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At least 487 records · Page 27Linked to original sources
PubMed1998

Generalization and exclusive allocation of credit in unsupervised category learning.

A new way of measuring generalization in unsupervised learning is presented. The measure is based on an exclusive allocation, or credit assignment, criterion. In a classifier that satisfies the criterion, input patterns are parsed so that the credit for each input feature is assigned exclusively to one of multiple, possibly overlapping, output categories. Such a classifier achieves context-sensitive, global representations of pattern data. Two additional constraints, sequence masking and uncertainty multiplexing, are described; these can be used to refine the measure of generalization. The generalization performance of EXIN networks, winner-take-all competitive learning networks, linear decorrelator networks, and Nigrin's SONNET-2 network are compared.

Computer Simulation↗
PubMed2003

Hereditary cerebellar ataxia progressively impairs force adaptation during goal-directed arm movements.

We investigated how humans with hereditary cerebellar degeneration [spinocerebellar ataxia (SCA) type 6 and 8, n = 9] and age- and sex-matched healthy controls (n = 9) adapted goal-directed arm movements to an unknown external force field. We tested whether learning could be generalized to untrained regions in the workspace, an aspect central to the idea of an internal model, and if any learning could be retained. After removal of the force field, SCA patients showed little or no learning-related aftereffects indicating that repeated force-field exposure never led to successful force compensation. In contrast, healthy control subjects quickly adapted their movements to the new force field. The difference in force adaptation was significant for movements to targets that required both the shoulder and elbow joint (P < 0.001). Moreover, the generalization of learned movements to targets outside the learned workspace was prevented by the cerebellar degeneration (P < 0.01). Retention of force adaptation was significantly lower in SCA patients (P = 0.003). The severity of ataxia in SCA patients correlated negatively with the extent of learning (r = -0.84, P = 0.004). Our findings imply that progressive loss of cerebellar function gradually impairs force adaptation. The failure to generalize learning suggests that cerebellar degeneration prevents the formation of an internal representation of the limb dynamics.

Adaptation, Physiological↗
PubMed2001

Consistent contrast aids concept learning.

We suggest that coherence among concepts and correspondence between concepts and the world are important in concept learning. We identify one aspect of coherence, consistent contrast, and investigate its role in supervised concept learning. Concepts that contrast consistently carry information about the same attributes across the concepts within a contrast set. Concepts that contrast inconsistently predict and are predicted by values of different attributes. Experiment 1 revealed a large advantage for consistent contrast in learning and generalization. Experiment 2 pitted similarity against consistency and still revealed an advantage of consistency. Experiment 2 also broadened the range of tasks considered to include inductions about novel categories and subjects' category descriptions. We discuss relations to theories of concept learning, to attentional mechanism, and to alignability, and we suggest practical implications.

Adult↗
PubMed1992

[Group-based learning in continuing education in general practice. A further experiences with the working method in a guidance group].

We are seven general practitioners who have developed and tested a two-year programme to follow up the group-based training programme for general practice in Norway. The basic idea is to learn by reflecting on one's own consultations with patients. All consultations are registered by each doctor on a special form which allows both a narrative description of the consultation and a formal registration of data, including reasons for contact, diagnostic considerations, the doctor's attempts to elicit the patient's concerns and provide information, and specification of the doctor's satisfaction or dissatisfaction with the consultation. The material is shared and deepened at monthly group meetings. Simple statistical analysis is used. Each doctor also shows videotaped consultations to the group. Our learning has taken place at four levels: clinical medicine, knowledge about one's own practice and about general practice as a discipline, and experience of collecting and analyzing clinical data. We conclude that the programme is enjoyable and feasible, we recommend it to other groups.

Education, Medical, Continuing↗
PubMed1969

Stimulus generalization as a function of discrimination learning with and without errors.

