A syntactic and a semantic task were performed by German-speaking healthy subjects and aphasics with lesions in the dominant left hemisphere. In both tasks, pictures of objects were presented that ...had to be classified by pressing buttons. The classification was into grammatical gender in the syntactic task (masculine or feminine gender?) and into semantic category in the semantic task (man- or nature made?). Behavioral data revealed a significant Group by Task interaction, with aphasics showing most pronounced problems with syntax. Brain event-related potentials 300-600 ms following picture onset showed different task-dependent laterality patterns in the two groups. In controls, the syntax task induced a left-lateralized negative ERP, whereas the semantic task produced more symmetric responses over the hemispheres. The opposite was the case in the patients, where, paradoxically, stronger laterality of physiological brain responses emerged in the semantic task than in the syntactic task. We interpret these data based on neuro-psycholinguistic models of word processing and current theories about the roles of the hemispheres in language recovery.
Previous experiments with picture sorting and matching tasks have shown aphasics to give more deviant responses than controls when decisions require the identification of single features of concepts, ...whereas their responses are close to normal whenever decisions have to be based on the relative overlap of broad associative fields. The present experiment was designed to compare picture matching based on single features (property verification) with picture matching based on category membership (category verification). Fifty-five aphasics (14 amnesics, 18 Brocas, 13 Wernickes, 10 global aphasics) and 29 right-brain-damaged control patients served as subjects. Aphasics were poorer than right hemisphere controls on property as well as on category sortings, especially when the sorting criterion was not a dominant property of the object or when the object in question was not a typical member of the criterion category. Contrary to other studies, the “semantic distance” variable did not differentially affect Brocas as compared to Wernickes aphasics. Verbal labels denoting the sorting criterion and added to the picture presentation did not affect the performance of the right hemisphere controls but significantly improved that of the aphasics.
A slowly rising cortical potential shift with negative polarity following the imperative stimulus of a forewarned reaction time task, the ‘post-imperative negative variation’ (PINV), is regularly ...observed in schizophrenic patients but not in controls. The topography of the PINV suggests that it may originate in frontal cortical regions. We used a task designed to test two putative prefrontal cortical functions: working memory and processing of ambiguity. Nineteen patients with a chronic schizophrenic disorder and 19 control subjects matched for age, sex, and education participated in two experimental sessions. The EEG was recorded from frontal, central, temporal, and parietal leads over both hemispheres using a DC amplifier. PINV amplitudes were generally larger in patients than in controls. If the result of comparing physical features of the two successively presented stimuli (warning and imperative stimulus) was ambiguous rather than clear, an augmentation of the PINV amplitudes was seen in both groups. If this comparison required high rather than low involvement of working memory functions, PINV amplitudes were augmented in schizophrenic patients only. Scalp distribution of the PINV indicated a left-hemisphere fronto-central PINV maximum in patients, and a right-hemisphere predominance in controls, which was larger following ambiguous stimulus comparisons. These results suggest that ambiguity during the comparison of physical features of successively presented stimuli may be a general factor of the PINV in schizophrenic patients and healthy controls. Augmented involvement of working memory functions, presumably subserved by the prefrontal cortex, specifically affected the fronto-centrally predominant PINV in schizophrenic patients. This result is compatible with the hypothesis of prefrontal cortical dysfunctions in schizophrenia.
Slow event‐related potentials (ERP) were examined in healthy and aphasic subjects in two‐stimulus designs comprising a word comprehension and a rhyming task. Aphasics, though selected to perform ...above chance level, made significantly more errors and responded more slowly than controls, although canonical correlations did not indicate a statistical relationship between performance measures and ERP amplitudes. A discriminant analysis of ERP amplitudes distinguished the groups for the slow wave (SW; 0.5–1.0 s post‐S1 onset) in the word comprehension, for the SW and the initial contingent negative variation (iCNV; 1.0–2.0 s post‐S1 onset) in the rhyming task. Similarly for both tasks, ERP topography showed left‐anterior predominance of the negative SW and iCNV in controls, whereas participants with aphasia showed smaller anterior and larger left‐posterior amplitudes. The centroparietal terminal CNV (tCNV; 1 s pre‐S2) was smaller in participants with aphasia than in controls, but similar in topography. Results suggest left‐anterior activation for those language processes that were presumably provoked in the present tasks, like lexical access, or phonological encoding. The pattern of participants with aphasia may indicate effects of language impairment and recovery, but also consequences of the brain damage.
Startle-elicited blinks were measured during the presentation of affective slides in order to investigate emotional responsiveness in 24 male healthy subjects and 34 male schizophrenic patients. ...Although the two groups did not differ with regard to their subjective and autonomic responses to the slide stimuli, there was a significant difference between the groups in their responses to the startle probes. Patients rated low in affective expression showed a linear response pattern comparable to that of normal controls with largest amplitudes during unpleasant slides and smallest during pleasant slides. Patients without apparent deficit in affective expression showed a quadratic relationship with smaller blink amplitudes during both pleasant and unpleasant slides. Diminished affective expression rated on the basis of a clinical interview is not associated with a general attenuation of the blink reflex or of its modulation by exposure to emotional slides. Thus, we found no indication of an impairment in the perception of affective stimuli nor of reduced appreciation of pleasant stimuli (anhedonia) in these patients.
Event-related potentials (ERPs) were recorded from 65 channels in 12 schizophrenics and 12 age- and sex-matched controls during a delayed matching-to-sample design with variation of working-memory ...(WM) challenge: following a 500
ms visual sample stimulus (called S1, two diamonds varying in size, rotation angle and vertical position), the same pattern was either presented throughout a 6
s retention interval (no challenge) or a diamond pattern differing from the first one in at least one dimension was presented during this interval (WM challenge). The 500
ms matching stimulus (called S2) comprised one diamond, which had to be matched for identity to either the left or the right diamond of the sample stimulus. The topographical distribution of ERPs during an interval of 500
ms after S1-onset, 5
s of the retention interval, a 500
ms-interval preceding the S2, and a 1
s postimperative interval were evaluated. No WM challenge during the retention interval induced a right-posterior accentuation of the slow negative potentials in either group, while WM challenge evoked a tendency for left-hemispheric negativity in controls, but not in patients. Patients exhibited a postimperative negative variation (PINV) with left-anterior focus irrespective of the preceding WM challenge, while in controls, the left-anterior PINV was found only following WM challenge. In schizophrenic patients the lack of a left-anterior accentuation of negative ERPs under WM challenge might be related to WM dysfunction, and the condition-independent PINV might be considered either the consequence of this dysfunction or indication of processes related more to the diagnoses than to WM-challenge and -dysfunction.
Drawings of objects were presented in series of 54 each to 14 German speaking subjects with the tasks to indicate by button presses a) whether the grammatical gender of an object name was masculine ...("der") or feminine ("die") and b) whether the depicted object was man-made or nature-made. The magnetoencephalogram (MEG) was recorded with a whole-head neuromagnetometer and task-specific patterns of brain activity were determined in the source space (Minimum Norm Estimates, MNE). A left-temporal focus of activity 150-275 ms after stimulus onset in the gender decision compared to the semantic classification task was discussed as indicating the retrieval of syntactic information, while a more expanded left hemispheric activity in the gender relative to the semantic task 300-625 ms after stimulus onset was discussed as indicating phonological encoding. A predominance of activity in the semantic task was observed over right fronto-central region 150-225 ms after stimulus-onset, suggesting that semantic and syntactic processes are prominent in this stage of lexical selection.
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