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PubMed2006

Theory-based Bayesian models of inductive learning and reasoning.

Inductive inference allows humans to make powerful generalizations from sparse data when learning about word meanings, unobserved properties, causal relationships, and many other aspects of the world. Traditional accounts of induction emphasize either the power of statistical learning, or the importance of strong constraints from structured domain knowledge, intuitive theories or schemas. We argue that both components are necessary to explain the nature, use and acquisition of human knowledge, and we introduce a theory-based Bayesian framework for modeling inductive learning and reasoning as statistical inferences over structured knowledge representations.

Association Learning↗
PubMed2002

[Models for understanding personality pathology].

BACKGROUND: The prevalence of personality disorders is high and patients with personality disorders are known to be difficult to treat. The assessment of different types of personality disorders has been facilitated by the development of explicit diagnostic criteria. However, the diagnostic manuals have tended to be atheoretical, defining and classifying personality disorders mainly on a descriptive level of behaviour and symptoms. There is no consensus on a theoretical understanding of personality pathology. The concept of personality disorder is currently under debate and investigation, theoretically as well as empirically. MATERIAL AND METHODS: This paper presents some of the major theories of personality disorders that are currently discussed in the literature. RESULTS: The models represent different schools of thought, lean on different methodological assumptions, and focus on different aspects of personality. The theories are to varying degrees focused on aetiology, classification and treatment. A major trend is to supplement theories developed within the context of clinical psychiatry with models from normal psychology. INTERPRETATION: Personality disorder is a complex phenomenon. Different theories are probably useful for different aspects of personality pathology and for different groups of personality disorders. More empirical research is needed in order to clarify the validity of the different models.

Behavior↗
PubMed1977

Can the singularity of chronic peptic ulcers be described by catastrophe theory and explained by biofeedback?

The damaging effect of hydrochloric acid within the lumen of the stomach and duodenum should be diffuse, but chronic peptic ulcers are discrete and usually single. The search for localizing effects on acid attack, or localized defects in mucosal defense have so far been fruitless. If attacking forces increase, or mucosal defense diminishes to the point where ulceration occurs, mucosal breakdown should be progressive. In chronic peptic ulceration, however, the process usually seems to be self-limiting. The catastrophe theory of René Thom may describe the progressive change in the forces that leads to eventual breakdown in mucosal continuity. Possibly this catastrophe triggers off biofeedback mechanisms that hold in check further progress of the ulcer.

Chronic Disease↗
PubMed1978

Verification of the optimal probabilistic basis of aural processing in pitch of complex tones.

Periodicity pitch for complex tones has been quantitatively accounted for by a two-stage process of Fourier-frequency analysis subject to random errors and significant nonlinearities, followed by an harmonic pattern recognizer that makes an optimum probabilistic estimate of the fundamental period of musical and speech sounds. The theory predicts that periodicity pitch is a multimodal probabilistic function of a given stimulus. A clear and empirically supported distinction is made between limitations on the pitch mechanism caused by the stochastic nature of aural frequency representation and by the deterministic resolution bandwidths of aural frequency analysis. This model was developed earlier [J. L. Goldstein, J. Acoust. Soc. Am 54, 1496-1516 (1973)] to account for probabilistic data on pitch errors [A. J. M. Houtsma and J. L. Goldstein, J. Acoust. Soc. Am. 51, 520 (1972)] measured with periodic stimuli comprising two successive harmonics. This paper presents new predictions by the theory that were calculated, with computer simulation where needed, for known probabilistic pitch data from stimuli comprising three to six successive harmonics. Predicted pitch errors increase with increasing errors in estimating the frequencies of stimulus harmonics and decrease as more harmonics are added to the stimulus. Optimum processor theory fully accounts for the multicomponent pitch data on the basis of similar errors in estimating component stimulus frequencies as reported earlier, thus providing further evidence for the optimum probabilistic basis of aural signal processing in pitch of complex tones.

Auditory Cortex↗
PubMed1996

New techniques for predicting solar proton fluences for radiation effects applications.

