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H H Stassen

Publications and source records attributed to H H Stassen.

At least 37 records · Page 2Linked to original sources
PubMed1996

Reliable computer-assisted classification of the EEG: EEG variants in index cases and their first degree relatives.

A method which optimizes on global properties of sample recordings is proposed for the definition of and the discrimination between electroencephalogram (EEG) classes. The sample was drawn from students at the University of Heidelberg from 1974 to 1978 and consists of 15 healthy index cases clinically ascertained as belonging to the low voltage EEG group. In addition, the three clinically defined groups: diffuse beta (18 index cases), borderline alpha (12 index cases) and monomorphous alpha (18 index cases) have been included in the study, as well as the first degree relatives of the index cases, thus providing a clinical classification into four groups. The proposed method provides an automatic and reliable classification algorithm using discriminant and cluster analysis. The relation between such an automatized classification and clinical classification schemes is investigated. In particular, the inheritance of the low voltage EEG, the question on sex differences and the question of a simple Mendelian mechanism had been examined. The method of random splittings had been applied for discriminant and cluster analysis. Our findings can be summarized as follows: (1) except for the monomorphous alpha EEG group, the clinical classification shows rather marginal separation (discriminating performance 60% to 75%), while a new and more reliable grouping scheme improves the discriminating performance up to 87% to 91%. The latter scheme leads to the concept of personal channel pattern (PCP) and was compared to the clinical classification scheme by means of contingency tables; (2) only a weak correlation between the clinically and PCP-based groups could be found (Cramér Index: 0.27). Accordingly, we continued to investigate the extent to which the proposed EEG classification scheme can nevertheless explain the genetic mechanisms apparently involved in the low voltage EEG. We thus considered the role of sex differences manifest in our proposed new grouping scheme; (3) males occurred more frequently in the new group 3 and females more frequently in the new group 1. In this regard, a much better correlation of the new groups between mothers and children than between fathers and children was observed; and (4) with help of our new PCP scheme, we have been able to reproduce a simple two gene Mendelian scheme to explain inheritance of the clinical low voltage EEG group. In this PCP-based scheme, the low voltage property does not occur when dominance of a certain gene (called gene A) is absent.

Adult↗
PubMed1996

Delayed onset of action of antidepressant drugs? Survey of results of Zurich meta-analyses.

The onset of action of antidepressant drugs was investigated on the basis of two independent, multicenter, double-blind studies, comparing amitriptyline (N = 120), oxaprotiline (N = 120), imipramine (N = 506) and moclobemide (N = 580) with placebo (N = 189/+191). Highly significant differences between the active drugs and placebo were found with respect to the total number of improvers and the total number of responders. In addition, significant differences between treatment modalities showed up in both the percentage rate and the time distribution of premature withdrawals. However, among improvers, the distribution of time spans to onset of improvement was found to be independent of treatment modality, indicated by virtually identical cumulative percentages of improvers over the whole observation period. This picture of treatment-independent improvement rates was essentially the same for the HAMD, HAMA and ZUNG assessments, except for a significant time lag between observerratings and self-ratings. Specifically, our analyses revealed no evidence for a delayed onset of action of various antidepressants with large biochemical and pharmacological differences when compared to placebo. The early onset of improvement was highly predictive of later outcome: on average, 70% of patients showing improvement within the first 14 days became responders. Differences between active treatments and placebo emerged within the first five days and reached a point of maximum distinction around day 14. After this time point, differences between treatment modalities remained constant until the end of the observation period. Not more than 20-25% of patients were, on average, "true" drug responders, thus suggesting that the therapeutic qualities of antidepressants do not lie in the suppression of symptoms, but rather relate to their ability to elicit and maintain certain conditions which enable recovery in a subgroup of patients who would otherwise remain nonresponders.

Adolescent↗
PubMed1995

Cognitive performance in patients recovering from depression.

