Biomedical subjects

Stefan Frisch

Publications and source records attributed to Stefan Frisch.

13 recordsLinked to original sources

PubMed2005

Topographic voltage and coherence mapping of brain potentials by means of the symbolic resonance analysis.

We apply the recently developed symbolic resonance analysis to electroencephalographic measurements of event-related brain potentials (ERPs) in a language processing experiment by using a three-symbol static encoding with varying thresholds for analyzing the ERP epochs, followed by a spin-flip transformation as a nonlinear filter. We compute an estimator of the signal-to-noise ratio (SNR) for the symbolic dynamics measuring the coherence of threshold-crossing events. Hence, we utilize the inherent noise of the EEG for sweeping the underlying ERP components beyond the encoding thresholds. Plotting the SNR computed within the time window of a particular ERP component (the N400) against the encoding thresholds, we find different resonance curves for the experimental conditions. The maximal differences of the SNR lead to the estimation of optimal encoding thresholds. We show that topographic brain maps of the optimal threshold voltages and of their associated coherence differences are able to dissociate the underlying physiological processes, while corresponding maps gained from the customary voltage averaging technique are unable to do so.

Algorithms↗

PubMed2005

The resolution of case conflicts from a neurophysiological perspective.

We present two ERP experiments examining the resolution of language processing conflicts involving the multidimensional linguistic feature case, which determines processing in both syntactic and interpretive respects. Ungrammatical German structures with two identically case-marked arguments (double subject or double object constructions) were tested. In earlier studies, double subject constructions have been shown to elicit a biphasic pattern consisting of an N400 effect (a marker of thematic integration problems) followed by a P600 effect (a marker of syntactic ill-formedness). Here, we compare double nominative (subject case) constructions with double datives (indirect object case; Experiment 1) and double accusatives (direct object case; Experiment 2). All types of double case ungrammaticalities elicited a biphasic N400-P600 response. However, double datives differed from double nominatives in that they elicited a larger P600, suggesting that the ill-formedness is more salient in structures with two dative arguments. Double accusatives, by contrast, elicited a stronger N400 in comparison to double nominatives, suggesting that they induce more severe semantic-thematic integration problems. The results demonstrate that the human language comprehension system is sensitive to fine grained linguistic distinctions between different cases and utilizes these in its attempts to solve processing conflicts.

Adolescent↗

PubMed2005

Diagnosis and repair of negative polarity constructions in the light of symbolic resonance analysis.

In a post hoc analysis, we investigate differences in event-related potentials of two studies (Drenhaus et al., 2004, Drenhaus et al., to appear, Saddy et al., 2004a and Saddy et al., 2004b) by using the symbolic resonance analysis (Beim Graben & Kurths, 2003). The studies under discussion, examined the failure to license a negative polarity item (NPI) in German: Saddy et al. (2004a) reported an N400 component when the NPI was not accurately licensed by negation; Drenhaus et al., 2004 and Drenhaus et al., to appear considered additionally the influence of constituency of the licensor in NPI constructions. A biphasic N400-P600 response was found for the two induced violations (the lack of licensor and the inaccessibility of negation in a relative clause). The symbolic resonance analysis (SRA) revealed an effect in the P600 time window for the data in Saddy et al., which was not found by using the averaging technique. The SRA of the ERPs in Drenhaus et al., showed that the P600 components are distinguishable concerning the amplitude and latency. It was smaller and earlier in the condition where the licensor is inaccessible, compared to the condition without negation in the string. Our findings suggest that the failure in licensing NPIs is not exclusively related to semantic integration costs (N400). The elicited P600 components reflect differences in syntactic processing. Our results confirm and replicate the effects of the traditional voltage average analysis and show that the SRA is a useful tool to reveal and pull apart ERP differences which are not evident using the traditional voltage average analysis.

Analysis of Variance↗

PubMed2005

Finding needles in haystacks: symbolic resonance analysis of event-related potentials unveils different processing demands.