At geosynchronous altitudes, solar proton events can be a significant source of radiation exposure for devices such as optical imagers, memories and solar cells. These events appear to occur randomly with respect to time and magnitude during the active period of each solar cycle. New probabilistic descriptions, including extreme value theory, are given in forms applicable to assessing mission risks for both single events and the cumulative fluence of multiple events. The analyses yield simpler forms than previous models, include more recent data, and can easily be incorporated into existing computer programs.

Electronics↗
PubMed1996

Fuzzy gating and the problem of screening.

The problem of population screening is very important for medical statistics. It allows one to analyze the expression of certain parameters in the population of healthy persons, in order to compare it to the expression of these parameters in the persons with a specific disease. If a parameter is expressed differently in ill and healthy persons, then this parameter may serve as a pointer to the disease, especially in its earlier stages. While the analysis of given parameters in people with the established diagnosis does not represent many difficulties, the analysis of the general population is not easily carried out. The problem is that the general population contains both ill and healthy people. The population of healthy people is said to be 'contaminated' by the noise-subpopulation of ill people. The resulting statistical parameters are, therefore, biased and in order to find their correct values one needs to cancel out the input of the noise. In this paper we propose a new method to cancel out the noise, based on the theory of fuzzy sets. We assume that an auxiliary parameter is measured simultaneously and it is used to separate the subpopulations. If two subpopulations (the data and the noise) form clearly distinguished clusters in respect to this auxiliary parameter, one creates a gate and throws out the events outside the gate assuming that they are noise. However, when the clusters overlap, this procedure is no longer useful, and it is this particular situation for which we have developed fuzzy gating. In addition to the fact that the gate is fuzzified, a specifically designed algorithm is applied to compute the probability density functions for both subpopulations. Our algorithm gives a very high precision and is very robust as to the level of noise and the type of distributions.

Algorithms↗
PubMed1979

Probabilistic theories of coalition formation in groups.

Chertkoff's (1967) and Walker's (1973) theories of coalition formation for decision making, which attempt to predict the probabilities of the occurrence of coalitions in three-person group systems, are extended to apply to certain situations involving groups larger than these triads. These two extended theories and Komorita's (1974) weighted probability theory, which attempts to predict the probabilities of occurrence of coalitions in groups of any size, are compared according to how well they can account for the results of a number of previously reported experiments, both on triads and on larger groups. In general, this comparison shows that: (a) Chertkoff's theory cannot account for the results; (b) Walker's theory can account only for the results of experiments in which all the minimal winning coalitions are equal in size; and (c) Komorita's theory can account only for the results of experiments in which there is some difference in size among the minimal winning coalitions. It is suggested that the theories of Chertkoff and Walker do not attribute enough importance to size as a factor in coalition formation, while weighted probability theory attributes too much importance to this factor.

Decision Making↗
PubMed2000

Information processing in multigame environments modeling the evolution of sex via punctuated equilibria.

Uncertain environments are properly described by probability distributions which, as usual, can be collapsed or conditioned into distributions with reduced uncertainty through the processing of environmental information. Organisms which force this collapse gain evolutionary advantage by being able to employ strategies in a known environment rather than in a merely probable one. The accrued benefit gained from processing information can be precisely quantified by comparing benefits returned using distributions prior to, and after collapse, and these often large and immediate benefits can amply justify the evolutionary cost of information processing systems. More importantly, the evolution of information processing systems must necessarily occur in a predictable evolutionary sequence from less complex to more complex. Practical applications include modeling the evolution of sex modeled here as a sequence from asexual reproduction, to single gene exchange, to gene packet exchange, to same species packet exchange, and finally to sexual reproduction, sexual selection, Red Queen contests and so on. Modeling this sequence requires extensions to game theory originally designed to model a single game, to allow the simultaneous operation of many games. This extension is called a multigame environment. The dynamical evolution of the development sequence shows punctuated equilibria.

Animals↗
PubMed1993

The behavioral theory of timing: transition analyses.