Investigations into the development of cognitive impairment in 30 hospitalized depressive patients have suggested that such disturbances encompass two dichotomous entities: a core entity of long-persisting, therapy-resistant impairment and an entity of reversible impairment with a prompt onset of improvement. The course of improvement turned out to evolve largely independently with respect to psychopathology: about one half of patients displayed severe cognitive dysfunctions which remained virtually unchanged until hospital discharge, while 80% significantly improved within the first 12 days with respect to their depressive symptoms, and 53.3% displayed a clear response to treatment at the time of hospital discharge. In particular, a considerable number of patients with a significant reduction of depressive symptomatology at hospital discharge still suffered from severe cognitive dysfunctions. Neither antidepressant or antipsychotic medication nor acute side effects due to medication explained the development of cognitive impairment. Accordingly, cognitive impairment seems to represent an essentially independent syndrome complex comparable to 'deficits' or 'negative symptoms' in schizophrenia. On the other hand, single case correlation analysis revealed a somewhat closer relationship of cognitive impairment with speech behavior and voice sound characteristics. Two thirds of patients displayed significant correlations between cognitive performance scores and second-order constructs like speech flow, dynamics or intonation. However, the respective subgroups defined by significant correlations with single speech parameters were relatively small (< or = 35% of cases), thus indicating that there exist large interindividual differences as to how cognitive impairment affects the patients' speech.

Adjustment Disorders↗
PubMed1993

Time course of improvement under antidepressant treatment: a survival-analytical approach.

A meta-analysis of an earlier multicenter, double-blind efficacy study comparing placebo, oxaprotiline and amitriptyline was performed in order to test the survival-analytical approach in modelling the onset of improvement and response to treatment with antidepressants. The sample consisted of moderately depressed male (n = 154) and female (n = 275) patients (aged 17-73), diagnosed according to DSM-III criteria for major depression. Of these, 120 were treated with oxaprotiline, 120 with amitriptyline and 189 with placebo. Efficacy criteria were Hamilton Depression (HAMD) and Anxiety (HAMA) and Zung Self-Rating scales. Up to eight ratings over a period of 40 days were available for analysis. The results showed that the sensitivity in discriminating between groups was substantially enhanced through the inclusion of drop-outs and consideration of the effect of time to withdrawal from the study due to lack of improvement. Withdrawal from the trial due to inefficacy occurred earliest under placebo (50% within the first 8 days), whereas less than 40% dropped out within the first 12 days under active treatments. The most interesting and unexpected finding of the analysis was that the time course of improvement among responders was independent of the treatment modality, and thus identical in all three groups. Specifically, the efficacy of any of the given treatments was reflected only by the total number of responders or nonresponders. Once triggered, the time course of recovery from illness becomes identical to that of spontaneous remissions as observed, for example, under placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Speech characteristics in depression.

This study examined the relationship between speech characteristics and psychopathology throughout the course of affective disturbances. Our sample comprised 20 depressive, hospitalized patients who had been selected according to the following criteria: (1) first admission; (2) long-term patient; (3) early entry into study; (4) late entry into study; (5) low scorer; (6) high scorer, and (7) distinct retarded-depressive symptomatology. Since our principal goal was to model the course of affective disturbances in terms of speech parameters, a total of 6 repeated measurements had been carried out over a 2-week period, including 3 different psychopathological instruments and speech recordings from automatic speech as well as from reading out loud. It turned out that neither applicability nor efficiency of single-parameter models depend in any way on the given, clinically defined subgroups. On the other hand, however, no significant differences between the clinically defined subgroups showed up with regard to basic speech parameters, except for the fact that low scorers seemed to take their time when producing utterances (this in contrast to all other patients who, on the average, had a considerably shorter recording time). As to the relationship between psychopathology and speech parameters over time, we found significant correlations: (1) in 60% of cases between the apathic syndrome and energy/dynamics; (2) in 50% of cases between the retarded-depressive syndrome and energy/dynamics; (3) in 45% of cases between the apathic syndrome and mean vocal pitch, and (4) in 71% of low scores between the somatic-depressive syndrome and time duration of pauses. All in all, single parameter models turned out to cover only specific aspects of the individual courses of affective disturbances, thus speaking against a simple approach which applies in general.

Adult↗
PubMed1991

Long-term prognosis of schizophrenia.

