SEARCH · PubMed Health

Results for “CONDITIONED 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 451 records · Page 25Linked to original sources

PubMed1993

Synaptic remodelling and elimination as integral processes of synaptogenesis.

It has become increasingly clear that the development and maintenance of synaptic connectivity patterns in the central and peripheral nervous system are not only based on the formation of synapses but include the selective elimination of synaptic subpopulations. Synaptic remodeling and elimination apparently also play a key role in the specification of neuronal connections during ontogenesis of the neocortex in various species. At least three types of synapse elimination have been demonstrated until now, i.e. physiological cell death of synaptically connected neurons, synaptic disconnection and lysosomal degradation, predominantly of presynaptic elements. Occurrence of different elimination types appears to depend on (1) whether the presynaptic or postsynaptic element induces the synaptic reorganization and (2) whether or not the neuron inducing the synapse elimination survives. The same type of synapse elimination may be seen during normal development and under pathological conditions. Factors inducing mental retardation may then either retard synapse formation or interfere with the process of synapse removal. In order to undergo plastic changes in synaptic connections, neurons may respond to exogenous factors such as lack of trophic factors or sensitivity for them (e.g. NGF), long-lasting changes in neuronal activity (e.g. due to drug application or sensory deprivation), hormonal influences (e.g. thyroxin or sexual hormones), learning conditions, or lesions (partial deafferentation and axotomy). The neurons, in turn, may change their responsiveness to exogenous stimuli by inducing synaptic reorganisation.

Age Factors↗

PubMed1989

Text recall in adulthood: the roles of text imagery and orienting tasks.

Three experiments were conducted to investigate dual-code theory and the levels-of-processing approach in discourse processing. Three concrete and three abstract tests were constructed to be equivalent in the degree to which they were perceived as concrete vs. abstract. All experiments presented concrete and abstract texts under three orienting tasks. Results of the first experiment showed main effects for both text concreteness and orienting tasks and an interaction that can be described by the lack of a difference between the recall rates for the concrete and the abstract texts under the intentional-learning condition. In the second experiment, longer texts were used and a second trial was introduced. The interaction was not replicated. There were main effects for concreteness, orienting tasks, and trials. The third experiment replicated Experiment 2 with subjects in their late 40s and over 70. Main effects were obtained as before. Age interacted with both orienting task and concreteness, indicating that older adults gain less than middle-aged adults from intentional-learning instructions and benefit less from highly concrete texts. The discussion focuses on the relation of Materials and Subjects as factors to dual-code theory and levels of processing approach.

Adolescent↗

PubMed1989

The processing of spatially transformed text.

The present study shows that previous attempts to demonstrate explicit memory for orientation of spatially transformed text were inconclusive. In the present experiments, subjects read spatially transformed sentences and were then given a recognition test that permitted the use of only nonsemantic information. The results revealed clear evidence of incidental retention of nonsemantic information on an immediate test, no improvement in performance under intentional learning conditions, reduced but still better than chance retention following a 48-h delay, and little change in performance with anomalous sentences. These and other results involving the reading of spatially transformed materials are discussed in terms of the interaction of processing requirements at encoding and retrieval.

Humans↗

PubMedDate not supplied

Do rat strain differences in ethanol consumption reflect differences in ethanol sensitivity or the preparedness to learn?

Three strains of rats (Wistar, Sprague-Dawley, Long-Evans; n = 10/strain) were trained to drink various concentrations of ethanol (ETOH) in the rats' home cage in daily 30-min drinking sessions using a modified "Samson" sucrose-fading procedure. Wistar and Sprague-Dawley rats were similar in their voluntary intake of a wide range of ETOH concentrations and both of these strains drank considerably more ETOH than the Long-Evans strain. For comparison purposes only, pharmacological pretreatment tests were later conducted with the Sprague-Dawley strain of rats using a maintenance concentration of 20% w/v ETOH. Low-dose ETOH pretreatments increased (125% of control), and high-dose ETOH pretreatments decreased the subsequent voluntary consumption of ETOH. Low-dose nicotine pretreatments increased ETOH consumption to 148% of control intake, and high doses of nicotine decreased ETOH consumption. Both opiate antagonists, naloxone and naltrexone, produced dose-dependent decreases in ETOH consumption. The dopamine antagonist, haloperidol, produced dose- and time-dependent increases in voluntary ETOH consumption. The strain differences in voluntary ETOH consumption described in the present study differ from those previously described by other labs. We suggest that this strain-dependent disparity between laboratories, with respect to ETOH consumption/preference tasks, may reflect genetic differences in the preparedness to condition (learn) voluntary ETOH consumption rather than genetic differences in ETOH's reward/reinforcement attributes.

Alcohol Drinking↗

PubMed1975

Reversal of the 6-hydroxydopamine-induced suppression of a CAR by drugs facilitating central catecholaminergic mechanisms.

