Jackknife-based method for measuring LRP onset latency differences

A new method based on jackknifing is presented for measuring the difference between two conditions in the onset latencies of the lateralized readiness potential (LRP). The method can be used with both stimulus- and response-locked LRPs, and simulations indicate that it provides accurate estimates of onset latency differences in many common experimental conditions.     

Effects of task variables on measures of the mean onset latency of LRP depend on the scoring method

The lateralized readiness potential (LRP) can be used to index the start of response activation, The onset of the average LRP can be computed as the latency at which the component starts to deviate significantly from zero or as the latency at which a certain proportion of its maximum amplitude is attained. The properties of both measures as estimates of the mean onset latency of the LRP were examined. Experiment I was a simulation study in which the mean onset latencies were known, Results indicated different types of bias for the two measures and greater reliability for a proportional measure. In Experiment 2, the sensitivity to bias, consistency, and linearity of both measures were evaluated in a set of empirical data. By all three criteria, a proportional onset measure was superior. It is recommended that the choice of the measure should depend on the hypothesis to he tested, so that conclusions are based on the more conservative test.     

Using the jackknife-based scoring method for measuring LRP onset effects in factorial designs

Miller, Patterson, and Ulrich (1998) introduced a jackknife-based method for measuring the differences between two conditions in the onset latencies of the lateralized readiness potential (LRP). The present paper generalizes such jackknife-based methods to factorial experiments with any combination of within- and between subjects factors. Specifically, we introduce a subsample scoring method to assess potential main and interaction effects on LRP onsets within conventional yet slightly adjusted analyses of variance (ANOVAs) and post hoc comparison procedures.     

Stimulus and response ERP analyses of a two-level reaction time task

Higher cognitive processes include the ability to reliably transform sensory or mnemonic information. These processes either occur automatically or they are consciously controlled. To compare these two types of information processing, we developed a reaction time task that requires either a rule operation or else a direct sensory association. We were interested in evaluating the brain's electrical activity corresponding to both tasks, using event-related potentials (ERPs). In order to gain complete insight into the electrical activity of a stimulus-response segment, we analyzed the ERPs corresponding to the processing of the stimulus and the ERPs corresponding to the preparation of the response. To complete the analysis, we also evaluated the lateralized readiness potential (LRP) matched to the stimulus and to the response onset. Compared with the sensory association task, rule operation generated a higher negative potential field at frontocentral scalp areas in a latency range of 312–512 ms after the stimulus. In contrast, the LRP showed a negative component in the sensory association task which was absent during the rule operation; the latency of the difference was in the range 374–532 ms after the stimulus. The ERP component obtained by the response onset analysis was more negative in the rule condition up to a latency of –214 ms before the generation of the movement; the effect was localized at frontal and central scalp regions. We failed to find any significant difference in the LRP matched to the response onset. These results suggest that the brain computation of the rule operation takes place approximately in the middle of the stimulus-response time interval and that it is an additive process to the sensory association response.     

A carry-over task rule in task switching: An ERP investigation using a Go/Nogo paradigm

Investigations of executive control using a task-switching paradigm have consistently found longer reaction times for task-switch trials than task-repetition trials. This switch cost may result from interference by a stimulus-response (SR) rule carried over from the preceding alternative task. We examined event-related brain potential (ERP) evidence for such carry-over effects using a combined paradigm of task switching with Go/Nogo; Nogo trials, which require no response execution, should expose carry-over effects from preceding trials. On Go trials, twelve participants performed a button-pressing task in compatible (hand and signal direction consistent) and incompatible conditions, which switched predictably every three trials. Reaction times were longer on switch than on repetition trials. On compatible switch trials, a stimulus-locked lateralized readiness potential (sLRP) for Nogo stimuli revealed a positive dip, suggesting incorrect response activation in the early automatic process that was induced by a SR rule carried over from the preceding task.     

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.     

Cortical gamma activity during auditory tone omission provides evidence for the involvement of oscillatory activity in top-down processing

Perception is an active process in which our brains use top-down influences to modulate afferent information. To determine whether this modulation might be based on oscillatory activity, we asked seven subjects to detect a silence that appeared randomly in a rhythmic auditory sequence, counting the number of omissions (“count” task), or responding to each omission with a right index finger extension (“move” task). Despite the absence of physical stimuli, these tasks induced a ‘non-phase-locked’ gamma oscillation in temporal–parietal areas, providing evidence of intrinsically generated oscillatory activity during top-down processing. This oscillation is probably related to the local neural activation that takes place during the process of stimulus detection, involving the functional comparison between the tones and the absence of stimuli as well as the auditory echoic memory processes. The amplitude of the gamma oscillations was reduced with the repetition of the tasks. Moreover, it correlated positively with the number of correctly detected omissions and negatively with the reaction time. These findings indicate that these oscillations, like others described, may be modulated by attentional processes. In summary, our findings support the active and adaptive concept of brain function that has emerged over recent years, suggesting that the match of sensory information with memory contents generates gamma oscillations.     

