Jutta Stahl

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.

Predicting Perceptual Decision Biases from Early Brain Activity

Perceptual decision making is believed to be driven by the accumulation of sensory evidence following stimulus encoding. More controversially, some studies report that neural activity preceding the stimulus also affects the decision process. We used a multivariate pattern classification approach for the analysis of the human electroencephalogram (EEG) to decode choice outcomes in a perceptual decision task from spatially and temporally distributed patterns of brain signals. When stimuli provided discriminative information, choice outcomes were predicted by neural activity following stimulus encoding; when stimuli provided no discriminative information, choice outcomes were predicted by neural activity preceding the stimulus. Moreover, in the absence of discriminative information, the recent choice history primed the choices on subsequent trials. A diffusion model fitted to the choice probabilities and response time distributions showed that the starting point of the evidence accumulation process was shifted toward the previous choice, consistent with the hypothesis that choice priming biases the accumulation process toward a decision boundary. This bias is reflected in prestimulus brain activity, which, in turn, becomes predictive of future decisions. Our results provide a model of how non-stimulus-driven decision making in humans could be accomplished on a neural level.

Dynamics of response-conflict monitoring and individual differences in response control and behavioral control : An electrophysiological investigation using a stop-signal task

OBJECTIVES The aim of the present study was to investigate the functional significance of error (related) negativity Ne/ERN and individual differences in human action monitoring. A response-conflict model of Ne/ERN should be tested applying a stop-signal paradigm. After a few modifications of Ne/ERN response-conflict theory (Yeung N, Botvinick MM, Cohen JD. The neural basis of error detection: conflict monitoring and the error-related negativity. Psychological Review 2004:111(4);931-959), strength and time course of response conflict could be modeled as a function of stop-signal delay. METHOD In Experiment 1, 35 participants performed a visual two-choice response-time task but tried to withhold the response if an auditory stop signal was presented. Probability of stopping errors was held at 50% using variable delays between visual and auditory stimuli. Experiment 2 (n=10) employed both auditory go and stop signals and confirmed that Ne/ERN effects are due to conflict induced by the auditory stop signal, and not the mere presence or absence of an additional stimulus. RESULTS As predicted, amplitudes of both the stimulus-locked and response-locked Ne/ERN were largest for non-stopped responses, followed by successfully stopped and go responses. However, independently of response type Ne/ERN also increased with increasing stop-signal delay. Since longer delay invokes stronger response conflict, results specifically support the notion of Ne/ERN reflecting response-conflict monitoring. Furthermore, individual differences related to measures of response control and behavioral control were observed. Both low response control estimated from stop-task performance and high psychometric impulsivity were accompanied by smaller Ne/ERN amplitude on stop trials, suggesting reduced response-conflict monitoring. CONCLUSIONS The present study supported the response-conflict view of Ne/ERN. Furthermore, the observed relationship between impulsivity and Ne/ERN amplitude suggested that individuals with low behavioral control were characterized by lower activity in anterior cingulate cortex, the neural generator of Ne/ERN, in situations of strong response conflict. SIGNIFICANCE The present study, for the first time, employed a stop-signal paradigm to verify predictions regarding the temporal dynamics of response-conflict processing as derived from response-conflict theory of ERN.

Differences in personality characteristics between body-modified and non-modified individuals: associations with individual personality traits and their possible evolutionary implications

After a long history of negative stigmatisation, the practices of tattooing and body piercing have become fashionable in the last decade. Today, 10% of the population in modern western societies have some form of body modification. The aim of this study was to quantify the demographic and personality traits of tattooed and pierced individuals and to compare them with a control group of individuals without body modifications. These comparisons are based on questionnaires completed by 359 individuals that investigate the details of body modification, and which incorporate five personality scales. We describe several sex differences in ornament style and location. We found no relevant differences between modified and non‐modified individuals in relation to demographic variables. This indicates that some of the traditional attitudes towards tattoos and piercings appear to be outdated. However, we found striking differences in personality traits which suggest that body‐modified individuals are greater sensation seekers and follow a more unrestricted mating strategy than their non‐modified contemporaries. We discuss these differences in light of a potential signalling function of tattoos and piercings in the mating context. Copyright

Error detection and the use of internal and external error indicators: An investigation of the first-indicator hypothesis

The error-related negativity (Ne/ERN) and the feedback-related negativity (FRN) are electrophysiological markers of error processing, which originate from the medial frontal cortex. A digit-flanker task with a strict individual response time (RT) limit was employed to test the first-indicator hypothesis. This hypothesis postulates an increase in medial frontal brain activity only after the first, internal (response related) or external (feedback related), indicator of an incorrect response. In order to examine whether this hypothesis also holds for RT errors, a simple digit-flanker task was employed. The participants (n=14) committed three error types: a hand error, an RT error, and a combination of hand and RT error (double error). It was assumed that they were able to detect hand errors at the time of responding, whereas reliable RT error detection should require an external feedback. The experimental findings demonstrated that hand errors were followed by an increase in Ne/ERN amplitude, but not in FRN amplitude. RT errors committed marginally beyond the RT limit showed an increase in FRN amplitude but not in Ne/ERN amplitude, whereas RT errors that were far beyond RT limit affected Ne/ERN, but not FRN. The present findings supported the first-indicator hypothesis. Evidence was given of an error detection system, which was sensitive to a violation of an RT limit.

