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Results for “Utility Theory”

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PubMed2005

GC composition of the human genome: in search of isochores.

The isochore theory, proposed nearly three decades ago, depicts the mammalian genome as a mosaic of long, fairly homogeneous genomic regions that are characterized by their guanine and cytosine (GC) content. The human genome, for instance, was claimed to consist of five distinct isochore families: L1, L2, H1, H2, and H3, with GC contents of <37%, 37%-42%, 42%-47%, 47%-52%, and >52%, respectively. In this paper, we address the question of the validity of the isochore theory through a rigorous sequence-based analysis of the human genome. Toward this end, we adopt a set of six attributes that are generally claimed to characterize isochores and statistically test their veracity against the available draft sequence of the complete human genome. By the selection criteria used in this study: distinctiveness, homogeneity, and minimal length of 300 kb, we identify 1,857 genomic segments that warrant the label "isochore." These putative isochores are nonuniformly scattered throughout the genome and cover about 41% of the human genome. We found that a four-family model of putative isochores is the most parsimonious multi-Gaussian model that can be fitted to the empirical data. These families, however, are GC poor, with mean GC contents of 35%, 38%, 41%, and 48% and do not resemble the five isochore families in the literature. Moreover, due to large overlaps among the families, it is impossible to classify genomic segments into isochore families reliably, according to compositional properties alone. These findings undermine the utility of the isochore theory and seem to indicate that the theory may have reached the limits of its usefulness as a description of genomic compositional structures.

Base Composition↗

PubMed2026

Trade-offs in avian parental care: a review of theory and meta-analysis of brood size manipulations.

The selective forces shaping parental care have been studied for over 50 years. While theoretical and experimental work has yielded qualitative progress, the large body of empirical work testing predictions about parental investment based on life-history trade-offs has yet to be synthesized. We first provide an overview of the core life-history theory exploring how selection might shape parental care. We then conduct a systematic review and meta-analysis on studies that experimentally manipulated brood size in birds, a widely used experimental approach to manipulate parental investment. We extracted 313 estimates from 62 studies representing 31 species of birds from 19 different families and tested key predictions on trade-offs in parental care derived from theory. Our analysis provides strong support for some predictions about life-history trade-offs in parental care, but weak or equivocal support for others. Specifically, we found that overall, avian parents respond to brood size manipulations as predicted by life-history theory: they increased care in response to brood enlargement, and decreased care in response to brood reductions. Furthermore, for the same relative manipulation size, responses to brood reductions were greater than responses to brood enlargements. This finding is consistent with predictions derived from life-history theory based on some types of non-linear utility curves. However, many predictions derived from theory are not well supported by our comparative analysis. Species' life-history traits such as clutch size (a measure of current reproduction), adult survival, and broods per year (two measures of future reproduction), explained little, if any, among-species variation in response to brood size manipulations. Several factors may explain this. We highlight that brood size manipulations may affect more than just perception of the value of current reproduction, such as altering parents' perception of predation risk. Importantly, these unintended consequences could lead to asymmetric responses like those we observed. Other common experimental approaches - such as hormone manipulations, altering a partner's effort, and food supplementation - often affect multiple traits or fitness components simultaneously, or may involve cues that poorly match the evolved mechanisms guiding parental behaviour. Our review of both theory and experimental approaches suggests that there are multiple opportunities for more precise experiments. We offer several recommendations for effective designs. One is improved understanding of the biology underlying the functions relating to costs and benefits, with careful consideration of not only how the manipulation will affect only one of those, but also the mechanisms that might alter how parents perceive the manipulation. We also emphasize general principles, such as assessing alternative hypotheses and devising multiple independent tests. Armed with these recommendations, we believe there are new opportunities to increase the strength of inference achieved from studies aimed at understanding the trade-offs affecting the evolution of parental care.

Animals↗

PubMed1992

Clinical problem solving and the biopsychosocial model.

