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PubMed1985

Visual signal detection. III. On Bayesian use of prior knowledge and cross correlation.

Experimental results are presented demonstrating that humans can make effective use of prior knowledge for detecting and identifying visual signals in static noise. The signals were selected from an orthogonal Hadamard set. There was a marked drop in detection performance when observers did not know which signal was present. The drop was in excellent quantitative agreement with that predicted by the theory of signal detectability. The statistical efficiency of the human observers was 33% in both cases (detection with and without prior knowledge). When interpreted in terms of channel uncertainty, the detection results demonstrated an upper limit of 10 orthogonal, uncertain channels. The statistical efficiency for the Hadamard signal-identification task was 40%. All the results are consistent with the standard theory of signal detectability based on a Bayesian maximum a posteriori probability decision strategy using cross correlation (or matched filtering) of expected signal profiles with those present in the display.

Attention↗
PubMedDate not supplied

Construction of diagnostic rules based on assessments of subjects.

This paper is based on assessments of subjects which are not defined by formal procedures. Logically structured assignment rules are constructed which are stable over time and which have a low number of disagreements with the assessments of the subjects. Recent results obtained from a computational learning theory show that the proposed construction of rules leads with high probability to rules with similar performances on large enough learning and validation sets of subjects. The construction of a set of stable rules is illustrated by using as a case study the psychophysiological, personality and speech behaviour data of a repeated-measures Type A behaviour study. This case study is also used for a discussion of the issue of biased ratings in the presence of assessments which are not defined by formal procedures.

Adult↗
PubMed1998

[Psychosomatic medicine and gastroenterology].

The possible relationship between psychosomatic medicine and gastroenterology is described and more specifically in the question of peptic ulcer which gave rise to the psychosomatic theory, prevalent in 1950-85. The infectious theory (H. pylori), that arose within the last decade, was discussed and the question was posed in the direction that one theory was not exclusive of the other but in fact were probably complementary of each other.

Duodenal Ulcer↗
PubMed2004

Septate uterus with a double cervix and longitudinal vaginal septum.

OBJECTIVE: To report the clinical features of 9 cases and review the previously reported 8 cases of an uncommon müllerian anomaly, characterized by the presence of a complete uterine septum with cervical duplication and represent a a longitudinal vaginal septum. STUDY DESIGN: Retrospective clinical study. RESULTS: Nine patients aged 21-32 presented to our clinic with complaints of dyspareunia, dysmenorrhea, and primary or secondary infertility. All 9 patients displayed a single uterus with smooth fundal contour, double cervix and longitudinal vaginal septum. Some additional abnormal findings were associated with these anomalies in some patients: polycystic ovaries in 3 cases and different degrees of endometriosis in 2 cases. Most of the patients had normal tubal patency. CONCLUSION: According to a MEDLINE search, only 8 cases of septate uterus with cervical duplication and a longitudinal vaginal septum have been reported to date. We report 9 more cases, which suggest that this atypical septate uterus type is probably more frequent than reported. These cases support the bidirectional müllerian theory and may imply the presence of another type of mullerian anomaly.

Abnormalities, Multiple↗
PubMedDate not supplied

[A simple model based on the first principles].

A simple model based on the first principles is proposed, which describes the reduplication of a molecular structure as a sequence of stages with probabilities that can be estimated on the basis of the general theory of molecular transformations. It is demonstrated that the reproduction of genetic information in time (life phenomenon) over a long period is impossible without the simultaneous "death effect". Taking into account the peculiarities of transient states (quantum beats) leads to the appearance of self-oscillations.

Animals↗
PubMed1985

Family or individual therapy: the determinants of modality choice.

There are powerful non-rational forces in patients and therapists alike, and in the therapeutic context. These forces often determine whether individual or family therapy is chosen. Historical, cultural, and economic forces, patient and family motivations, and therapist preferences are all powerful determinants of modality choice. This is partly due to the newness of the field of family therapy, and will probably continue until we have a better conceptual grasp of family theory and nosology, the interrelation of individual and family pathology, and a clearer delineation of the criteria for these modalities.

