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Results for “Predictive Learning Models”

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PubMed1992

A comparison of drug conditioning and craving for alcohol and cocaine.

Craving is a potentially important concept that is difficult to define and study in the laboratory. Although alcohol and cocaine are very different pharmacologically, this discussion emphasizes common factors in addiction to these drugs, such as the tendency of alcoholics and cocaine abusers to crave these substances. I review commonalities in drug conditioning and cue reactivity to alcohol and cocaine. Both drugs support Pavlovian conditioning when they are presented as unconditioned stimuli, whether studied in rodents or humans. In addition, both drugs are craved when abusers are presented with stimuli associated with these drugs. Finally, I propose a theoretical definition of craving based on autoshaping and sign-tracking phenomena that suggests a common mechanism of addiction to these drugs. This model defines craving as a reflection of sign tracking to internal and external stimuli that have in the past reliably predicted presentation of these drugs.

Alcoholism↗

PubMed2006

Discriminating signal from noise: recognition of a movement-based animal display by artificial neural networks.

In this study, we investigated the feasibility of applying neural networks to understanding movement-based visual signals. Networks based on three different models were constructed, varying in their input format and network architecture: a Static Input model, a Dynamic Input model and a Feedback model. The task for all networks was to distinguish a lizard (Amphibolurus muricatus) tail-flick from background plant movement. Networks based on all models were able to distinguish the two types of visual motion, and generalised successfully to unseen exemplars. We used curves defined by the receiver-operating characteristic (ROC) to select a single network from each model to be used in regression analyses of network response and several motion variables. Collectively, the models predicted that tail-flick efficacy would be enhanced by faster speeds, greater acceleration and longer durations.

Agonistic Behavior↗

PubMed2001

Estimation of oxygen mass transfer coefficient in stirred tank reactors using artificial neural networks.

The estimation of volumetric mass transfer coefficient, k(L)a, in stirred tank reactors using artificial neural networks has been studied. Several operational conditions (N and V(s)), properties of fluid (µ(a)) and geometrical parameters (D and T) have been taken into account. Learning sets of input-output patterns were obtained by k(L)a experimental data in stirred tank reactors of different volumes. The inclusion of prior knowledge as an approach which improves the neural network prediction has been considered. The hybrid model combining a neural network together with an empirical equation provides a better representation of the estimated parameter values. The outputs predicted by the hybrid neural network are compared with experimental data and some correlations previously proposed in the literature for tanks of different sizes.

Journal Article↗

PubMedDate not supplied

On-line learning in changing environments with applications in supervised and unsupervised learning.

An adaptive on-line algorithm extending the learning of learning idea is proposed and theoretically motivated. Relying only on gradient flow information it can be applied to learning continuous functions or distributions, even when no explicit loss function is given and the Hessian is not available. The framework is applied for unsupervised and supervised learning. Its efficiency is demonstrated for drifting and switching non-stationary blind separation tasks of acoustic signals. Furthermore applications to classification (US postal service data set) and time-series prediction in changing environments are presented.

Algorithms↗

PubMed1995

Competing global and local completions in visual occlusion.

In visual occlusion 2 amodal-completion tendencies occur frequently. One tendency leads toward the simplest completed shape (a global completion) and the other to a shape for which the completion itself is as simple as possible (a local completion). Two experimental paradigms were used to test the strengths of these completion tendencies: a drawing task and a simultaneous matching task. The experimental results support the notion that the preference for either a global or a local completion is the consequence of a competition between interpretations. Finally, the authors discuss how the preference for a completion can be predicted by a model that is based on a quantification of both global and local aspects.

Adult↗

PubMed1995

Separation of low-level and high-level factors in complex tasks: visual search.

A method for assessing the role of low-level factors in complex tasks is described. The method, which involves comparing simple-discrimination performance and complex-task performance for the same stimuli, was used to assess the role of low-level factors in multiple-fixation visual search. In one experiment, the target and background were composed of line segments that differed in color, orientation, or both; in another, target and background were composed of filtered-noise textures that differed in spatial frequency, orientation, or both. Most of the variance in search time was found to be predictable from the discrimination data, suggesting that low-level factors often play a dominant role in limiting search performance. A signal-detection model is presented that demonstrates how current psychophysical models of visual discrimination might be generalized to obtain a theory that can predict search performance for a wide range of stimulus conditions.