The question of determining prognostically relevant features for schizophrenia was approached with multivariate statistical methods applied to the data from the Bonn longitudinal study of 502 schizophrenic patients. In this study, personal interviews according to a clinical classification scheme allowed every patient to be ranked within each of three different outcome classes: psychopathological remission, occupational remission, and course type. Our multivariate analysis encompassed a total of 50 items pertinent to the time up to and including the first 6 months after the first psychotic manifestation. Despite the introduction of mathematical methods considerably more sophisticated than those employed in earlier studies, no satisfactory solution could be found to the problem of predicting end states of schizophrenia. Reliable predictions could be made only for 'extreme' end states (i.e. full remission versus (1) characteristic residues in the narrower sense; (2) total unemployment, or (3) surging or simple courses to mixed residues or to typical schizophrenic defect psychoses). Accordingly, sufficiently reliable assertions applied only to a minority of about 1/3 of patients, whereas for the majority of 2/3, no generalizable prognostication was possible (67-71% true-positive predictions on 36-63% of total population in extreme states). By contrast, our analyses have clearly uncovered a fundamental problem of investigations into the long-term prognosis of schizophrenia: the extreme dependence of results on the clinical definition of end states. The further the phenomenon 'end state' is qualitatively subdivided, the poorer and less reproducible is the mutual discrimination between intermediate states and the less reliable are allocations of patients to these intermediate states by means of multivariate classifiers. Furthermore, our analyses have also demonstrated the usefulness of multivariate, adaptive procedures for investigations into the structural properties of long-term courses, so that predictions might be considerably improved if more reliable definitions of schizophrenic end states are available.

Activities of Daily Living↗
PubMed1991

The octave approach to EEG analysis.

A "tonal" approach to EEG spectral analysis is presented which is compatible with the concept of physical octaves, thus providing a constant resolution of partial tones over the full frequency range inherent to human brain waves, rather than for equidistant frequency steps in the spectral domain. The specific advantages of the tonal approach, however, mainly pay off in the field of EEG sleep analysis where the interesting information is predominantly located in the lower octaves. In such cases the proposed method reveals a fine structure which displays regular maxima possessing typical properties of "overtones" within the three octaves 1-2 Hz, 2-4 Hz and 4-8 Hz. Accordingly, spectral patterns derived from tonal spectral analyses are particularly suited to measure the fine gradations of mutual differences between individual EEG sleep patterns and will therefore allow a more efficient investigation of the genetically determined proportion of sleep EEGs. On the other hand, we also tested the efficiency of tonal spectral analyses on the basis of our 5-year follow-up data of 30 healthy volunteers. It turned out that 28 persons (93.3%) could be uniquely recognized after five years by means of their EEG spectral patterns. Hence, tonal spectral analysis proved to be a powerful tool also in cases where the main EEG information is typically located in the medium octave 8-16 Hz.

Algorithms↗
PubMed1991

Affective state and voice: the specific properties of overtone distributions.

Motivated by psychiatric interests and as part of our investigations into the basic properties of human speech, we carried out a normative study with 192 healthy subjects--stratified according to sex, age and education--in order to derive reference values of the general population and to learn to distinguish between normal fluctuations and significant changes over time. In the present investigation, our interest focused on the individual sound characteristics of speakers ("timbre") rather than on speech behavior. Accordingly, we determined the optimum parameter setting for a problem-specific, reliable estimation of time-dependent spectra. An interval of one second length was found to be optimum for reproducibly assessing formants and corresponding bandwidths for more than 95% of the cases. Based on these findings, we adapted the concept of "spectral patterns" to speech analysis. It turned out that spectral voice patterns are stable over time and measure the fine graduations of mutual differences between human voices. A highly reliable computerized recognition of persons was possible by means of these quantities, on the basis of 16-32 s time series: 93% of persons could be uniquely recognized after a 14-day interval. Hence, we succeeded in developing specific means for modelling intra-individual changes of voice timbres over time. This is of particular interest for investigations of the speech characteristics of affectively disturbed patients, since the tonal expressiveness of human voices, or the lack thereof, essentially depends on the actual distribution of overtones and the corresponding variabilities.

Affect↗
PubMed1989

Effect of neuroleptics on positive and negative symptoms and the deficit state.

