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Results for “Model explainability”

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At least 1,783 records · Page 99Linked to original sources

PubMed2003

Investigation of cervical muscle mechanisms during jaw movement--using a prototype head-jaw-neck model--.

To explain the pain and dysfunction of neck during jaw movement associated with malocclusion, the physiologic relationships between jaw and cervical movement should be understood. However the complicated reflex effects made it difficult to investigate the biomechanical relationship between the head-neck components. For this reason we have created a model for mechanical system dynamic analysis of the normal stomatognathic system to assess the biomechanics of the cervical movement and muscle activity during jaw movement. We have also statistically validated the model and quantitatively verified the model to the human subject by the amounts and conditions of cervical muscle activity. During jaw opening-closing phases the movement of the model was highly correlated to the subject with an identical movement. However low consistency was achieved during intercuspid phase. These findings indicate the establishment of a valid system, which can be used to evaluate the biomechanical relationships between jaw and cervical movement. Moreover the model verification of cervical muscle activity indicate the mechanical action of jaw can be the primary factor to modify cervical muscles, and cervical muscles coordinate to resist changes in head balance during jaw movement to maintains head posture.

Adult↗

PubMed1996

Gastrointestinal illness and the biopsychosocial model.

The derivation of and concepts underlying the biopsychosocial model have not been well explained. This model does not relate psychosocial processes to illness in a linear fashion (e.g., as "psychogenic" or "psychophysiologic"). Rather, the model considers the degree to which factors interact to explain an illness condition. As an example, the irritable bowel syndrome is not caused by a single etiology. Rather, it may result from dysregulation of central and enteric nervous system (CNS/ENS) function manifest as dysmotility and/or visceral sensitivity, and modified by psychosocial processes, all of which uniquely determine the experience of the illness. In this discussion, I trace the derivation of the biopsychosocial model and its application in modern gastroenterologic research and clinical practice.

Gastrointestinal Diseases↗

PubMed2003

Separating trait effects from trait-specific method effects in multitrait-multimethod models: a multiple-indicator CT-C(M-1) model.

An overview of several models of confirmatory factor analysis for analyzing multitrait-multimethod (MTMM) data and a discussion of their advantages and limitations are provided. A new class of multi-indicator MTMM models combines several strengths and avoids a number of serious shortcomings inherent in previously developed MTMM models. The new models enable researchers to specify and to test trait-specific-method effects. The trait and method concepts composing these models are explained in detail and are contrasted with those of previously developed MTMM models for multiple indicators. The definitions of the models are explained step by step, and a practical empirical application of the models to the measurement of 3 traits x 3 methods is used to demonstrate their advantages and limitations.

Affect↗

PubMed2000

A qualitative model for the histamine H3 receptor explaining agonistic and antagonistic activity simultaneously.

A pharmacophore model for histamine H3 ligands is derived that reveals the putative interaction of both H3 agonists and antagonists with an aspartate residue of the receptor. This interaction is determined by applying the density functional theory implemented in a program package adapted for parallel computers. The model reveals a molecular determinant explaining efficacy as the conformation of the aspartic acid residue differs according to whether it is binding to agonists or antagonists. The differences in structure-activity relationships (SAR) observed for the lipophilic tails of different classes of H3 antagonists are now explained, since the model reveals two distinct lipophilic pockets available for antagonist binding.

Aspartic Acid↗

PubMed2000

Sheath model for radio-frequency-biased, high-density plasmas valid for all omega/omega(i)

A model is proposed for sheaths in high-density discharges, with radio-frequency (rf) bias applied at frequencies omega comparable to omega(i), the ion plasma frequency at the edge of the sheath. The model treats ion dynamics using fluid equations, including all time-dependent terms. Model predictions for current, impedance, and power were compared to measurements performed in high-density discharges in argon at 1.33 Pa (10 mTorr) at rf bias frequencies from 0.1 to 10 MHz (omega/omega(i) from 0.006 to 1.8) and rf bias voltages from 1 to 200 V. Model predictions were in good agreement with measurements, much better than that obtained by models that neglect time-dependent ion dynamics. In particular, differences of as much as 40-50 % between power measurements and the power predicted by previous models are now explained and eliminated. The model also explains why methods of extracting plasma parameters from electrical measurements using previous sheath models may fail, and it suggests more accurate methods of extracting these parameters.

Journal Article↗

PubMed1995

Health belief and self-efficacy models: their utility in explaining college student condom use.