Previous ERP studies have found an N400-P600 pattern in sentences in which the number of arguments does not match the number of arguments that the verb can take. In the present study, we elaborate on this question by investigating whether the case of the mismatching object argument in German (accusative/direct object versus dative/indirect object) affects processing differently. In general, both types of mismatches elicited a biphasic N400-P600 response in the ERP. However, traditional voltage average analysis was unable to reveal differences between the two mismatching conditions, that is, between a mismatching accusative versus dative. Therefore, we employed a recently developed method on ERP data analysis, the symbolic resonance analysis (SRA), where EEG epochs are symbolically encoded in sequences of three symbols depending on a given parameter, the encoding threshold. We found a larger proportion of threshold crossing events with negative polarity in the N400 time window for a mismatching dative argument compared to a mismatching accusative argument. By contrast, the proportion of threshold crossing events with positive polarity was smaller for dative in the P600 time window. We argue that this difference is due to the phenomenon of "free dative" in German. This result also shows that the SRA provides a useful tool for revealing ERP differences that cannot be discovered using the traditional voltage average analysis.

Adult↗

PubMed2005

Detection of early cognitive processing by event-related phase synchronization analysis.

In order to investigate the temporal characteristics of cognitive processing, we apply multivariate phase synchronization analysis to event-related potentials. The experimental design combines a semantic incongruity in a sentence context with a physical mismatch (color change). In the ERP average, these result in an N400 component and a P300-like positivity, respectively. Synchronization analysis shows an effect of global desynchronization in the theta band around 288 ms after stimulus presentation for the semantic incongruity, while the physical mismatch elicits an increase of global synchronization in the alpha band around 204 ms. Both of these effects clearly precede those in the ERP average. Moreover, the delay between synchronization effect and ERP component correlates with the complexity of the cognitive processes.

Adult↗

PubMed2004

Fractionating language comprehension via frequency characteristics of the human EEG.

We present a new analysis technique for EEG research on language comprehension, which dissociates superficially indistinguishable event-related potential (ERP) components. A frequency-based analysis differentiated between two apparently identical but functionally distinct N400 effects in terms of activity in separable frequency bands, and whether the activity stemmed from increased power or phase locking. Whereas linguistic problem detection is associated with theta band activity (approximately 3.5-7.5 Hz), conflict resolution correlates with activity in the delta band (1-3 Hz). The data further differentiate between the neuronal processing mechanisms involved in different types of conflict resolution on the basis of frequency characteristics (power vs phase locking).

Conflict, Psychological↗

PubMed2004

Word category and verb--argument structure information in the dynamics of parsing.

One of the core issues in psycholinguistic research concerns the relationship between word category information and verb-argument structure (e.g. transitivity) information of verbs in the process of sentence parsing. In two experiments (visual versus auditory presentation) using event-related brain potentials (ERPs), we addressed this question by presenting sentences in which the critical word simultaneously realized both a word category and a transitivity violation. ERPs for sentences with both types of violation clustered with the patterns for sentences with a word category violation only, but were different from the patterns elicited by argument structure violations in isolation, since only the latter elicited an N400 ERP component. The finding that an argument structure violation evoked an N400 only if the phrase structure of the respective sentence was correct suggests that a successful integration of the word category information of a verb functionally precedes the application of its argument structure information.

Adult↗

PubMed2004

Is it positive or negative? on determining ERP components.

In most experiments using event-related brain potentials (ERPs), there is a straightforward way to define--on theoretical grounds-which of the conditions tested is the experimental condition and which is the control condition. If, however, theoretical assumptions do not give sufficient and unambiguous information to decide this question, then the interpretation of an ERP effect becomes difficult, especially if one takes into account that certain effects can be both a positivity or a negativity on the basis of the morphology of the pattern as well as with respect to peak latency (regard for example, N400 and P345). Exemplified with an ERP experiment on language processing, we present such a critical case and offer a possible solution on the basis of nonlinear data analysis. We show that a generalized polarity histogram, the word statistics of symbolic dynamics, is in principle able to distinguish negative going ERP components from positive ones when an appropriate encoding strategy, the half wave encoding is employed. We propose statistical criteria which allow to determine ERP components on purely methodological grounds.

