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.     

EVOKED RESPONSE AND STARTLE BLINK TO STRONG ACOUSTIC STIMULI OF DIEEERENT SIGNAL MEANING

In healthy man, the effects of stimulus intensity and a preceding optic signal with different meaning upon: the latencies and amplitudes of the startle blink reflex; the peaks P₁, N₁ and P₂ of the auditory cortical evoked response (ACER); and on the strength of the subjective startle response were investigated.

• 1 A pistol-shot elicited a startle blink of shorter latency and larger amplitude, and an ACER with shorter latency of peak N₁ and larger amplitude of P₁– N₁ than a click, which was produced by a condenser discharge into a loudspeaker.
• 2 If an optic stimulus preceded the acoustic stimuli, the amplitudes of the ACER peaks and the latency of peak N₁ decreased. The startle blink, however, displayed only a latency shortening. The subjective startle response was weaker.
• 3 If the preceding optic signal had an undifferentiated meaning, the amplitudes of the startle blink and the ACER peaks were larger than if an optic signal with differentiated meaning preceded the acoustic stimulus. In the first case, the latency of the startle blink was shorter, but that of the peak N₁ longer; the subjective startle response was stronger.
• 4 It was shown that only the amplitude of the peak P₁– N₁ of the ACER is directly correlated with the strength of the subjective startle response.
• 5 The underlying neurophysiological mechanisms were discussed.

     

Cortical evoked potentials in monozygotic twins and unrelated subjects: Comparisons of exogenous and endogenous components

Cortical evoked potentials to auditory stimulation were recorded in six pairs of monozygotic twins and six pairs of unrelated subjects matched for age and sex while they performed a stimulus detection task. The cortical potentials were coherently averaged, and the peak latencies of the exogenous (P₁, N₁, and P₂) and endogenous (N₂ and P₃) components of the average evoked potential (AEP) were investigated. It was hypothesized that latency of the exogenous components of the AEP would be similar in all matched pairs since the characteristics of these components depend primarily on the physical parameters of the stimulus. As endogenous components appear to be associated with a person's intentions, expectations, and decisions, we expected them to be more alike in twins than in unrelated individuals. Findings were in accord with the hypothesis. Latencies of the exogenous components were closely similar in all pairs of subjects. By contrast, latencies of the endogenous components were significantly (P0.001) more alike in twins than in unrelated subjects.This investigation was supported by United States Public Health Service Research Grant HD 02395 from the National Institutes of Health.     

Sequential processing in the classic oddball task: ERP components,probability, and behavior

This study compared the ERP components and behavior associated with the auditory equiprobable and classic oddball tasks, to relate the cognitive processing stages in those paradigms and continue the development of the sequential processing schema. Target and nontarget ERP data were acquired from 66 healthy young adults (M_age = 20.1, SD = 2.4 years, 14 male) who completed both equiprobable (target p = 0.5) and oddball tasks (target p = 0.3). Separate temporal PCAs were used to decompose the ERP data in each task and condition, and the similarity of the components identified in each condition was examined between tasks. Probability effects on component amplitudes and behavior were also analyzed to identify task differences in cognitive demands. A highly similar series of components was identified in each task, closely matching the schema: targets elicited N1‐3, N1‐1, PN, N2c, P3b, SW1, SW2; whereas nontargets elicited N1‐3, N1‐1, PN, N2b, P3a, SW1, SW2. N1‐1 and PN amplitudes increased as stimulus probability decreased, irrespective of the condition. N2b, P3b, SW1, and SW2 amplitudes also varied between tasks, illustrating task‐specific demands on those processing stages. These findings complemented the behavioral outcomes, which demonstrated greater accuracy and control in the classic oddball task. Overall, this study demonstrated comparable processing in the auditory equiprobable and classic oddball tasks, extending the generalizability of the schema and enabling further integration of the ERP theory associated with these tasks. This study also clarifies stimulus probability effects on the schema, providing important insight into the functionality of common ERP components.     