Attention↗

PubMedDate not supplied

Predicting neuronal responses during natural vision.

A model that fully describes the response properties of visual neurons must be able to predict their activity during natural vision. While many models have been proposed for the visual system, few have ever been tested against this criterion. To address this issue, we have developed a general framework for fitting and validating nonlinear models of visual neurons using natural visual stimuli. Our approach derives from linear spatiotemporal receptive field (STRF) analysis, which has frequently been used to study the visual system. However, prior to the linear filtering stage typical of STRFs, a linearizing transformation is applied to the stimulus to account for nonlinear response properties. We used this approach to compare two models for neurons in primary visual cortex: a nonlinear Fourier power model, which accounts for spatial phase invariant tuning, and a traditional linear model. We characterized prediction accuracy in terms of the total explainable variance, given intrinsic experimental noise. On average, Fourier power STRFs predicted 40% of explainable variance while linear STRFs were able to predict only 21% of explainable variance. The performance of the Fourier power model provides a benchmark for evaluating more sophisticated models in the future.

Animals↗

PubMed2006

Student evaluation of the clinical 'curriculum in action'.

AIM: To examine how students' evaluations of the environment, process and outcome of clinical learning interrelated and correlated with assessment results. METHOD: A post hoc study in the 3rd of 5 years in a student-centred, horizontally integrated, objective-based medical curriculum. In the last week of each module, students evaluated what they had learned and how they had learned it using a previously validated, web-based scale. The interrelationships between scale variables and their relationships with summative assessment results were tested using factor analysis, correlation analysis and stepwise multiple regression analysis. RESULTS: Student evaluation yielded 4 summary measures: 2 reflected learning outcomes ('real patient learning' and 'curriculum coverage'), 1 reflected process ('quality of instruction') and 1 reflected environment ('conditions for learning'). They fitted a causal model according to which instruction, conditions for learning and curriculum coverage favoured real patient learning. Real patient learning was rated higher in women than men, and the measures were associated more strongly in women. Performance in end-of-year summative assessments was predicted strongly by mid-year performance but by no other measure. CONCLUSIONS: Students' evaluations of their learning environment and instructional processes correlated with their assessments of 2 outcomes of the curriculum in action: curriculum coverage and real patient learning. There was little shared variance between those measures and students' performance in summative assessments. Given its formative potential, students' evaluation of their curriculum in action could play a useful part in learner-centred clinical education. There is a possibility, which needs further research, that women's evaluations have greater predictive validity than men's. Assessment performance should be regarded not as a solitary gold standard but as just 1 measure of educational outcome.

Attitude of Health Personnel↗

PubMed2000

Bounds on error expectation for support vector machines.

We introduce the concept of span of support vectors (SV) and show that the generalization ability of support vector machines (SVM) depends on this new geometrical concept. We prove that the value of the span is always smaller (and can be much smaller) than the diameter of the smallest sphere containing the support vectors, used in previous bounds (Vapnik, 1998). We also demonstrate experimentally that the prediction of the test error given by the span is very accurate and has direct application in model selection (choice of the optimal parameters of the SVM).

Learning↗

PubMed2002

Racial differences in service utilization: the Forsyth County Aging Study.

Racial differences in correlates and use of formal home and community services and in the predictive ability of the Andersen-Newman model were examined in older African American and white, community-dwelling adults. Results show greater service use by older African Americans and suggest racial differences in the correlates of service use. Racial differences in the predictive ability of the Andersen-Newman model were also evident. While approximately 78 percent of participants (82 percent of whites and 66 percent of African Americans) were correctly identified, findings regarding sensitivity and specificity suggest that much remains to be learned about factors associated with the use of formal home and community services among older adults.

Activities of Daily Living↗

PubMed2006

Predictability of locomotion: effects on updating of spatial situation models during narrative comprehension.