Choice Behavior↗
PubMed1984

[Effects of nifedipine and verapamil on body temperature in cats].

Nifedipine and verapamil injected into the cerebral ventricles of unanaesthetized cats produced a longlasting rise in the body temperature. The hyperthermic effect of nifedipine and verapamil were not dose-dependent. The hyperthermic effect of verapamil was preceded by a shortlasting fall in the body temperature, which was not dose-dependent. Calcium antagonists, nifedipine and verapamil also produced mydriasis, tachypnoea, dyspnoea, ataxia, tremor and muscular weakness. These symptoms were inconsistent and of slight intensity. In agreement with the theory of ionic set point controlling the body temperature, the most probable explanation is that calcium antagonists, nifedipine and verapamil produced changes in the body temperature by acting on sodium and calcium fluxes in the posterior hypothalamus.

Animals↗
PubMedDate not supplied

[Aging: genetic aspects].

Although most gerontologists, sometimes unconsciously, are ready to admit that ageing and life-span are genetically determined, it is a paradox to recognize that for the last 25 years most theories of ageing were stochastic in nature. The evidence in favour of such theories is reviewed and it is shown that they are most probably wrong. Yet the evidence in favour of a genetic basis for ageing and life-span is scarce and, until now, no definite proof of such a determinism has been provided.

Aging↗
PubMed1977

A psychophysiological re-evaluation of Eysenck's theory concerning cigarette smoking. Part I. The central nervous system.

According to Eysenck, extraverts are characterized by inhibited cortical activity accompanied by prominent alpha brain rhythms. This prevents efficient cortical functioning. They have a 'stimulus hunger' in order to increase cortical efficiency. Assuming that nicotine is a stimulant drug, Eysenck puts forward his theory that extraverts will also have a 'stimulus hunger' for the nicotine in cigarettes and will therefore smoke more than introverts, to whom the reverse applies. Implicit in Eysenck's theory is a positive, causal relationship between the amount of alpha brain rhythms and the number of cigarettes smoked. Inspection of the literature, however, indicated that small doses of nicotine stimulate the nervous system, whereas large doses tend to inhibit it. Eysenck's theory was therefore challenged by the alternative hypothesis that light smokers are characterized by prominent alpha brain rhythms and smoke for stimulation. Heavy smokers are, however, characterized by a small amount of alpha activity (overactivated cortex which also prevents efficient functioning), and therefore smoke for inhibition to enhance their cortical efficiency and thus their alpha activity. The results were reconcilable with this hypothesis. The positive relationship implied by Eysenck's theory only held good for light and moderate smokers. Heavy smokers probably smoke for cortical inhibition.

Adult↗
PubMed2001

Market structure and performance: evaluating the U.S. health system reform.

First, U.S. health system evolution over the last several years is assessed and found to be in line with what could be anticipated from economic theory. The immature market appears to be giving way to the concentration and the oligopolies of the mature market. This is explained in a manner accessible to non-economists. Next, the performance of market competition as a vehicle for health system reform is assessed in the areas of cost containment, quality of care, access, research/education and social mission. Overall, results have not measured up to promise. Market competition has not succeeded in bringing U.S. health care costs in line with those of other industrialized countries. There is no evidence of sustained quality improvement. Market based reform has not expanded health insurance coverage but has rather, directly or indirectly, increased the number of underinsured and uninsured Americans. Medical research and education have suffered and medicine's social mission has declined. These failures could probably have been anticipated, in advance, had policy makers carefully examined economic theory concerning market evolution. While these are some reasons to be hopeful for market performance in the future there are also potential pitfalls. Non-market oriented policy alternatives for health system reform are worth considering based on the experiences of the states and other countries.

Antitrust Laws↗
PubMed1989

The theory of five elements in acupuncture.

