Hartmut Leuthold

Control Over Location-Based Response Activation in the Simon Task: Behavioral and Electrophysiological Evidence

In 4 Simon experiments the authors examined control over 2 routes of sensorimotor processing: response priming in the unconditional route and response selection via the conditional route. The Simon effect diminished as the frequency of noncorresponding trials increased. Location-based response priming was observed only when the stimulus followed a corresponding event but not after a noncorresponding trial. Therefore, the unconditional route appears to be suppressed whenever the task context indicates priming as potentially disadvantageous. Moreover, the task-irrelevant stimulus location was used for response selection as a function of correspondence probability. Although exact repetitions of stimulus-response sequences caused a marked speed-up of responses, this 3rd mechanism is independent of unconditional route suppression and frequency-based adjustments in the conditional route.

Early emotion word processing: Evidence from event-related potentials

Behavioral and electrophysiological responses were monitored to 80 controlled sets of emotionally positive, negative, and neutral words presented randomly in a lexical decision paradigm. Half of the words were low frequency and half were high frequency. Behavioral results showed significant effects of frequency and emotion as well as an interaction. Prior research has demonstrated sensitivity to lexical processing in the N1 component of the event-related brain potential (ERP). In this study, the N1 (135-180 ms) showed a significant emotion by frequency interaction. The P1 window (80-120 ms) preceding the N1 as well as post-N1 time windows, including the Early Posterior Negativity (200-300 ms) and P300 (300-450 ms), were examined. The ERP data suggest an early identification of the emotional tone of words leading to differential processing. Specifically, high frequency negative words seem to attract additional cognitive resources. The overall pattern of results is consistent with a time line of word recognition in which semantic analysis, including the evaluation of emotional quality, occurs at an early, lexical stage of processing.

Partial Advance Information and Response Preparation: Inferences From the Lateralized Readiness Potential

Response speed to a signal is faster when advance information about the forthcoming movement is provided before signal onset. Although this precuing effect is well established, the location of this saving in reaction time (RT) in the information-processing system is controversial. Some authors have claimed that the precuing effect resides at a motoric level, whereas others have suggested a nonmotoric locus. The present experiments used onset latencies of the lateralized readiness potential (LRP) to locate the precuing effect. The results of 2 experiments with a highly compatible (Experiment 1) and with an incompatible (Experiment 2) stimulus-response mapping indicate that this effect resides, at least partially, in the motoric portion of RT. In addition, the LRP amplitude before signal appearance increased with the amount of advance information, supporting a muscle-specific preparation hypothesis.

Mechanisms of Priming by Masked Stimuli: Inferences From Event-Related Brain Potentials

A metacontrast procedure was combined with the recording of event-related potentials (ERPs) to examine the mechanisms underlying the priming effect exerted by masked visual stimuli (primes) on target processing. Participants performed spatially arranged choice responses to stimulus locations. The relationship between prime and target locations (congruity) and the mapping between target and response locations (compatibility) were factorially manipulated. Although participants were unaware of prime locations, choice responses were faster for congruent than incongruent conditions irrespective of the mapping. Visual ERP components and the onset of the lateralized readiness potential (LRP), an index of specific motor activation, revealed that neither perceptual nor preselection processes contributed to the congruity effect. However, the LRP waveform indicated that primes activated responses that fit the stimulus-response mapping. These results support the view that sensorimotor processing of masked stimuli is functionally distinct from their conscious perception.

ERP correlates of error processing in spatial S-R compatibility tasks

When participants in reaction time (RT) tasks commit errors, the event-related brain potential (ERP) has been reported to show a negative-going deflection, the so-called error negativity (NE), followed by a positive-going component (PE). To examine the locus of NE within information processing and in order to test whether two successive P300 components are elicited in error trials, we manipulated the duration of perception- and response-related processing stages in visual and auditory spatial S-R compatibility tasks. Our results suggest that NE is closely coupled to motoric processes and elicited when information about the incorrectly executed response is available. The latency of the subsequent PE was influenced by perceptual as well as by response-related variables. Its scalp topography was not different from that of the P300 in correct trials and from a preceding positivity in incorrect trials. Therefore, we concluded that an additional error-related P300 is elicited by error events presumably relating to error recognition and the updating of the error context.

