Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Probability Learning”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed1999

Probabilistic synaptic transmission in the associative net.

The associative net model of heteroassociative memory with binary-valued synapses has been extended to include recent experimental data indicating that in the hippocampus, one form of synaptic modification is a change in the probability of synaptic transmission. Pattern pairs are stored in the net by a version of the Hebbian learning rule that changes the probability of transmission at synapses where the presynaptic and post-synaptic units are simultaneously active from a low, base value to a high, modified value. Numerical calculations of the expected recall response of this stochastic associative net have been used to assess the performance for different values of the base and modified probabilities. If there is a cost incurred with generating the difference between these probabilities, then a difference of about 0. 4 is optimal. This corresponds to the magnitude of change seen experimentally. Performance can be greatly enhanced by using multiple cue presentations during recall.

Association↗
PubMedDate not supplied

[Frequency of acquired helplessness and initial probability of showing an elaborated reaction].

The defense reflex of random performance of instrumental reaction (RPIR) had been produced in rats with different probabilities which were equal to 0.5; 0.25; 0.125 and 0.05 in respective experimental groups. Learning of animals was found to take place much faster when probabilities of RPIR were equal to 0.125 and 0.25 as compared with 0.5 and 0.05 values. One third rats which learned at 0.05 and 0.5 probabilities did not produce the reflex; the decrease in aroused, fall of body weight and other disturbances were observed and these findings may evident development of acquired helplessness about. It is supposed that optimal circumstances are occurred at different probabilities of RPIR conditions.

Animals↗
PubMedDate not supplied

[The theory of functional systems and probabilistic prognosis of behavior].

The article is dedicated to possible probability prediction of behavior in system organization of behavioral acts. System mechanisms of anticipation of required results of behavioral activity by living organisms adapted to stable and changing conditions of life are discussed. The author proposes that in all forms of behavior, an organism strictly predicts parameters for satisfaction of dominating needs of results that constitute the goal of a given form of behavior. In author's opinion, the probabilistic prognosis concerns only methods, acts and attendant emotional states, as well as possible ways of attaining the results (i.e., the means rather than action parameters).

Affect↗
PubMed2006

Disorders of learning and memory processes in a monkey model of Alzheimer's disease: the role of the associative area of the cerebral cortex.

The processes of learning and storage of the results of learning were studied in a model of Alzheimer's disease in two groups of rhesus macaques (three individuals in each group). Studies were performed after injection of neurotoxins (group I) and physiological saline (group II, controls). Two months after injections (stage C1), learning parameters were studied in monkeys of both groups using a new stimulus discrimination test (filled geometrical figures versus outline figures). There were significant differences between the animals of the two groups. Learning was hindered in monkeys of group I, with significant increases in the learning time (the time to achieve a stable probability of correct responding of 0.85) and in the probability of refusals. Monkeys of group II showed no learning impairment. Animals were trained to discriminate new stimuli (images of two monkeys) six months after injections (stage C3). Learning was impaired in animals of group I, such that learning measures had the same levels as previously; monkeys of group II showed no learning impairment. Analysis of the characteristics of working memory, which is involved in storing the results of new learning, was performed at stage C1; monkeys of group I showed significant degradation of these measures, with a significant decrease in the probability of correct solutions at stage C1 (to a level of 0.5), with some increase at stages C2 (at four months) and C3, along with a significant increase in the probability of refusals, values being similar at all time points. For monkeys of group II, these characteristics showed no degradation. Motor response times at stages C1, C2, and C3 were not different for the two groups of monkeys. The structural-functional organization of interactions between sensory and cognitive processes during learning and the storage of information in working memory are discussed, as is the role of the associative areas of the cortex in these interactions.

Alzheimer Disease↗
PubMed2004

Failure to construct and transfer correct representations across probability problems.

Previous studies carried out on "purely random" situations (with dice or poker chips) show the difficulties encountered by people in such situations, however simple they may be. In fact, in this type of situation, prior knowledge guides spontaneous representations, and the "errors" observed could be explained by the activation of "implicit models" which form the basis of erroneous representations. 42 statistically naïve undergraduates were given several variants of a probability problem on which errors are common. In a learning phase, subjects were given four problems involving geometric figures which were pairwise related by complementarity and equivalence relations. In a subsequent transfer phase, they were given a fifth problem involving poker chips, which was structurally isomorphic to the fourth geometric-figures problem. The findings show that people do not realize the relations between problems, and that transfer occurred only for the subset of subjects who performed correctly on the training problems of the learning phase. These results appear to have some significant implications in teaching mathematical concepts.