Algorithms↗

PubMed2003

The neurophysiological basis of word order variations in German.

This paper aims to dissociate grammatical and general cognitive (e.g., working-memory based) accounts of the processing costs elicited by word order variations in German. To this end, we present a study using event-related brain potentials (ERPs), in which dislocated arguments were instantiated either by non-pronominal or by pronominal noun phrases. This manipulation allows for a dissociation of the two competing accounts, since only a dislocation of non-pronominal arguments gives rise to a non-canonical structure. The results show that (a) in sentences with non-pronominal arguments, the determiner of a non-canonical noun phrase elicited a broadly distributed negativity, and (b) in sentences with pronominal arguments, no differences were observed for object- vs. subject-initial word orders. These findings show that the human parser is sensitive to fine-grained grammatical regularities. We therefore argue that the negativity is a reflection of a local syntactic mismatch, rather than of an increase in working-memory load.

Adult↗

PubMed2003

Why the P600 is not just a P300: the role of the basal ganglia.

One of the important issues in event-related brain potential research is whether the language-related P600 and the P300 oddball effect are distinct components or not. We addressed this question by testing 14 aphasic patients, half of them with lesions including the basal ganglia and half of them with temporo-parietal lesions, in both an auditory oddball task and an experiment with auditory presented verb inflection violations. Whereas both patient groups displayed a clear P300 effect in the oddball experiment, only the group with temporo-parietal lesions showed a P600 in the language experiment. These data indicate that the basal ganglia seem to play a crucial role in the modulation of the P600, but not of the P300 component.

Aphasia↗

PubMed2003

Syntactic language processing: ERP lesion data on the role of the basal ganglia.

The role of the basal ganglia in syntactic language processing was investigated with event-related brain potentials in fourteen neurologically impaired patients. Seven of these patients had basal ganglia lesions while 7 other patients primarily had lesions of the left temporo-parietal region excluding the basal ganglia. All patients listened to sentences that were either correct or included a verb argument structure violation. In previous experiments this type of violation elicited a biphasic pattern of an N400-P600 complex in young healthy participants. While the N400 may result from incorrect semantic-thematic role assignment, the P600 reflects the fact that verb information does not license the syntactic structure at present. Results of the patient experiment revealed a double dissociation: patients with left temporo-parietal lesions only show a P600, whereas patients with lesions of the basal ganglia showed no P600, but a negativity with extended duration that resembled an N400. The latter pattern not only confirms previous reports that the basal ganglia modulate the P600 but extends these results by showing that the N400 as a late semantic-thematic integration process appears partially modulated by the basal ganglia.

Adult↗

PubMed2002

The P600 as an indicator of syntactic ambiguity.

In a study using event-related brain potentials, we show that the current characterization of the P600 component as an indicator of revision processes (reanalysis and repair) in sentence comprehension must be extended to include the recognition of syntactic ambiguity. By comparing the processing of ambiguous and unambiguous sentence constituents in German, we show that the P600 is elicited when our language processing system has syntactic alternatives at a certain item given in the input string. That the P600 is sensitive to syntactic ambiguity adds crucial evidence to current debates in psycholinguistic modelling, as the results clearly favour parallel models of syntactic processing which assume that ambiguity is recognized and costly.

Adult↗

PubMedDate not supplied

Processing polarity items: contrastive licensing costs.

We describe an experiment that investigated the failure to license polarity items in German using event-related brain potentials (ERPs). The results reveal distinct processing reflexes associated with failure to license positive polarity items in comparison to failure to license negative polarity items. Failure to license both negative and positive polarity items elicited an N400 component reflecting semantic integration cost. Failure to license positive polarity items, however, also elicited a P600 component. The additional P600 in the positive polarity violations may reflect higher processing complexity associated with a negative operator. This difference between the two types of violation suggests that the processing of negative and positive polarity items does not involve identical mechanisms.

Adult↗