Averaged Evoked Responses To Tapping: A One-Subject Scalp Study of Large Signals

Somatosensory evoked responses (SERs) of unusual amplitude were averaged from the scalp of one subject, for inspection of the time-course of the early positive-negative waveform (P₁ to N_H). These early components had a peak-to-peak half period of 10–14 msec, for varied stimulus locations and intensities, while their amplitude and latencies varied monotonically with stimulus intensity and sensory level. The time-course of the P₁ to N_H components conformed with that observed for the postsynaptic soma-dendritic response to direct stimulation of sensory cortex (DCR) in other mammals. Inspection of the later waveform, up to 125 msec poststimulus-onset (PSO), revealed no negative later than the N_H, which peaked at 43–45 msec for digital stimulation. Mechanical stimulation of the digits in the absence of the usual masking noise evoked a different waveform having significant earlier and later components.     

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.     

Reconsidering electrophysiological markers of response inhibition in light of trigger failures in the stop-signal task

This study investigates the neural correlates underpinning response inhibition using a parametric ex-Gaussian model of stop-signal task performance, fit with hierarchical Bayesian methods, in a large healthy sample (N = 156). The parametric model accounted for both stop-signal reaction time (SSRT) and trigger failure (i.e., failures to initiate the inhibition process). The returned SSRT estimate (SSRT_EXG3) was attenuated by ≈65 ms compared to traditional nonparametric SSRT estimates (SSRT_int). The amplitude and latency of the N1 and P3 event-related potential components were derived for both stop-success and stop-failure trials and compared to behavioral estimates derived from traditional (SSRT_int) and parametric (SSRT_EXG3, trigger failure) models. Both the fronto-central N1 and P3 peaked earlier and were larger for stop-success than stop-failure trials. For stop-failure trials only, N1 peak latency correlated with both SSRT estimates as well as trigger failure and temporally coincided with SSRT_EXG3, but not SSRT_int. In contrast, P3 peak and onset latency were not associated with any behavioral estimates of inhibition for either trial type. While the N1 peaked earlier for stop-success than stop-failure trials, this effect was not found in poor task performers (i.e., high trigger failure/slow SSRT). These findings are consistent with attentional modulation of both the speed and reliability of the inhibition process, but not for poor performers. Together with the absence of any P3 onset latency effect, our findings suggest that attentional mechanisms are important in supporting speeded and reliable inhibition processes required in the stop-signal task.     

The Simon effect modulates N2cc and LRP but not the N2pc component

Previous studies have reported that the horizontal arrangement of the stimuli in Simon tasks elicits three different components: LRP, N2pc and N2cc. Although N2cc may play a key role in Simon tasks, as it is involved in preventing responses based on stimulus position, modulation of the N2cc component according to the experimental conditions has not previously been investigated because of N2cc/LRP overlap in similar regions and temporal window. The aim of the present study was to investigate how the Simon effect modulates N2pc, N2cc and LRP components. For this purpose, participants were asked to respond to an arrow according to its colour. Three conditions, which depended on the congruency between stimulus position and the required response, were analysed: compatible position (CP), incompatible position (IP), and neutral position (NP). The LRP peak latency was delayed in IP with respect to CP and NP conditions. Lateralized minus neutral position (L-NP) subtractions were carried out to remove the common motor activity and isolate the N2cc and N2pc components in the lateralized conditions. The N2cc amplitude in L-NP waveforms was larger in IP than in CP, in accordance with the greater effort required to monitor selection of the correct response in the first condition. eLORETA analysis also revealed greater premotor activity at 150-200 ms in IP and CP, than in NP, which was attributed to the N2cc component present in IP/CP conditions. Evidence of functional dissociation between N2pc and N2cc components was obtained, because N2cc, but not N2pc, was affected by the experimental conditions.     

Dissociation of the mismatch negativity and processing negativity attentional waveforms with nitrous oxide.

