Axel Mecklinger

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.

Differential Contribution of Frontal and Temporal Cortices to Auditory Change Detection: fMRI and ERP Results

The present study addresses the functional role of the temporal and frontal lobes in auditory change detection. Prior event-related potential (ERP) research suggested that the mismatch negativity (MMN) reflects the involvement of a temporofrontal network subserving auditory change detection processes and the initiation of an involuntary attention switch. In the present study participants were presented with repetitive spectrally rich sounds. Infrequent changes of either small (10% change), medium (30% change), or large (100% change) magnitude were embedded in the stimulus train. ERPs and fMRI measures were obtained in the same subjects in subsequent sessions. Significant hemodynamic activation in the superior temporal gyri (STG) bilaterally and the opercular part of the right inferior frontal gyrus was observed for large and medium deviants only. ERPs showed that small deviants elicited MMN when presented in silence but not when presented with recorded MR background noise, indicating that small deviants were hardly detected under fMRI conditions. The MR signal change in temporal lobe regions was larger for large than for medium deviants. For the right fronto-opercular cortex the opposite pattern was observed. The strength of the temporal activation correlated with the amplitude of the change-related ERP at around 110 ms from stimulus onset while the frontal activation correlated with the change-related ERP at around 150 ms. These results suggest that the right fronto-opercular cortex is part of the neural network generating the MMN. Three alternative explanations of these findings are discussed.

Interfacing mind and brain: A neurocognitive model of recognition memory

A variety of processes contribute to successful recognition memory, some of which can be associated with spatiotemporally distinct event-related potential old/new effects. An early frontal and a subsequent parietal old/new effect are correlated with the familiarity and recollection subcomponents of recognition memory, respectively, whereas a late, postretrieval old/new effect seems to reflect an ensemble of evaluation processes that are set by the task context in which retrieval occurs. Both the early frontal and the parietal old/new effects are differentially modulated by the informational content (e.g., object forms and spatial locations) of recognition and seem to rely on brain systems damaged in amnesia. The late frontal effect appears to reflect prefrontal cortex activation. A neurophysiologically based model of recognition memory retrieval is presented and it is shown that coupling recognition memory subprocesses with distinct old/new effects allow examination of the time course of the processes that contribute to correct and to illusory memories. In conjunction with event-related functional magnetic resonance imaging activation patterns the brain systems recruited by various aspects of episodic memory retrieval can be identified.

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 questionanswering 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.

Prefrontal cortex involvement in preattentive auditory deviance detection:: neuroimaging and electrophysiological evidence

Previous electrophysiological and neuroimaging studies suggest that the mismatch negativity (MMN) is generated by a temporofrontal network subserving preattentive auditory change detection. In two experiments we employed event-related brain potentials (ERP) and event-related functional magnetic resonance imaging (fMRI) to examine neural and hemodynamic activity related to deviance processing, using three types of deviant tones (small, medium, and large) in both a pitch and a space condition. In the pitch condition, hemodynamic activity in the right superior temporal gyrus (STG) increased as a function of deviance. Comparisons between small and medium and between small and large deviants revealed right prefrontal activation in the inferior frontal gyrus (IFG; BA 44/45) and middle frontal gyrus (MFG; BA 46), whereas large relative to medium deviants led to left and right IFG (BA 44/45) activation. In the ERP experiment the amplitude of the early MMN (90-120 ms) increased as a function of deviance, by this paralleling the right STG activation in the fMRI experiment. A U-shaped relationship between MMN amplitude and the degree of deviance was observed in a late time window (140-170 ms) resembling the right IFG activation pattern. In a subsequent source analysis constrained by fMRI activation foci, early and late MMN activity could be modeled by dipoles placed in the STG and IFG, respectively. In the spatial condition no reliable hemodynamic activation could be observed. The MMN amplitude was substantially smaller than in the pitch condition for all three spatial deviants in the ERP experiment. In contrast to the pitch condition it increased as a function of deviance in the early and in the late time window. We argue that the right IFG mediates auditory deviance detection in case of low discriminability between a sensory memory trace and auditory input. This prefrontal mechanism might be part of top-down modulation of the deviance detection system in the STG.