This investigation tested the ability of the Health Belief Model (HBM), dimensions of self-efficacy, various behavioral variables (i.e., number of sex partners in the past 12 months, frequency of drunkenness during sexual intercourse, and number of diagnosed sexually transmitted diseases), and demographic measures to distinguish between three condom user groups (i.e., nonusers, sporadic users, and consistent users). The usable sample consisted of 366 college students, ages 18 to 24. The study operationalized the following HBM components: perceived susceptibility, perceived benefits, and perceived barriers. The multidimensional Condom Use Self-Efficacy Scale (CUSES) was also used in this investigation. Results from a discriminant analysis indicated that sporadic users were best distinguished from both consistent and nonusers by number of sex partners in the past year, frequency of drunkenness during sexual intercourse, perceived susceptibility to HIV/AIDS and other STDs, and a self-efficacy factor labeled Assertive. The sporadic users had significantly more sex partners, were drunk more often when engaging in sexual intercourse, perceived themselves as more susceptible to HIV/AIDS and other STDs, and were less confident in their ability to discuss and insist on condom use with a partner. It was also discovered that each condom user group was best defined by different subsets of discriminating variables. Implications of these findings for campus-based prevention programs and future research are discussed.

Adolescent↗

PubMed2006

The development of a Local Index of Need (LIN) and its use to explain variations in social services expenditure on mental health care in England.

Wide variations in deprivation exist across England and it is likely that these variations translate into differences in the need for mental health care. Social Services Departments in England account for a substantial proportion of mental health expenditure. It is important that the distribution of expenditure reflects mental health needs. This paper's aims are to (1) describe the development of a new indicator of mental health needs, (2) use the index to explain variations in social services expenditure on mental health, and (3) compare the index with other established measures of need. A principal components analysis of sociodemographic variables considered to be indicators of need was used to produce four distinct factors for 148 Local Authority areas in England. A weighted sum of these factors was used to produce a single index. (Weights were the proportion of variance explained by each factor.) The index was used in a regression model to explain variations in spending on mental health care and was compared with (1) a model containing the four individual factors, (2) the current method of allocating resources, (3) the index used to allocate resources to primary care trusts, (4) the Mental Illness Needs Index (MINI), (5) four indices of deprivation produced by the Office of the Deputy Prime Minister, and (6) the average of the above four indices. The new index could explain 54% of variation, compared with 56% using the current method. The four-factor model could explain 66%, whilst the other models could explain between 37% and 20%. This new index has the advantage that it is not based on previous levels of utilisation or expenditure and yet still explains a comparable amount of variation as the current method. However, a disaggregated model containing individual factors may be preferable.

Adolescent↗

PubMed2002

Dynamic model for the popularity of websites.

In this paper, we have studied a dynamic model to explain the observed characteristics of websites in the World Wide Web. The dynamic model consists of the self-growth term for each website and the external force term acting on the website. With simulations of the model, we can explain most of the important characteristics of websites. These characteristics include a power-law distribution of the number of visitors to websites, fluctuation in the fractional growth of individual websites, and the relationship between the age and the popularity of the websites. We also investigated a few variants of the model and showed that the ingredients included in the model adequately explain the behavior of the websites.

Journal Article↗

PubMedDate not supplied

[A model of oligomeric enzymes explaining stepwise kinetic curves].

The complex kinetics of some oligomeric enzymes has been analysed. For interpreting such kinetics a theoretical model of an oligomeric enzyme is suggested, which is a modification of the "flip-flop" mechanism considered by Lazdunski et al. in 1971. Using our model, one can qualitatively interpret stepwise kinetic curves, i.e. the curves with few intermediate plateaus. Such curves are known from literature but have not exhaustively been explained. It is supposed that the enzyme kinetic curves can sometimes be of non-differential functions. The model used can also be applied to the kinetics of polyenzyme complexes.

Catalysis↗

PubMed2003

Mass discrimination in mammography: experiments using hybrid images.

RATIONALE AND OBJECTIVES: In a previous publication concerning detection of masses in mammograms it was shown that the amplitude (contrast) required for detection increased as mass size increased. The work presented here was designed to measure the variation of amplitude threshold for discrimination between masses as a function of lesion size. MATERIALS AND METHODS: A hybrid image method with digitized masses added to digitized normal mammograms was used. The masses were extracted from surgical specimen radiographs. Observer experiments were performed using the two-alternative forced-choice method with images displayed on a computer monitor. There were two tasks: (1) discrimination between a ductal carcinoma and a fibroadenoma, and (2) discrimination between two ductal carcinomas. Masses were scaled to cover the linear size range from 1 to 16 mm. Three observers took part, two physicists and a radiologist. RESULTS: The discrimination contrast-detail (CD) diagrams were found to have minimum threshold amplitudes at lesion sizes near 4 mm. The detection results had demonstrated an unusual contrast-detail diagram form with threshold amplitudes monotonically increasing with lesion size for lesions larger than 1 mm, which was opposite the usual result for image noise. Discrimination thresholds or masses larger than 4 mm were approximately 1.5-2 times those reported for detection of the lesions. CONCLUSION: The detection results had been explained using a relatively simple model based on signal detection theory with some characteristics of the human visual system included. The observer model cannot explain the discrimination results, so additional complexity must be introduced to the observer model.