In Näätänen's model of early attention, the role of arousal in influencing the permanent feature detection system (indexed by mismatch negativity [MMN]) and the temporary feature-detection system (indexed by processing negativity [PN]) is unclear. To address this question, we investigated the effects of the anesthetic gas nitrous oxide (N₂O) on the MMN and PN. Ten subjects performed a dichotic listening task in which discrimination difficulty and breathing mixture (air or 25% N₂O) were manipulated factorially. MMN, PN, N1 and P300 at Fz, Cz, and Pz, as well as reaction time (RT), were measured. N₂O had no effect on the PN, but decreased MMN amplitude. As expected, N₂O decreased the amplitude of the N1 and P300 and increased the latency of the P300 and RT. The dissociation of MMN and PN by N₂O suggests that this agent decreases the ability to detect automatic stimulus change without affecting voluntary selective attention. We interpret these results as indicating that arousal has multidimensional effects on early attentional mechanisms. These dimensions can be differentiated chemically by neurotransmitters in the reticular formation of the brain.     

Developmental changes in point-light walker processing during childhood and adolescence: An event-related potential study

To investigate developmental changes in the neural responses to a biological motion stimulus, we measured event-related potentials (ERPs) in 50 children aged from 7 to 14 years, and 10 adults. Two kinds of visual stimuli were presented: a point-light walker (PLW) stimulus and a scrambled point-light walker (sPLW) stimulus as a control. The sPLW stimulus had the same number of point-lights and the same velocity vector of point-lights as the PLW stimulus, but the initial starting positions were randomized. Consistent with previous ERP studies, one positive peak (P1) and two negative peaks (N1 and N2) were observed at around 130, 200 and 330 ms, respectively, in bilateral occipitotemporal regions, in all age groups. The latency of the P1 component was significantly shorter for the PLW than sPLW stimulus in all age groups, whereas the amplitude was significantly larger for the PLW than sPLW stimulus only for the 7-year-old group. The P1 amplitude and N1 latency were linearly decreased with age. The negative amplitudes of both N1 and N2 components of the PLW stimulus were significantly larger than those of the sPLW stimulus in all age groups. P1-N1 amplitude was changed by development, but not N2 amplitude. These results suggest that the intensity (P1) and timing (N1) of early visual processing for the PLW stimulus changed linearly throughout childhood and P1-N1 amplitude at occipitotemporal electrodes and N1 latency in 10-year-olds, but not 11-year-olds, was significantly larger than that in adults. For the amplitudes of the N2 component in response to PLW and sPLW stimuli in 7–8-year-old subjects were not statistically different from those in adults at occipitotemporal electrodes. These results suggest that the neural response to the PLW stimulus has developed by 10 years of age at the occipitotemporal electrode.     

Do Task and Sex Differences Influence the Visual Evoked Potential?

Visual evoked potentials were recorded from each hemisphere of both male and female subjects at a parietal and a central site while concurrent spatial or verbal mental tasks were performed. The data were analyzed by means of an automated procedure for peak identification and each component's latency and amplitude was submitted to analysis of variance. No convincing taskhemisphere interactions were found, although several components, particularly the later ones, showed either task or hemisphere related effects. At both sites, females showed greater amplitude of the N2 component for both hemispheres and both cognitive tasks. Sex differences also emerged on components P6 and N6 which were consistent with the idea that females show differential hemisphere involvement in spatial tasks.     

The effect of warning stimulus novelty on the P300 and components of the contingent negative variation

This experiment evaluated the effects of stimulus and response probability on the P300 and components of the contingent negative variation (CNV) in three different reaction tasks. In the first task the warning stimulus (S1) indicated that the imperative stimulus (S2) would require either a left or a right button press response; in the two other tasks the S1 indicated that S2 would either require a button press response or not. The a priori probability of S1 and the response to S2 were independently varied. The results show that a novel S1 significantly increased the amplitude and latency of the P300 and early CNV component: the late CNV component, however, increased significantly when a motor response to S2 was required. Early and late CNV components also differed in midline distribution. It is concluded that the early CNV can be viewed as the slow wave part of the event-related potential to S1, while the late CNV is an event preceding shift that strongly relates to the motor requirements of S2. It is finally suggested that both the P300 and early CNV reflect an orienting response to S1.     

