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Biomedical subjects

A Mecklinger

Publications and source records attributed to A Mecklinger.

At least 37 records · Page 2Linked to original sources
PubMed1999

The functional neuroanatomy of novelty processing: integrating ERP and fMRI results.

Recent research indicates that non-tonal novel events, deviating from an ongoing auditory environment, elicit a positive event-related potential (ERP), the novel P3. Although a variety of studies examined the neural network engaged in novelty detection, there is no complete picture of the underlying brain mechanisms. This experiment investigated these neural mechanisms by combining ERP and functional magnetic resonance imaging (fMRI). Hemodynamic and electrophysiological responses were measured in the same subjects using the same experimental design. The ERP analysis revealed a novel P3, while the fMRI responses showed bilateral foci in the middle part of the superior temporal gyrus. When subjects attended to the novel stimuli only identifiable novel sounds evoked a N4-like negativity. Subjects showing a strong N4-effect had additional fMRI activation in right prefrontal cortex (rPFC) as compared to subjects with a weak N4-effect. This pattern of results suggests that novelty processing not only includes the registration of deviancy but may also lead to a fast access and retrieval of related semantic concepts. The fMRI activation pattern suggests that the superior temporal gyrus is involved in novelty detection, whereas accessing and retrieving semantic concepts related to novel sounds additionally engages the rPFC.

Acoustic Stimulation↗
PubMed1998

Double dissociation of processing temporal and spatial information in working memory.

Based on the converging evidence supporting the view of domain specific object and spatial working memory processes, the question was addressed whether the property of domain specificity holds equally for temporal information. Using a selective interference paradigm the objective was to test a dissociation of the processing of temporal duration and spatial location information in working memory of intact human subjects. Subjects performed a temporal and a spatial memory task in which they were required to indicate whether the study and the test stimuli were the same or different in duration (temporal memory) or in location (spatial memory) as primary tasks. Both primary tasks were combined with three types of interference tasks, a spatial classification memory task, a temporal classification memory task and a non-interference baseline task--to be performed in-between the presentation of study and test stimuli. Memory for temporal duration was shown to be impaired by the temporal classification task but not by the spatial classification task; memory for spatial position showed the opposite pattern of impairment. These data thus provide evidence for the view that temporal and spatial working memory contents are subject to selective interference, reflecting a functional dissociation in the processing of temporal duration and spatial location information. The results are interpreted as evidence for the domain specificity in the processing of temporal information in working memory.

Adult↗
PubMed1998

On the modularity of recognition memory for object form and spatial location: a topographic ERP analysis.

Event-related potentials from 61 scalp sites were used to examine the brain processes subserving recognition memory for object forms and spatial locations. Subjects memorized line drawings of highly familiar objects and their spatial locations within a two-dimensional matrix. Prior to the test phases a cue indicated whether object-based or spatially-based recognition judgements were required. Recognition judgements were faster and more accurate for spatially-based than for object-based judgements. A variety of topographical differences in the ERP waveforms as a function of recognition task emerged: First, when the cue indicated that object-based judgements were required, negative slow wave activity extending for several hundred ms with a maximum at frontal recording sites was obtained. Conversely when spatially-based judgements were required, slow wave activity developed over parieto-occipital areas. Second, early portions of the old/new effects evoked by the test items (i.e. 300-600 ms after stimulus onset) showed a similar anterior-posterior dissociation as a function of recognition task. Third, for object-based, but not for spatially-based, judgements, late old/new effects (i.e. 700-1600 ms) were found with a clear maximum at right frontal recordings. The results are consistent with the view that functionally and anatomically different brain systems are involved in recognition memory for object form and spatial location. They further suggest that the retrieval of object forms involves conceptual semantic integration processes.

Adult↗
PubMed1998

A MEG analysis of the P300 in visual discrimination tasks.

Based on recent research that indicated that P300 scalp topography varies as a function of task and/or information to be processed, this study examined scalp-recorded magnetic fields correlated with the P300 by means of whole-head magnetoencephalography. Subjects performed two discrimination tasks, in which targets, defined on either object or spatial characteristics of the same visual stimuli, had to be discriminated. Based on the across-subject root mean square (RMS) functions a sequence of 4 components could be identified in both tasks, N1m, P3m, and two later components, which, based on their estimated neuronal sources, were classified as representing motor processes during and following the manual responses to target stimuli. Reliable between-task differences in source localization were obtained for the P3m component, but not for the other components. Inferior-medial sources were found for the P3m evoked by both spatial and object targets, with these sources being located about 3.5 cm more anterior for object targets. These results suggest that different neuronal sources, possibly located in subcortical regions in the vicinity of the thalamus, contribute to the P3m evoked by target stimuli defined by either object or spatial stimulus characteristics.

