activation that is related to information processing of the exogenous stimulus property. The second is the long-latency activation that may be involved in execution of the cognitive task, and in generation of long-latency ERP components.

Attention-sensitive visual event-related potentials elicited by kinetic forms

Previous event-related potential (ERP) studies have shown that selectively attending to a relevant stimulus feature was associated with selection negativity (SN) components. The present study aimed at investigating the ERP indices of attentional selection based on forms defined by motion (kinetic forms). ERPs were recorded from subjects who attended selectively to sequentially presented kinetic forms of bars in one visual field and detected occasional tilted bar targets. Two kinds of kinetic forms were used as the visual stimuli in separate experiments. The main findings were that spatial attention enhanced the amplitude of early ERP components P1 and N1 as well as the late component N2. Topographic maps of voltage and low resolution electromagnetic tomography (LORETA) of the dN2 wave (difference waveform between N2 under attended condition and N2 under unattended condition) suggested an origin in the right occipitotemporal cortex. According to its timing and morphology, the dN2 wave was considered to be an endogenous ERP (like the SN) and was interpreted as reflecting attentional facilitation of the processing of forms defined by motion primarily involving the right occipitotemporal areas.

Spatio-temporal dynamics of attention to color: evidence from human electrophysiology.

This study characterized patterns of brain electrical activity associated with selective attention to the color of a stimulus. Multichannel recordings of event-related potentials (ERPs) were obtained while subjects viewed randomized sequences of checkerboards consisting of isoluminant red or blue checks superimposed on a grey background. Stimuli were presented foveally at a rapid rate, and subjects were required to attend to the red or blue checks in separate blocks of trials and to press a button each time they detected a dimmer target stimulus of the attended color. An early negative ERP component with an onset latency of 50 ms was sensitive to stimulus color but was unaffected by the attentional manipulation. ERPs elicited by attended and unattended stimuli began to diverge after approximately 100 ms following stimulus onset. Inverse dipole modelling of the attended-minus-unattended difference waveform indicated that an initial positive deflection with an onset latency of 100 ms had a source in lateral occipital cortex, while a subsequent negative deflection with an onset at 160 ms had a source in inferior occipito-temporal cortex. Longer-latency attention-sensitive components were localized to premotor frontal areas (onset at 190 ms) and to more anterior regions of the fusiform gyrus (onset at 240 ms). These source localizations correspond closely with cortical areas that were identified in previous neuroimaging studies as being involved in color-selective processing. The present ERP data thus provide information about the time course of stimulus selection processes in cortical areas that subserve attention to color.

ERP assessment of visual and auditory language processing in schizophrenia.

Language disturbance in schizophrenia has been recently attributed to disturbed priming mechanisms. In the present study, event-related potentials (ERPs), were recorded to final words in sentences presented to 13 chronic patients with schizophrenia and 12 normal controls. Half of the final words fit a sentence context and another half did not. The N400 (the ERP sensitive to language) latency was prolonged, and its amplitude was more negative to both correct and incorrect sentence endings in the group with schizophrenia relative to the group of normal controls. The early ERP components, N100 and P200, were similar in both groups. These results suggest that language abnormalities in schizophrenia are related to a dysfunction in the language system and not to a general cognitive dysfunction, and may be related to poor use of context in patients with schizophrenia.

ERP assessment of visual and auditory language processing in schizophrenia.

Language disturbance in schizophrenia has been recently attributed to disturbed priming mechanisms. In the present study, event-related potentials (ERPs), were recorded to final words in sentences presented to 13 chronic patients with schizophrenia and 12 normal controls. Half of the final words fit a sentence context and another half did not. The N400 (the ERP sensitive to language) latency was prolonged, and its amplitude was more negative to both correct and incorrect sentence endings in the group with schizophrenia relative to the group of normal controls. The early ERP components, N100 and P200, were similar in both groups. These results suggest that language abnormalities in schizophrenia are related to a dysfunction in the language system and not to a general cognitive dysfunction, and may be related to poor use of context in patients with schizophrenia.