The effect of warning stimulus modality on blink startle modification in reaction time tasks

The present study investigated the effects of lead stimulus modality on modification of the acoustic startle reflex during three reaction time tasks. In Experiment 1, participants (N = 48) were required to press a button at the offset of one stimulus (task relevant) and to ignore presentations of a second (task irrelevant). Two tones that differed in pitch or two lights served as signal stimuli. Blink startle was elicited during some of the stimuli and during interstimulus intervals. Skin conductance responses were larger during task-relevant stimuli in both groups. Larger blink facilitation during task-relevant stimuli was found only in the group presented with auditory stimuli, whereas larger blink latency shortening during task-relevant stimuli was found in both groups. Experiment 2 (N = 32) used only a task-relevant stimulus. Blink magnitude facilitation was significant only in the group presented with tones, whereas blink latency shortening was significant in both groups. Experiment 3 (N = 80) used a go/nogo task that required participants to press a button if one element of a compound stimulus ended before the second, but not if the asynchrony was reversed. The offset asynchrony was varied between groups as a manipulation of task difficulty. Startle magnitude facilitation was larger during acoustic than during visual stimuli and larger in the easy condition. The present data indicate that startle facilitation in a reaction time task is affected by stimulus modality and by task demands. The effects of the task demands seem to be independent of lead stimulus modality.     

Effects of ISI and stimulus probability on event-related go/nogo potentials after somatosensory stimulation

The present study investigated the characteristics of the middle-latency negative potential of event-related potentials (ERPs) using somatosensory go/nogo tasks. We manipulated interstimulus interval (ISI) in Experiment 1 and stimulus probability in Experiment 2 and analyzed the subtracted difference waveform resulting from subtraction of the ERP evoked by the go stimulation from that evoked by the nogo stimulation. In Experiment 1, the peak latency of negativity became significantly longer as the ISI increased, but the peak amplitude was unchanged. The reaction time (RT) was longer with increasing ISI. In Experiment 2, manipulation of the stimulus probability yielded an increase in peak amplitude with decreasing probability of the nogo stimulus, but did not affect the latency. The RT increased as the probability of a nogo stimulus rose. Because manipulation of the ISI and stimulus probability elicited different brain activities, we hypothesized that manipulation of the ISI elicited a delay of the stimulus evaluation process including response inhibition, and that stimulus probability significantly affected the strength of the response inhibition process.     

Morphometric analysis of gastric adenoma and well-diferentiated adenocarcinoma as a basis for microscopic discrimination

Morphometric analyses were performed on 11 cases of welldifferentiated gastric adenocarcinoma and six cases of gastric adenoma. The values for the mean nuclear area (A_N), the index for roundness of the nucleus (F_x), and the nucleus/cytoplasm ratio (N/C) were larger in the carcinoma group than in the adenoma group (P < 0.01; t-test). The value of nuclear numerical density (N_A) was larger in the adenoma group than in the carcinoma group (P < 0.01; t-test). There was an overlap between the N/C ratio in the carcinoma and adenoma groups. It was concluded that roundness and enlargement of the nucleus, and a low nuclear density are important prerequisites for distinguishing the common type of adenocarcinomas from adenomas. An additional mor-phometric analysis was performed on seven cases of mucosal carcinoma. A three-dimensional discriminant analysis using A_N, F_x and N_A revealed that of these seven cases, three were consistent with the carcinoma group while one case was consistent with the adenoma group. The remaining three cases were judged as borderline.     

