Erwin Hennighausen

Missed prime words within the attentional blink evoke an N400 semantic priming effect

When subjects identified a target among distractors in a rapid serial visual presentation task, the detection of a subsequent target is impaired (attentional blink). By measuring event-related potentials (ERPs) we investigated if the processing of an unidentified prime word elicits the N400 semantic priming effect. Subjects (N = 12) had to identify three target words among distractors in a rapid serial visual presentation task. We varied the association strength between a prime (second target) and a probe (third target). The detection of the prime was impaired. Missed primes did not elicit a P300, indicating that they were not explicitly recognized. Despite this difference between recognized and missed primes, the N400 effect was present in both cases. This result suggests that automatic spread of activation (ASA) can be evoked by missed primes within the attentional blink. It furthermore demonstrates that ASA is sufficient to evoke the N400 effect.

Event-related potentials during auditory and somatosensory discrimination in sighted and blind human subjects.

The objective of the present study was to test if and to what extent phasic and tonic event-related potentials of the human EEG may reflect phenomena of cortical plasticity. In particular, it was tested if the occipital cortex of blind subjects participates in the processing of non-visual stimuli. To this end, 12 blind and 12 blindfolded sighted subjects were tested in an auditory and a somatosensory discrimination task with 2 levels of discrimination difficulty. Slow and fast event-related potentials were recorded from 18 scalp electrodes. In addition to the negative slow waves found in sighted subjects over frontal and central sites during auditory and somatosensory discrimination, a pronounced negative wave was revealed in the blind also over occipital brain areas. These negative shifts were time-locked to the train of stimuli which had to be monitored with sustained attention, i.e. they rised and resolved with the beginning and the end of a 20-s discrimination time epoch. The P300 complex, on the other hand, which is a slow positive deflection over the posterior part of the scalp and which follows rare and task-relevant events 200-800 ms after stimulus onset was significantly smaller at occipital electrodes in the blind than in the sighted subjects. Combined with neurophysiological and neuronanatomical evidence originating from studies with visually deprived animals, these data suggest that the occipital cortex of blind human subjects is coactivated whenever the system is engaged in a task which requires sustained attention and is less effectively inhibited at the end of a perceptual time epoch. In total, the data cast doubt on the hypothesis that the occipital cortex of blind subjects participates in modality-specific non-visual information processing.

N200 in the Eriksen-Task: Inhibitory Executive Processes?

Abstract Event-related potentials were recorded (N = 18) in a hybrid go/no-go Eriksen flanker task to study the neural correlates of response inhibition. Three letters were assigned to either a left-hand, a right-hand, or a no-go response. These three letters appeared either as targets signaling the assigned response or as flankers surrounding the target. The lateralized readiness potentials revealed erroneous cortical response priming on go trials, in which the target and flankers were assigned to different hands, as well as on no-go trials, in which the flankers primed one of the two hands. Exactly these two conditions were accompanied by a fronto-central amplitude modulation of the N200, suggesting that this ERP component may reflect inhibitory executive functions. The data replicate and extend recent studies by Kopp, Rist, and Mattler (1996) and Kopp, Mattler, Goertz, and Rist (1996).

A correction method for DC drift artifacts

In order to cope with the problem of drift artifacts in ERP research a new off-line correction method is described. It estimates the DC drift from all prestimulus baselines of an experiment. For this end, an amplifier reset is performed at regular intervals and the DC off-set preceding any reset is stored. A regression is calculated between the prestimulus baseline amplitudes of consecutive trials and the time that has passed by. The amplitude trend which can be explained by either a linear or non-linear regression model is then subtracted from all data points. The power of the method is illustrated by two examples. The first shows that detrending increases the signal-to-noise ratio in ANOVA designs. The second shows that amplitude differences of event-related slow potentials, which appeared between the first and the second half of an experiment, could be explained by a non-linear drift component.

Distinct cortical activation patterns during long-term memory retrieval of verbal, spatial, and color information

Slow, DC-like event-related brain potentials (ERPs) were recorded from the scalp of 30 healthy young adults to test the hypothesis that distinct cortical areas are activated when different types of information are retrieved from long-term memory. Three groups of 10 subjects each were first trained with associations between either pictures and spatial positions (spatial condition), pictures and color patches (color condition), or nouns and nouns (verbal condition). All three experimental conditions were completely analogous with respect to the established associative structure, the learning procedure, the performance criterion, and the retrieval test that followed 1 day after learning. Slow event-related brain potentials being recorded during retrieval had a significantly distinct topography. The maximum of a DC-like negative wave was found in the verbal condition over the left frontal, in the spatial condition over the parietal, and in the color condition over the right occipital to temporal cortex. These results are consistent with the idea that memory representations are either down-loaded into or directly reactivated within those cortical processing modules in which the same material was handled during perception. Response times, on the other hand, revealed no difference between the three retrieval conditions. In each case RT increased monotonically, if more items had to be scanned. Thus, while the ERPs suggest the involvement of different cortical processors during memory search the response times suggest that a sequentially operating scanning mechanism applies to all of them.