We investigated how the updating of spatial situation models during narrative comprehension depends on the interaction of cognitive abilities and text characteristics. Participants with low verbal and visuospatial abilities and participants with high abilities read narratives in which the protagonist's motions in a fictitious building were either highly predictable or very hard to predict. In Experiment 1, high-ability readers updated spatial situation models only if the protagonist's motions were hard to predict, whereas low-ability readers did so only if the motions were highly predictable. In Experiment 2, facilitated integrative spatial processing compensated for the low-ability participants' resource limitations. As a result, both ability groups updated spatial situation models with hard-to-predict protagonist motions. These results highlight the interactions of cognitive abilities and text characteristics in spatial situation model updating.

Adolescent↗

PubMed2001

Processing bottlenecks in dual-task performance: structural limitation or strategic postponement?

Recent evidence indicates that a central bottleneck causes much of the slowing that occurs when two tasks are performed at the same time. This bottleneck might reflect a structural limitation inherent in the cognitive architecture. Alternatively, the bottleneck might reflect strategic (i.e., voluntary) postponement, induced by instructions to emphasize one task over the other. To distinguish structural limitations from strategic postponement, we examine a new paradigm in which subjects are told to place equal emphasis on both tasks and to emit both responses at about the same time. An experiment using this paradigm demonstrated patterns of interference that cannot easily be attributed to strategic postponement, preparation effects, or conflicts in response production. The data conform closely to the predictions of structural central bottleneck models.

Adult↗

PubMed1993

Comparing decision bound and exemplar models of categorization.

The performance of a decision bound model of categorization (Ashby, 1992a; Ashby & Maddox, in press) is compared with the performance of two exemplar models. The first is the generalized context model (e.g., Nosofsky, 1986, 1992) and the second is a recently proposed deterministic exemplar model (Ashby & Maddox, in press), which contains the generalized context model as a special case. When the exemplars from each category were normally distributed and the optimal decision bound was linear, the deterministic exemplar model and the decision bound model provided roughly equivalent accounts of the data. When the optimal decision bound was non-linear, the decision bound model provided a more accurate account of the data than did either exemplar model. When applied to categorization data collected by Nosofsky (1986, 1989), in which the category exemplars are not normally distributed, the decision bound model provided excellent accounts of the data, in many cases significantly outperforming the exemplar models. The decision bound model was found to be especially successful when (1) single subject analyses were performed, (2) each subject was given relatively extensive training, and (3) the subject's performance was characterized by complex suboptimalities. These results support the hypothesis that the decision bound is of fundamental importance in predicting asymptotic categorization performance and that the decision bound models provide a viable alternative to the currently popular exemplar models of categorization.

Adult↗

PubMed1992

[Effects of self-efficacy and outcome expectation on observational learning of altruistic behavior].

The purpose of the present study was to examined the hypothesis that the effects of observational learning of altruistic behavior are related to personal viewpoint, self-efficacy, outcome expectation, and other factors. One hundred and fifty-five fourth-grade school children were assigned randomly to four conditions; distress viewpoint, outcome expectation, altruistic behavior, or non-observational control. After observational learning, the students were immediately administered the generalization test of altruistic behavior, empathy, reward and punishment expectations, and rating tests of self-efficacy belief. It was found that; (a) altruistic behavior and outcome expectation conditions had significant learning effects, (b) self-efficacy was able to predict altruistic response in the altruistic behavior viewpoint condition, and (c) from an outcome expectation viewpoint, altruistic behavior toward peers and adults related to punishment expectation, whereas social sharing was related to reward expectation. According to these findings, an observational learning model of altruistic behavior was proposed.

Altruism↗

PubMed1991

Modulation of a discrete Pavlovian conditioned reflex by a putative emotive Pavlovian conditioned stimulus.

Three experiments showed the modulation of a rabbit eyeblink conditioned response (CR) to a Pavlovian conditioned stimulus (CS) by 30-s stimuli (A & B) that had been differentially paired with paraorbital shock. The CS (Y) was a 1,050-ms cue that had been paired with paraorbital shock outside A or B. In testing, the amplitude of CRs was greater when Y was presented within A than within B. Differential modulation occurred whether shock in A had been preceded by another 1,050-ms cue, X(AX+,BX-;Experiment 1) or not (A+B-;Experiment 2). Experiment 3 compared the technique of Experiment 1 (AX+) with that of Experiment 2 (A+) and found the latter to be advantageous for facilitation of CRs to Y by A. These data are consistent with the predictions of a model of Pavlovian conditioning (AESOP, Wagner & Brandon, 1989) that distinguishes between emotive and sensory conditioning as did Konorski (1967).