Adolescent↗
PubMed1991

Basic medical physiology: the whole is more than the sum of its parts.

In this article we examine the role of basic medical physiology in medical school education. We discuss the historical background, courses in this subject, and methods of teaching it. We conclude that the teaching of medical physiology should emphasize the study of organ systems and of the intact body. The techniques should emphasize meticulous observation, the posing of hypotheses, and the subsequent testing of the hypotheses, i.e., the use of the method used successfully in research. Students should learn the power of the experimental approach and to appreciate the immense variability possible in responses in complex organisms. They should also learn that principles of statistical probability applied logically can detect important differences in data that may be obscured by this variability. They should learn that there are no rigid answers when studying an individual and that they must continue to learn throughout their lives.

Animals↗
PubMed2001

Laparoscopic cholecystectomy in the new millennium.

BACKGROUND: Laparoscopic cholecystectomy has become the gold standard for the treatment of symptomatic cholelithiasis. Many authors-including investigators at our institution, who reported one of the initial experiences with laparoscopic cholecystectomy in July 1992-have documented a definite learning curve associated with this procedure. We present a follow-up study of our experience with laparoscopic cholecystectomy and compare these data to an earlier study of the initial experience with laparoscopic cholecystectomy at the Beth Israel Medical Center. METHODS: We retrospectively reviewed 300 consecutive patients from March 1998 through March 1999. The patient population was epidemiologically similar to that of the original study with regard to age, sex, and American Society of Anesthesia (ASA) classification. However, whereas the initial population included only patients with chronic disease, in our study 13.7% of the patients had been admitted through the emergency room with acute stone disease of the biliary tract. RESULTS: We found a 5.7% conversion rate, a 1% rate of major complication, and a 5.7% rate of minor complication rates, as compared to the initial study's rates of 12%, 4%, and 10%, respectively. Whereas none of the patients in the original study left the hospital on the day of surgery and only 49% were discharged within 1 day, in our group, 29 patients (10%) underwent ambulatory procedures and an additional 186 patients (62%) were discharged on the 1st post-operative day. The average duration of the operation was 90 min, which did not represent a statistical improvement over the time of 93 min reported in the earlier study. CONCLUSIONS: Since 1992, both the conversion rate and length of stay have declined at our hospital, but operative time has remained essentially the same. These findings probably reflect a bimodal learning curve, the increase in the number of cholangiograms and additional intraoperative procedures now performed, the greater severity of gallbladder disease currently treated with laparoscopic cholecystectomy, and increases in the number of attending physicians as well as the level of residents who perform this procedure.

Adolescent↗
PubMed2005

Sequential memory: a putative neural and synaptic dynamical mechanism.

A key issue in the neurophysiology of cognition is the problem of sequential learning. Sequential learning refers to the ability to encode and represent the temporal order of discrete elements occurring in a sequence. We show that the short-term memory for a sequence of items can be implemented in an autoassociation neural network. Each item is one of the attractor states of the network. The autoassociation network is implemented at the level of integrate-and-fire neurons so that the contributions of different biophysical mechanisms to sequence learning can be investigated. It is shown that if it is a property of the synapses or neurons that support each attractor state that they adapt, then every time the network is made quiescent (e.g., by inhibition), then the attractor state that emerges next is the next item in the sequence. We show with numerical simulations implementations of the mechanisms using (1) a sodium inactivation-based spike-frequency-adaptation mechanism, (2) a Ca(2+)-activated K+ current, and (3) short-term synaptic depression, with sequences of up to three items. The network does not need repeated training on a particular sequence and will repeat the items in the order that they were last presented. The time between the items in a sequence is not fixed, allowing the items to be read out as required over a period of up to many seconds. The network thus uses adaptation rather than associative synaptic modification to recall the order of the items in a recently presented sequence.

Action Potentials↗
PubMed2001

A double-dissociation of English past-tense production revealed by event-related potentials and low-resolution electromagnetic tomography (LORETA).