Gamma responses and ERPs in a visual classification task

OBJECTIVE We examined event-related potentials (ERPs) and gamma range EEG activity in a visual classification task to assess which variables affect these responses. METHODS Ten subjects silently counted the occurrence of rare Kanizsa squares (targets) among Kanizsa triangles and non-Kanizsa figures (standards). By applying a time-frequency analysis to the data and selectively calculating topographical maps of certain frequencies. RESULTS We were able to find 3 different types of gamma responses to Kanizsa figures: an early phase-locked gamma response at 40 Hz in the N100 time range, late phase-locked gamma activity (200-300 ms) at 40 Hz and a continuous phase-locked gamma response at 80 Hz due to the monitor refresh frequency. The two 40 Hz responses were significantly higher for Kanizsa figures than for non-Kanizsa figures and within the Kanizsa figures were higher for the target figure than for the non-target. CONCLUSION The phase-locking of these two responses, previously found also as non-phase-locked activity, could be synchronized due to the monitor flicker frequency. Also, our findings suggest that the gamma responses are not solely associated with the binding of stimulus features, but reflect some processes related to target processing.

Combining electrophysiological and hemodynamic measures of the auditory oddball.

The neural mechanisms of deviancy and target detection were investigated by combining high density event-related potential (ERP) recordings with functional magnetic resonance imaging (fMRI). ERP and fMRI responses were recorded using the same paradigm and the same subjects. Unattended deviants elicited a mismatch negativity (MMN) in the ERP. In the fMRI data, activations of transverse/superior temporal gyri bilateral were found. Attended deviants generated an MMN followed by an N2/P3b complex. For this condition, fMRI activations in both superior temporal gyri and the neostriatum were found. These activations were taken as neuroanatomical constraints for the localization of equivalent current dipoles. Inverse solutions for dipole orientation provide evidence for significant activation close to Heschls gyri during deviancy processing in the 110-160-ms time interval (MMN), whereas target detection could be modeled by two dipoles in the superior temporal gyrus between 320 and 380 ms.

Better or worse than expected? Aging, learning, and the ERN

This study examined age differences in error processing and reinforcement learning. We were interested in whether the electrophysiological correlates of error processing, the error-related negativity (ERN) and the feedback-related negativity (FRN), reflect learning-related changes in younger and older adults. To do so, we applied a probabilistic learning task in which we manipulated the validity of feedback. The results of our study showed that learning-related changes were much more pronounced (a) in a response-locked positivity for correct trials compared to the ERN and (b) in a feedback-locked positivity for positive feedback compared to the FRN. These findings provide an important extension to recent theoretical accounts [Holroyd, C. B., & Coles, M. G. H. (2002). The neural basis of human error processing: Reinforcement learning, dopamine, and the error-related negativity. Psychological Review, 109, 679-709; Nieuwenhuis, S., Ridderinkhof, K. R., Talsma, D., Coles, M. G. H., Holroyd, C. B., Kok, A., et al. (2002). A computational account of altered error processing in older age: Dopamine and the error-related negativity. Cognitive, Affective and Behavioral Neuroscience, 2, 19-36] since they suggest that positive learning signals on correct trials contribute to the reward-related variance in the response- and feedback-locked ERPs. This effect has been overlooked in previous studies that have focused on the role of errors and negative feedback for learning. Importantly, we did not find evidence for an age-related reduction of the ERN, when controlling for performance differences between age groups, which questions the view that older adults are generally impaired in error processing. Finally, we observed a substantial reduction of the FRN in the elderly, which indicates that older adults are less affected by negative feedback and rely more on positive feedback during learning. This finding points to an age-related asymmetry in the processing of feedback valence.

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.

Recognition Memory for Emotional and Neutral Faces: An Event-Related Potential Study

This study examined emotional influences on the hypothesized event-related potential (ERP) correlates of familiarity and recollection (Experiment 1) and the states of awareness (Experiment 2) accompanying recognition memory for faces differing in facial affect. Participants made gender judgments to positive, negative, and neutral faces at study and were in the test phase instructed to discriminate between studied and nonstudied faces. Whereas oldnew discrimination was unaffected by facial expression, negative faces were recollected to a greater extent than both positive and neutral faces as reflected in the parietal ERP oldnew effect and in the proportion of remember judgments. Moreover, emotion-specific modulations were observed in frontally recorded ERPs elicited by correctly rejected new faces that concurred with a more liberal response criterion for emotional as compared to neutral faces. Taken together, the results are consistent with the view that processes promoting recollection are facilitated for negative events and that emotion may affect recognition performance by influencing criterion setting mediated by the prefrontal cortex.