PubMed Health⌕ Search

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 181 records · Page 10Linked to original sources
PubMedDate not supplied

Development of the acquisition and control of action-effect associations.

Voluntary action is anticipatory and, hence, must depend on associations between actions and their perceivable effects. We studied the acquisition of action-effect associations in 4-5-vs. 7-year-old children. Children carried out key-pressing actions that were arranged to produce particular auditory effects. In a subsequent test phase, children were to press keys in response to the previous effect sounds, with the sound-key mapping being either consistent or inconsistent with previous key-sound practice. As the processes underlying voluntary action controls are known to significantly improve between 4 and 7 years of age, it was expected that younger children were more prone to automatic effects of acquired sound-key associations. This hypothesis was confirmed, but reaction times and accuracy measures showed different and dissociable patterns. Four-year-olds but not 7-year-olds were more likely to commit an error--i.e., to perform a sound-compatible rather than the correct action--if the sound-key mapping was inconsistent with previous practice. This effect strongly depended on previous practice, suggesting that it reflects long-term learning. In contrast, reaction time effects of mapping consistency did not depend on previous experience but only on the consistency between stimulus and action effect in the present task. Taken altogether, the results suggest that children acquire response-effect associations automatically and that younger children are more likely to suffer from frequent goal neglect; i.e., they tend to forget the current action goal, so that their behavior is dominated by automatic, stimulus-triggered response tendencies.

Age Factors↗
PubMed1986

Presentation rate effects on paired associate learning by attention deficit disordered children.

2 methods of varying presentation rate during paired associate learning were contrasted in attention deficit disordered (ADD) children. Previous studies have varied presentation rate across different (fixed rate) lists, and they have demonstrated that ADD children perform poorly at slower rates. In the present study, this method of presentation was contrasted with one in which half the items within a single list were presented at a fast rate and half at a slow rate. The debilitating effect of the slow rate was obtained in ADD children (but not in normal controls) only with the fixed list method. This finding suggests that the rate effects occur in ADD children because they are vulnerable to the experimental context created when items are presented at a slow rate over an extended time period.

Attention↗
PubMed1999

Functional specificity of ventral striatal compartments in appetitive behaviors.

The nucleus accumbens and its associated circuitry subserve behaviors linked to natural or biological rewards, such as feeding, drinking, sex, exploration, and appetitive learning. We have investigated the functional role of neurotransmitter and intracellular transduction mechanisms in behaviors subserved by the core and shell subsystems within the accumbens. Local infusion of the selective NMDA antagonist, AP-5, into the accumbens core, but not the shell, completely blocked acquisition of a bar-press response for food in hungry rats. This effect was apparent only when infused during the early stages of learning. We have also recently shown that infusion of certain protein kinase inhibitors into the core also impairs learning in the same paradigm. These results suggest that plasticity-related mechanisms within the accumbens core, involving glutamate-linked intracellular second messengers, are important for response-reinforcement learning. In contrast to the core, which primarily connects to somatic motor output systems, the shell is more intimately linked to viscero-endocrine effector systems. We have shown that both AMPA and GABA receptors within the medial shell (but not the core) are critically involved in controlling the brain's feeding pathways, via activation of the lateral hypothalamus (LH). This effect is blocked by local inhibition of the LH in double-cannulae experiments and also strongly and selectively activates Fos expression in the LH. These results provide a newly emerging picture of the differentiated functions of this forebrain region and suggest an integrated role in the elaboration of adaptive motor actions.

Animals↗
PubMed1998

Functional plasticity after left anterior temporal lobectomy: reconstitution and compensation of verbal memory functions.

PURPOSE: This study investigated the functional plasticity of the brain to reconstitute and compensate for verbal memory functions after epilepsy surgery of left temporocortical and temporomesial structures. We hypothesized that memory outcome would be best when surgery is performed within the period of cerebral plasticity, and that the outcome should be worst when fluid intelligence starts to decrease with physiologic aging. We also raised the question of different plasticity and compensation mechanisms for temporomesial and temporocortical memory functions. METHODS: We evaluated preoperative and 1-year-postoperative memory data and other verbal functions in 104 patients with epilepsy, who underwent a standard left anterior temporal lobe resection. We used memory measures that had been previously shown to be most selective for mesial and lateral functions, respectively. Determinants of postoperative memory outcome were evaluated by multiple regression analysis. Group statistics were calculated on the basis of the periods that are usually assumed to be significant for plasticity and behavioral compensation. Individual postoperative changes in memory functions were evaluated on the basis of test-retest data obtained in a group of 100 nonsurgical patients with localization-related epilepsies (mean retest interval >12 months). RESULTS: Only changes in cortically represented learning and data acquisition were related to age, plasticity, and capacities for behavioral compensation. No patient in the youngest group (younger than 15 years), 33% of patients who had surgery between the ages of 15 and 30 years, and 61% of the patients undergoing surgery older than age 30 years had significant deterioration in verbal learning. In contrast, postoperative changes in temporomesial consolidation/retrieval processes were independent of age at the time of surgery, plasticity, and capacities for behavioral compensation. CONCLUSIONS: Our data indicate different time windows for the reconstitution and compensation of mesial and cortical aspects of memory. Whereas the reconstitution of and compensation for cortical functions appear restricted by decreasing plasticity and physiological aging, mesial functions seem to be reconstituted by contralateral mesial structures over a much longer period. Concerning drug-resistant localization-related epilepsies, our results justify early consideration of surgery, especially when cortical structures are affected.