Animals↗

PubMed1980

Evaluation of blocking and conditioned inhibition to a CS signaling a decrease in US intensity.

Two experiments employing a conditioned emotional response procedure with rats evaluated the associative tendencies acquired by a target CS when a compound of that stimulus and another CS was reinforced by a low-intensity US whereas the latter CS alone was reinforced by a higher intensity US. Experiment 1 involved a blocking sequence in which the element and compound trials occurred in successive phases, followed by eventual testing of the responding to the target CS alone. Less evidence of excitatory conditioning was observed than in a comparison group which had the element and compound paired with the same low-intensity US. Experiment 2 included contemporaneous differential reinforcement of the element and compound CSs and periodic summation tests in which the target CS was compounded with another independently trained CS. Clear evidence was obtained of the development of inhibitory tendencies by the target CS. The results are consistent with the predictions of the Rescorla-Wagner model and are discussed in relation to the several determining assumptions of the model.

Animals↗

PubMed2002

Empirical evaluation of a dynamic experiment design method for prediction of MHC class I-binding peptides.

The ability to predict MHC-binding peptides remains limited despite ever expanding demands for specific immunotherapy against cancers, infectious diseases, and autoimmune disorders. Previous analyses revealed position-specific preference of amino acids but failed to detect sequence patterns. Efforts to use computational analysis to identify sequence patterns have been hampered by the insufficiency of the number/quality of the peptide binding data. We propose here a dynamic experiment design to search for sequence patterns that are common to the MHC class I-binding peptides. The method is based on a committee-based framework of query learning using hidden Markov models as its component algorithm. It enables a comprehensive search of a large variety (20(9)) of peptides with a small number of experiments. The learning was conducted in seven rounds of feedback loops, in which our computational method was used to determine the next set of peptides to be analyzed based on the results of the earlier iterations. After these training cycles, the algorithm enabled a real number prediction of MHC binding peptides with an accuracy surpassing that of the hitherto best performing positional scanning method.

Algorithms↗

PubMedDate not supplied

On the relation of oxidative stress to neuroinflammation: lessons learned from the G93A-SOD1 mouse model of amyotrophic lateral sclerosis.

The central nervous system (CNS) presents both challenges and opportunities to researchers of redox biochemistry. The CNS is sensitive to oxidative damage during aging or disease; excellent transgenic models of specific neurodegenerative diseases have been created that reproduce oxidative stress components of the corresponding human disorder. Mouse models of familial amyotrophic lateral sclerosis (ALS) based on overexpressed mutant human Cu, Zn-superoxide dismutase (SOD1) are cases in point. These animals experience predictably staged, age-dependent motor neuron degeneration with profound cellular and biochemical damage to nerve fibers and spinal cord tissue. Severe protein and lipid oxidation occurs in these animals, apparently as an indirect consequence of protein aggregation or cytopathic protein-protein interactions, as opposed to aberrant redox catalysis by the mutant enzyme. Recent studies of G93A-SOD1 mice and rats suggest that oxidative damage is part of an unmitigated neuroinflammatory reaction, possibly arising in combination from mitochondrial dysfunction plus pathophysiologic activation of both astrocytes and microglia. Lesions to redox signal-transduction pathways in mutant SOD1+ glial cells may stimulate broad-spectrum upregulation of proinflammatory genes, including arachidonic acid-metabolizing enzymes [e.g., cyclooxygenase-II (COX-II) and 5-lipoxygenase (5LOX)]; nitric oxide synthase (NOS) isoforms; cytokines (particularly tumor necrosis factor alpha, TNF-alpha); chemokines; and immunoglobulin Fc receptors (FcgammaRs). The integration of these processes creates a paracrine milieu inconsistent with healthy neural function. This review summarizes what has been learned to date from studies of mutant SOD1 transgenic animals and demonstrates that the G93A-SOD1 mouse in particular is a robust laboratory for the study of neuroinflammation and redox biochemistry.

Amyotrophic Lateral Sclerosis↗