Delayed flanker effects on lateralized readiness potentials

When participants were required to respond to a relevant central target and ignore irrelevant flanking stimuli, the flankers produced a response compatibility effect. Electrophysiological studies have shown that irrelevant flanker stimuli can affect the motor system. The present experiments further examined the characteristics of flanker effects on the motor system. Sixty participants responded in the flanker task to arrows (experiment 1) or letters (experiment 2). To examine time and extent of flanker effects on the motor system, target onset was delayed with blocked or random stimulus-onset asynchronies (SOA). With SOA of 0 and 100 ms, flanker effects on behavioral measures were reduced in random as compared to blocked conditions, but enhanced with SOA of 400 ms. With SOA of 400 ms, flanker effects on the early lateralized readiness potentials (LRP) were reduced in blocked as compared to random conditions, indicating that the onset of flanker effects on the LRP was delayed. Response-locked LRPs suggest that flanker and target stimuli activate the motor system successively. Findings challenge current theories of the flanker compatibility effect.     

Motor cortex activation induced by a mirror: evidence from lateralized readiness potentials

Similar motor regions are activated during voluntarily executed or observed movements. We investigated whether observing movements of one's own hand through a mirror will generate activations in the cortical motor regions of both the moving and nonmoving hands. Using the lateralized readiness potential (LRP), an electrophysiological correlate of premotor activation in the primary motor cortex, we recorded evoked responses to movements while subjects were viewing the performing (right) hand through a mirror placed sagittally, giving the impression that the left hand was performing the task. Reliable LRPs were recorded in relation to the seen hand, indicating motor cortex activity in the contralateral hemisphere of the inactive hand while the opposite hand was performing the movement.     

Asymmetric switch cost: an investigation using lateralized readiness potentials

Switching to a dominant task incurs larger costs than switching to a non-dominant task. This study investigated whether this cost asymmetry derives from the inhibition of the dominant task rule that occurred during the previous trial. Participants were presented with a five-letter array consisting of (left) and (right), and asked to respond to the central target letter after being informed about the task rule with a pre-cue. The rule was switched between dominant (left-hand to, right-hand to) and non-dominant tasks (right-hand to, left-hand to) every two trials. Reaction times revealed the asymmetrical switch cost and the effect of target-flanker congruency. Stimulus-locked lateralized readiness potentials showed that the dominant task rule was inhibited during the non-dominant task, whereas this inhibition was not carried over to the dominant task trial.     

Extraversion-related differences in response organization: evidence from lateralized readiness potentials

Research utilizing a mental-chronometry approach to examine individual differences in extraversion suggests that extraversion-related individual differences may involve stimulus analysis, response organization, and peripheral motor processes. In a sample of 14 introverted and 14 extraverted female volunteers event-related potentials (ERP) and lateralized readiness potentials (LRPs) were recorded concurrently with reaction time (RT) measures as participants performed a two-choice go/no-go task. Although there were no extraversion-related differences in mean reaction time, introverts showed higher N1 amplitudes and shorter P3 latencies compared to extraverts. Furthermore, response-locked LRP latencies were reliably shorter for extraverts than for introverts. The latter finding provides first direct evidence for the contribution of central processes related to motor activation to account for extraversion-related individual differences.     

Response activation impairments in schizophrenia: evidence from the lateralized readiness potential

Previous research has demonstrated deficits in preresponse motor activity in schizophrenia, as evidenced by a reduced lateralized readiness potential (LRP). The LRP deficit could be due to increased activation of the incorrect response (e.g., failure to suppress competition) or to reduced activation of the correct response (e.g., a low-level impairment in response preparation). To distinguish these possibilities, we asked whether the LRP impairment is increased under conditions of strong response competition. We manipulated the compatibility of stimulus-response mappings (Experiment 1) and the compatibility of the target with flankers (Experiment 2). In both experiments, the patient LRP was reduced as much under conditions of low response competition as under high competition. These results are incompatible with a failure of patients to suppress competition and are instead consistent with a deficit in activating the correct response.     

Primes and targets in rapid chases: tracing sequential waves of motor activation

Single-cell recordings have indicated that visual stimuli elicit rapid waves of neuronal activation that propagate so fast that they might be free of intracortical feedback. Here, the time course of feedforward activation was traced by measuring pointing responses to color targets preceded by color primes initiating either the same or opposite response. The early time course of priming effects was strictly time locked to prime onset and depended only on properties of the primes, but was independent of the onset times of the actual targets as well as the perceptual effects of targets on primes. Results indicated that nonoverlapping feedforward signals by primes and targets traverse the visuomotor system in a rapid chase, controlling associated motor responses in strict sequence.     

The structure of motor programming: Evidence from reaction times and lateralized readiness potentials

There is a widely accepted notion that movement elements are assembled prior to movement execution in a central motor programming stage. However, it is not clear how this stage is structured—whether it is a unitary stage allowing different motor parameters to cross talk or whether there are several independent processes dealing with each motor parameter. We addressed this question by orthogonally manipulating two movement‐related factors: response sequence complexity and movement duration. Both factors yielded main effects on reaction time but no interaction. Additive effects of both factors on the onsets of response‐ but not stimulus‐synchronized lateralized readiness potentials suggest separable motoric loci of sequence complexity and duration. These findings are at variance with the notion of a unitary movement programming stage.     