OBJECTIVES: Evidence of systematic double-dissociations of neural activity associated with the generation of regular and irregular past tense in healthy individuals may prove decisive in distinguishing between single- and dual-route models of morphological processing, because the former (connectionist models of morphological processing) have only been able to simulate double-dissociations of past-tense morphology as low-probability phenomena. METHODS: Twenty-eight channel event-related potentials (ERPs) were recorded in response to past-tense production and subsequently analyzed using a 3-stage strategy. RESULTS: A data-driven algorithm temporally segmented the ERPs into 16 distinct epochs of stable field configuration (microstates). A space-oriented brain electric field analysis determined that one of those epochs, 288-321 ms after the verb stem presentation, showed significant differences between the regular and irregular verb conditions. As a further test of these results, a novel source localization technique that computes 3-dimensional distribution of cortical current density in the Talairach brain atlas--low-resolution electromagnetic tomography--found in the above microstate more activity for regulars in the right prefrontal and right temporal areas and for irregulars in the left temporal areas and the anterior cingulate cortex, which can be taken as evidence of systematic double-dissociation. CONCLUSIONS: The present results achieved with a source localization technique provide evidence of a two-way compartmentalization of neural activity corresponding to regular and irregular past tense, thus corroborating the dual-mechanism character of verb morphology.

Adult↗
PubMed1988

From conditioning to category learning: an adaptive network model.

We used adaptive network theory to extend the Rescorla-Wagner (1972) least mean squares (LMS) model of associative learning to phenomena of human learning and judgment. In three experiments subjects learned to categorize hypothetical patients with particular symptom patterns as having certain diseases. When one disease is far more likely than another, the model predicts that subjects will substantially overestimate the diagnosticity of the more valid symptom for the rare disease. The results of Experiments 1 and 2 provide clear support for this prediction in contradistinction to predictions from probability matching, exemplar retrieval, or simple prototype learning models. Experiment 3 contrasted the adaptive network model with one predicting pattern-probability matching when patients always had four symptoms (chosen from four opponent pairs) rather than the presence or absence of each of four symptoms, as in Experiment 1. The results again support the Rescorla-Wagner LMS learning rule as embedded within an adaptive network model.

Association Learning↗
PubMed2003

Complications after laparoscopic gastric bypass: a review of 3464 cases.

HYPOTHESIS: The type and frequency of complications after open Roux-en-Y gastric bypass (GBP) have changed with the development of laparoscopic technique. BACKGROUND: The number of laparoscopic GBP cases performed in the United States has increased dramatically during the past several years. We compared the type and frequency of complications after laparoscopic and open GBP. METHODS: We searched MEDLINE from January 1, 1994, through December 31, 2002, using the keywords morbid obesity, laparoscopy, bariatric surgery, and gastric bypass. We selected studies on laparoscopic or open GBP with more than 50 patients and published in the English language for analysis. We excluded studies with reoperative Roux-en-Y GBP cases or other bariatric procedures. The type and frequency of postoperative complications were recorded from each study. We used chi2 and Fisher exact tests to determine statistical significance. RESULTS: Ten laparoscopic GBP studies with 3464 patients and 8 open GBP studies with 2771 patients were considered. The mean of the reported average age for patients undergoing laparoscopic GBP was 41 years compared with 43 years for open GBP. The mean percentages of female patients were 87% for laparoscopic GBP and 82% for open GBP; the mean reported average body mass index (calculated as weight in kilograms divided by the square of height in meters), 48.7 and 49.5, respectively. Compared with open GBP, laparoscopic GBP was associated with a decrease in the frequency of iatrogenic splenectomy, wound infection, incisional hernia, and mortality; however, there was an increase in the frequency of early and late bowel obstruction, gastrointestinal tract hemorrhage, and stomal stenosis. There were no significant differences in the frequency of anastomotic leak, pulmonary embolism, or pneumonia. CONCLUSIONS: The type and frequency of postoperative complications after laparoscopic and open GBP are different. Certain complications increase with laparoscopic GBP, probably owing to the learning curve of this complex procedure, whereas other complications decrease because of the advantages of the smaller access incision.

Adult↗
PubMed1997

Leukemia: lessons from the Japanese experience.

Probably more has been learned about radiation-induced leukemia from intensive study of Japanese atomic bomb survivors than about radiation damage to any other organ system. This has been the result of an intensive binational effort at the Atomic Bomb Casualty Commission and the Radiation Effects Research Foundation in Hiroshima and Nagasaki to monitor the occurrence of leukemia in a large group of atomic bomb survivors over a period of more than 50 years (the Life Span Study). The focus in the leukemia studies has been on disease latency, time of peak incidence rates, clinical course, shape of the dose-response curve and changes in risk over time for various types of leukemia in relationship to shielded kerma and bone marrow radiation dose, age at time of exposure, and gender. The extreme understanding and cooperation of the Japanese atomic bomb survivors, control subjects, physicians of Hiroshima and Nagasaki, government authorities, and the citizens of both cities has resulted in an epidemiological study that is almost unparalleled in medical history.

