SEARCH · PubMed Health

Results for “Contrastive learning”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,477 records · Page 82Linked to original sources

PubMed1999

Fragile-X syndrome, Down's syndrome and autism: awareness and knowledge amongst special educators.

Fragile-X syndrome is the commonest cause of inherited intellectual disability. There is good evidence for a behavioural phenotype. This has implications for school staff using standard educational techniques. Similarly, autism is known to create particular educational requirements. The present study examined the awareness and knowledge of fragile-X syndrome, Down's syndrome and autism amongst staff in special and mainstream education. One hundred and two special school staff and 40 mainstream school staff completed questionnaires. Most staff offered a variety of features 'typical' of Down's syndrome and autism. In contrast, staff knew less about fragile-X syndrome. Specific knowledge about the learning styles of these children was very poor, but was associated with having taught an affected child. Mainstream and special school staff offered similar levels of knowledge for all three conditions. Staff did not demonstrate a sufficiently specialized knowledge of fragile-X syndrome to ensure that the special educational needs of these children were being met fully.

Adult↗

PubMed2001

Central tendencies, extreme points, and prototype enhancement effects in ill-defined perceptual categorization.

In three perceptual classification experiments involving ill-defined category structures, extreme prototype enhancement effects were observed in which prototypes were classified more accurately than other category instances. Such empirical findings can prove theoretically challenging to exemplar-based models of categorization if prototypes are psychological central tendencies of category instances. We found instead that category prototypes were sometimes better characterized as psychological extreme points relative to contrast categories. Extending a classic and widely cited study (Posner & Keele, 1968), participants learned categories created from distortions of dot patterns arranged in familiar shapes. Participants then made pairwise similarity judgments of the patterns. Multidimensional scaling (MDS) analyses of the similarity data revealed the prototypes to be psychological extreme points, not central tendencies. Evidence for extreme point representations was also found for novel prototype patterns displaying a symmetry structure and for prototypes of grid patterns used in recent studies by McLaren and colleagues (McLaren, Bennet, Guttman-Nahir, Kim, & Mackintosh, 1995). When used in combination with the derived MDS solutions, an exemplar-based model of categorization, the Generalized Context Model (Nosofsky, 1986), provided good fits to the observed categorization data in all three experiments.

Adult↗

PubMed2006

Decision making in children with ADHD only, ADHD-anxious/depressed, and control children using a child version of the Iowa Gambling Task.

OBJECTIVE: The goal of this study is to investigate decision making in children with ADHD using a child version of the Iowa Gambling Task (IGT). The effect of internalizing symptoms is also of interest. METHOD: Twenty-one children with ADHD (high anxiety/depression and no anxiety/depression) are compared to an age- and sex-matched control group on the gambling task. Children in the ADHD-alone group demonstrate impaired performance on the IGT. In contrast, children in the control group and the ADHD-anxiety/depression group learn to choose more from the advantageous decks over time. RESULTS: These findings of impaired decision making in children with ADHD parallel findings of real-life decision-making problems in this population. CONCLUSION: Furthermore, the findings suggest that having a high number of internalizing symptoms leads to better performance for children with ADHD on this variant of the IGT.

Anxiety↗

PubMed2006

The role of awareness in delay and trace fear conditioning in humans.

Expression of conditional fear without awareness has been previously demonstrated during delay conditioning, a procedure in which the conditioned stimulus (CS) and unconditioned stimulus (UCS) overlap. However, less is known about the role of awareness in trace fear conditioning, where an interval of time separates the CS and UCS. The present study assessed skin conductance response (SCR) and UCS expectancy during delay and trace conditioning. UCS predictability was varied on a trial-by-trial basis by presenting perithreshold auditory CSs. Differential UCS expectancies were demonstrated only on perceived delay and trace trials. Learning-related SCRs were observed during both perceived and unperceived delay CSs. In contrast, differential SCRs were demonstrated only for perceived trace CSs. These data suggest that awareness is necessary for conditional responding during trace, but not delay, fear conditioning.

Adult↗

PubMed1990

Molecular analysis of two group B streptococcal virulence factors.

Molecular biology has provided new technology for evaluating the traits of bacterial pathogens that are important in the pathogenesis of infections. The ability to derive isogenic strains that differ by a single trait provides a powerful tool for investigating the interaction of a putative virulence factor with the host at any of the various steps in pathogenesis. Recombinant DNA techniques afford the opportunity to clone the genes involved in the biosynthesis of a particular virulence factor. Once the gene(s) are cloned, a vast amount of information can be learned about their composition, structure, and regulation, and similarity with genes in other organisms. Understanding the molecular biology of a virulence factor also provides information about potential targets for future therapies and preventive modalities. The molecular analysis of two virulence factors from the type III group B streptococcus has been reviewed to provide specific examples of how these techniques can be used. The data has shown that the capsular polysaccharide is an essential factor in GBS virulence. The structural influence of sialic acid on the capsule plays a major role in its virulence properties. The importance of the capsule has been tested in several assays to identify its role in pathogenesis. Its primary role appears to be evading host phagocytic mechanisms, but it does not appear to be essential in the vascular response observed during GBS sepsis. Using the isogenic strains, we have also learned that the capsule does not mask a fibronectin receptor on GBS. In contrast to the capsule, the beta-hemolysin of GBS does not appear to be essential for systemic disease once the organism has invaded. Its role in the initial invasive steps in GBS pathogenesis has not been tested, but the availability of isogenic mutants in beta-hemolysin production will allow this question to be answered once the model systems are available.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed2003

Task-specific internal models for kinematic transformations.

