Sources of P300 attenuation after head injury: Single-trial amplitude, latency jitter, and EEG power

Single trial amplitude, latency jitter, and electroencephalographic (EEG) power were examined as sources of the group difference in averaged P300 amplitude among 15 traumatically brain injured and 20 control individuals in an auditory oddball paradigm. Mean amplitude of the individual trials was highly correlated with the amplitude of the averaged P300, with little additional unique variance attributable to latency jitter or EEG power. The group difference in P300 amplitude was also explained by the mean amplitude of the single trials. These results support the robustness of the event-related potential averaging technique within the paradigm used.     

Changes in the somatosensory N250 and P300 by the variation of reaction time

We investigated the relationship between somatosensory event-related potentials (ERP) and the variation of reaction time (RT). For this purpose, we recorded the ERPs (N250 and P300) in fast- and slow-reaction trials during a somatosensory discrimination task. Strong, standard, and weak target electrical stimuli were randomly delivered to the left median nerve at the wrist with a random interstimulus interval (900–1,100 ms). All the subjects were instructed to respond by pressing a button with their right thumb as fast as possible whenever a target stimulus was presented. We divided all the trials into fast- and slow-RT trials and averaged the data. N250 latency tended to be delayed when the RT was slow, but not significantly. P300 latency was delayed significantly when the RT was slow, but to a much lesser extent than the RT delay, so we concluded that the change of RT was not fully determined by the processes reflected by the somatosensory N250 or P300. Furthermore, the larger and earlier P300 in the fast-RT trials implied that when larger amounts of attentional resources were allocated to a given task, the speed of stimulus evaluation somewhat increased and RT was shortened to a great extent. N250 amplitude did not significantly vary in the two RT clusters. In conclusion, the somatosensory N250 reflects active target detection, which is relatively independent of the modulation of the response speed, whereas the somatosensory P300 could change without manipulation of either the stimulus or the response processing demand. Electronic Publication     

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.     

Stimulus presentation rate dissociates sequential effects in event-related potentials and reaction times

The present study explored the impact of the stimulus presentation rate on sequential effects in event-related potentials (ERPs) and reaction times (RTs). Random series of equiprobable tones were presented at interstimulus intervals (ISIs) of 1.3, 2.1, and 2.9s. Fast and accurate choice responses to the tones were required. Although sequential effects in RTs were stable across all ISIs, the common first-order repetition effect in P300 amplitude was only observed at the 1.3-s ISI and not at the slower presentation rates. This dissociation between the first-order effects in RTs and ERPs speaks against an explanation of both effects by a common expectancy mechanism. In addition, sequential effects were observed as early as about 100 ms after stimulus onset in the lateralized readiness potential. Together with similar sequential effects in P300 latency, this finding supports a continuous flow model of information processing.     

Instability in the latency of P3a/P3b brain potentials and cognitive function in aging

Instability in performance is a prominent feature of aging. In this study, 133 participants evenly distributed across the adult lifespan underwent a three-stimulus event-related potentials (ERPs) paradigm, and instability in P3a/P3b latency and reaction time (RT) were measured. P3a is related to alertness or reorientation of attention and it was elicited by distractor stimuli. P3b is related to controlled attentional processes and it was triggered by target stimuli. Maximum-likelihood estimation (MLE) was used to quantify the level of variability in latency across the single sweep ERPs. The results revealed increased variability in RT but not in P3a/P3b latency with age. Variability in P3a/P3b latency was related to executive functions, and variability in RT to speed. Generally, the relationships tended to increase with age. It can be concluded that increased variability in RT with age is caused by instability in processes related to response execution and possibly response selection, but not stimulus classification. Further, the results indicate that intraindividual variability is not a uniform concept, but has unique explanatory value at the neurophysiological and behavioral level.     

Electroencephalographic correlates of target and outcome errors

Different neural systems underlie the evaluation of different types of errors. Recent electroencephalographic evidence suggests that outcome errors—errors indicating the failure to achieve a movement goal—are evaluated within medial-frontal cortex (Krigolson and Holroyd 2006, 2007a, b). Conversely, evidence from a variety of manual aiming studies has demonstrated that target errors—discrepancies between the actual and desired motor command brought about by an unexpected change in the movement environment—are mediated within posterior parietal cortex (e.g., Desmurget et al. 1999, 2001; Diedrichsen et al. 2005). Here, event-related brain potentials (ERP) were recorded to assess medial-frontal and parietal ERP components associated with the evaluation of outcome and target errors during performance of a manual aiming task. In line with previous results (Krigolson and Holroyd 2007a), we found that target perturbations elicited an ERP component with a parietal scalp distribution, the P300. However, the timing of kinematic changes associated with accommodation of the target perturbations relative to the timing of the P300 suggests that the P300 component was not related to the online control of movement. Instead, we believe that the P300 evoked by target perturbations reflects the updating of an internal model of the movement environment. Our results also revealed that an error-related negativity, an ERP component typically associated with the evaluation of speeded response errors and error feedback, was elicited when participants missed the movement target. Importantly, this result suggests that a reinforcement learning system within medial-frontal cortex may play a role in improving subsequent motor output. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Influence of task difficulty on the features of event-related potential during visual oddball task