Engel's biopsychosocial model, while unifying the sciences relevant to medicine under general systems theory, is of limited utility in organizing bedside clinical problem solving. The authors consider this issue in light of the structure and goals of the clinical encounter. The biopsychosocial model is a model for organizing the sciences relevant to medicine; however, medical/psychiatric practice poses problems both within and outside the scientific realm. Since the biopsychosocial model cannot account for clinical problems to which the methods of science do not apply, the authors seek to facilitate biopsychosocial problem solving by proposing a clinical decision-making model that complements the biopsychosocial model. Their model directs the clinician's attention to three core aspects of the clinical encounter: problems of knowledge, ethics, and pragmatics. The authors reconsider Engel's case of Mr. Glover to demonstrate the anticipatory emphasis of the model. Other clinical examples are used to demonstrate the difficulties arising from mistaking one kind of aspect of medicine for another. When these three aspects of medicine are respected equally, a biopsychosocial practice is unavoidable.

Decision Making↗

PubMed1979

Framing pictures: the role of knowledge in automatized encoding and memory for gist.

In general, frame theories are theories about the representation and use of knowledge for pattern recognition. In the present article, the general properties of frame theories are discussed with regard to their implications for psychological processes, and an experiment is presented which tests whether this approach yields viable predictions about the manner in which people comprehend and remember pictures of real-world scenes. Normative ratings were used to construct six target pictures, each of which contained both expected and unexpected objects. Eye movements were then recorded as subjects who anticipated a difficult recognition test viewed the targets for 30 sec each. Then, the subjects were asked to discriminate the target pictures from distractors in which either expected or unexpected objects had been changed. One consequence of the embeddedness of frame systems is that global frames may function as "semantic pattern detectors," so that the perceptual knowledge in them could be used for relatively automatic pattern recognition and comprehension. Thus, subjects might be able to identify expected objects by using automatized encoding procedures that operate on global physical features. In contrast, identification of unexpected objects (i.e., objects not represented in the currently active frame) should generally require more analysis of local visual details. These hypotheses were confirmed with the fixation duration data: First fixations to the unexpected objects were approximately twice as long as first fixations to the expected objects. On the recognition test, subjects generally noticed only the changes that had been made to the unexpected objects, despite the fact that the proportions of correct rejections were made conditional on whether the target objects had been fixated. These data are again consistent with the idea that local visual details of objects represented in the frame are not neccesary for identification and are thus not generally encoded. Further, since subjects usually did not notice when expected objects were deleted or replaced with different expected objects, it was concluded that if two events instantiate the same frame, they may often be indistinguishable, as long as any differences between them are represented as arguments in the frame. Thus, for the most part, the only information about an event that is episodically "tagged" is information which distinguishes that particular event from others of the same general class. The data reinforce the utility of a frame theory approach to perception and memory.

Discrimination Learning↗

PubMed1996

Risk factors for youth victimization: beyond a lifestyles/routine activities theory approach.

Past efforts to understand the risks for youth victimization have primarily utilized concepts from lifestyle or routine activity theory, such as the increased exposure and reduced guardianship that are entailed when youth engage in risky or delinquent behavior. In this article, we argue that other personal characteristics put youth at risk, not through any lifestyle or routine activity mechanism, but by making certain youth more "congruent" with the needs, motives, or reactivities of potential offenders. Three specific types of such characteristics are those that increase the potential victim's target vulnerability (e.g., physical weakness or psychological distress), target gratifiability (e.g., female gender for the crime of sexual assault), or target antagonism (e.g., behaviors or ethnic or group identities that may spark hostility or resentment). Using data from a national youth survey, we test variables measuring such aspects of target congruence and show that they make a significant contribution over and above lifestyle variables alone in predicting nonfamily, sexual, and parental assault.

Adolescent↗

PubMed2000

Physical activity and exercise counseling in primary care.

Despite the known health benefits of regular physical activity and exercise, physical inactivity is prevalent among American adults. The primary care provider is in an optimal position to provide physical activity and exercise counseling. The Physician-based Assessment and Counseling for Exercise (PACE) program, which utilizes the stages of change theory, provides a valuable framework for exercise counseling. This article discusses exercise counseling theories and research and provides an overview of the PACE program, including the PACE protocols and the model's utility in primary care.