Numerous studies of motor learning have focused on how people adapt their reaching movements to novel dynamic and visuomotor perturbations that alter the actual or visually perceived motion of the hand. An important finding from this work is that learning of novel dynamics generalizes across different movement tasks. Thus adaptation to an unusual force field generalizes from center-out reaching movements to circular movements (Conditt et al. 1997). This suggests that subjects acquired an internal model of the dynamic environment that could be used to determine the motor commands needed for untrained movements. Using a task interference paradigm, we investigated whether transfer across tasks is also observed when learning visuomotor transformations. On day 1, all subjects adapted to a +30 degrees rotation while making center-out-and-back reaching movements. After a delay of 5 min, different groups of subjects then adapted to a -30 degrees rotation while performing either a continuous tracking task, a figure-eight drawing task, or the center-out-and-back reaching task. All subjects were then retested the next day on the +30 degrees rotation in the reaching task. As expected, subjects who experienced the opposing rotations while performing the same reaching tasks showed no retention of learning for the first rotation when tested on day 2 (Krakauer et al. 1999). In contrast, such retrograde interference was not observed in the two groups of subjects who experienced the opposing rotations while performing different tasks. In fact, their performance on day 2 was similar to that of control subjects who never experienced the opposite rotation. This lack of interference suggests that memory resources for visuomotor rotations are task specific.

Adult↗

PubMed1984

Changes of membrane currents during learning.

The integrated response of a population of neurones during conditioning results in long-term (days) changes of specific membrane currents within identified neurones. Prolonged elevation of intracellular calcium during conditioning causes a persistent increase of excitability by reducing K+ currents (IA and probably ICa2+-K+) in the membranes of identified somata. This Ca2+-mediated reduction of K+ currents, which encodes a learned stimulus association is thought to involve changes of Ca2+-calmodulin-dependent phosphorylation of distinct membrane proteins. These changes are contrasted with the short-term regulation of currents by neurohormones during altered behavioural states such as arousal.

Animals↗

PubMed2001

Learning object representations using a priori constraints within ORASSYLL.

In this article, a biologically plausible and efficient object recognition system (called ORASSYLL) is introduced, based on a set of a priori constraints motivated by findings of developmental psychology and neurophysiology. These constraints are concerned with the organization of the input in local and corresponding entities, the interpretation of the input by its transformation in a highly structured feature space, and the evaluation of features extracted from an image sequence by statistical evaluation criteria. In the context of the bias-variance dilemma, the functional role of a priori knowledge within ORASSYLL is discussed. In contrast to systems in which object representations are defined manually,the introduced constraints allow an autonomous learning from complex scenes.

Artificial Intelligence↗

PubMedDate not supplied

Learning-induced physiological memory in adult primary auditory cortex: receptive fields plasticity, model, and mechanisms.

It is well established that the functional organization of adult sensory cortices, including the auditory cortex, can be modified by deafferentation, sensory deprivation, or selective sensory stimulation. This paper reviews evidence establishing that the adult primary auditory cortex develops physiological plasticity during learning. Determination of frequency receptive fields before and at various times following aversive classical conditioning and instrumental avoidance learning in the guinea pig reveals increased neuronal responses to the pure tone frequency used as a conditioned stimulus (CS). In contrast, responses to the pretraining best frequency and other non-CS frequencies are decreased. These opposite changes are often sufficient to shift cellular tuning toward or even to the frequency of the CS. Learning-induced receptive field (RF) plasticity (i) is associative (requires pairing tone and shock), (ii) highly specific to the CS frequency (e.g., limited to this frequency +/- a small fraction of an octave), (iii) discriminative (specific increased response to a reinforced CS+ frequency but decreased response to a nonreinforced CS- frequency), (iv) develops extremely rapidly (within 5 trials, the fewest trials tested), and (v) is retained indefinitely (tested to 8 weeks). Moreover, RF plasticity is robust and not due to arousal, but can be expressed in the deeply anesthetized subject. Because learning- induced RF plasticity has the major characteristics of associative memory, it is therefore referred to as "physiological memory". We developed a model of RF plasticity based on convergence in the auditory cortex of nucleus basalis cholinergic effects acting at muscarinic receptors, with lemniscal and nonlemniscal frequency information from the ventral and magnocellular divisions of the medial geniculate nucleus, respectively. In the model, the specificity of RF plasticity is dependent on Hebbian rules of covariance. This aspect was confirmed in vivo using microstimulation techniques. Further, the model predicts that pairing a tone with activation of the nucleus basalis is sufficient to induce RF plasticity similar to that obtained in behavioral learning. This prediction has been confirmed. Additional tests of the model are described. RF plasticity is thought to translate the acquired significance of sound into an increased frequency representation of behaviorally important stimuli.