Adult↗
PubMed1998

Working memory constraints on syntactic ambiguity resolution as revealed by electrical brain responses.

Parsing strategies in temporarily ambiguous sentences were investigated in readers with different sentence memory capacities using event-related brain potentials (ERPs). Readers with a high memory span as well as readers with a low memory span were required to read subject and object relative sentences which were either ambiguous until the last word (late disambiguation) or were disambiguated by case marking either the clause initial pronoun (immediate disambiguation) or the noun phrase following it (early disambiguation). ERPs registered during sentence reading elicited the following effects: In the late disambiguation condition, high span readers, but not low span readers, displayed a more positive going wave at the disambiguating number marked auxiliary for the object relative sentences than for the subject relative sentences. This positivity is taken to reflect processes of revision that become necessary at the disambiguating element if the initial structure considered is a subject relative clause. When case marking was available in the clause initial at the relative pronoun, both high and low span readers showed a positivity at the disambiguating element for the object relative sentences, suggesting the immediate use of case marking information for revision. When case marking was available in the noun phrase following an ambiguous pronoun both groups showed no clear effect of revision at the disambiguating element, but only at the sentence final number marked auxiliary. This non-immediate use of the case marking information seems to be due to an inherent ambiguity in the German case marking system which interacts with the disambiguating element's position in the sentence. The combined data indicate that morphological information can be used immediately by high and low span readers to resolve syntactic ambiguity during sentence processing whenever the information given is clearly unambiguous. In addition they suggest that possible processing differences in ambiguity resolution between high and low span readers may only appear when the ambiguous regions are long.

Adult↗
PubMed1998

Event-related potential evidence for a specific recognition memory deficit in adult survivors of cerebral hypoxia.

Transient global ischaemia due to cardiac arrest may lead to profound neuropsychological disorders. Recent research indicates that memory processes are particularly impaired after hypoxic brain injury. Visual recognition memory functions were examined in these patients by means of event-related potential (ERP) and performance data. Eight chronic hypoxic patients, matched with controls for sex and age, performed a visual recognition memory task requiring recognition judgements for either object forms or spatial locations and a visual classification (i.e. oddball) task that imposed negligible memory demands. Reliable P300 oddball effects were obtained both for patients and for controls, whereas the two groups differed in P300 latency and P300 scalp topography. In the memory task, old/new effects (i.e. larger ERP waveforms for previously studied than for unstudied items) were found for the controls. In contrast, in patients these old/new effects were absent or even inverted in polarity while recognition performance was well above chance level, except for one patient. These results suggest that recognition, based on the retrieval of an item's study episode, is degraded in patients who have suffered a period of transient global ischaemia. In the light of the patients' above-chance level of recognition performance and the outcome of post hoc analysis of practice-related changes in recognition performance, it is argued that the patients' memory disorders are best characterized as a degradation of explicit memory functions such as episodic retrieval of a study episode. Implicit functions such as cognitive skill learning were intact.

Adult↗
PubMed1998

Recognition memory for object form and object location: an event-related potential study.

In this study, the processes associated with retrieving object forms and object locations from working memory were examined with the use of simultaneously recorded event-related potential (ERP) activity. Subjects memorized object forms and their spatial locations and made either object-based or location-based recognition judgments. In Experiment 1, recognition performance was higher for object locations than for object forms. Old responses evoked more positive-going ERP activity between 0.3 and 1.8 sec poststimulus than did new responses. The topographic distribution of these old/new effects in the P300 time interval was task specific, with object-based recognition judgments being associated with anteriorly focused effects and location-based judgments with posteriorly focused effects. Late old/new effects were dominant at right frontal recordings. Using an interference paradigm, it was shown in Experiment 2 that visual representations were used to rehearse both object forms and object locations in working memory. The results of Experiment 3 indicated that the observed differential topographic distributions of the old/new effects in the P300 time interval are unlikely to reflect differences between easy and difficult recognition judgments. More specific effects were obtained for a subgroup of subjects for which the processing characteristics during location-based judgments presumably were similar to those in Experiment 1. These data, together with those from Experiment 1, indicate that different brain areas are engaged in retrieving object forms and object locations from working memory. Further analyses support the view that retrieval of object forms relies on conceptual semantic representation, whereas retrieving object locations is based on structural representations of spatial information. The effects in the later time intervals may play a functional role in post-retrieval processing, such as recollecting information from the study episode or other processes operating on the products of the retrieval process, and presumably are mediated by right frontal cortical areas. The results support the view of functionally dissociable object and spatial visual working memory systems.

Adult↗
PubMed1997

Semantic aspects of novelty detection in humans.