Adult↗

PubMed1989

Impact of juvenile arthritis on families. An educational assessment.

State of the art patient education programs have as their goals changes in behaviors, coping styles, health status, and/or costs. The accomplishment of these goals often involves not only the patient but also his or her whole family. This is especially true if the patient is a child. Based on this premise, we undertook an educational needs assessment of 50 children with juvenile arthritis (JA) and their families. Through utilization of a grounded theory methodology, open-ended questionnaires were completed by JA children, their parents, and their siblings. The resulting analysis suggests (1) the need for family-based education, (2) differing needs of various family members, and (3) several hypotheses for further study.

Adolescent↗

PubMed2005

On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.

Journal Article↗

PubMed1981

Effect of chronic ethanol exposure on the electric membrane properties of DRG neurons in cell culture.

Neural cell cultures of adult mouse dorsal root ganglia were utilized to investigate the effects of chronic ethanol exposure on neuronal electric membrane properties (EMP). After 12 days of exposure to various ethanol concentrations, the EMP of the neurons were determined in ethanol-free medium. Significant changes in a number of EMP were observed. Of particular physiological significance were decreased specific membrane resistance, increased specific membrane capacitance, relatively little change in membrane time constant, and increased electrical excitability. Various features of the action potential were also affected, e.g., reduced overshoot, afterhyperpolarization, and rate of rise. In preliminary experiments, EMP were determined at varying periods after the cultures had been withdrawn from ethanol medium and maintained in ethanol-free medium. These results indicated that the altered EMP persisted as long as one (Cm) to two (Rm) weeks after ethanol withdrawal. A possible mechanism for these ethanol-induced changes in EMP was suggested, utilizing the membrane expansion theory of anesthesia. Because of few previous reports demonstrating significant electrophysiological effects of ethanol at pharmacological concentrations, the neural cell culture system provides a useful new experimental model for studying the action of chronic ethanol exposure on neuronal EMP and the physical basis of the tolerance and withdrawal phenomena found in alcoholism and addiction in general. After being maintained for 12 days in culture media containing various concentrations of ethanol, non-neuronal cell survival was observed to have decreased in an approximately linear manner with increasing ethanol levels. By contrast, neuron survival was not affected until ethanol concentrations greater than 0.34 g % were used. This decreased cell survival due to chronic exposure to physiological levels of ethanol has not been reported previously. Neural cell cultures may therefore be useful for investigating the cellular pathology of chronic alcoholism and fetal alcohol syndrome.

Animals↗

PubMed1997

A general statistical framework for frequency-domain analysis of EEG topographic structure.

A wide variety of rhythmic electrophysiological phenomena--including driven, induced, and endogenous activities of cortical neuronal masses--lend themselves naturally to analysis using frequency--domain techniques applied to multichannel recordings that discretely sample the overall spatial pattern of the rhythmic activity. For such cases, a large but so far poorly utilized body of statistical theory supports a third major approach to topographic analysis, complementing the more familiar mapping and source-recovery techniques. These methods, many of which have only recently become computationally feasible, collectively provide general solutions to the problem of detecting and characterizing systematic differences that arise--not only in the spatial distribution of the activity, but also in its frequency-dependent between-channel covariance structure--as a function of multiple experimental conditions presented in conformity with any of the conventional experimental designs. This application-oriented tutorial review provides a comprehensive outline of these resources, including: (1) real multivariate analysis of single-channel spectral measures (and measures of between-channel relationships such as coherence and phase), (2) complex multivariate analysis based on multichannel Fourier transforms, and (3) complex multivariate analysis based on multichannel parametric models. Special emphasis is placed on the potential of the multichannel autoregressive model to support EEG (and MEG) studies of perceptual and cognitive processes.

Cerebral Cortex↗

PubMed1999

The Detection of Structural Transformations in Kaolin Suspensions by Ultrasound.