Electrophysiological evidence against parallel motor processing during multitasking

We combined behavioral measures with electrophysiological measures of motor activation (i.e., lateralized readiness potentials, LRPs) to disentangle the relative contribution of premotor and motor processes to multitasking interference in the prioritized processing paradigm. Specifically, we presented stimuli of two tasks (primary and background task) in each trial, but participants were instructed to perform the background task only if the primary task required no response. As expected, task performance was substantially influenced by a task probability manipulation: Background task responses were faster, psychological refractory period effects were smaller, and interference from the second task (i.e., backward compatibility effects) was larger when there was a larger probability that this task required a response. Critically, stimulus-locked and response-locked LRP analyses indicate that these behavioral effects of parallel processing were not driven by background task motor processing (e.g., motoric response activation) taking place during primary task processing. Instead, the LRP results suggest that these effects were exclusively localized during premotor stages of processing (e.g., response selection). Thus, the present results generally provide evidence for multitasking accounts allowing parallel task processing during response selection, whereas the task-specific motor responses are activated in a serial manner. One plausible account is that multiple task information sources can be processed in parallel, with sharing of limited cognitive resources depending on task relevance, but a primary and still active task goal prevents motor activation related to the goals of other tasks in order to avoid outcome conflict.     

Anticipated action consequences as a nexus between action and perception: evidence from event-related potentials

We used high-density event-related potentials (ERP) in a modified flanker paradigm to study the role of anticipated action consequences in action planning and the role of anticipation in the perception of action consequences. Prior to the experiment, participants were trained to classify target letters in a four-alternative forced-choice task; another letter was presented as an effect following each response. After participants had thus acquired the response-effect contingencies, in the experiment effect letters were presented as flankers to target letters. Effect-compatible flankers were letters that were learned as effects of the correct response to the target; effect-incompatible ones were learned as effects of other responses; neutral flankers were never presented as action effects. To help distinguish early and late effects of flankers on target processing, flankers were presented either simultaneously with the target or after a delay. We found that effect-incompatible flankers resulted in longer, than other flankers, time between the onset of the response-locked lateralized readiness potential and the response, indicating extended motor processing. ERP evoked by the effect-incompatible flankers differed from those evoked by other flankers in early perceptual component P1 and in later frontal component P2 reflecting stimulus evaluation and conflict detection. These results show that anticipating action consequences involves brain systems ranging from perceptual to executive; anticipated action effects constitute a link between perception and action.     

Functional brain-electrical correlates of negative priming in the flanker task: Evidence for episodic retrieval

Negative priming (NP) refers to inefficient responding when previous distractors become targets. NP may reflect persisting inhibition of former distractors and/or retrieval of task-inappropriate information from the primes. In an event-related potential (ERP) study of the flanker task, NP was accompanied by reduced positivity in the P300 time range. The early portion of this effect was shared with a target-repetition condition and hence may indicate retrieval processes cued by repeated stimuli. A subsequent N400-like component was specific for NP and may reflect processing of the retrieved task-inappropriate information. In addition, NP effects on the lateralized readiness potential (LRP) matched predictions of the episodic-retrieval view. NP effects on P300, N400, and response-locked LRP were stronger in participants with above-median behavioral NP, confirming the significance of these ERP effects for NP. Overall, findings support episodic-retrieval explanations of NP.     

结合小波分解和径向基神经网络进行事件相关电位的单次提取

从单次实验记录中提取事件相关电位，无论在临床诊断上还是在大脑高级功能的研究中都起着重要的作用。介绍了一种将小波多分辨率分解和重建与径向基神经网络结合起来进行事件相关电位单次提取的方法。它基于事件相关电位主要是低频信号的事实，发挥径向基神经网络对连续函数的逼近能力，从信号的小波分解系数中提取出与低频响应相关的成分，构造了一种新的时频域滤波的方法，实验表明本方法较好地从单次记录中提取出了事件相关电位。     