The effect of changing stimulus intensities on median nerve somatosensory-evoked potentials

We investigated median nerve somatosensory-evoked potentials (SEP) in 31 healthy volunteers to test the hypothesis that 1) increasing stimulus intensity influences SEP components in both amplitude and latency 2) SEP components respond differently to changing intensities. Cluster analysis and analysis of variance were used for statistical testing. Three groups of components could be found according to latency changes in response to increasing stimulus intensities: N13, and P15, the primary cortical response (N19, P22) and the components over 30 ms. In general, SEP components below 30 ms significantly shortened in latency and increased in amplitude with subsequent saturation. In contrast, in components over 30 ms latencies decreased linearly and amplitudes changed inhomogeneously. The clear effect of stimulus intensity on most median nerve SEP components makes it necessary to maintain comparable stimulus intensities when comparing intra- and interindividual registrations.     

Visual motion direction is represented in population-level neural response as measured by magnetoencephalography

We investigated whether direction information is represented in the population-level neural response evoked by the visual motion stimulus, as measured by magnetoencephalography. Coherent motions with varied speed, varied direction, and different coherence level were presented using random dot kinematography. Peak latency of responses to motion onset was inversely related to speed in all directions, as previously reported, but no significant effect of direction on latency changes was identified. Mutual information entropy (IE) calculated using four-direction response data increased significantly (>2.14) after motion onset in 41.3% of response data and maximum IE was distributed at approximately 20 ms after peak response latency. When response waveforms showing significant differences (by multivariate discriminant analysis) in distribution of the three waveform parameters (peak amplitude, peak latency, and 75% waveform width) with stimulus directions were analyzed, 87 waveform stimulus directions (80.6%) were correctly estimated using these parameters. Correct estimation rate was unaffected by stimulus speed, but was affected by coherence level, even though both speed and coherence affected response amplitude similarly. Our results indicate that speed and direction of stimulus motion are represented in the distinct properties of a response waveform, suggesting that the human brain processes speed and direction separately, at least in part.     

Electroencephalography effects to semantic and non-semantic mismatch in properties of visually presented single-characters: the N2b and the N400

Event-related potential (ERP) correlates of semantic and non-semantic mismatch in the 200-400ms time interval were dissociated. Twelve subjects observed pairs of single letters and digits presented serially, and decided whether the colour (blue or red) or the category membership (letter or number) of the second item in a pair matched the first one. In both tasks mismatch elicited central N2b components (220ms peak latency in the colour matching task, and 280ms peak latency in the category matching task). Furthermore, in the category matching task a centro-parietal negativity (N400) emerged. The topography of the N2b effect was clearly distinct from that of the N400 effect. Analysis of event-related spectral perturbations confirmed that N400 time-range effects were specific to category matching. We conclude that while the N400 effect is a specific marker of semantic mismatch, the N2b effect is a general correlate of detecting mismatch between the representations of task-relevant features.     

Stability of Pathway-Hemisphere Differences in the Auditory Event-Related Potential (ERP) to Monaural Stimulation

The evidence for ERP manifestations of contralateral dominance in the auditory pathways is not entirely compelling. The effect when found has involved either latency or amplitude of a variety of components obtained from averaged or subtraction waveforms. Also, the effect appears to have as much to do with hemisphere as pathway differences. The objectives of this experiment were to establish whether a specific ERP peak reflected contralateral dominance, to assess its long-term stability, and to clarify the apparent pathway-hemisphere interactions which result from monaural stimulation. Ten male subjects were tested on 6 occasions (generally weekly intervals). On each occasion, 76 monaural tones were presented while EEG was recorded at C₂, P₂, T₃, and T₄ referred to linked earlobes. P70, N120, and P200 peak amplitudes and latencies and N1–P2 amplitudes were examined. N120 amplitudes proved to be larger at the temporal site contralateral to the ear stimulated. This contralateral dominance effect was observed on all 6 occasions for right ear stimuli and on all but one occasion for left ear stimuli. N1–P2 amplitudes less reliably reflected contralateral dominance because possible hemisphere effects appeared with this measure. Methodological issues related to assessment of ERP contralateral dominance and to the variety of effects seen in the literature are discussed. The data are examined with reference to neurophysiological substrates thought to underlie auditory ERPs. Finally, the utility of a stable ERP phenomenon in assessing drug or pathology effects is evaluated.