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.     

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.     

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.     

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.     

Tracing sequential waves of rapid visuomotor activation in lateralized readiness potentials

Feedforward activation processes are widely regarded as crucial for the automatic initiation of motor responses, whereas recurrent processes are often regarded as crucial for visual awareness. Here, we used a set of behavioral criteria to evaluate whether rapid processing in the human visuomotor system proceeds as would be expected of a feedforward system that works independent of visual awareness. We measured lateralized readiness potentials (LRPs) for key-press responses to color targets ("masks") preceded by masked color primes mapped onto the same or opposite response, and traced the time-course of motor activation as a function of different prime and mask characteristics. LRP time-courses showed that initial motor activation occurred in prime direction and was time-locked to prime onset. Response activation was then captured on-line by the mask signal, with motor activation now time-locked to the mask and proceeding in mask direction. Crucially, the time-course of early activation by the prime was independent of all mask characteristics. This invariance in early priming effects contrasted with large differences in visual awareness for the prime produced by different masks. Results suggest that primed responses to color stimuli are controlled by feedforward waves of activation sequentially elicited by prime and mask signals traveling rapidly enough to escape the recurrent processes leading to backward masking.     

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.     

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.     

The time course of the asymmetrical "local" switch cost: evidence from event-related potentials

The goal of the study was to explore the time-course of the asymmetrical “local” switch cost observed in task switching. We investigated event-related potentials induced by cue and target processing when participants were engaged in a card-sorting switching task. Participants were instructed to match each card (target) following one of two possible task rules, the color or the form. The correct task rule changed unpredictably after a variable number of trials, and was signalled by cues indicating to switch or repeat the previous task rule. We observed that transition type (switch versus repeat) and task rule (color versus form) influenced both cue and target processing. Interestingly, the interaction between transition type and task rule, indicating an asymmetry in the local switch cost, affected the brain responses during target processing but not during cue processing. These results suggest that the asymmetry in the local switch cost relates to task execution processes.     

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.     

Preparation of response force and movement direction: onset effects on the lateralized readiness potential

Two experiments assessed the preparatory effects of advance information about response force and movement direction on the lateralized readiness potential (LRP). In a choice reaction time (RT) task, an imperative stimulus required an isometric flexion or an extension of the left or right index finger. Prior information about response force or about movement direction reduced RT and shortened the interval from the onset of the imperative stimulus up to the onset of the LRP. Advance information, however, about direction but not about force decreased the interval from LRP onset to the onset of the overt response. The identical pattern of results was obtained in a second experiment, in which each participant performed both precue conditions. The findings of both experiments support the notion that response force is specified before movement direction. These results are consistent with the view accordingly different mechanisms are involved in the specification of muscle force and movement direction.     

Detecting the onset of the lateralized readiness potential: a comparison of available methods and procedures

Studies that measure the onset of the lateralized readiness potential (LRP) could well provide researchers with important new data concerning the information-processing locus of experimental effects of interest. However, detecting the onset of the LRP has proved difficult. The present study used computer simulations involving both human and artificial data, and both stimulus- and response-locked effects, to compare a wide variety of techniques for detecting and estimating differences in the onset latency of the LRP. Across the two sets of simulations, different techniques were found to be the most accurate and reliable for the analysis of stimulus- and response-locked data. On the basis of these results, it is recommended that regression-based methods be used to analyze most LRP data.     

Impaired response selection in schizophrenia: Evidence from the P3 wave and the lateralized readiness potential

Reaction times (RTs) are substantially prolonged in schizophrenia patients, but the latency of the P3 component is not. This suggests that the RT slowing arises from impairments in a late stage of processing. To test this hypothesis, 20 schizophrenia patients and 20 control subjects were tested in a visual oddball paradigm that was modified to allow measurement of the lateralized readiness potential (LRP), an index of stimulus-response translation processes. Difference waves were used to isolate the LRP and the P3 wave. Patients and control subjects exhibited virtually identical P3 difference waves, whereas the LRP difference wave was reduced in amplitude and delayed in latency in the patients. These results indicate that, at least in simple tasks, the delayed RTs observed in schizophrenia are primarily a consequence of impairments in the response selection and preparation processes that follow perception and categorization.     

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.     