PS-45-10 Event-related potentials in children with depression or attention deficit hyperactivity disorder

Auditory P300 latency prolongation or amplitude reduction has been reported in patients affected by bipolar disorder and in schizophrenia. The purpose of this study was to test whether the auditory P300 and earlier event-related potential (ERP) components elicited during an auditory discrimination task could differentiate between these two disorders. Thirteen patients with manic or mixed bipolar disorder, 12 patients with schizophrenia, and 24 control subjects were evaluated. None of the subjects had a history of alcohol or substance abuse or dependence. ERPs were elicited during an auditory discrimination task in which a subject pressed a key to infrequent 1500 Hz tones interspersed amid a series of 1000 Hz tones. The amplitude and latency of N100 and P200 were measured from ERPs to non-target tones, and N200 and P300 were measured from ERPs to target tones. N100, P200 and N200 amplitudes were reduced in schizophrenia patients, but not in bipolar patients. Both bipolar disorder and schizophrenia patients showed reduced P300 amplitude and prolonged P300 latency. Amplitude reduction in the early ERP components implicates auditory processing deficits in schizophrenia. Both groups showed reductions in P300 amplitude, suggesting a disturbance of the temporal–parietal generators of this component. Prolonged P300 latency is consistent with impaired attentional processing in schizophrenia and symptomatic bipolar disorder patients.

Event-related potentials to odor stimuli

Fifteen subjects participated in a study designed to record event-related potentials (ERPs) to various concentrations of the odorant n-butyl alcohol. Subjects pressed a response key upon detection of the odor, while ERPs were recorded from nine electrode positions. Results indicated a concentration-dependent increase in amplitude of a P300-like component 320–520 msec following the stimulus onset. Correlations between subjects’ sensory thresholds and activity at frontal electrode sites were also found. The absence of early ERP components is discussed.

Parallel and serial visual search after closed head injury: Electrophysiological evidence for perceptual dysfunctions

Event-related potentials (ERPs) were recorded from closed head injury (CHI) patients at least 2 years postinjury and from controls in order to assess their parallel and serial processing abilities during visual search. In Experiment 1, stimuli consisted of arrays of eight triangles; half of the arrays contained a target item. In the “feature-present” condition, the target item was a triangle with an additional horizontal line that could be detected automatically and in parallel, while in the “feature-absent” condition all items except for the target triangle had an additional horizontal line, thus requiring a serial search. In Experiment 2, stimuli consisted of eight solid bar (50%), seven solid bars and a vertical open bar (25%), and seven solid bars and a horizontal open bar (25%): the array containing the horizontal bar served as a target. By recording ERPs to the arrays containing vertical open bars, which were similar to the target items, parallel processing of “pop-out” stimuli could be studied in the absence of any overt response. ERP data were compared with the results of neuropsychological and neuroimaging (MRI, CAT) examination. Patient exhibited a decreased behavioral performance both in the parallel and in the serial processing mode. Furthermore, abnormalities of early and intermediate ERP components (P1, N1, P2, N2) were found, whereas the late component (P3) was less affected by CHI. The results were interpreted as an index of CHI-induced dysfunctions in perceptual processes such as simple feature registration and early target discrimination. It was suggested that these dysfunctions contribute to impairments of parallel as well as serial processes in visual search.

Visual and auditory sentence processing: A developmental analysis using event‐related brain potentials

Subjects aged 5 to 26 years listened to and read (7 to 26 years) sentences that ended either with a highly expected (best completion) or a semantically inappropriate (anomalous completion) word. Event‐related potentials (ERPs) to sentence final words displayed effects of contextual priming in both modalities in all age groups. Early and late ERP components displayed large decreases in amplitude and latency with age. These changes necessitated normalization procedures so that overall changes in amplitude with age could be assessed separately from changes in the amplitude of the differences between best‐completion and anomalous‐completion words. There were significant reductions in the contextual priming effects with age. Moreover, these age‐related changes were different for the auditory and visual modalities, and for the early and later phases of the priming effect. These results suggest that nonidentical systems, with different developmental time courses, generate the early and late priming effects in the two modalities.