Partial information can be transmitted in an auditory channel: inferences from lateralized readiness potentials

With the two-choice go/no-go paradigm, we investigated whether timbre attribute can be transmitted as partial information from the stimulus identification stage to the response preparation stage in auditory tone processing. We manipulated two attributes of the stimulus: timbre (piano vs. violin) and acoustic intensity (soft vs. loud) to ensure an earlier processing of timbre than intensity. We associated the timbre attribute more with go trials. Results showed that lateralized readiness potentials (LRPs) were consistently elicited in no-go trials. This showed that the timbre attribute had been transmitted to the response preparation stage before the intensity attribute was processed in the stimuli identification stage. Such a result provides evidence for the continuous model and asynchronous discrete coding (ADC) model in information processing. We suggest that partial information can be transmitted in an auditory channel.     

The functional locus of the lateralized readiness potential

The lateralized readiness potential (LRP) is considered to reflect motor activation and has been used extensively as a tool in elucidating cognitive processes. In the present study, we attempted to more precisely determine the origins of the LRP within the cognitive system. The response selection and motor programming stages were selectively manipulated by varying symbolic stimulus response compatibility and the time to peak force of an isometric finger extension response. Stimulus response compatibility and time to peak force affected response latency, as measured in the electromyogram, in a strictly additive fashion. The effects of the experimental manipulations on stimulus- and response-synchronized LRPs indicate that the LRP starts after the completion of response-hand selection and at the beginning of motor programming. These results allow a more rigorous interpretation of LRP findings in basic and applied research.     

The lateralized readiness potential: relationship between human data and response activation in a connectionist model.

Psychophysiological measures such as the lateralized readiness potential (LRP) have been used to study information processing in the Eriksen flankers task. The data provided by these measures are consistent with a continuous flow theory, which proposes that the output of stimulus evaluation is continuously available to the response channels. Cohen et al. (1992) realized this theory in a connectionist model and showed that its behavior corresponded to that of human subjects in the flankers task. We report here a modification of the model and an analysis of the degree to which simulated LRPs (based on the activation functions of the response units of the model) resemble the actual LRPs of human subjects in the same task. Across a variety of different experimental conditions and outcomes, there was a marked correspondence between the simulated and actual LRPs. These observations strengthen the propriety of the connectionist model and of the continuous flow theory on which it is based.     

Rate of force development and the lateralized readiness potential

We examined the relationship between force and rate of force development aspects of movement dynamics and electroencephalogram motor components as reflected in the lateralized readiness potential (LRP). Using self-paced tasks, in Studies 1 and 3 we investigated whether differential speed and accuracy constraints in discrete and repetitive finger force production tasks influenced the LRP. These studies showed that speed tasks produced larger LRP than accuracy tasks regardless of whether the movement type was discrete or repetitive. In Studies 2 and 4 we studied four conditions with two levels of force and two levels of rate of force development. The largest LRPs were found with the greatest rate of force development. Overall, the four studies demonstrated that preparation for differential rates of force development is a major component reflected in the LRP.     

The lateralized readiness potential and response kinetics in response-time tasks

Previous studies have found that the magnitude of the lateralized readiness potential (LRP) at the time of response initiation is constant across spontaneous variations in response time in both cued and uncued, speeded tasks. Other studies have found that the LRP is also unaffected by instructed changes in peak response force and time to peak force in cued, self-paced tasks, but that the LRP is sensitive to instructed changes in force gain rate in uncued, self-paced tasks. The present study examined the LRP in an uncued, speeded task as a function of response time and several measures of response kinetics. The magnitude of the LRP at the time of electromyographic onset was constant across spontaneous variations in all measures. The peak of the contingent negative variation did vary as a function of peak response force and integrated force to peak, but not response time. These findings support the idea that the LRP in speeded tasks is a selective, on-line index of the preparation associated with using a particular hand, and is not an index of the elements of motor programming that determine subsequent response kinetics.     

The lateralized readiness potential and P300 of stimulus-set switching

The present study aimed at investigating whether stimulus-set switching involves the same stages of information processing as response-set switching. A pair-wise task switching paradigm in which the trial sequences comprised only two tasks was used. The effect of preparation was manipulated so that the participants performed only the repeat trials in some blocks and only the switch trials in other blocks, or both the repeat and switch trials were randomly mixed within a single block. P300 peak latency and stimulus- and response-locked lateralized readiness potential intervals were used to indicate the processing stage of stimulus identification, response selection and motor execution, respectively. The results demonstrated that the stimulus-set switching involves stages of information processing following stimulus identification and before motor execution.     