Early time-locked gamma response and gender specificity

The aim was to investigate whether gender is a causative factor in the gamma status according to which some individuals respond with time-locked, early gamma response, G+, while the others do not show this response, G−. The sample consisted of 42 volunteer participants (between 19 and 37 years of age with at least 9 years of education). There were 22 females and 20 males. Data were collected under the oddball paradigm. Auditory stimulation (10 ms r/f time, 50 ms duration, 65 dB SPL) consisted of target (2000 Hz; p = .20) stimuli that occurred randomly within a series of standard stimuli (1000 Hz; p = .80). Gamma responses were studied in the amplitude frequency characteristics, in the digitally filtered event-related potentials (f-ERPs) and in the distributions which were obtained using the recently developed time–frequency component analysis (TFCA) technique. Participants were classified into G+ and G− groups with a criterion of full agreement between the results of an automated gamma detection technique and expert opinion. The 2 × 2 × 2 ANOVA on f-ERPs and 2 × 2 × 2 multivariate ANOVA on TFCA distributions showed the main effect of gamma status and gender as significant, and the interaction between gamma status and gender as nonsignificant. Accordingly, individual difference in gamma status is a reliable phenomenon, but this does not depend on gender. There are conflicting findings in the literature concerning the effect of gender on ERP components (N100, P300). The present study showed that if the gamma status is not included in research designs, it may produce a confounding effect on ERP parameters.     

Linking components of event-related potentials and autonomic measures of the orienting reflex

This study examined autonomic measures and event-related potentials (ERPs) associated with elicitation and habituation of the basic Orienting Reflex (OR). Subjects received 16 innocuous tones with intensity alternating between 60 and 80 dB, at long inter-stimulus intervals. There was no stimulus-related task, so we could examine the effects of stimulus novelty and intensity in the absence of task demands. Cardiac, respiratory, peripheral vasoconstriction, and electrodermal measures were recorded, as well as continuous EEG. Single-trial ERPs were obtained, and components extracted by Principal Components Analysis were examined for potential response fractionation in the central indices of stimulus processing. The predicted fractionation of autonomic measures was obtained: cardiac deceleration showed no systematic change with intensity or trials, respiratory pause showed a substantial main effect of trials but no intensity effects, peripheral vasoconstriction showed intensity but no trials effects, and electrodermal responses showed substantial main effects of trials and intensity. A range of intensity and novelty effects were obtained in components identified as the N1, P3a, P3b, Novelty P3, and the classic Slow Wave. The different stimulus–response profiles of the ERP components are discussed in relation to the autonomic response profiles within the context of a sequential processing theory of OR elicitation.     

Modern Mind-Brain Reading: Psychophysiology, Physiology, and Cognition

This paper reviews the actual and potential benefits of a marriage between cognitive psychology and psychophysiology. Psychophysiological measures, particularly those of the event-related brain potential, can be used as markers for psychological events and physiological events. Thus, they can serve as "windows" on the mind and as "windows" on the brain. These ideas are illustrated in the context of a series of studies utilizing the lateralized readiness potential, a measure of electrical brain activity that is related to preparation for movement. This measure has been used to illuminate presetting processes that prepare the motor system for action, to demonstrate the presence of the transmission of partial information in the cognitive system, and to identify processes responsible for the inhibition of responses. The lateralized readiness potential appears to reflect activity in motor areas of cortex. Thus, this measure, along with other psychophysiological measures, can be used to understand how the functions of the mind are implemented in the brain.     

A new method of simulating surface electromyograms using probability density functions

A new method based on probability density functions (inverse Gaussian distributions) to simulate surface electromyograms (sEMGs) was developed for the specific use of the 'T(P) technique', which discriminates sEMG activity patterns. First, four prototypes with different activity patterns were generated from inverse Gaussian distributions by changing their geometrical parameters, which were derived from actual recorded sEMGs. Then, four simulated sEMGs were produced on the basis of the prototypes. The validity of the simulation method in relation to the T(P) technique was statistically examined and verified. The new simulation method will be useful.     

Novelty P3 reductions in depression: Characterization using principal components analysis (PCA) of current source density (CSD) waveforms

We previously reported a novelty P3 reduction in depressed patients compared to healthy controls ( n =20 per group) in a novelty oddball task using a 31-channel montage. In an independent replication and extension using a 67-channel montage ( n =49 per group), reference-free current source density (CSD) waveforms were simplified and quantified by a temporal, covariance-based principal components analysis (PCA) (unrestricted Varimax rotation), yielding factor solutions consistent with other oddball tasks. A factor with a loadings peak at 343 ms summarized the target P3b source as well as a secondary midline frontocentral source for novels and targets. An earlier novelty vertex source (NVS) at 241 ms was present for novels, but not targets, and was reduced in patients. Compatible CSD-PCA findings were also confirmed for the original low-density sample. Results are consistent with a reduced novelty response in clinical depression, involving the early phase of the frontocentral novelty P3.