The concept of negative symptoms tries to operationalize a deficit syndrome observed in schizophrenia, but also in other disorders. The instruments for the measurement developed so far are unclear in their dimensional structure and validity. Further methodological development is needed. A new scale for measuring negative symptoms was derived from the AMDP-system and applied to results of drug trials with clozapine, fluperlapine, and haloperidol. The three drugs were equally effective on negative symptoms of acute and chronic schizophrenics.

Antipsychotic Agents↗
PubMed1989

Affective state and voice: results of a pilot study with six depressive patients.

As part of an investigation into the nonverbal information in human speech, a pilot study with depressive patients was designed in order to model the global affective state as a function of time and in terms of speech parameters. Over a two-week period, six patients were examined six times at two-day intervals under comparable experimental conditions. The psychopathologic status of these patients was assessed during a psychiatric exploration half an hour before the actual examination was carried out. Besides the solution of the baisc methodological problems, a principal goal of this study was to test the ability and cooperation of depressive patients when asked to speak in the laboratory. It turned out that even scalar parameters such as energy and dynamics give insight into the intraindividual variation of global affective state, and that the examination procedure is practicable even it patients are considerably handicapped by their illness.

Adult↗
PubMed1988

Familial syndrome patterns in schizophrenia, schizoaffective disorder, mania, and depression.

A major problem with studies in the field of quantitative genetics is that of phenotypical heterogeneity. In particular, such heterogeneities show up in psychiatric investigations: index cases often tend to display more severe forms of disorders than the respective affected relatives. The principal goal of the present investigation was to test the phenotypical equivalence of the two populations of index cases and their affected relatives. Our analyses were based on 269 hospitalized patients with functional psychoses and 350 affected first degree relatives. As opposed to the majority of earlier investigations in which phenotypes were uniquely defined by diagnoses, phenotypes were represented in this study by a list of 22 psychiatric syndromes. Accordingly, multivariate statistical procedures were applied to analyze the intrinsic properties of the empirical lists. The results showed that typical syndrome patterns clearly appeared in both populations and that the phenotypical equivalence of the corresponding population sample sets lay between satisfactory and good. Furthermore, it was possible to select phenotypically homogeneous and reproducible subsets on the basis of the 22 syndromes. These subgroups can be used as basic material to study the genetic modes via current models from quantitative genetics. Nevertheless, our analyses revealed no clear breeding true of either affective disorders or schizophrenia.

Bipolar Disorder↗
PubMed1988

The within-pair EEG similarity of twins reared apart.

Within the broader context of our investigations into the heredity of the human EEG, we analysed the EEGs of 28 pairs of monozygotic and 21 pairs of dizygotic twins who were separated as infants and reared apart. The principal goal of this study was to determine the degree to which environmental factors possibly influence the development of a person's EEG. Monozygotic twins reared apart were, with respect to their EEGs, only slightly less similar to each other (if there is any difference at all) than the same person is to himself over time. For dizygotic twins reared apart, we verified the findings of our previous study, namely, that the average within-pair similarity of EEGs estimated from a sufficiently representative sample of fraternal twins was significantly higher than the average inter-individual similarity of EEGs obtained from unrelated persons. The results on both monozygotic and dizygotic twins, yielded conclusive proof that the individual EEG pattern is predominantly determined by hereditary factors.

Adult↗
PubMed1988

Genetic determination of the human EEG. Survey of recent results on twins reared together and apart.

In this article, we have discussed recent progress in quantifying the genetically determined component of the resting EEG. This progress has been made possible in particular by the application of advanced information processing techniques such as "supervised learning," and the development of a problem-oriented "similarity" concept. Our work aimed at modeling previous findings regarding the distinct individuality of human brain-wave patterns, the high similarity between the EEGs of monozygotic twins, and the average within-pair similarity of dizygotic twins. Thus, we had three objectives: First, we wanted to improve the quantification of EEG characteristics with respect to reproducibility and specificity by means of adaptive procedures and repeated measurements. Second, we wanted to compare the "typical" within-subject EEG similarity with the "typical" within-pair EEG similarity of monozygotic and dizygotic twins brought up together. Finally, we were interested in the degree to which environmental factors affect the characteristics of human brain-wave patterns. Our investigations were based on the empirical data derived from five different populations: (1) 81 healthy subjects, (2) 24 pairs of monozygotic twins brought up together, (3) 25 pairs of dizygotic twins brought up together, (4) 28 pairs of monozygotic twins reared apart, and (5) 21 pairs of dizygotic twins reared apart. Following our similarity conception, repeated measurements on the set of 81 individuals were used as design samples, and new registrations from the same individuals taken 14 days later were referred to as test samples in order to develop the appropriate method and to determine all required calibration parameters. This specific approach allowed us to construct EEG spectral patterns which, with a specificity and reproducibility of greater than 90% each, largely met the requirements of genetic EEG studies. Hence, we were able systematically to investigate the within-pair EEG similarity of our twin samples.(ABSTRACT TRUNCATED AT 400 WORDS)