Adolescent↗
PubMed2000

Striatum forever, despite sequence learning variability: a random effect analysis of PET data.

This PET study is concerned with the what, where, and how of implicit sequence learning. In contrast with previous studies imaging the serial reaction time (SRT) task, the sequence of successive locations was determined by a probabilistic finite-state grammar. The implicit acquisition of statistical relationships between serially ordered elements (i.e., what) was studied scan by scan, aiming to evidence the brain areas (i.e., where) specifically involved in the implicit processing of this core component of sequential higher-order knowledge. As behavioural results demonstrate between- and within-subjects variability in the implicit acquisition of sequential knowledge through practice, functional PET data were modelled using a random-effect model analysis (i.e., how) to account for both sources of behavioural variability. First, two mean condition images were created per subject depending on the presence or not of implicit sequential knowledge at the time of each of the 12 scans. Next, direct comparison of these mean condition images provided the brain areas involved in sequential knowledge processing. Using this approach, we have shown that the striatum is involved in more than simple pairwise associations and that it has the capacity to process higher-order knowledge. We suggest that the striatum is not only involved in the implicit automatization of serial information through prefrontal cortex-caudate nucleus networks, but also that it plays a significant role for the selection of the most appropriate responses in the context created by both the current and previous stimuli, thus contributing to better efficiency and faster response preparation in the SRT task.

Adult↗
PubMed1986

Lashley's shift from bacteriology to neuropsychology, 1910-1917, and the influence of Jennings, Watson, and Franz.

From 1910 to 1917, Karl S. Lashley's research moved from bacteriology to neuropsychology through intermediate stages of zoology, comparative psychology, and the psychology of learning. This shift is examined with particular reference to Lashley's associations with John B. Watson, Shepherd I. Franz, and Herbert S. Jennings. Watson's impact was substantial, for he attracted Lashley to comparative psychology and was the source of many of his later research interests. The bridge to neuropsychological research was provided by Franz who trained Lashley in the lesion method of investigating the brain bases of learning. The influence of Jennings, Lashley's Ph.D. supervisor, was most evident in the divergence of the post-1915 interests of Lashley and Watson. Lashley's search for brain mechanisms of learning, as contrasted with Watson's concern with behavioral prediction and control, mirrored a similar earlier difference between Jennings and Jacques Loeb.

Animals↗
PubMed1987

Relaxation training through muscle stretching procedures: a pilot case.

The present paper introduces a relaxation procedure based upon muscle stretching exercises. Traditional progressive relaxation training starts from muscle tensing exercises to teach voluntary control of muscle tension, but the literature shows widely varying results. An alternative method of relaxation training starts from muscle stretching exercises. Muscle stretching provides sensation contrasts for learning relaxation in addition to fostering relaxation through the stretching of muscles. The present report documents the rationale for the procedure and presents data from a clinical case study, including six months' follow-up, in support of its efficacy.

Anxiety Disorders↗
PubMed2006

Social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens) on a two-action artificial fruit.

An artificial fruit (AF) was used to test for social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens). A monkey demonstrator opened the AF, showing alternative methods to 2 groups of cage mates. Video films of the monkey demonstrations were presented to adult humans. Compared with chimpanzees and children, the macaques watched the demonstrations significantly less and in a much more sporadic manner. They also produced only very weak and transitory evidence of social learning. In contrast, the adult humans performed as one might expect of optimum imitators, even producing evidence of components of a "ratchet effect."

Adult↗
PubMed2005

Explaining age differences in temporal working memory.