Pirecetam and event-related potentials in dyslexic males

The effect of piracetam on visual event-related potentials (ERP) was investigated in a double-blind placebo-controlled study. Eight- to 12-year-old dyslexic males were randomly assigned to 3.3 g/day of piracetam or matching placebo in two divided doses over a 12-week period. Children performed a vigilance task in which they pressed a key when two alphabetic letters or shapes occured in sequence. ERPs to letters and shapes, for active and passive responses, were recorded at the vertex and left and right parietal areas of the scalp. Performance measures included letter- and form-hits, misses, commission errors and reaction times. Piracetam increased the amplitude of a late positive component (believed to correspond to P300) at the vertex for letter-hits. Piracetam also increased the latency of this component in both hemispheres, but only for active responses (letter-hits) in the left hemisphere and passive responses (correct rejections and misses) in the right hemisphere. Although piracetam did not significantly affect performance, reaction time to letter-hits was significantly correlated with the latency of the P300 component, suggesting that letters created increased effort or attentional demand on the subjects compared with forms. An early ERP component (P225) also showed increased amplitude to piracetam in both hemispheres and effects were limited to form-hits. These effects were thought to possibly reflect slow negative potentials arising from stimulus anticipation in the CNV-like paradigm. In view of the small sample size, the results were cautiously interpreted as indicating a facilitation of verbal processing mechanisms responsible for analyzing the verbal significance of visual stimuli.

Event-related potentials of the brain and cognitive processes: Approaches and applications

Event-related potentials (ERPs) are recordings of the electric field which the brain produces in fixed time-relation to an event. ERPs open a time and space window onto covert steps of brain information processing which need not be accompanied by overt behavior or private experiences. ERPs are the only noninvasive method which resolves the dynamic pattern of events in the human brain down to the millisecond range. Early ERP components are valuable tools in clinical testing of the afferent sensory systems in the absence of anamnestic or clinical pathology. Later components (e.g. the ‘P300’) index intermediate, covert steps of information processing and have clarified the time course and the contingencies of processes in attention, decisions and language. ERP waveshapes show electric potential differences between two recording points. Conventional analysis often ignores the fact that there is no unique voltage amplitude or signal latency for a single point, and interprets ambiguous results. Although important insights have emerged with such strategies, full utilization of ERP data requires unambiguous ERP assessment and converging evidence from neuropsychological and cognitive experimentation. Sequences of field distribution maps offer an unbiased display of ERP data. Spatial analysis yields unambiguous values for further comprehensive assessment, and should precede analysis over time. Examples of spatial analysis have shown that different ERP field configurations follow the presentation of noun and verb meaning of homophone words; that the ERP effects to subjective contours resemble those to attention in time course and topography; that the ‘cognitive’ P300 component reflects the specific stimulus location; and that subliminal information influences the configuration of late ERP fields.

Variability of head posture during sleep and considerations relating to palate and dental arch form: By C. S. C. Lear. Arch. Oral Biol. 12: 1229–1240, 1967

The aim of the present study was to evaluate the effects of gender on sensory and cognitive information processing in children by analyzing auditory event-related potentials (ERPs). The major questions were: (1) do ERPs differ between girls and boys aged 7–10 years, (2) do gender differences in ERPs depend on the development with age, on task-processing demands, and on the development of neuroelectric networks as reflected by the spontaneous EEG?Thirty-six healthy children (18 girls and 18 boys) were divided in two age groups (7- to 8- and 9- to 10-year-old). Boys and girls were pairwise matched for age. Auditory ERPs were analyzed in a passive listening condition (PLC), a simple reaction task (SRT) and a serial learning reaction task (SLRT), in which memory and sensorimotor processes were varied in a balanced way. Cognitive performance, reaction times (RTs), and the spontaneous electroencephalogram (EEG) were also measured.Cognitive performance improved earlier in girls than boys, whereas response speed was not affected by gender. Independent of processing demands, ERP components within 300 ms after stimulation (N1, P2, N2 and P3) increased with development only in the group of girls. For later components, the developmental speeding of the parietal P3b component to task-relevant stimuli also tended to be more expressed in girls than boys, whereas a late frontal negative wave N400–700 was shorter in the girls than boys from the two age groups. Likewise, independently of age, the spontaneous EEG manifested a larger theta activity in girls than boys.Developmental changes of basic auditory processing mechanisms strongly depend on gender in children between 7 and 10 years by being faster in girls. This gender-specific development of early ERP components is not modulated by processing demands, cannot be attributed to a faster cognitive maturation of girls, nor can it be explained with the gender-specific maturation of background neuroelectric networks. Rather, it reflects an accelerated functional activation of auditory processing networks in girls. Interestingly, the cognitive development was also faster in girls, but it occurred earlier than the functional activation of auditory processing networks.This study provides evidence for accelerated neuroelectric (as reflected by spontaneous EEG), neurofunctional (as reflected by auditory ERPs), and neurocognitive (as reflected by learning performance) development in 7- to 10-year-old girls than boys.