The ability to detect unusual and novel events is an important prerequisite for storage of information in memory. Non-tonal novel sounds that deviate from an ongoing auditory environment elicit a positive event-related potential (ERP) component, the so-called novel P3. Though there is converging evidence on the neuronal network engaged in novelty detection, little attention has been paid to the properties of novel sounds, such as their typicality or relationship to mental concepts. Here we report the ERPs evoked by two types of generically novel stimuli, namely identifiable (meaningful) and non-identifiable (non-meaningful) novel sounds. The ERP analysis revealed a novel P3 for both types of sounds. However, when subjects actively attended to the stimuli only identifiable novel sounds evoked a right-lateralized negativity (N4) that peaked shortly after the novel P3. We conclude that novelty detection not only includes the registration of deviancy but also fast access and identification of related semantic concepts.

Adult↗
PubMed1997

[Probability and strategy: an event-related potential study of processing syntactic anomalies].

Syntactic ambiguities requiring additional processing usually elicit positive going waveforms with onset latencies between 300 and 600 ms in the event-related potential (ERP). It is still unclear to what extent these components can be viewed either (a) as language specific in nature or (b) as members of the domain-unspecific P300 family of components. The present study investigates this question by means of probability manipulations applied to German sentences with subject-object ambiguities. Non-preferred object-subject (OS) word order requires structural revisions whereas the initially preferred subject-object (SO) word order does not. In the present experiment, the proportions of OS and SO structures were varied across experimental blocks (i.e., .25/.75 vs. .75/.25). The data of 20 participants reveal that ERP components were predominantly influenced when the subjects were explicitly informed about the actual proportions before each single block. In this case an early frontal positive component at about 400 ms and a subsequent posterior positivity were elicited by rare sentence structures irrespective of word order, suggesting that sentence processing was under strategic control. Conversely, participants that were not informed about sentence proportions showed larger positivities to the unpreferred OS sentences. Probability manipulations did not affect this pattern significantly. The data suggest that positivities evoked by syntactic ambiguities respond differently to probability manipulations than the P300 component.

Adult↗
PubMed1997

[Electrophysiologic dissociations in memory encoding of abstract and concrete words].

This study examined memory encoding of auditorily presented abstract and concrete nouns. 22 subjects performed various blocks of a free recall memory task in which lists of 22 either abstract or concrete words had to be memorized. Consistent with a large variety of memory studies, recall performance was better for concrete than for abstract words. When the event-related potentials (ERPs) recorded during study were selectively averaged for those words that were subsequently recalled and those subsequently not recalled, the ERPs were more positive going for words that were subsequently recalled. These Dm effects (Difference due to memory) started around 500 ms post-stimulus and differed in timing and scalp topography for both types of words: For abstract words, they were present in an early (i.e., 600 to 1100 ms) time interval at parieto-occipital electrodes only. In contrast, for concrete words, Dm effects were obtained with a broad topographic distribution in the 600 to 1000 ms time range and were also present in a late time interval (1100 to 1600 ms) at fronto-central recording sites. The topographical dissociations of the Dm effects in the early time interval are taken to reflect the larger distinctiveness of concrete words during encoding, whereas the late effects presumably play a functional role in elaborative processing of concrete words. The results do not agree with models of word concreteness that propose separate processing systems for the two types of words, and rather support those models that propose quantitative differences in the processing of abstract and concrete words.

Adult↗
PubMed1996

Syntactic parsing as revealed by brain responses: first-pass and second-pass parsing processes.

This paper reviews a series of electrophysiological experiments on syntactic processing against the background of a psycholinguistic two-stage model of parsing. The data reveal two event-related brain potential components in correlation with syntactic processes: an early left anterior negativity and a late centro-parietal positivity. It is argued that these two components can be correlated with two separate stages of syntactic processing: the early left anterior negativity reflecting first-pass parsing processes and the late positivity reflecting second-pass parsing processes possibly including processes of reanalyses.

Adult↗
PubMed1996

Event-related potentials reveal topographical and temporal distinct neuronal activation patterns for spatial and object working memory.

This study examined whether working memory processes for object and spatial information are associated with different patterns of ERP activity. Subjects performed two versions of a delayed match-to-sample task in which either object forms or two-dimensional spatial configurations (S1) had to be encoded and retained in working memory for 6800 ms for comparison with a subsequent stimulus (S2). Event-related potentials (ERPs) were recorded from 29 electrode sites in the S1-S2 interval. Negative slow wave activity in the ERP varied with both, the type of memory task and the amount of materials held in working memory. When spatial information was maintained in working memory negative slow wave activity rapidly rose at recording sites overlying posterior parietal and occipital cortical areas. At these recording sites, slow wave increased in amplitude with increasing spatial memory load. For object information, load-sensitive negative slow wave activity was obtained approximately 2000 ms later than in the spatial task and it was focused to mid-frontal recording sites. Moreover, in the object memory task more pronounced negative slow wave activity was found at right inferior temporal recording sites indicating a larger involvement of the right temporal lobe in the processing of object as compared to spatial information. The results provide evidence for the notion that encoding and retention processes for object information and for spatial information can be functionally dissociated and involve differential patterns of neuronal activation rapidly shifting in time.