Control over response priming in visuomotor processing: a lateralized event-related potential study

In a typical Simon task responses are faster when the task-irrelevant stimulus location corresponds to the response location than when it does not. In the case of noncorrespondence it is assumed that externally triggered and internally selected responses are in conflict. Crucially, such conflict appears to be subject to contextual modulations as induced by the immediately preceding event, i.e., the Simon effect was found to be absent when a conflict trial preceded the current event (Stürmer et al. 2002, JEP:HPP). Here, we examined two possible accounts of this context effect in terms of early suppression of externally triggered S-R coding at a premotoric level versus late suppression at a motoric level. Lateralized event-related brain potentials (L-ERPs) were recorded in a Simon task and analyzed as a function of the correspondence sequence. L-ERP activity started earliest over occipito-parietal brain areas and revealed location-based S-R priming irrespective of the prior correspondence context. By contrast, when a noncorresponding trial preceded, such location-based priming was absent in L-ERP activity over the motor cortex (MC). Thus, in support of the late suppression view L-ERPs suggest a clear dissociation in function between externally triggered visuomotor functions within the dorsal stream and the MC reflecting context-controlled response activation.     

The application of jackknife-based onset detection of lateralized readiness potential in correlative approaches

The onset of the lateralized readiness potential (LRP) represents an interesting parameter within mental chronometry. According to Miller, Patterson, and Ulrich (1998), reliability increases when LRP onsets are detected in jackknifed LRP waveforms. Until now, jackknifed LRP onsets could be analyzed in factorial designs only. The aim of the present study was to extend the application of jackknifing to correlative approaches (e.g., in personality research). Using different onset scoring techniques, in several simulations run on realistic LRP data jackknifing and single-subject procedures were compared regarding their estimates of a simulated true correlation. For all scoring techniques but regression, jackknifed coefficients were on average higher than the respective single-subject coefficients, and statistical power was higher. Overall, combining jackknifing with a 50%-relative onset criterion is recommended.     

The effect of task preparation in task switching as reflected on lateralized readiness potential.

The present study examined whether task preparation had an equivalent beneficial effect for both switch and repeat trials in the context of a task switching paradigm. A pair-wise task-switching paradigm was used where each trial was comprised of two tasks that were either the same (task repeat) or different (task switch). The effect of preparation was manipulated so that participants either performed pure repeat trials or pure switch trials in separate blocks (foreknowledge conditions) or performed both switch and repeat trials within the same block (non-foreknowledge conditions). In addition, the time interval between the response to the first task and the onset of the next task's stimulus (response-stimulus interval, RSI) was set at either 300 ms or 600 ms. Both stimulus-locked and response-locked lateralized readiness potentials were measured to examine at what stage in time that task preparation affects the task performance. The results showed that task preparation had the same amount of beneficial effect on the stage of response selection for both switch and repeat trials, regardless of whether the RSI was short or long.     

Scalp potentials to pitch change in rapid tone sequences. A correlate of sequential stream segregation

The object of the study was to look for a neurophysiological substrate of sequential auditory stream segregation. When a sequence of tones alternates rapidly between pitches separated by more than a few semitones, there is a tendency for it to be perceived as two independent "streams". We examined the scalp potentials evoked when the pitch interval abruptly changes, to see whether there are response parameters which might be correlated with sudden stream segregation and/or integration. For 3 s a continuous synthesized tone of "clarinet" timbre oscillated between pitches of F4 and F#4 (one semitone higher) at 16 notes/s, perceived as an integrated stream. The upper note was then raised to E5 (11 semitones above F4, perceived as segregated streams) for a further 3 s and the cycle was repeated 40 times. In a second condition also starting with oscillation between F4 and F#4, the upper note was lowered to E4 (one semitone below F4, still perceived as a single stream). Further conditions examined the changes between oscillations of 1 and 11 semitones down from E5, 1 and 23 semitones up from F4, and 10 and 11 semitones up from F4. Virtually no potentials were detectable during the periods of unchanging oscillation, but an N1/P2 complex was evoked on each change in the pitch interval. The N1 was termed "MN1" on account of its arguable relatedness to the mismatch negativity, recorded in a separate experiment using discontinuous tones at a much slower rate. The mean peak latency of the MN1 varied between 96 and 123 ms, the shortest latencies being recorded, not to the largest changes of pitch interval but to the widest pitch intervals between the new tone and the immediately preceding one. Therefore, although a causal relationship with streaming cannot necessarily be inferred, the MN1 latency appears to mark the degree of pitch contrast between consecutive tones, in correlation with the streaming effect. Electronic Publication     

Locus of the effect of temporal preparation: evidence from the lateralized readiness potential

It is well established that reaction time (RT) is shorter when a response signal is preceded by a warning signal, because the warning signal causes the participant to prepare for the upcoming response. A review of chronometric and psychophysiological studies reveals the prevailing view that this temporal preparation operates mainly at a motor level speeding up rather late processes. To assess the locus of this preparation effect, we conducted two experiments employing the lateralized readiness potential (LRP). Contrary to this prevailing view, the results of both experiments clearly indicate that temporal preparation enhances the processing speed of relatively early processes, because a manipulation of temporal uncertainty affected RT, the P300 latency, and the stimulus-to-LRP interval but not the LRP-to-keypress interval.