Thefractal dimension of kaolin flocs suspended in water was increased by the addition of potassium chloride and indirectly monitored by low-power ultrasonic pulses in a test cell with a "pitch-catch" configuration. The results from these measurements were compared with fractal dimensions obtained from quasi-elastic light-scattering measurements in a kaolin suspension of a much lower solid volume fraction. Further comparison with a coupled phase theory of ultrasound propagation, utilizing measured slope viscosity and particle size distribution, revealed that the observed changes in the ultrasound signature were commensurate with changes in the fractal dimension observed by light scattering over a potassium chloride concentration range of approximately 0-1 mM. Copyright 1999 Academic Press.

Journal Article↗

PubMed1994

Topography of alpha and theta oscillatory responses upon auditory and visual stimuli in humans.

Brain resonance phenomena and induced rhythms in the brain recently gained importance in electroencephalographic, magnetoencephalographic and cellular studies (Başar and Bullock 1992). It was hypothesized that evoked potentials are superpositions of induced rhythms caused by resonance phenomena in neural populations (Başar et al. 1992). According to Başar (1972), such resonance phenomena are reflected in the main peaks of the amplitude frequency characteristics computed from EEG responses. The present study is based on a frequency domain approach for the evaluation of topography- and modality-dependent properties of oscillatory brain responses. EEG and evoked potentials were recorded from vertex, parietal and occipital scalp locations in 24 volunteers. Two combined methods were applied: (1) amplitude frequency characteristics were computed from the transient evoked responses, and (2) frequency components of the transient responses were obtained by adaptive digital filtering. Our main goal was to investigate theta (4-7 Hz) and alpha (8-15 Hz) response components. (1) Amplitude frequency characteristics. Auditory stimuli elicited theta-alpha compound responses in the 4-11 Hz frequency band (e.g. typical peaking frequency around 7 Hz for vertex recordings). Visual stimuli elicited alpha responses (e.g. typical peaking frequency for vertex recordings around 9-12 Hz). Frequency maxima for visual stimuli thus had main peaks at higher frequency values than frequency maxima for auditory stimuli. (2) Digital filtering confirmed these results: for vertex recordings, theta vs. alpha response amplitudes were 9 muV vs 6 muV for auditory stimuli and 5 muV vs 5 muV for visual stimuli, thus confirming a shift towards higher frequencies, i.e. a more prominent contribution of the alpha range, in the case of visual stimulation. We hypothesize that these properties might reflect site- and modality-specific features of stimulus encoding in the brain in which resonance properties of neuron populations are involved. Furthermore we emphasize the utility of the systems theory approach for a better understanding of brain function by means of EPs.

Biological Clocks↗

PubMed1996

An evolution of pulse speed in arteries.

In this work, treating the artery as a thick-walled cylindrical shell made of an incompressible, isotropic and elastic solid, utilizing the large deformation theory and the stress-strain relation proposed by Demiray (1976b, Trans. ASME Ser. E, J. Appl. Mech., 98, 194-197), an explicit expression for the pulse speed is obtained and the effect of lumen pressure and the axial stretch on wave speed is discussed. Numerical results indicate that the wave speed increases with lumen pressure but decreases with the axial stretch. The results of the present model are compared with our previous work (Demiray, 1988, J. Biomech. 21, 55-58) on the same subject.

Animals↗

PubMed1993

The fear of fear concept: stability, retest artefact and predictive power.

Three related issues concerning the theory, measurement and clinical utility of the fear of fear construct as operationalized by the Agoraphobic Cognitions and Bodily Sensations Questionnaires (Chambless, Caputo, Bright & Gallagher, Journal of Consulting and Clinical Psychology, 52, 1090-1097, 1984) were addressed: stability of ranked scores, stability of means (retest effect) and predictive ability. In addition to measures assessing moods and enduring personality traits, the relevant fear of fear scales (and introducing a companion frequency measure to the BSQ-intensity scale) were administered to somewhat over 60 clients with "panic disorder with agoraphobia" or "agoraphobia without a history of panic attacks" on two occasions, 3 months apart, with no intervention having taken place between first and second testing. As predicted, ranked fear of fear scores were highly stable. In addition, Howarth's mu index values pointed to the description of the fear of fear constructs in terms of traits. Specific fear of fear scales showed evidence of a retest effect. The short-term course of agoraphobic avoidance behaviour in untreated cases was predictable from specific fear of fear variables, even after controlling for their shared variance with pre-test measures of either state anxiety-panic or trait neuroticism. Implications of the findings are discussed.