Preparing for Action: Inferences from CNV and LRP

Abstract The execution of efficient motor actions is often preceded by preparation in the central nervous system. Although this kind of preparation cannot be observed directly, it, nevertheless, shortens reaction time. In this review we focus on two types of action preparation, namely event and temporal preparation. In particular, we show how modern event-related brain potential techniques can be employed to determine both the covert processes underlying such preparatory effects as well as their locus within the processing chain between stimulus input and action output.

Motor programming of response force and movement direction

Effects of movement advance information were assessed on the prestimulus amplitude of the lateralized readiness potential (LRP), on the contingent negative variation (CNV), and on reaction time (RT). In a precuing paradigm with movement parameters hand, direction, and force, partial precues provided advance information about either hand alone, hand plus force, or hand plus direction, and the full precue specified all response parameters. The full precue produced the shortest RTs and the largest CNV amplitude, precuing hand and force or hand and movement direction produced somewhat slower RTs and a somewhat smaller CNV amplitude, and precuing only hand yielded slowest RTs and the smallest CNV amplitude. In contrast, the LRP amplitude was largest for the full precue and was the same for the remaining precues. The CNV appears to index the central assembling of a motor program, and the LRP represents the implementation of the program at more peripheral levels.

Neural correlates of advance movement preparation: a dipole source analysis approach

This study examined cortical motor structures that are involved in preprogramming and execution of movements. In two independent experiments a response precuing task was employed that combined the recording of movement-related brain potentials (MRPs) with spatio-temporal source localization. Behavioral and MRP results indicated the utilization of advance information about movement direction and hand. Dipole source modeling of foreperiod MRPs revealed a reliable three-dipole solution with sources located in lateral and medial brain regions anterior to the precentral gyrus. These dipoles were located in the lateral premotor area (PMA) and supplementary/cingulate motor areas (SMA/CMA). Activity of the medial dipole increased with the extent of advance motor preparation, whereas lateral dipole activity revealed parallel preparation of both response hands when only partial information about movement direction was available. The dissociation in the strength and the onset of medial and lateral dipole activity indicated two phases of motor preparation. We propose that medial motor areas like SMA and CMA are involved in the assembling and selection of abstract movement programs, whereas lateral PMA and primary motor cortex are involved in effector-specific motor preparation.

Distinguishing neural sources of movement preparation and execution: An electrophysiological analysis

The present study examined lateralized event-related potentials (L-ERPs) associated with movement preparation and execution. In a response precuing task that involved hand and foot movements a precue conveyed either information about side and effector, side alone, or no information. Advance movement preparation was indicated by RT shortening with increasing amount of precue information. L-ERPs revealed during the preparatory interval an initial parietal activity when movement side was precued. Later in the preparatory interval L-ERPs revealed a polarity inversion for foot versus hand movements when effector and side were specified in advance. This polarity inversion showed up also in execution-related L-ERP waveforms. Comparison of preparation- versus execution-related brain signals yielded topographic differences and dissimilar dipole sources for hand-related L-ERP activity. We take present findings to indicate that brain generators within the parietal lobe and anterior MI are hierarchically related to precue-induced motor preparation, whilst posterior MI is associated with motor execution functions.

Consciousness of attention and expectancy as reflected in event-related potentials and reaction times

The effects of conscious expectancies and attention on event-related potentials (ERP) and choice reaction times (RT) and their modulation by stimulus sequence were studied. Subjects retrospectively reported their expectancy of, and attention to, the terminal tones of short series. ERPs and RTs showed the usual sequential effects that were modulated by practice. As ratings were affected by only a few of the stimulus sequence, conscious access to sequence-based expectancy or attention appears to be fragmentary. Increased P300 amplitude with attention indicates conscious access to processing capacity. RTs and P300 latencies suggest stimulus processing time to decrease with sequence-based and consciously accessible expectancy. Differential effects of stimulus sequences and conscious expectancies on P300 amplitude indicate influences of two varieties of expectancy.