Foundations↗
PubMed2002

The 20S proteasome.

In contrast to our detailed knowledge of prokaryotic proteasomes, we have only a limited understanding of the prokaryotic regulators and their functional interaction with the proteasome. Most probably, we will soon learn more about the molecular structure and the mechanism of action of the prokaryotic regulators. Nevertheless, it still remains to be unravelled which signals or/and modifications transform an endogenous prokaryotic protein into a substrate of the proteasomal degradation machinery.

Adenosine Triphosphatases↗
PubMed1985

Opposing acute and chronic behavioural effects of a beta-blocker, propranolol, in the rat.

Rats were trained over 40 days to lever-press for food reward under a schedule of differential reinforcement of low rates of response with a 20-s criterion (DRL 20), following seven sessions of continuous reinforcement. The effect of injecting a beta-adrenergic blocker, propranolol (5 mg/kg IP), before and at two different delays after each daily session of DRL were investigated. In Experiment I, rats drugged 5-8 min before every session earned fewer reinforcements compared to controls, and showed impaired temporal discrimination. In Experiment II, this result was not replicated, but similar effects were clear in animals drugged pre-session from the 15th day of acquisition. By contrast, an improved temporal discrimination, and increased number of reinforcements were seen in rats drugged 5-8 min after every session. In Experiment III, the post-session effects were replicated and found also in rats drugged 4-5.5 h after each session. These results suggest that propranolol has an acute effect on DRL responding which resembles that of anxiolytics, and a chronic effect which opposes the acute one.

Animals↗
PubMed1989

Development and loss of tolerance to the effects of ethanol on DRL performance of rats.

Six male Sprague-Dawley rats were trained on a DRL-20 operant schedule for food presentation. When stable performance was established, they were exposed to an escalating regimen of daily ethanol administration (1.125-3.75 g/kg, IP). This dosing regimen continued until the maximally tolerable dose for each subject was reached. Tolerance loss then was monitored for approximately 6 months by periodic ethanol challenge doses (1.5 g/kg). Dose-effect curves (DECs) were obtained prior to (DEC-1), immediately after (DEC-2), and 6 months following termination of (DEC-3) the ethanol exposure. Rate-increasing effects (DEC-1) were noted at low doses (0.75 and 1.125 g/kg), with a higher dose (2.25 g/kg) resulting in a decreased rate of responding. Tolerance, following chronic ethanol exposure, developed to both the rate-increasing and rate-decreasing effects of ethanol (DEC-2). While some tolerance was lost within the 6 months following the daily ethanol exposure (DEC-3), a significant degree of tolerance was still indicated by most of the response measures. This duration of tolerance was considerably longer than that generally reported, and is probably attributable to persistent learned compensatory behavior and/or intermittent ethanol challenge tests.

Animals↗
PubMed1986

The velo-cardio-facial (Shprintzen) syndrome. Clinical variability in eight patients.

Eight patients (three sporadic, five from two families) with the velo-cardio-facial syndrome (VCFS) or Shprintzen syndrome are reported. Major clinical findings of this syndrome include a characteristic pattern of facial dysmorphisms, cleft palate, cardio-vascular malformations, and (mostly mild-to-moderate) mental retardation or learning difficulties. The syndrome probably is caused by a dominant gene with very variable expression. From previous reports mostly ascertained from cardio-vascular or cleft palate clinics, the incidence of cleft palate and heart defects was calculated to be 98% and 82%, respectively. Out of eight patients of this study who were diagnosed mainly through their pattern of facial dysmorphisms, only two and four had clefts and heart defects, respectively, further demonstrating the variability in the expression of this gene. Similarly, mental retardation, noted in 100% of previous publications, was not present in all of our patients. In two instances, examination of the mother revealed that she probably carried the mutant gene, but that she showed a milder clinical expression than the index patient. It is suggested that careful family investigations should be performed following detection of an index patient, and that the rate of fresh mutations might be not as high as previously assumed.

Abnormalities, Multiple↗