Topographic differences of slow event-related brain potentials in blind and sighted adult human subjects during haptic mental rotation

Twelve blindfolded sighted, nine congenitally blind, and seven adventitiously blind subjects were tested in a haptic mental rotation task while slow event-related brain potentials in the EEG were recorded from 17 scalp locations. The overall topography of the slow wave pattern which prevailed during the task differed for sighted and for blind, but not for congenitally and adventitiously blind subjects. While the tactile stimuli were encoded, the blind showed a pronounced occipital and the sighted a pronounced frontal activation. The task-specific amplitude increment of a negative slow wave which can be understood as a manifestation of the process of mental rotation proper, showed a different topography for sighted and for blind subjects too. It had its maximum over central to parietal cortical areas in both groups, but it extended more towards occipital regions in the blind. In both groups, the effects were very similar to those observed in former studies with visual versions of the mental rotation task, i.e. the slow wave amplitude over central to parietal areas increased monotonously with an increasing angular disparity of the two stimuli to be compared. These results are discussed with respect to the question of whether visual deprivation in the blind can cause a reorganization of cortical representational maps.

Differences in incidental and intentional learning of sensorimotor sequences as revealed by event-related brain potentials.

The present study investigated differences in sequential learning between subjects who were or were not informed of the presence of a repeating sequence (intentional or incidental group, respectively). Subjects had to learn a 16-letter-long repeating sequence that was irregularly disrupted by deviating stimuli. Reaction times indicated that both groups learned the sequential regularities. Intentional learners showed a larger learning effect. Event-related brain potentials (ERPs) recorded during performance of the task showed a reliably enhanced amplitude for the N2b- and P3b-components for deviant letters for intentional learners, but not for incidental learners. These results are discussed in the context of models proposing that different neural structures are involved in implicit and explicit serial learning.

Response preparation begins before mental rotation is finished : Evidence from event-related brain potentials

Behavioral data (response time (RT) and accuracy) and psychophysiological data (event-related brain potentials of ERPs, and lateralized readiness potential or LRP) were studied in an experiment in which rotated alphanumeric characters were presented normally or mirror-reversed. In half of the trials, character classification (letter versus digit) determined whether or not the response was to be executed (go versus nogo) and parity determined the responding hand. In the other half, classification determined the responding hand and parity determined go versus nogo. LRP data indicated that response preparation occurred before mental rotation was finished. These data contradict strictly sequential discrete models of information processing and suggest continuous flow of information.

Comparing arithmetic and semantic fact retrieval: effects of problem size and sentence constraint on event-related brain potentials.

Event-related potentials were recorded with 61 electrodes from 16 students who verified either the correctness of single-digit multiplication problems or the semantic congruency of sentences. Multiplication problems varied in size and sentence fragments in constraint. Both semantic and arithmetic incongruencies evoked a typical N400 with a clear parieto-central maximum. In addition, numerically larger problems (8x7), in comparison to smaller problems (3x2), evoked a negativity starting at about 360 ms whose maximum was located over the right temporal-parietal scalp. These results indicate that the arithmetic incongruency and the problem-size effect are functionally distinct. It is suggested that the arithmetic and the semantic incongruency effects are both functionally related to a context-dependent spread of activation in specialized associative networks, whereas the arithmetic problem-size effect is due to rechecking routines that go beyond basic fact retrieval.

Event-related responses to pronoun and proper name anaphors in parallel and nonparallel discourse structures

The present study investigated event-related potential (ERP) effects of pronoun and proper name anaphors in both parallel and nonparallel discourse structures. Thirty-seven students processed 400 semantically different text passages. Each trial consisted of two sentences and a comprehension question. The first sentence introduced a protagonist who was referred to by an anaphoric word in the second sentence. The anaphoric word was either a pronoun or a repetition of the proper name of the protagonist and had either the same or a different syntactic role as its antecedent (subject or object). The sentences were presented word by word as rapid serial visual display. Event-related potentials were recorded from 61 scalp electrodes. In agreement with the parallel function strategy, nonparallel discourse structures required longer decision times and exhibited higher error rates than parallel structures. The ERPs revealed two effects: First, pronoun anaphors evoked a more pronounced negativity than proper name anaphors between 270 and 420 ms latency over the frontal cortex electrodes. Another relative negativity occurred between 510 and 600 ms over the parietal cortex electrodes. Second, anaphors in nonparallel positions were accompanied by a more pronounced negativity over the parietal cortex. These data support the idea that an anaphor in nonparallel position triggers extra processing steps, probably search processes in working memory which integrate currently encountered information with previously activated representations.