Adult↗
PubMed1996

Attention and mental performance in confinement: evidence from cognitive psychophysiology.

In summary, the results provide several lines of evidence for the assumption that confinement and isolation for a period of 60 days attenuate attentional capacity differentially during auditory classification: the extraction of information from low probability events, but not from high probability events, is decreased by attentional limitations. With the advent of automatic control systems there is an increasing number of operations which require the monitoring of information sources for low probability critical stimuli for extended periods of time. Given the functional similarities of the task employed in this study and the monitoring tasks in practical settings, the results of this study should be considered as a human factor concern for control operations taking place under conditions of confinement and isolation.

Adult↗
PubMed1996

Temporal structure of syntactic parsing: early and late event-related brain potential effects.

Event-related brain potentials (ERPs) were recorded from participants listening to or reading sentences that were correct, contained a violation of the required syntactic category, or contained a syntactic-category ambiguity. When sentences were presented auditorily (Experiment 1), there was an early left anterior negativity for syntactic-category violations, but not for syntactic-category ambiguities. Both anomaly types elicited a late centroparietally distributed positivity. When sentences were presented visually word by word (Experiment 2), again an early left anterior negativity was found only for syntactic-category violations, and both types of anomalies elicited a late positivity. The combined data are taken to be consistent with a 2-stage model of parsing, including a 1st stage, during which an initial phrase structure is built and a 2nd stage, during which thematic role assignment and, if necessary, reanalysis takes place. Disruptions to the 1st stage of syntactic parsing appear to be correlated with an early left anterior negativity, whereas disruptions to the 2nd stage might be correlated with a late posterior distributed positivity.

Adult↗
PubMed1995

The P300 to novel and target events: a spatiotemporal dipole model analysis.

It has been reported that frontal lobe structures are critical for the generation of P300 activity in the human event-related potential (ERP) evoked by novel events. In this study spatial-temporal dipole model analyses were employed to obtain further evidence on the temporal dynamics and the approximate location of neuronal activity involved in P300 generation for target and novel events. A triple dipole configuration was found to describe the scalp recorded P300 activity for novel and target events with less than 2.5% residual variance. For the novel, but not the target dipole configuration a frontally oriented dipole was obtained whose temporal activity function suggests that the brain areas involved in the processing of novel events are engaged about 70 ms earlier than those relevant for target processing.

Analysis of Variance↗
PubMed1995

Processing relative clauses varying on syntactic and semantic dimensions: an analysis with event-related potentials.

Event-related potentials were used to study how parsing of German relative clauses is influenced by semantic information. Subjects read well-formed sentences containing either a subject or an object relative clause and answered questions concerning the thematic roles expressed in those sentences. Half of the sentences contained past participles that on grounds of semantic plausibility biased either a subject or an object relative reading; the other half contained past participles that provided no semantic information favoring either reading. The past participle elicited an N400 component, larger in amplitude for neutral than for semantically biased verbs, but this occurred only in the case of subject relative clauses. More specific effects were obtained only for a subgroup of subjects, when these were grouped into fast and slow comprehenders on the basis of their question-answering reaction times. Fast comprehenders showed larger N400 amplitudes for neutral than for semantically biased past participles in general and larger N400s for the latter when there was a bias for an object relative reading as opposed to a subject relative reading. Syntactic ambiguity resolution, indicated by an auxiliary in sentence final position, was associated in this subgroup with a positive component (P345), larger in amplitude for auxiliaries indicating an object relative reading than for those indicating a subject relative reading. The latter component was independent of semantically biasing information given by a preceding past participle. Implications of these findings for models of language comprehension are considered.

Adult↗
PubMed1995

Relationship between flanker identifiability and compatibility effect.

What is the relation between the identifiability of masked flankers and their ability to induce compatibility effects in a letter classification task? Using a within-subjects design (n = 8), we first determined identification performance for two flankers (H or N) around an irrelevant target letter as a function of the time (stimulus onset asynchrony, or SOA) after which the flankers were masked. In a second condition, subjects classified the central letter of the same stimulus patterns irrespectively of the identity of the flankers. The compatibility effects increased with increasing identification performance as a function of SOA, and we found a significant compatibility effect even at an SOA at which the identifiability of the flankers did not differ significantly from zero. We discuss the statistical power of our design and an interpretation of our results in terms of a dissociation between perceptual processes and processes directly activating the motor system (direct parameter specification; cf. Neumann, 1990).

Adult↗