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PubMed1997

An Incremental Adaptive Network for On-line Supervised Learning and Probability Estimation.

In this paper, a novel hybrid utilization of the Fuzzy ARTMAP (FAM) neural network and the Probabilistic Neural Network (PNN) is proposed for on-line learning and probability estimation tasks. There are two distinct advantages to the hybrid network. First, FAM is used as an underlying clustering algorithm to classify the input patterns into different recognition categories during the learning phase, resulting in a significant reduction in the number of pattern nodes required in the PNN. Second, a non-parametric posterior probability distribution estimation procedure, in accordance with the PNN paradigm (i.e. the Parzen-windows estimator), is employed during the prediction phase, where a probabilistic interpretation corresponding to Bayes decision theory can be provided for the predictions of FAM. In addition, several modifications are proposed to integrate both of the networks effectively into a unified platform for enhancing generalization. This hybrid approach also realizes an incremental learning system in which the necessity to specify a static network configuration a priori is eliminated as the network is able to "grow" to accommodate new input patterns sequentially and can thus operate in non-stationary environments. The performance of the network is evaluated with benchmark classification tasks and the results are compared with other approaches. Simulation results indicate that this hybrid network is capable of achieving a value near to the Bayes optimal classification rate. Copyright 1997 Elsevier Science Ltd.

Journal Article↗
PubMed1999

How well do elderly people cope with uncertainty in a learning task?

The relation between age, task complexity and learning performance in a Multiple Cue Probability Learning task was studied by systematically varying the level of uncertainty present in the task, keeping constant the direction of relationships. Four age groups were constituted: young adults (mean age = 21), middle-aged adults (45), elderly people (69) and very elderly people (81). Five uncertainty levels were considered: predictability = 0.96, 0.80, 0.64, 0.48, and 0.32. All relationships involved were direct ones. A strong effect of uncertainty on 'control', a measure of the subject's consistency with respect to a linear model, was found. This effect was essentially a linear one. To each decrement in predictability of the task corresponded an equal decrement in participants' level of control. This level of decrement was the same, regardless of the age of the participant. It can be concluded that elderly people cope with uncertainty in probability learning tasks as well as young adults.

Adaptation, Psychological↗
PubMedDate not supplied

Aging and probabilistic learning in single- and multiple-cue tasks.

The objective of the study was to examine some of the conditions under which elderly people are able to learn probabilistic inverse relationships and when this type of learning is no longer possible. Two kind of tasks were used: (a) two single-cue learning tasks with either direct or inverse relationships (the Single-Cue Probability Learning paradigm), and (b) three two-cue learning tasks, one with two direct relationships, one with a combination of direct and inverse relationships, and one with two inverse relationships (the Multiple-Cue Probability Learning paradigm). Four groups of participants were included in the study: young adults (18- to 25-year-olds), adults (40- to 50-year-olds), elderly people (65- to 74-year-olds), and very elderly people (75- to 90-year-olds). It was shown that (a) older adults are able to reject the direct relationship "default" hypothesis and select the inverse relationship hypothesis when outcome feedback contradicting the default hypothesis is given, and provided that the learning setting be a very simple one, involving only one cue; (b) some older adults are able to select the inverse relationship hypothesis provided that the learning setting be a simple one,involving only two inverse relationship cues; and (c) very few older adults are able to select the inverse relationship hypothesis when the learning setting is a complex one, involving two cues with both direct and inverse relationships with the criterion. These results led to the revision of the "gradual decrease of cognitive flexibility in older adults" hypothesis proposed by Chasseigne, Mullet, and Stewart (Acta Psychologicgrave;a, 103, 229-238, 1997).

Adolescent↗
PubMed1976

[The role of uncertainty in the conditioned-reflex learning behavior for selected cardiovascular functions].

As a contribution to quantitative analysis of exogenous stress action, the role of probability learning (probability stress, probability affirmation) for selected cardio-vascular functions was studied in 25 albino rats and 8 dogs. It has been shown in the rats learning with probability stress that a dependence exists between stress probability, on the one hand, and conditional-reflectory processes and systolic blood pressure rise, on the other, that is, the pathogenic action of probability stress increases from a probability of p = 1.0 to p = 0.5. An analogous picture was found with the probability affirmation being applied in dogs. While a probability affirmation with p = 1.0 promoted adaptational processes, a value of p = 0.5 led to experimental neurosis, tachycardia and ECG alterations. The results obtained are discussed in context with the information entropy and information theory of emotions.

Animals↗
PubMed2006

Orangutan leaf-carrying for nest-building: toward unraveling cultural processes.