Breast Neoplasms↗

PubMed1987

Kaposi's sarcoma: a trifactorial model.

To explain the epidemiology of Kaposi's sarcoma, including its predominance in men, I present a theory based on three concurrent factors: immunodeficiency, exposure to a specific viral agent, and a recessive, highly prevalent X-linked regulatory gene. The X-linked locus is inferred from comparing the aberrant lymphaticovenous nature of immature lesions with absence of lymphaticovenous connections in XO karyotypes. The theory predicts that for heterosexual populations without sex differences in viral exposure or degree of immunodeficiency, the male-to-female ratio of Kaposi's sarcoma will equal the inverse of the lesion's frequency causative virus. In addition, an increased incidence of Kaposi's sarcoma is expected outside of the context of the acquired immunodeficiency syndrome as the causative virus is transmitted separately from the human immunodeficiency virus.

Humans↗

PubMedDate not supplied

A temporal model for early vision that explains detection thresholds for light pulses on flickering backgrounds.

A model is presented for the early (retinal) stages of temporal processing of light inputs in the visual system. The model consists of a sequence of three adaptation processes, with two instantaneous nonlinearities in between. The three adaptation processes are, in order of processing of the light input: a divisive light adaptation, a subtractive light adaptation, and a contrast gain control. Divisive light adaptation is modeled by two gain controls. The first of these is a fast feedback loop with square-root behavior, the second a slow feedback loop with logarithm-like behavior. This can explain several aspects of the temporal behavior of photoreceptor outputs. Subtractive light adaptation is modeled by a high-pass filter equivalent to a fractional differentiation, and it can explain the attenuation of low frequencies observed in ganglion cell responses. Contrast gain control in the model is fast (Victor, 1987), and can explain the decreased detectability of test signals that are superimposed on dynamic backgrounds. We determine psychophysical detection thresholds for brief test pulses that are presented on flickering backgrounds, for a wide range of temporal modulation frequencies of these backgrounds. The model can explain the psychophysical data for the full range of modulation frequencies tested, as well as detection thresholds obtained for test pulses on backgrounds with increment and decrement steps in intensity.

Adaptation, Ocular↗

PubMed2005

Explained variation in a model of therapeutic decision making is partitioned across patient, physician, and clinic factors.

BACKGROUND AND OBJECTIVE: Data on therapeutic decision making have a multilevel structure that can include patient-, provider-, and facility-level variables. A statistical method is presented for attributing explained variation in patient care to different levels of aggregation in a multilevel model with the aim of prioritizing and targeting quality improvement interventions. STUDY DESIGN AND SETTING: The proposed method is used in an analysis of adherence to evidence-based guidelines for the care of patients at risk of osteoporosis. Explained variation from a multilevel model of appropriate care is partitioned across patient-, physician-, and clinic-level factors. RESULTS: The combination of patient, physician, and clinic factors explained 20.0% of the variation in patient care. Individual physician effects explained 14.0% of the variation in the data; however, more than half of this explained variation could have been attributed to the individual clinic effect. Patient fixed effects alone explained 13.4% of the variation in the observed clinical decisions. CONCLUSION: The proposed approach is an intuitive and statistically valid method for attributing explained variation in a multilevel analysis of therapeutic decision making.

Administration, Oral↗

PubMed2003

Attention-biased multi-stable surface perception in three-dimensional structure-from-motion.

Retinal velocity distributions can lead to a percept of three-dimensional (3D) structure (structure-from-motion [SFM]). SFM stimuli are intrinsically ambiguous with regard to depth ordering. A classic example is the orthographic projection of a revolving transparent cylinder, which can be perceived as a 3D cylinder that rotates clockwise and counterclockwise alternately. Prevailing models attribute such bistable percepts to inhibitory connections between neurons that are tuned to opposite motion directions at equal binocular disparities. Cylinder stimuli can yield not only two but as many as four different percepts. Besides the well-documented clockwise and counterclockwise spinning transparent cylinders, observers can also perceive two transparent half-cylinders, either convex or concave, one in front of the other. Observers are able to bias the time during which a percept is present by attending to one or the other percept. We examined this phenomenon quantitatively and found that in standard SFM stimuli, the percept of two convex transparent half-cylinders can occur just as often as the percept of (counter-) clockwise spinning cylinders. So far, however, all interpretations of experimental (neurophysiological) data and all proposed mechanisms for SFM perception have focused solely on the two classical cylinder percepts. Prevailing models cannot explain the existence of the other two percepts. We suggest an alternative model to explain attention-biased multi-stable perception.