After discrimination learning with and without errors, three groups of pigeons were tested for generalization to the angularity (negative stimulus) dimension. For half the subjects from each group, each angle was superimposed on a light of 555-nanometer wavelength, the positive stimulus during training; for the other half, the angles were on a black background. When tested to the angularity alone, the group which had made errors (pecked at the negative stimulus) during discrimination training showed a typical incremental (inverted) gradient of responding to the negative stimulus dimension. The control group and the one learning the discrimination without errors showed no differential control by the negative stimulus dimension. When each angle was superimposed on the positive stimulus during testing, a decremental gradient with maximum response strength to the negative stimulus was evidenced by the group learning with and the one group learning without errors.

Animals↗
PubMed2006

Value transfer across odor stimuli using probability of reinforcement in the rat.

In a series of experiments value transfer across odor stimuli using probability of reinforcement was demonstrated in rats. Rats were trained with the following pairs of simple simultaneous discriminations A(100) B(0) and C(50) D(0) where the letter represents a particular scent mixed with sand presented in a cup and the number in parentheses represents the probability of reinforcement given that the rats dug to the bottom of the cup. In test, the rats were confronted with a choice between the B and D stimuli and (in experiments 2 and 3) the rats preferred to dig in the B stimulus providing evidence for value transfer using procedures similar to those that have been used in the pigeon literature.

Animals↗
PubMed1984

Stimulus control and associative learning.

Interest in operant research on stimulus control has declined at the same time that much interest has burgeoned in nonoperant areas. Several examples of this shift toward traditional learning theory are considered, all of which have sponsored theoretical approaches that attempt to characterize the underlying associative units. These theoretical approaches are defended on the grounds that they have generated a deeper understanding of a variety of often puzzling phenomena. My projection is that future research will be determined even more strongly by theories about the structure of associations. Particular issues for which such discussion will have major impact include (1) whether conditional stimulus control is qualitatively different than simpler forms of stimulus control, (2) whether stimulus control is organized hierarchically, and (3) the origin of categories of stimulus equivalence.

Animals↗
PubMedDate not supplied

HSV gene functions: what have we learned that could be generally applicable to its near and distant cousins?

Herpes simplex virus 1 (HSV-1) encodes at least 84 polypeptides to perform two functions: to enable viral replication and to create the environment in which the entry of the virus into host cells, synthesis of virion components, assembly and egress are optimized. Whereas the former are indispensable for viral replication, the latter, numbering 47, can be deleted without a major effect on viral replication in cells in culture. Of particular interest are gene products whose function is either to modify cellular proteins (set 1) or to block entirely their function (set 2). An example of set 1 is the infected cell protein No. 0 (ICP0), a promiscuous transactivator of genes introduced into cells by infection or transfection. In its nuclear phase this protein binds to cyclin D3, extends its life by many hours, and sequesters it in nuclear structures known as ND10. In its cytoplasmic phase, ICP0 binds the translation elongation factor EF-1 delta. Another viral protein, the UL13 protein kinase, hyper-phosphorylates EF-1 delta. ICP0 and the protein kinase stimulate protein synthesis and cause the cell to induce the synthesis of pre-S phase cellular proteins the virus needs for its replication. The gamma 134.5 protein, a prototype of set 2, also has multiple functions. One, mapped at its carboxyl terminus, blocks the effects of double-stranded RNA-dependent protein kinase R (PKR) that is activated by all wild-type and mutant viruses examined to date. PKR phosphorylates eIF-2 alpha and shuts off protein synthesis. gamma 134.5 protein binds protein phosphatase 1 and redirects it to dephosphorylate eIF-2 alpha. Although PKR is activated in wild-type-infected cells, protein synthesis is unaffected. HSV-1 encodes in addition at least two proteins, ORF O and ORF P that are repressed during productive infection. The ORF P protein localizes in spliceosomes and blocks the synthesis of viral proteins derived from spliced mRNA. The ORF O protein binds ICP4, the major regulatory protein, and prevents it from binding to DNA. The role of ORF O and ORF P proteins in the establishment of latency is uncertain. A significant discovery that has emerged from these studies is that viral proteins can perform several functions that may be totally unrelated.

Gene Expression↗