We report an empirical study on leaf-carrying, a newly discovered nest-building technique that involves collecting nest materials before reaching the nest site. We assessed whether leaf-carrying by rehabilitant orangutans on Kaja Island, Central Kalimantan, owes to cultural influences. Findings derive from ca 600 h observational data on nesting skills and nesting associations in Kaja's 42 resident rehabilitants, which yielded 355 nests and 125 leaf-carrying cases by 34 rehabilitants. Regional contrasts with 14 other communities (7 rehabilitant, 7 wild) indicated cultural influences on leaf-carrying on Kaja. Association data showed exceptional social learning opportunities for leaf-carrying on Kaja, with residents taking differential advantage of these opportunities as a function of development, experience, and social position. Juvenile males with basic nesting skills were most influenced by social input. Most (27) leaf-carriers had probably learned leaf-carrying when caged and 7 probably learned it on Kaja. Social priming was probably the main impetus to leaf-carrying on Kaja, by simply prompting observers to copy when leaf-carrying associates collected nesting materials, what they collected, and where they used their collected materials. Implications concern acquisition processes and ontogenetic schedules that orchestrate sets of features-needs or interests, cognitive abilities, social preferences-which enable cultural transmission.

Animals↗
PubMed1975

Molecular contingencies: reinforcement probability.

Pigeons obtained food by responding in a discrete-trials two-choice probability-learning experiment involving temporal stimuli. A given response alternative, a left- or right-key peck, had 11 associated reinforcement probabilities within each session. Reinforcement probability for a choice was an increasing or a decreasing function of the time interval immediately preceding the choice. The 11 equiprobable temporal stimuli ranged from 1 to 11 sec in 1-sec classes. Preference tended to deviate from probability matching in the direction of maximizing; i.e., the percentage of choices of the preferred response alternative tended to exceed the probability of reinforcement for that alternative. This result was qualitatively consistent with probability-learning experiments using visual stimuli. The result is consistent with a molecular analysis of operant behavior and poses a difficulty for molar theories holding that local variations in reinforcement probability may safely be disregarded in the analysis of behavior maintained by operant paradigms.

Journal Article↗
PubMed2005

Prior belief and polarity in multicue learning.

We report two experiments in which participants are trained using a multicue probability learning (MCPL) task, which attempts to simulate the acquisition of expert judgement by experience in the real world. Participants were asked to predict performance in certain occupations given a profile of personality test results with trial-by-trial outcome feedback. Only some cues were relevant, and the polarity of the cues (positive or negative predictors) was unspecified. In addition, 25% of random noise was added to the feedback to simulate real world uncertainty. The main factor of interest was that the role of prior belief (determined in a separate study of stereotypes) interfered with the learning process. Experiment 1 failed to find any influence of prior belief in the cues that were irrelevant to the criterion being trained. However, in Experiment 2 people learned to use the relevant cues better when their effect conformed with rather than conflicted with prior belief Both experiments showed strong effects of cue polarity, with positive predictors much more easily learned. The results are discussed with reference to the cognitive processes involved in MCPL and closely related tasks.

Achievement↗
PubMed2000

Probability density estimation using incomplete data

An unsupervised method of learning probability density function parameters in the framework of mixture densities from incomplete data is developed. Unsupervised learning can be considered as learning from observations as they are received. In real-world processes, there are many imperfections in the observations. The Expectation-Maximization algorithm is used to iteratively find the maximum likelihood estimate of the missing values and the parameters of the probability density function. Reliability of the Expectation-Maximization algorithm and its convergence properties during the learning process from incomplete data are presented. Three examples of learning mixture probability density function parameters from an incomplete data set are presented and the boundaries of properly estimating the mixture probability density function parameters as the percentage of missing data increases are examined.

Journal Article↗
PubMed1991

Choice as a function of local versus molar reinforcement contingencies.

Rats were trained on a discrete-trial probability learning task. In Experiment 1, the molar reinforcement probabilities for the two response alternatives were equal, and the local contingencies of reinforcement differentially reinforced a win-stay, lose-shift response pattern. The win-stay portion was learned substantially more easily and appeared from the outset of training, suggesting that its occurrence did not depend upon discrimination of the local contingencies but rather only upon simple strengthening effects of individual reinforcements. Control by both types of local contingencies decreased with increases in the intertrial interval, although some control remained with intertrial intervals as long as 30 s. In Experiment 2, the local contingencies always favored win-shift and lose-shift response patterns but were asymmetrical for the two responses, causing the molar reinforcement rates for the two responses to differ. Some learning of the alternation pattern occurred with short intertrial intervals, although win-stay behavior occurred for some subjects. The local reinforcement contingencies were discriminated poorly with longer intertrial intervals. In the absence of control by the local contingencies, choice proportion was determined by the molar contingencies, as indicated by high exponent values for the generalized matching law with long intertrial intervals, and lower values with short intertrial intervals. The results show that when molar contingencies of reinforcement and local contingencies are in opposition, both may have independent roles. Control by molar contingencies cannot generally be explained by local contingencies.