We present a comprehensive analysis of the change in event-related potential (ERP) due to task difficulty during a visual oddball task. Specifically, we investigated the inter-subject difference in difficulty-related change of ERP patterns using single-trial ERP analysis focusing on P300 and P2 components. ERPs were recorded and analyzed from 14 subjects while performing a visual oddball task with two difficulty levels. After extracting independent components (ICs) from single-trial ERPs, the averaged ERPs were used to identify which ICs originated from major ERP components. The ERP components were estimated from single-trial waveforms by back-projecting relevant ICs onto scalp electrodes after removing all other ICs; thus, the comparison of ERP components could be performed for each subject. The averaged P300 amplitude was smaller and latency was larger for the more difficult task, and this tendency was also observed for single-trial ERP analysis within each subject. P2 amplitude increased for the hard task for both group and individual analyses, suggesting that the P2 may be interpreted as a manifestation of task relevance evaluation or response generation. The P2 amplitude and latency were more notably correlated with response time for the more difficult task.     

The left-to-right difference in warned reaction times of finger movements

The electromyographic reaction times (RTs) in bilateral finger movements and their left-to-right (l-r) difference were measured in right-handed subjects under conditions of different preparatory intervals (PIs), i.e., periods between warning and command signal. RTs without warning were always longer than warned RTs with PIs of 2–15 sec. Consistent right or left leading l-r differences occurred for PIs ranging from 2 to 6 or 7 sec, but were reduced for longer PIs. Significant l-r differences in warned RTs were consistently maintained regardless of the sensory modality of command signals, and even between separately performed right and left movements. In these tests RTs and their l-r difference changed independently. It is suggested that the warning signal acts on RTs and their l-r difference through two separate facilitatory mechanisms in the central information processing.     

The usefulness of partial information: effects of go probability in the choice/Nogo task.

In the present study, we examined whether the use of partial information for response preparation depends on the utility of that partial information for meeting task demands. Using a choice/Nogo task, the utility of the partial information was varied by manipulating the proportion of Go relative to Nogo signals, and preliminary response preparation was indexed by the degree of lateralized readiness potential (LRP) activity on Nogo trials. The Nogo LRP was clearly present when Go probability was high (67% Go) and, to a lesser extent, when Go and Nogo signals were equiprobable. However, the Nogo LRP disappeared when the probability of a Go signal was low (25% Go). This pattern of results supports the hypothesis that response preparation will be based on partial stimulus information only when the information has significant utility in the context of the overall task requirements.     

Effects of task complexity in young and old adults: reaction time and P300 latency are not always dissociated

Twelve young and 11 elderly men (mean ages 21.1 and 70.1) performed a choice-reaction time (RT) task in which stimulus degradation and stimulus-response (S-R) compatibility were manipulated. The extant literature has suggested that the effects of age on RT are usually augmented (multiplicative) in more difficult task conditions, but also that the effects of age on the latency of the P300 component of the event-related brain potential (ERP) are constant (additive). The results indicated that the effects of age on RT were enhanced in more difficult conditions, whether the difficulty consisted of stimulus degradation or S-R incompatibility. However, the effects of age on P300 latency were enlarged as the stimuli were degraded, but not if the S-R mapping was incompatible. Thus, it appears that task content determines if effects of age on P300 latency are additive or multiplicative. A simple model is proposed that produces the obtained pattern of effects.     

P300 and S-R Compatibility: A Reply to Magliero et al.

Some recent papers have been devoted to simultaneous analysis of RT and P300 latency effects with S-R compatibility. This, indeed, can be particularly fruitful since it may provide some insight into response choice, a crucial stage of information processing taking place between stimulus analysis and response production. Apparent contradictions have arisen between these studies because of the different kinds of S-R compatibilities involved. The aim of this reply is to emphasize the discrepancies between experimental designs that use semantic versus spatial compatibilities.     