To determine the cognitive mechanisms underlying age differences in temporal working memory (WM), the authors examined the contributions of item memory, associative memory, simple order memory, and multiple item memory, using parallel versions of the delayed-matching-to-sample task. Older adults performed more poorly than younger adults on tests of temporal memory, but there were no age differences in nonassociative item memory, regardless of the amount of information to be learned. In contrast, a combination of associative and simple order memory, both of which were reduced in older adults, completely accounted for age-related declines in temporal memory. The authors conclude that 2 mechanisms may underlie age differences in temporal WM, namely, a generalized decline in associative ability and a specific difficulty with order information.

Adult↗
PubMed2006

Neural mechanisms of birdsong memory.

The process through which young male songbirds learn the characteristics of the songs of an adult male of their own species has strong similarities with speech acquisition in human infants. Both involve two phases: a period of auditory memorization followed by a period during which the individual develops its own vocalizations. The avian 'song system', a network of brain nuclei, is the probable neural substrate for the second phase of sensorimotor learning. By contrast, the neural representation of song memory acquired in the first phase is localized outside the song system, in different regions of the avian equivalent of the human auditory association cortex.

Animals↗
PubMed1980

Tactual speech perception by minimally trained deaf subjects.

Research on tactual perception of speech has shown that many phonetic contrasts can be transmitted to the deaf through artificial hearing devices that stimulate the sense of touch. Past research has emphasized long-term training with tactual reception for the achievement of maximal perceptual performance. The present study demonstrates that, with a brief training period, deaf adolescents can attain a high level of perceptual performance with a tactual speech system in discrimination of certain hard-to-lipread word pairs pronounced by both a male and female speaker. Thus some speech sounds previously indistinguishable by the deaf people can be immediately available for speech comprehension through the tactual vocoder; and other speech sounds will be recognized with further training. The reason that some contrasts are learned quickly and others require extensive training may be found in a pattern perception postulate proposed by Gavin (1979): word patterns that result in stimulation across a greater area of skin tend to be more discriminable than word patterns which stimulate only small areas of the skin.

Adolescent↗
PubMed2002

What are the clinical skills levels of newly graduated physicians? Self-assessment study of an intended curriculum identified by a Delphi process.

OBJECTIVE: To compare and contrast the learned and an intended curricula of practical clinical skills across the three Danish medical schools. CONTEXT: The three Danish medical schools had comparable discipline-based curricula with 3 years of mainly basic science and 3(1/2) years of mainly clinical education. Danish physicians work as pre-registration house officers (PRHOs) for 1(1/2) years after graduation. METHODS: An anonymous questionnaire listing 210 practical clinical skills was mailed to 226 newly graduated Danish physicians. They were asked if they could meet the minimum level for each of the skills listed as identified by a previous Delphi study. RESULTS: The response rate was 80%. None of the responders met the minimum of all the 210 skills. Only 8% (14) met the minimum level for at least 90% (189) of the skills. On average the responders met the minimum of 74% (155) of the skills. More than 90% of the responders mastered basic history and examination skills. The responders did not meet 28 medical emergency procedures. CONCLUSIONS: We found that the learned curriculum of clinical skills constituted 75% of the intended curriculum. Those responsible for pre- and postgraduate medical education should be aware of the discrepancy between expected and learned curriculum. We discuss the role of experts in the process of defining the core curriculum.

Clinical Competence↗
PubMed2004

Episodic memory impairment in bipolar disorder and obsessive-compulsive disorder: the role of memory strategies.

BACKGROUND: There is evidence that individuals with bipolar disorder exhibit neuropsychological impairments not only during mood episodes but also when they are euthymic. One of the most consistently reported cognitive problems in euthymic individuals with bipolar disorder is an impairment in verbal episodic memory. Verbal learning and memory depend on individuals' ability to organize verbal information appropriately during learning. The purpose of the present study was (i) to determine whether episodic memory impairment in euthymic individuals with bipolar disorder is mediated by impairments in organization of verbal information during learning and (ii) to compare the characteristics of memory impairment in bipolar disorder with that previously found in obsessive-compulsive disorder (OCD). METHODS: Study participants were 30 individuals with DSM-IV bipolar I disorder (BP-I), 30 individuals with DSM-IV OCD and 30 normal control participants matched for age, gender and education. Participants completed the California Verbal Learning Test (CVLT), a well-established measure of verbal learning and memory that enables assessment of verbal organization strategies during learning. RESULTS: Compared with control subjects, both BP-I and OCD participants showed impaired performance in long-delayed free recall and verbal organization strategies during learning. BP-I participants showed greater long-delay free recall difficulties but not greater verbal organization difficulties during learning than OCD participants. For OCD participants, the long-delay recall impairment was mediated by difficulties using verbal organizational strategies during learning. In contrast, the group difference in long-delayed free recall between BP-I and control participants remained significant even when semantic clustering was introduced as a mediator. This indicated that BP-I participants' long-delayed free recall difficulties were mediated to a lesser extent by difficulties using verbal organizational strategies than for OCD participants. CONCLUSIONS: Verbal episodic memory problems in individuals with bipolar I disorder and OCD are mediated to different degrees by difficulties using semantic clustering encoding strategies compared with control participants.