Animals↗
PubMedDate not supplied

Analysis of probabilistic classification learning in patients with Parkinson's disease before and after pallidotomy surgery.

This study examined the characteristics of probabilistic classification learning, a form of implicit learning previously shown to be impaired in patients with basal ganglia dysfunction (e.g., Parkinson's disease). In this task, subjects learn to predict the weather using associations that are formed gradually across many trials, because of the probabilistic nature of the cue-outcome relationships. Patients with Parkinson's disease, both before and after pallidotomy, and age-matched control subjects, exhibited evidence of probabilistic classification learning across 100 training trials. However, pallidotomy appears to hinder the learning of associations most implicit in nature (i.e., weakly associated cues). Although subjects were most sensitive to single-cue associations when learning the task, there is evidence that cue combinations contribute significantly to probability learning. The utility of multiple dependent measures is discussed.

Aged↗
PubMed2006

Category dimensionality and feature knowledge: when more features are learned as easily as fewer.

Three experiments compared the learning of lower-dimensional family resemblance categories (4 dimensions) with the learning of higher-dimensional ones (8 dimensions). Category-learning models incorporating error-driven learning, hypothesis testing, or limited capacity attention predict that additional dimensions should either increase learning difficulty or decrease learning of individual features. Contrary to these predictions, the experiments showed no slower learning of high-dimensional categories; instead, subjects learned more features from high-dimensional categories than from low-dimensional categories. This result obtained both in standard learning with feedback and in noncontingent, observational learning. These results show that rather than interfering with learning, categories with more dimensions cause individuals to learn more. The authors contrast the learning of family resemblance categories with learning in classical conditioning and probability learning paradigms, in which competition among features is well documented.

Concept Formation↗
PubMed1995

Rapid cycling bipolar affective disorder and familial learning disability associated with temporal lobe (occipitotemporal gyrus) cortical dysplasia.

This case report describes a hitherto unreported association between temporal cortical dysplasia and rapid cycling bipolar affective disorder in a learning disabled young man with a family history of rapid cycling bipolar affective disorder in two dysmorphic and learning disabled maternal uncles, and probably learning disability in the mother and grandmother. An identical family with similar findings could not be located in the English literature.

Adult↗
PubMed1964

FURTHER EXPERIMENTS ON PROBABILITY-MATCHING IN THE PIGEON.

In a discrete-trials, two-key choice situation, probability-learning by pigeons was studied under a variety of training conditions. Matching was found in simultaneous and in successive problems, but a spatial problem produced only maximizing. In the simultaneous problem, noncorrection produced maximizing, while correction produced matching. Guidance produced maximizing when the animals were required to earn each opportunity for choice by pecking a center key on FR-5, but matching when the center key was not used. In a discrete-trials one-key situation, with latency as the measure, frequency and probability of reinforcement were varied independently. Differences in probability produced differences in latency of response, but differences in frequency did not.

Animals↗
PubMed1966

Probabilistically reinforced choice behavior in pigeons.

A single principle, "momentary maximizing", may account for much of a pigeon's steady-state behavior in both probability learning and concurrent variable interval experiments. The principle states that a pigeon tends to choose the alternative that momentarily has the higher probability of reinforcement. A successive discrimination procedure, which produced matching in an earlier experiment, produced here a tendency to maximize if training were adequately extended. Maximizing was produced also by other procedures, in which no reinforcing event was presented on some trials: one procedure did and two did not provide a bird with information about the availability of reinforcement on a key after an unreinforced response on the other key. The latter two procedures were analogous to concurrent variable interval schedules in two respects: the reinforcement probability on one key increased while a bird responded on the other key; and they produced matching. But sequential statistics suggested that matching resulted from momentary maximizing. Depending on the procedure, the tendency to maximize produced different relative frequencies of pecking a key for a fixed relative frequency of reinforcement. Computer simulation of maximizing behavior in several concurrent variable interval schedules produced matching and sequential statistics similar to those produced by a real bird.

Animals↗