Attention↗

PubMed2006

A neural network implementation of a saliency map model.

The saliency map model proposed by Itti and Koch [Itti, L., & Koch, C. (2000). A saliency-based search mechanism for overt and covert shifts of visual attention. Vision Research, 40, 1489-1506] has been a popular model for explaining the guidance of visual attention using only bottom-up information. In this paper we expand Itti and Koch's model and propose how it could be implemented by neural networks with biologically realistic dynamics. In particular, we show that by incorporating synaptic depression into the model, network activity can be normalized and competition within the feature maps can be regulated in a biologically plausible manner. Furthermore, the dynamical nature of our model permits further analysis of the time course of saliency computation, and also allows the model to calculate saliency for dynamic visual scenes. In addition to explaining the high saliency of pop-out targets in visual search tasks, our model explains attentional grab by sudden-onset stimuli, which was not accounted for by previous models.

Attention↗

PubMed1995

Consciousness: perspectives from symbolic and connectionist AI.

While consciousness has not been a major concern of most AI researchers, some theorists have tried to explore how computational models might explain consciousness. I explore how far computational models might go in explaining consciousness, focusing on three aspects of conscious mental states: their intrinsic intentionality, the awareness a subject has of the contents of these intentional states, and the distinctive qualitative character of these states. I describe and evaluate strategies for developing connectionist systems that satisfy these aspects of consciousness.

Animals↗

PubMed1980

Deoxyribonuclease I generates single-stranded gaps in chromatin deoxyribonucleic acid.

Production of 10-base multiple DNA ladder fragments during DNase I digestion of chromatin is explained by a model which does not involve site-specific nicking by the DNase I. This model was tested because it explains why 10-base (actually 10.4 base) multiple-related fragments are paradoxically generated by both endonucleolytic (DNase I) and exonucleolytic (exonuclease III) mechanisms. This new model also explains the phenomenon of substantial single-stranded DNA production during DNase I digestion of chromatin. The latter phenomenon has been widely observed but is not explained by previous models. The single-stranded gap model to be presented makes testable predictions. Primarily, these are that DNase I produces single-stranded gaps in chromatin DNA and that the termini of 10-base multiple ladder fragments are separated by single-stranded gaps. Single-stranded gap production by DNase I was confirmed by a number of methods. Sensitivity of ladder band components (from DNase I but not staphylococcal nuclease digests) to S1 nuclease suggested that the ladder fragments themselves may compose a significant portion of these gaps. Separation of ladder fragment termini by single-stranded gaps was verified by demonstrating both resistance to the nick-specific NAD+-dependent ligase and sensitivity to T4 ligase which can ligate across gaps. Many single-stranded gaps, occurring both individually and clusters, were observed by electron microscopy using either cytochrome c labeling (where the gaps) are thinner than duplex) or gene 32 protein labeling (gaps thicker than duplex). Gap sizes were estimated by protecting them with gene 32 protein and digesting away unprotected duplexes. By this method, gap sizes fall into a ladder distribution (from 10 or 20 bases up to 120 bases), which, at least in the region of the shorter sizes, clearly indicates the sizes of single-stranded gaps formed in chromatin by DNase I.

Animals↗

PubMed2006

The C-terminus of complement regulator Factor H mediates target recognition: evidence for a compact conformation of the native protein.

The complement inhibitor Factor H has three distinct binding sites for C3b and for heparin, but in solution uses specifically the most C-terminal domain, i.e. short consensus repeats (SCR) 20 for ligand interaction. Two novel monoclonal antibodies (mABs C14 and C18) that bind to the most C-terminal domain SCR 20 completely blocked interaction of Factor H with the ligands C3b, C3d, heparin and binding to endothelial cells. In contrast, several mAbs that bind to the N-terminus and to the middle regions of the molecule showed no or minor inhibitory effects when assayed by enzyme-linked immunosorbent assay (ELISA) and ligand interaction assays. This paradox between a single functional binding site identified for native Factor H versus multiple interaction sites reported for deletion constructs is explained by a compact conformation of the fluid phase protein with one accessible binding site. On zymosan particles mAbs C14 and C18 blocked alternative pathway activation completely. Thus demonstrating that native Factor H makes the first and initial contact with the C terminus, which is followed by N terminally mediated complement regulation. These results are explained by a conformational hypothetical model: the native Factor H protein has a compact structure and only one binding site accessible. Upon the first contact the protein unfolds and exposes the additional binding sites. This model does explain how Factor H mediates recognition functions during complement control and the clustering of disease associated mutations in patients with haemolytic uraemic syndrome that have been reported in the C-terminal recognition domain of Factor H.

Antibodies, Monoclonal↗