Adult↗
PubMed2005

Methylazoxymethanol acetate does not fully block cell genesis in the young and aged dentate gyrus.

During adulthood, new neurons are continuously added to the mammalian dentate gyrus (DG). An increasing number of studies have correlated changes in rates of dentate neurogenesis with memory abilities. One study based on subchronic treatment with the toxin methylazoxymethanol acetate (MAM) has provided causal evidence that neurogenesis is involved in hippocampal-dependent trace conditioning. In contrast, spatial learning is not impaired following MAM treatment. We hypothesized that this was due to the small residual number of new cells produced following MAM treatment. In the present experiment, we attempted to achieve a higher level of reduction of adult-generated cells following MAM treatment in young and aged rats. We found only a partial reduction of adult-generated cells in the DG. More importantly, independently of the age of the animals, MAM treatment at a dose necessary to reduce neurogenesis altered the overall health of the animals. In conclusion, the behavioural results obtained following subchronic treatment with high doses of MAM in adulthood must be interpreted with extreme caution.

Age Factors↗
PubMed2002

The making of a complex spike: ionic composition and plasticity.

Climbing fiber (CF) activation evokes a large all-or-nothing electrical response in Purkinje cells (PCs), the complex spike. It has been suggested that the role of CFs (and thus complex spikes) is that of a "teacher" in simple learning paradigms such as associative eyeblink conditioning. An alternative hypothesis describes the olivocerebellar system as part of a timing device and denies a role of the CF input in learning. To date, neither of these hypotheses nor others can definitively be verified or discounted. Similarly, the complex spike evades a clear understanding when it comes to the cellular events underlying complex spike generation. What is known, however, is that complex spikes are associated with large dendritic calcium signals that are required for the induction of long-term depression (LTD) at the parallel fiber (PF)-PC synapse. PF-LTD is a form of long-term synaptic plasticity that has been suggested to underlie certain forms of cerebellar motor learning. In contrast to the PF input, the CF input has been considered invariant. Our recent discovery of LTD at the CF input shows that complex spikes are less static than previously assumed. In addition to depression of CF-evoked excitatory postsynaptic currents, long-lasting, selective reduction of slow complex spike components could be observed after brief CF tetanization. To understand the functional implications of CF-LTD, it is crucial to know the types of currents constituting the specific complex spike components. Here we review the "anatomy" of the complex spike as well as our observations of activity-dependent complex spike waveform modifications. In addition, we discuss which properties CF-LTD might add to the circuitry of the cerebellar cortex.

Action Potentials↗
PubMed2000

Instabilities and oscillation in the deterministic Boltzmann machine.

Simulations indicate that the deterministic Boltzmann machine, unlike the stochastic Boltzmann machine from which it is derived, exhibits unstable behavior during contrastive Hebbian learning of nonlinear problems, including oscillation in the learning algorithm and extreme sensitivity to small weight perturbations. Although careful choice of the initial weight magnitudes, the learning rate, and the annealing schedule will produce convergence in most cases, the stability of the resulting solution depends on the parameters in a complex and generally indiscernible way. We show that this unstable behavior is the result of over parameterization (excessive freedom in the weights), which leads to continuous rather than isolated optimal weight solution sets. This allows the weights to drift without correction by the learning algorithm until the free energy landscape changes in such a way that the settling procedure employed finds a different minimum of the free energy function than it did previously and a gross output error occurs. Because all the weight sets in a continuous optimal solution set produce exactly the same network outputs, we define reliability, a measure of the robustness of the network, as a new performance criterion.

Algorithms↗
PubMed2002

Training products of experts by minimizing contrastive divergence.

It is possible to combine multiple latent-variable models of the same data by multiplying their probability distributions together and then renormalizing. This way of combining individual "expert" models makes it hard to generate samples from the combined model but easy to infer the values of the latent variables of each expert, because the combination rule ensures that the latent variables of different experts are conditionally independent when given the data. A product of experts (PoE) is therefore an interesting candidate for a perceptual system in which rapid inference is vital and generation is unnecessary. Training a PoE by maximizing the likelihood of the data is difficult because it is hard even to approximate the derivatives of the renormalization term in the combination rule. Fortunately, a PoE can be trained using a different objective function called "contrastive divergence" whose derivatives with regard to the parameters can be approximated accurately and efficiently. Examples are presented of contrastive divergence learning using several types of expert on several types of data.

Journal Article↗