Effects of arterial and cardiopulmonary baroreceptor activation on simple and choice reaction times

Variations in simple reaction time over the cardiac cycle could be due to cortical inhibition associated with activation of the arterial baroreceptors. It has been proposed that higher order cognitive processing may also be modulated and, moreover, that cardiopulmonary baroreceptors may have similar inhibitory effects. This study examined arterial and cardiopulmonary baroreceptor effects on simple and choice reaction times by presenting visual stimuli at one of six intervals after the R-wave of the electrocardiogram (0, 150, 300, 450, 600, 750 ms) while participants lay supine with their legs raised or lowered. Reaction times were slower early in the cardiac cycle compared to later whereas reaction time slopes were not different. No cardiopulmonary baroreceptor effects were found. Cardiac cycle effects on reaction time are consistent with the arterial baroreceptor hypothesis and appear to be confined to lower order sensory-motor processing.     

P300 and Tracking Difficulty: Evidence For Multiple Resources in Dual-Task Performance

Subjects performed a visual tracking task while performing a concurrent task in which tones were covertly counted. The P300 component of the event-related potentials elicited by the tones was examined to determine the extent to which its amplitude was affected by variations in the forcing-function bandwidth, or difficulty, of the tracking task. P300 decreased in magnitude when tones were counted in conjunction with the performance of the tracking task, relative to a single-task counting condition. Increasing tracking difficulty failed to reduce P300 amplitude further. A second experiment obviated the possibility that movement-related potentials caused the P300 attenuation resulting from the introduction of the tracking task. In Experiment 3, subjects performed a reaction time task in conjunction with tracking in order to establish the validity of the tracking difficulty manipulation. The results are interpreted in terms of a theory of functionally-specific processing resources.     

Physiological variability of peak latency in evoked potentials: use of a property of asynchronous averaging

A method for estimating the physiological variability of peak latency in an evoked potential, of whom the peak latency and amplitude varied, by using the property of asynchronous averaging was proposed. A point estimate of the physiological variability was obtained by minimizing the mean square error between a standard waveform and the asynchronously averaged waveform. An interval estimate was obtained by using the relationship between the signal-to-noise ratio and the standard deviation of the point estimate for the variability of peak latency. The proposed method was evaluated by using simulation data, and was successfully applied to actual P300 data of six normal subjects. The method gave accurate estimates for the physiological variability of peak latency of P300, and would also be effectively applicable to any other evoked potential records for estimating the physiological variability.     

The Cerebral Laterality of Mental Image Generation in Normal Subjects

This research was an attempt to replicate and extend a published study that reported a left hemispheric locus for the generation of mental images. Several methodological problems were addressed, the stability of effects was assessed by repeating the experiment, and P300 latency was measured. A lateralized visual choice reaction time task was performed twice, once without the use of imagery and once with imagery. In each visual field, the use of imagery produced a speeding of reaction times when the target stimuli matched the image generated by the subject. A similar effect was present for P300 latency, and was still present in the reaction time data after partialling out the P300 latency effect. These results indicate that mental imagery can speed both stimulus evaluation and response processing. There was no difference in the amount of speeding for images in the two hemifields, providing no evidence for a preferential locus of mental image generation in either cerebral hemisphere.     

Human express saccades: extremely short reaction times of goal directed eye movements

Summary Human subjects were asked to execute a saccade from a central fixation point to a peripheral target at the time of its onset. When the fixation point is turned off some time ( 200 ms) before target onset, such that there is a gap where subjects see nothing, the distribution of their saccadic reaction times is bimodal with one narrow peak around 100 ms (express saccades) and another peak around 150 ms (regular saccades) measured from the onset of the target. Express saccades have been described earlier for the monkey.     

Behavioral and electrocortical evidence of an interaction between probability and task metrics in movement preparation

Recent neurophysiological evidence suggests that cognitive factors shape neural activity in cortical areas such as parietal (area 5), premotor, and primary motor cortex. The implication of these findings is that behavioral signatures of cognitive factors and movement-specific factors should likewise be interdependent. The present study provides evidence of this interdependence in both behavioral (reaction time) and electrophysiological (P300) measures. Subjects performed a two-choice pointing task, in which the angular distance between the two required movement directions (task metrics) and the probability of the two responses was varied. In a control condition, a single reaction was required in response to both stimuli to test for the influence of stimulus metrics. Results from the pointing task showed a clear interaction between the metrics and effects of probability. When the potential targets were widely separated (120 degrees), stimulus probability influences reaction time and P300 amplitude in the classic fashion (longer reaction times and larger P300 amplitudes to less probable responses). When pointing to targets that were narrowly separated (20 degrees), probability had no effect: both rare and frequent targets were "functionally frequent." The same interaction was not observed in the control condition, indicating that metrics were primarily influencing movement preparation rather than stimulus processing. The results are consistent with the theoretical framework of dynamic field theory and demonstrate that metrics are an important factor that must be taken into account when assessing the processes associated with movement preparation.     