Adult↗

PubMed1992

Modal reasoning, models, and Manktelow and Over.

Manktelow and Over (1991) argue that their studies of Wason's selection task favor explanations of deontic reasoning based on mental models, but that such theories need to incorporate utilities. This theoretical note proposes a simpler explanation of the phenomena: subjects in the selection task consider only those cards that are explicitly represented in their models of the conditional, and so insight into the task depends on constructing fully explicit models. Such models for modal conditionals of the form, If p occurs then q may occur are: [formula: see text] Each line denotes a separate model, and the models represent either what is possible, or, in the deontic interpretation, what is permissible. A deontic rule is accordingly violated by the contingency: [symbol: see text] p and q, for example the rule, "If you spend more than 100 pounds, then you may take a free gift" is violated by taking the free gift (q) but not spending more than 100 pounds ([symbol: see text] p). If the rule is interpreted as a bi-conditional, then the second of the models, p and [symbol: see text] q, is also now a violation, for example spending more than 100 pounds (p) but not getting the free gift ([symbol: see text] q). Manktelow and Over's instructions lead subjects to focus on one or other of the two sorts of violations of the rule. There is accordingly no need to introduce utilities into models in order to explain the phenomena.

Adult↗

PubMed1979

A computer program for survival comparisons to a standard population.

PROPHAZ is a computer program created for the analysis of survival data using the general proportional hazards model. It was designed specifically for the situation in which the underlying hazard function may be estimated from the mortality experience of a large reference population, but may be used for other problems as well. Input for the program includes the variables of interest as well as the information necessary for estimating the hazard function (demographic and mortality data). Regression coefficients for the variables of interest are obtained iteratively using the Newton-Raphson method. Utilizing large sample asymptotic theory, x2 statistics are derived which may be used to test hypotheses of the form C beta = 0. Input format is completely flexible for the variables of interest as well as the mortality data.

Computers↗

PubMed1984

Polydispersity effects on head-to-tail polymerization of F-actin. A theoretical treatment.

A theoretical description of the release of labeled subunits of F-actin that undergoes head-to-tail polymerization utilizing random-walk theory is extended to the case of a finite-length polymer. An exact expression is given for the number of released subunits in a suitable form for numerical calculation. By comparing the results for a finite-length polymer with that for an infinite-length case, the limitation of the infinite-length approximation is readily known. The results for finite-length polymers are applied to systems with polydispersity. It is shown that the number of labeled subunits released from F-actin depends strongly on the distribution functions of the polymer lengths and the values of the transition probabilities of the random walkers.

Actins↗

PubMed2004

Defining the limits of diving biochemistry in marine mammals.

The field of marine mammal diving biochemistry was essentially untouched when Peter Hochachka turned his attention to it in the mid-1970s. Over the next 30 years, his work followed three main themes in this area: first, most biologists at that time supported the theory that diving mammals utilized enhanced metabolic pathways for hypoxic energy production (glycolysis to lactate) and reduced their metabolic rate while diving. Peter began his work on potential hypoxic adaptations in marine mammals by working out the details of how these pathways would be regulated. By the 1980s, he started to ask how diving mammals balanced the increased demands of exercise with the apparently conflicting demands to reduce aerobic metabolism while exercising underwater. By the 1990s, his work involved complex models of the interplay between the neural, hormonal, behavioral and evolutionary components of diving biochemistry and animal exercise. From a comparative approach, he excelled at bringing themes of hypoxic adaptation from many different types of animals to the field of diving mammal biochemistry. This review traces the history of Peter Hochachka's work on diving biochemistry from the perspective of those of us who spent time with him both inside the laboratory and outside in the field from Antarctica to Iceland.

Adaptation, Physiological↗