Gibbon and Church (1990, 1992) have recently confirmed an important, parameter-free prediction of the behavioral theory of timing (Killeen & Fetterman, 1988): The times of exiting from a bout of activity are positively correlated with the times of entrance to it. The correlations were slightly less than predicted, however, and the correlations between the start of an activity and the time spent engaged in that activity were negative, rather than zero. We adapted their serial model as an augmented (one-parameter) version of the behavioral theory, positing a lag between the receipt of a pulse from the pacemaker and transition into the next class of responses. The augmented version of the behavioral theory further improved the correspondence between the theory and the correlational data reported by Gibbon and Church. It also accounts for previously unpublished data from our laboratory derived from a new timing technique, the "peak choice" procedure. We show that the measured variance of movement times from one key to another closely approximates the estimated variance of transition times recovered from fits of the augmented model to the data. Such correspondence both attests to the correct identification of this source of variance and suggests ways to remove it, both from behavior and from our models of behavior.

Animals↗
PubMed2006

Probabilistic inference in human semantic memory.

The idea of viewing human cognition as a rational solution to computational problems posed by the environment has influenced several recent theories of human memory. The first rational models of memory demonstrated that human memory seems to be remarkably well adapted to environmental statistics but made only minimal assumptions about the form of the environmental information represented in memory. Recently, several probabilistic methods for representing the latent semantic structure of language have been developed, drawing on research in computer science, statistics and computational linguistics. These methods provide a means of extending rational models of memory retrieval to linguistic stimuli, and a way to explore the influence of the statistics of language on human memory.

Association Learning↗
PubMed1975

Principles and applications of fluctuation analysis: a nonmathematical introduction.

The mechanisms underlying many of the processes studied by membrane biophysicists are inherently probabilistic, and therefore exhibit random fluctuations around the mean of behavior. These fluctuations reflect the underlying probabilistic mechanism and therefore can sometimes provide information, not otherwise available, about these mechanisms. Fluctuations may be characterized by their spectra which are obtained from a Fourier analysis of the experimental records. When a theory for membrane processes is available, it makes predictions about fluctuation spectra and therefore may be tested by examining these spectra. Theories about gating behavior at the frog neuromuscular junction have been tested in this way, and it has been possible, in addition, to estimate the conductance of one open channel, a quantity not susceptible to direct measurements. Various physical pictures are capable of yielding the same macroscopic behavior for axon membranes, that is, the Hodgkin-Huxley equations, but these various mechanisms predict that the current fluctuations around their mean values should have different characteristics. Fluctuation analysis may, then be of value in elucidating the physical basis for axon conductance changes.

Analysis of Variance↗
PubMed2001

Density functional computations of proton affinity and gas-phase basicity of proline.

The proton affinity and gas-phase basicity of proline were evaluated by using density functional theory coupling the B3-LYP hybrid functional with the extended 6--311++G** basis set. Cis and trans conformations of the carboxyl moiety for both exo and endo ring structures were considered for the neutral proline. The results show that the most stable structure of proline has the endo ring conformation with the carboxyl group in the cis position. The structure at the global minimum is stabilized by an intramolecular hydrogen bond. The nitrogen of the ring in the exo form is the preferred protonation site. The calculated proton affinity (924.3 kJ mol(-1)) and gas-phase basicity (894.4 kJ mol(-1)) are in very good agreement with the experimental counterparts.

Gases↗
PubMed2006

Automated in vivo segmentation of carotid plaque MRI with Morphology-Enhanced probability maps.

MRI is a promising noninvasive technique for characterizing atherosclerotic plaque composition in vivo, with an end-goal of assessing plaque vulnerability. Because of limitations arising from acquisition time, achievable resolution, contrast-to-noise ratio, patient motion, and the effects of blood flow, automatically identifying plaque composition remains a challenging task in vivo. In this article, a segmentation method using maximum a posteriori probability Bayesian theory is presented that divides axial, multi-contrast-weighted images into regions of necrotic core, calcification, loose matrix, and fibrous tissue. Key advantages of the method are that it utilizes morphologic information, such as local wall thickness, and coupled active contours to limit the impact from noise and artifacts associated with in vivo imaging. In experiments involving 142 sets of multi-contrast images from 26 subjects undergoing carotid endarterectomy, segmented areas of each of these tissues per slice agreed with histologically confirmed areas with correlations (R(2)) of 0.78, 0.83, 0.41, and 0.82, respectively. In comparison, manually identifying areas blinded to histology yielded correlations of 0.71, 0.76, 0.33, and 0.78, respectively. These results show that in vivo automatic segmentation of carotid MRI is feasible and comparable to or possibly more accurate than manual review for quantifying plaque composition.