Electroencephalography↗
PubMed1988

Modelling affect in terms of speech parameters.

It is well known that the human voice contains important information about the affective state of a speaker at a nonverbal level. Accordingly, we started an extensive investigation which aims at modelling intraindividual changes of the global affective state over time, as this state is reflected by the human voice, and can be inferred from measurable speech parameters. For the purpose of this investigation, a speech-recording procedure was designed which is especially suited to reveal intraindividual changes of voice patterns over time since each person serves as his or her own reference. On the other hand, the chosen experimental setup is less suited to classify patients in the sense of a traditional diagnostic scheme. In order to find an appropriate mathematical model on the basis of speech parameters, a calibration study with 190 healthy subjects was carried out which enabled us to investigate each parameter for its reproducibility, sensitivity and specificity. In particular, this calibration study yielded the information of how to draw the line between 'normal' fluctuations and 'significant' intraindividual changes over time. All speech parameters under discussion turned out to be sufficiently stable over time, whereas, in regard to their sensitivity to form and content of text, significant differences showed up. In a second step, a pilot study with 6 depressive patients was carried out in order to investigate the specificity of voice parameters with regard to psychopathology. It turned out that the registration procedure is realizable even if patients are considerably handicapped by their illness. However, no consistent correlations could be revealed between single speech parameters and psychopathological rating scales.(ABSTRACT TRUNCATED AT 250 WORDS)

Affect↗
PubMed1987

Genetic aspects of the EEG: an investigation into the within-pair similarity of monozygotic and dizygotic twins with a new method of analysis.

A considerable number of previous studies emphasized the importance of genetic factors in the spontaneous EEG. In this context MZ twins were found to resemble their co-twins as much as they resemble themselves over time, whereas investigations into the within-pair similarity of DZ twins yielded very inconsistent findings. To test these conclusions, we re-analysed the EEGs of an earlier twin study (24 MZ pairs/25 DZ pairs) by means of a new method of analysis. In our study, MZ twins proved to be less like one another than each person is to himself over time. However, this result might be because the EEG data were not optimal for the applied method of analysis, but the existence of true within-pair differences cannot be excluded. Contrary to earlier findings in the literature, the analysis of the EEG of DZ twins showed that, for a sufficiently representative sample, the within-pair similarity is significantly above the inter-individual similarity between unrelated persons.

Adult↗
PubMed1987

Morbid risks of subgroups of affective disorders: some methodological and empirical results.

Based on two independently ascertained family studies, the problem of analysing disorders with variable age of onset has been investigated by means of survival analysis. This method of approach results in empirical risk functions which can be used directly as weights for age correction in the analysis of pedigrees. The main interest of the present investigation has been focused on the reproducibility of such risk functions and on their specificity with respect to clinical diagnosis. For this purpose, one family study was referred to as a calibration sample for estimating empirical risk functions, whereas, the second family study served as a test sample in order to test the hypotheses under discussion. As it turned out, the empirically derived functions from both the calibration and test samples are indeed comparable, thus suggesting that, for sufficiently representative calibration samples, the differences between the two populations of (1) affected and (2) susceptible individuals may be less important than expected. As to the specificity of these risk functions, the underlying diagnostic structure of the calibration samples (as represented by four diagnostic subgroups) could be characterized by distinct types of risk functions, each of which, in addition, reflects the severity of the respective affective disorder.

Bipolar Disorder↗