Covert motor activity on NoGo trials in a task sharing paradigm: evidence from the lateralized readiness potential

Previous studies on task sharing propose that a representation of the co-actor's task share is generated when two actors share a common task. An important function of co-representation seems to lie in the anticipation of others' upcoming actions, which is essential for one's own action planning, as it enables the rapid selection of an appropriate response. We utilized measures of lateralized motor activation, the lateralized readiness potential (LRP), in a task sharing paradigm to address the questions (1) whether the generation of a co-representation involves motor activity in the non-acting person when it is other agent's turn to respond, and (2) whether co-representation of the other's task share is generated from one's own egocentric perspective or from the perspective of the actor (allocentric). Results showed that although it was the other agent's turn to respond, the motor system of the non-acting person was activated prior to the other's response. Furthermore, motor activity was based on egocentric spatial properties. The findings support the tight functional coupling between one's own actions and actions produced by others, suggesting that the involvement of the motor system is crucial for social interaction.     

An investigation of the auditory streaming effect using event-related brain potentials

There is uncertainty concerning the extent to which the auditory streaming effect is a function of attentive or preattentive mechanisms. The mismatch negativity (MMN), which indexes preattentive acoustic processing, was used to probe whether the segregation associated with the streaming effect occurs preattentively. In Experiment 1, alternating high and low those were presented at fast and slow paces while subjects ignored the stimuli. At the slow pace, tones were heard as alternating high and low pitches, and no MMN was elicited. At the fast pace a streaming effect was induced and an MMN was observed for the low stream, indicating a preattentive locus for the streaming effect. The high deviant did not elicit an MMN. MMNs were obtained to both the high and low deviants when the interval between the across-stream deviance was lengthened to more than 250 ms in Experiment 2, indicating that the MMN system is susceptible to processing constraints.     

Barking up the wrong free: readiness potentials reflect processes independent of conscious will

In the early 1980s, Libet found that a readiness potential (RP) over central scalp locations begins on average several hundred milliseconds before the reported time of awareness of willing to move (W). Haggard and Eimer Exp Brain Res 126(1):128–133, (1999) later found no correlation between the timing of the RP and W, suggesting that the RP does not reflect processes causal of W. However, they did find a positive correlation between the onset of the lateralized readiness potential (LRP) and W, suggesting that the LRP might reflect processes causal of W. Here, we report a failure to replicate Haggard and Eimer’s LRP finding with a larger group of participants and several variations of their analytical method. Although we did find a between-subject correlation in just one of 12 related analyses of the LRP, we crucially found no within-subject covariation between LRP onset and W. These results suggest that the RP and LRP reflect processes independent of will and consciousness. This conclusion has significant implications for our understanding of the neural basis of motor action and potentially for arguments about free will and the causal role of consciousness.     

Reflexive attention in touch: an investigation of event related potentials and behavioural responses

Exogenous attention has been extensively studied in vision but little is known about its behavioural and neural correlates in touch. To investigate this, non-informative tactile cues were followed after 800 ms by tactile targets and participants either detected targets or discriminated their location. Responses were slowed for targets at cued compared to uncued locations (i.e. inhibition of return (IOR)) only in the detection task. Concurrently recorded ERPs showed enhanced negativity for targets at uncued compared to cued locations at the N80 component and this modulation overlapped with the P100 component but only for the detection task indicating IOR may, if anything, be linked to attentional modulations at the P100. Further, cue-target interval analysis showed an enhanced anterior negativity contralateral to the cue side in both tasks, analogous to the anterior directed attention negativity (ADAN) previously only reported during endogenous orienting.     

Attributions, deception, and event related potentials: an investigation of the self-serving bias

Self-serving attributions occur when negative personal outcomes are ascribed to external circumstances and when positive outcomes are ascribed to internal factors. Individuals strategically employ the self-serving bias to maintain and protect positive self-views. The current study investigated the neural correlates of the self-serving bias using dense array EEG, giving 20 participants false (success or failure) feedback during a facial working memory task. Participants made self-serving attributions during the task, primarily following failure feedback. Voltage and source analyses in response to attribution stimuli revealed that, compared to self-serving responses, non-self-serving attributions were preceded by enhanced dorsomedial frontal cortex activity. This finding suggests that unbiased attributions require greater self-control, overriding the automatic tendency for self-enhancement.     

Attentional control in dysphoria: an investigation using the antisaccade task

We examined inhibitory mechanisms in dysphoria using direct measures of attentional control. Dysphoric and non-dysphoric participants performed standard and delayed versions of the antisaccade and prosaccade tasks with facial expressions as stimuli. Results showed higher error rates in the standard antisaccade task than in the delayed tasks, with the dysphoric group having higher error rates in response to emotional facial expressions, in particular happy expressions. Our findings indicate impaired attentional processing in response to emotional facial expressions, in particular happy expressions, in dysphoria. Implications for understanding the mechanisms underlying attentional control in dysphoria are discussed.