Simultaneous identification of eye fixation related potentials and reaction related potentials from single-trial signals

To obtain the effective components from event related potentials (ERPs), it has been necessary to average the waveforms of several trials. ERP data reflect the psychophysiological state of a subject. Time variation is an important feature in ERP analysis, and so the single-trial method is required. A method is proposed to identify simultaneously both eye fixation related potentials (EFRPs) and reaction related potentials (RRPs) using wavelength transforms. The EFRP is an ERP associated with saccadic eye movement. The RRP is defined as a component similar to P300 gained from the reaction signal. Six subjects participate in the oddball task. The task takes 30 min for each subject. Electroencephalograms (EEGs), electro-oculograms (EOGs) and electromyograms (EMGs) are simultaneously recorded. The EFRP is extracted for the offset of saccade from EOG, and the RRP is extracted for the onset of reaction from EMG. The results show that the estimated waveforms described well each of the components in the EFRP and RRP. Moreover, the simulation results show that the amplitudes of the lambda wave are estimated to within an error of 4%, and those of the latencies are within 0.4%, with an SNR of 4.5dB. Those of P300 were 11 and 4%, respectively. The reliability of the method is proved to be sufficient for estimating ERPs.     

P300-based Stroop study with low probability and target Stroop oddballs: The evidence still favors the response selection hypothesis

This paper addresses the issue of the locus of action in cognitive processing during Stroop effects. It uses the P300 latency to assess stimulus processing effects, but, for the first time, under conditions in which Stroop stimuli are rare and target stimuli. The study was also concerned with demonstrating that apparent P300s during verbal responding are in fact uninterpretable due to contamination of EEG by speech-related artifact. Three studies were presented. In Study 1, there were 3 blocks, each containing 1 of 3 types of rare Stroop stimuli (p = .15), congruent, neutral, and incongruent. There were also 3 response modes: button press (BUTTON), speaking aloud (VERBAL), and speaking to self (SILENT). Three sessions were used, each for a different response style. The only task was to name the color on each trial. In the 2 non-verbal blocks, Reaction Time (RT) varied by stimulus type; congruent < neutral < incongruent. P300 latency was the same across blocks in these non-verbal conditions in which one saw the classic Pz > Cz > Fz distribution. The much larger, speech artifact-contaminated “P300s” in the VERBAL blocks did suggest a Stroop effect, especially at Fz and Cz, where “P300s” were larger than at Pz. In Study 2, there were 2 response modes, VERBAL and SILENT, and only two rare Stroop stimuli; neutral and incongruent, 1 per block. In each of these blocks, one word–color combination was a designated target requiring a unique response. The subject was to name the color followed by a yes or no to categorize the target or non-target. Again the RT for incongruents was greater than RT for neutrals, without a parallel effect in P300 latency. Again, the rostral ERPs appeared artifactual in the VERBAL condition. Study 3 was a replication of the second study, except that motivated subjects, versus Psychology pool recruits, were used. The latency–RT correlation still failed to obtain. Thus, using classic P300-eliciting antecedents–rare and target (Stroop) stimuli–this study supports the view that the locus of Stroop interference is in response processing.     

Electrocortical components of anticipation and consumption in a monetary incentive delay task

In order to improve our understanding of the components that reflect functionally important processes during reward anticipation and consumption, we used principle components analyses (PCA) to separate and quantify averaged ERP data obtained from each stage of a modified monetary incentive delay (MID) task. Although a small number of recent ERP studies have reported that reward and loss cues potentiate ERPs during anticipation, action preparation, and consummatory stages of reward processing, these findings are inconsistent due to temporal and spatial overlap between the relevant electrophysiological components. Our results show three components following cue presentation are sensitive to incentive cues (N1, P3a, P3b). In contrast to previous research, reward‐related enhancement occurred only in the P3b, with earlier components more sensitive to break‐even and loss cues. During feedback anticipation, we observed a lateralized centroparietal negativity that was sensitive to response hand but not cue type. We also show that use of PCA on ERPs reflecting reward consumption successfully separates the reward positivity from the independently modulated feedback‐P3. Last, we observe for the first time a new reward consumption component: a late negativity distributed over the left frontal pole. This component appears to be sensitive to response hand, especially in the context of monetary gain. These results illustrate that the time course and sensitivities of electrophysiological activity that follows incentive cues do not follow a simple heuristic in which reward incentive cues produce enhanced activity at all stages and substages.