Adult↗

PubMed1995

Memory deficits in a demented patient with probable corticobasal degeneration.

Anterograde and retrograde amnesia in a patient with probable corticobasal degeneration (pCBD) and dementia were studied in a university medical center setting. The patient with pCBD and four comparison patients of comparable global mental status (Mini-Mental State Exam) who met NINCDS-ADRDA criteria for Alzheimer's disease (AD) were included. Standard neuropsychological tests of naming, intelligence, achievement, verbal fluency, anterograde and remote verbal and visuospatial memory, and motor skill learning were given. The pCBD patient exhibited a progressive asymmetric akinetic-rigid syndrome, which was unresponsive to Sinemet. His initially mild, intellectual deficits consisted of apraxia, slowed speech, and word-finding and memory difficulties. Over a 2-year period, a dementia syndrome developed, which involved more-serious deficits in praxis and naming, as well as impairments in spelling, calculation, verbal fluency, IQ, anterograde verbal and visuospatial memory, and motor skill learning. When tested by recall methods, the pCBD patient exhibited marked deficits on several tests of remote memory; however, on recognition testing, he performed normally on the Famous Faces Test and on a test of geographical knowledge, which measures remote visuospatial memory. By contrast, the four AD patients, who showed equivalent naming difficulties, less-severe fluency deficits, and normal motor skill learning, showed severe impairments in recalling and recognizing the names of famous people from photographs. A magnetic resonance imaging (MRI) scan of the pCBD patient showed marked frontal and parietal lobe atrophy and central atrophy, with ventriculomegaly that was greater on the left side of the brain. The temporal lobes were relatively spared, and the amygdalae, hippocampi, and temporal horns were of normal size.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Behavioral effects of acute p-xylene inhalation in rats: autoshaping, motor activity, and reversal learning.

p-Xylene is a ubiquitous solvent and chemical precursor used in industry, gasoline, and household products. While the population at risk for exposure is thus quite large, little is known about its neurobehavioral effects. To evaluate the possibility that p-xylene affects cognitive behavior, male Long-Evans hooded rats inhaled p-xylene at concentrations of 0 or 1600 ppm, 4 hr per day for 1 to 5 days, and were evaluated after exposure on two learning tasks and a test of motor activity. Autoshaping was carried out across 5 successive days with p-xylene exposure in the morning followed by testing in the afternoon. For this test, the retraction of a single response lever on a variable-time 35-sec schedule was followed by delivery of a food pellet. When the force required to depress the lever was low (0.10 N), response acquisition was faster in animals having inhaled 1600 ppm p-xylene than in air-exposed controls. When the force was increased to 0.20 N, however, p-xylene-exposed rats acquired the response no faster than controls. In contrast, inhaled p-xylene at 1600 ppm suppressed response rates in an automaintained reversal learning paradigm without affecting reversal rate. Studies of motor activity showed that while vertically-directed activity was unaffected by p-xylene, horizontally-directed activity was increased by about 30% for the first 15 min of each daily 25-min test.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗

PubMed1999

Effects of diazepam or chronic alcohol treatment on spatial reversal learning in mice.

Mice submitted to chronic alcohol consumption (CAC; 11 months) or to systemic diazepam administration were trained in a spatial reversal learning task. Although CAC-treated mice were able to learn the initial acquisition at normal rates, they were impaired during the first reversal of the discrimination and subsequent reversal sessions. In contrast, diazepam administration induced no deficits for any behavioral measure. In conclusion, CAC, but not diazepam administration, induces an exaggerated sensitivity to proactive interference. The two treatments spared, however, the development of the learning set curve. These results are congruent with clinical data showing that nondeclarative or implicit forms of memory processes are spared in diazepam-treated subjects or in chronic alcoholics.

Animals↗

PubMed2003

Normal prism adaptation but reduced after-effect in basal ganglia disorders using a throwing task.

Prism adaptation is a form of visuomotor learning in which the visual and motor systems need to be adjusted because a visual perturbation is produced by horizontally displacing prisms. Despite being known for over two centuries, the neuronal substrates of this phenomenon are not yet completely understood. In this article the possible role of the basal ganglia in this kind of learning was analysed through a study of Huntington's and Parkinson's disease patients. A throwing technique requiring the use of open loop feedback was used. The variables analysed were visuomotor performance, adaptation rate and magnitude, and the after-effect. The results clearly showed that both Huntington's and Parkinson's disease groups learned at the same rate as control subjects. In addition, despite having a disturbed visuomotor performance, both experimental groups showed the same adaptation magnitude as the control group. Finally, the after-effect, which is measured after removing the prisms, is reduced in both patients groups. This reduction leads to a disruption in the normal adaptation-after-effect correlation found in normal volunteers. These results suggest that basal ganglia are not involved in this type of open-looped visuomotor learning. The large number of patients studied as well as the similarity of the findings between both populations support this hypothesis. By contrast, there is an impairment in the after-effect on both basal ganglia patient populations. This impairment may be the result of the deterioration of the perceptual recalibration process involved in visuomotor learning.

Adaptation, Ocular↗

PubMed1961