Multiple Sources of Positive- and Negative-Priming Effects: An Event-Related Potential Study

Event-related potential correlates of positive priming (PP) and negative priming (NP) were investigated in order to further elucidate the cognitive mechanisms involved. Thirty-six participants performed both an identity- and a location-based priming task. Repeating the target stimulus/location from the immediately preceding display produced behavioral PP. With localization, but not with identification, behavioral NP was observed when the target stimulus/location matched the preceding distractor stimulus/location. Smaller P300 amplitude accompanied identity-based PP, suggesting persisting target-specific activation. The lateralized readiness potential, an index of correct/incorrect response activation, indicated persisting central motor activation as another source of PP. Both location-based PP and NP were accompanied by reduced P1/N1 and P300 amplitudes, pointing to the involvement of inhibition of return in location-based priming. The results support the view that multiple brain processes underlie behavioral priming.

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.

Early Activity in the Lateralized Readiness Potential Suggests Prime-Response Retrieval as a Source of Negative Priming

Negative priming (NP) refers to increased response time (RT) for a probe target that was a distractor in a preceding prime presentation (distractor-target shift, DT), compared to novel targets. The present study used the lateralized readiness potential (LRP) to investigate, in a four-choice identification task, a novel episodic-retrieval explanation of NP introduced by Rothermund, Wentura, and de Houwer (2005). This theory proposes that retrieval reactivates the prime response which interferes with selection of the correct probe response, thereby producing NP. 20 participants responded to pairs of red and blue digits, contingent on the identity of the digit presented in the target color. Behavioral NP involved RT increase by 16 ms. With shift trials (different hands used for prime and probe responses), in the DT condition LRP onset was delayed relative to control. By contrast, earlier LRP onset was observed for DT relative to control with no-shift trials (same hand used for prime and probe responses). Behavioral NP effects showed similar magnitude for shift and no-shift trials. Results support the Rothermund et al. (2005) theory of prime-response retrieval.

Response-time corrected averaging of event-related potentials.

OBJECTIVE The present study presents a novel approach to averaging of event-related potentials (ERPs). Acknowledging latency variability of late ERP components as related to performance fluctuations across trials should improve the assessment of late portions of the ERP. METHODS Prior to the averaging procedure stimulus-to-response epochs in the electroencephalogram (EEG) were expanded/compressed in time to match mean RT in a certain condition and participant. By means of several mathematical functions RT variability was differentially distributed over late vs. early portions of the ERP. Data from 20 participants from two conditions of an identity-based priming task were analyzed using traditional stimulus- and response-locked averaging, as well as four different RT-corrected averaging procedures. RESULTS Area under the curve as an index of precision of LPC assessment was reliably enhanced for certain RT-corrected procedures relative to traditional ERP averaging. Moreover, a priming effect on amplitude of a distinct LPC subcomponent which could not be confirmed with traditional stimulus-locked averaging was reliably born out using a cubic RT-correction procedure. CONCLUSIONS RT-corrected ERP averaging can outperform traditional ERP averaging in the assessment of late portions of the ERP, and experimental effects upon. SIGNIFICANCE Cognitive ERP researchers may take advantage of the improved capability of RT-corrected averaging to establish experimental effects on amplitudes in the late ERP range.

Differences in the transmission of sensory input into motor output between introverts and extraverts: Behavioral and psychophysiological analyses

The present study was designed to investigate extraversion-related individual differences in the speed of transmission of sensory input into motor output. In a sample of 16 introverted and 16 extraverted female volunteers, event-related potentials, lateralized readiness potentials (LRPs), and electromyogram (EMG) were recorded as participants performed a visual choice reaction time task. As additional behavioral indicators of performance, measures of reaction time (RT) and response dynamics were obtained. Although extraversion-related differences were found neither for behavioral measures nor for the N1 and P3 components of the evoked potential, introverts showed a reliably shorter latency in stimulus-locked LRP than extraverts. This latter finding supports the notion of faster stimulus analysis in introverts compared to extraverts. Furthermore, there was no indication of extraversion-related individual differences in speed of response organization and response execution as indicated by response-locked LRP and EMG latencies, respectively. However, a significantly higher EMG amplitude observed with introverts pointed to a less accurately adjusted motor output system of introverts compared to extraverts.