The theory of five elements is extensively used in traditional Chinese medicine. It is proposed that the theory of five elements was developed on the basis of the theory of elements, the law of contagion and the law of similarity which were prevalent in that era. The theory of elements spread in various forms all over the face of the globe. The law of contagion stated that objects, which at one time had been in continuity or juxtaposition, continued to exert an effect one upon the other. The internal organs were coupled probably on the basis of the law of contagion. The law of similarity stated that objects or circumstances which bear apparent similarity in form, shape, color or sequence of events, were considered to be fundamentally related. On the basis of the law of similarity the coupled internal organs were classified into five elements and the theory of five elements was compared with various things like seasons, color, tastes, emotions, etc. The theory of five elements is probably the earliest documented evidence correlating physiology with pathogenesis of diseases and a guideline for treatment of diseases.

Acupuncture Therapy↗
PubMedDate not supplied

What white blood cell count should prompt antibiotic treatment in a febrile child? Tutorial on the importance of disease likelihood to the interpretation of diagnostic tests.

Most diagnostic tests are not dichotomous (negative or positive) but, rather, have a range of possible results (very negative to very positive). If the pretest probability of disease is high, the test result that prompts treatment should be any value that is even mildly positive. If the pretest probability of disease is low, the test result needed to justify treatment should be very positive. Simple decision rules that fix the cutpoint separating positive from negative test results do not take into account the individual patient's pretest probability of disease. Allowing the cutpoint to change with the pretest probability of disease increases the value of the test. This is primarily an issue when the pretest probability of disease varies widely between patients and depends on characteristics that are not measured by the test. It remains an issue for decision rules based on multiple test results if these rules fail to account for important determinants of patient-specific risk. This tutorial demonstrates how the value of a diagnostic test depends on the ability to vary the cutpoint, using as an example the white blood cell count in febrile children at risk for bacteremia.

Anti-Bacterial Agents↗
PubMed1995

Training and search methods for speech recognition.

Speech recognition involves three processes: extraction of acoustic indices from the speech signal, estimation of the probability that the observed index string was caused by a hypothesized utterance segment, and determination of the recognized utterance via a search among hypothesized alternatives. This paper is not concerned with the first process. Estimation of the probability of an index string involves a model of index production by any given utterance segment (e.g., a word). Hidden Markov models (HMMs) are used for this purpose [Makhoul, J. & Schwartz, R. (1995) Proc. Natl. Acad. Sci. USA 92, 9956-9963]. Their parameters are state transition probabilities and output probability distributions associated with the transitions. The Baum algorithm that obtains the values of these parameters from speech data via their successive reestimation will be described in this paper. The recognizer wishes to find the most probable utterance that could have caused the observed acoustic index string. That probability is the product of two factors: the probability that the utterance will produce the string and the probability that the speaker will wish to produce the utterance (the language model probability). Even if the vocabulary size is moderate, it is impossible to search for the utterance exhaustively. One practical algorithm is described [Viterbi, A. J. (1967) IEEE Trans. Inf. Theory IT-13, 260-267] that, given the index string, has a high likelihood of finding the most probable utterance.

Communication↗
PubMedDate not supplied

[Theoretical analysis of the amino acid sequence of receptors for growth hormones and prolactins. Prediction of ligand-binding segments].

At present the growth hormone and prolactin receptors were cloned along with their variant forms from human, rat, mouse, rabbit, bovine and sheep tissues. The functional topography of receptors is practically unknown. Because of the high price and difficulty of protein's total mutagenesis, it is reasonable to carry on a theoretical analysis of structures of receptors to predict the most probable ligand-binding sites. We studied the primary structures of known prolactin and growth hormone receptors using theoretical methods proved to be powerful in earlier structure--activity relationship investigations. We analyzed the secondary structure, conservative positions, hydrophilicity profiles of the growth hormone and prolactin receptors, and used the original method based on information theory to predict the sites which are promising for mutagenesis or peptide synthesis as probable ligand-binding sites. Three segments corresponding to the main conservative, hydrophilic and rare sites were predicted to form the ligand-binding determinant.

Amino Acid Sequence↗
PubMedDate not supplied

Bayesian approaches in pharmacokinetic decision making.