Algorithms↗
PubMed2004

Content-based interpretation aids for health-related quality of life measures in clinical practice. An example for the visual function index (VF-14).

BACKGROUND: In spite of a well-established development of instruments, difficulty in interpreting health related quality of life scores may limit its use in clinical practice. OBJECTIVE: To develop generalizable interpretation aids for a measure of perceived functional visual status, the VF-14 index. DESIGN: Item Response Theory (Rasch analysis) was used to analyze the performance of VF-14 items. The 'ruler' aid was derived from the most difficult activity (item) a patient is able to do without difficulty; the 'clinical scenarios' aid, first identified all significantly different clusters of items within the index and then estimated the mean expected difficulty (responses) to perform a benchmark item in each cluster. SETTING: The study was conducted in four hospitals and six ambulatory cataract surgery centers in Barcelona, Spain. PATIENTS: One hundred and ninety-eight patients scheduled for first eye cataracts surgery. MEASUREMENTS: The self-reported VF-14 index and clinical measures were used. RESULTS: All VF-14 items were found unidimensional with three items showing only partial misfit. For a patient with a VF-14 Rasch score of 71, the 'ruler' aid indicated that 'doing fine handwork' would be the most requiring activity he/she would perform without difficulty. The 'clinical scenarios' aid estimated that such a patient would be unable to 'drive at night', would have some difficulty 'reading small print' and no difficulty 'doing fine handwork', 'watching TV' or 'recognizing people'. Concordance between modeled and observed responses was fair to substantial. CONCLUSIONS: Simple content-based interpretation aids for the VF-14 scores were developed that should facilitate its use in clinical practice. These aids should be easily generalizable to other quality of life instruments.

Activities of Daily Living↗
PubMed1998

A multivariate logistic model (MLM) for analyzing binary family data.

We consider modeling the familial correlation between 2 related individuals using a multiple logistic regressive model. It is shown that there is a discrepancy in the marginal probability of the second individual. We investigate the conditions under which this discrepancy can be minimized and show how it can have a direct effect on handling missing values and ascertainment. We derive a functional relationship between the parameters in the model that eliminates this discrepancy, hence solving the problems that can arise in the handling of missing values and ascertainment. Because this methodology fails when there are more than 2 related individuals, we present a new model based on a multivariate logistic distribution. Residual familial correlations can be directly related to the parameters of this model. The likelihood for family data under this model is independent of the order in which the family members enter the calculation. The marginal probabilities can be easily computed.

Data Interpretation, Statistical↗
PubMed1996

Testing for adverse reactions using prescription event monitoring.

The Drug Safety Research Unit's current methods of investigating adverse drug reactions using prescription event monitoring are discussed. The statistical properties of estimators of rates of occurrence of events in post-marketing surveillance using prescription event monitoring are considered, and a simple model is proposed based on an exponential distribution of time to first occurrence of the event. It is shown that current methodology closely relates to the use of maximum likelihood estimation under this assumption and the distributions of the estimators are shown to be approximately normal, which allows simple confidence intervals and tests to be developed. Two recent applications are considered and corresponding simulations are presented to verify the approximate properties of the test statistics, based on ratios of rates over time and between drugs. Sources of bias in the rates and rate ratios are considered, including under-reporting in later months. A rule-of-thumb, developed from many years experience, is shown to be generally conservative, except when these under-reporting biases are large.

Adverse Drug Reaction Reporting Systems↗
PubMed1997

Estimating a relative risk across sparse case-control and follow-up studies: a method for meta-analysis.

Meta-analysis is the quantitative technique of combining results from different studies. There is a variety of procedures available for combining effect measures across epidemiologic studies. None of these methods provides an overall effect estimate when the data are sparse within studies and come from different study designs. In this paper we discuss the statistical relations between case-control studies and two types of follow-up studies. We use these relations to develop an exact methodology for combining results across study designs. We also use these relations to derive Mantel-Haenszel type formulae for summarizing results across studies. We illustrate these techniques with data pertaining to breast implants and connective tissue disease.

Breast Implants↗