The theory of Bayesian analysis and its application to therapeutic and pharmacokinetic decision making are discussed. Diagnostic and therapeutic decisions are commonly based on institution, experience, and laboratory information; these decisions reflect varying degrees of uncertainty. Bayesian analysis quantifies the decision process by attaching probabilities to the likelihood of accuracy of each of these decision-making factors to achieve an overall estimate of decision quality. Using Bayesian principles to quantify the probability of efficacy and toxicity associated with serum drug concentrations represents one application of Bayesian theory to enhance therapeutic decisions. The Bayesian approach in pharmacokinetics involves the prediction of pharmacokinetic values, dosage regimens, and serum concentrations for drugs. Beginning with mean population pharmacokinetic parameters, one uses observed serum concentrations in individual patients to modify these parameters through Bayesian analysis to improve the accuracy of future serum concentration predictions. As more clinical pharmacokinetic laboratories and consultation services become familiar with the procedure, Bayesian forecasting promises to expand markedly the sophistication of therapeutic drug monitoring.

Decision Making↗
PubMed1996

Origins of life: a comparison of theories and application to Mars.

The field of study that deals with the origins of life does not have a consensus for a theory of life's origin. An analysis of the range of theories offered shows that they share some common features that may be reliable predictors when considering the possible origins of life on another planet. The fundamental datum dealing with the origins of life is that life appeared early in the history of the Earth, probably before 3.5 Ga and possibly before 3.8 Ga. What might be called the standard theory (the Oparin-Haldane theory) posits the production of organic molecules on the early Earth followed by chemical reactions that produced increased organic complexity leading eventually to organic life capable of reproduction, mutation, and selection using organic material as nutrients. A distinct class of other theories (panspermia theories) suggests that life was carried to Earth from elsewhere--these theories receive some support from recent work on planetary impact processes. Other alternatives to the standard model suggest that life arose as an inorganic (clay) form and/or that the initial energy source was not organic material but chemical energy or sunlight. We find that the entire range of current theories suggests that liquid water is the quintessential environmental criterion for both the origin and sustenance of life. It is therefore of interest that during the time that life appeared on Earth we have evidence for liquid water present on the surface of Mars.

Earth, Planet↗
PubMed1979

A new theory of carcinogenesis.

Although many carcinogens are mutagens, there is no direct evidence that the cancer-cell phenotype is the result of gene mutation. Transplantation experiments have strongly indicated that malignant cells can arise or revert to the normal phenotype in the absence of mutation. It is suggested that damage to DNA followed by repair triggers the epigenetic changes in gene expression which are responsible for malignancy. We previously proposed that methylation of specific DNA sequences adjacent to structural genes determines whether or not transcription will occur. Specific methylases are required for the switching on of genes and for the stable maintenance of the methylated state, which provides a basis for the control of gene expression in differentiated cells. It is now seen that damage to DNA followed by repair, just before or just after DNA replication, can lead to the loss of methyl groups. This can induce a switch in gene activity which is heritable, but potentially reversible. The known large difference in the probability of malignant transformation in cells of rodents and large mammals is hard to explain if mutation is responsible. On the other hand, this new theory provides an explanation for this difference, since the probability of epigenetic changes in gene activity will depend on the activity of methylating enzymes and the rate of excision repair. The theory is supported by the evidence that excision repair is more efficient in cultured fibroblasts from large long-lived animals than from small short-lived ones.

Animals↗
PubMed1975

Raised intracranial pressure due to spinal tumours: 3 rare cases with a probable common mechanism.

Three cases are reported of raised intracranial pressure associated with spinal tumours. The theories which have been advanced to explain this complication are discussed and it is suggested that in many of the reported cases the underlying mechanism may have been intracranial spread of the tumour and not a blockage of the cerebrospinal fluid pathways with proteinaceous deposits, as has been widely maintained. Autopsy revealed the former process to have operated in 2 of the 3 cases and it may have done so in the third. Two cases had unusual features in common: they were malignant schwannomas (a very rare spinal tumour) and they had both developed within the field of irradiation given for benign conditions many years previously.

Adult↗