The intraventricular injection of 6-hydroxydopamine (200 mug) blocked a previously learned conditioned avoidance response (CAR) in rats. The administration of NE, DOPA, amphetamine, phenelzine, desipramine and clonidine induced the reappearance of the CAR. These results are in agreement with current hypotheses on the mechanism of action of 6-hydroxydopamine on the central nervous system.

Amphetamine↗

PubMed1998

Abstract and effector-specific representations of motor sequences identified with PET.

Positron emission tomography was used to identify neural systems involved in the acquisition and expression of sequential movements produced by different effectors. Subjects were tested on the serial reaction time task under implicit learning conditions. In the initial acquisition phase, subjects responded to the stimuli with keypresses using the four fingers of the right hand. During this phase, the stimuli followed a fixed sequence for one group of subjects (group A) and were randomly selected for another group (group B). In the transfer phase, arm movements were used to press keys on a substantially larger keyboard, and for both groups, the stimuli followed the sequence. Behavioral indices provided clear evidence of learning during the acquisition phase for group A and transfer when switched to the large keyboard. Sequence acquisition was associated with learning-related increases in regional cerebral blood flow (rCBF) in a network of areas in the contralateral left hemisphere, including sensorimotor cortex, supplementary motor area, and rostral inferior parietal cortex. After transfer, activity in inferior parietal cortex remained high, suggesting that this area had encoded the sequence at an abstract level independent of the particular effectors used to perform the task. In contrast, activity in sensorimotor cortex shifted to a more dorsal locus, consistent with motor cortex somatotopy. Thus, activity here was effector-specific. An increase in rCBF was also observed in the cingulate motor area at transfer, suggesting a role linking the abstract sequential representations with the task-relevant effector system. These results highlight a network of areas involved in sequence encoding and retrieval.

Adult↗

PubMed1984

Understanding biological computation: reliable learning and recognition.

We experimentally examine the consequences of the hypothesis that the brain operates reliably, even though individual components may intermittently fail, by computing with dynamical attractors. Specifically, such a mechanism exploits dynamic collective behavior of a system with attractive fixed points in its phase space. In contrast to the usual methods of reliable computation involving a large number of redundant elements, this technique of self-repair only requires collective computation with a few units, and it is amenable to quantitative investigation. Experiments on parallel computing arrays show that this mechanism leads naturally to rapid self-repair, adaptation to the environment, recognition and discrimination of fuzzy inputs, and conditional learning, properties that are commonly associated with biological computation.

Adaptation, Physiological↗

PubMed1992

Degree of learning, interpolated tests, and rate of forgetting.

The purpose of the two experiments reported here was to observe the effects of degree of learning, interpolated tests, and retention interval, primarily on the rate of forgetting of a list of words, and secondarily on hypermnesia for those words. In the first experiment, all the subjects had one study trial on a list of 20 common words, followed by two tests of recall. Half of the subjects had further study and test trials until they had learned the words to a criterion of three correct consecutive recalls. Two days later, half of the subjects under each learning condition returned for four retention tests, and 16 days later, all the subjects returned for four tests. Experiment 2 was similar, except that all the subjects had at least three study trials followed by four recall tests on Day 1, intermediate tests were given 2 or 7 days later, and they all had final tests 14 days later. The results showed that rate of forgetting was attenuated by an additional intermediate set of tests but not by criterion learning. Hypermnesia was generally found over the tests that were given after a retention interval of 2 or more days. The best predictor of the amount of hypermnesia over a set of tests was the difference between overall cumulative recall and net recall on the first test of the set.

Achievement↗

PubMed2026

Making multi-axis Gaussian graphical models scalable to millions of cells.

MOTIVATION: Networks underlie the generation and interpretation of many biological datasets: gene networks shed light on the regulatory structure of the genome, and cell networks can capture structure of the tumor micro-environment. However, most methods that learn such networks make the faulty "independence assumption"; to learn the gene network, they assume that no cell network exists. "Multi-axis" methods, which do not make this assumption, fail to scale beyond a few thousand cells or genes. This limits their applicability to only the smallest datasets. RESULTS: We develop a multi-axis method, which learns conditional dependency networks, capable of processing million-cell datasets within minutes. This was previously impossible, and unlocks the use of such methods on modern scRNA-seq datasets, as well as more complex datasets. We apply the method to a new scRNA-seq dataset for neuronal cell development, and compare the result to an existing state of the art method, hdWGCNA. We demonstrate that the new method yields gene networks that have a more focused biological interpretation and that the simultaneously learned cell network has advantages over a conventional kNN-based clustering. Further, our method yields novel biological insights by identifying long non-coding RNAs that potentially have a role in neuronal development. AVAILABILITY AND IMPLEMENTATION: Our methodology is available as a Python package GmGM on PyPI (https://pypi.org/project/GmGM/0.5.3/). The code for all experiments performed in this article is available on GitHub (https://github.com/BaileyAndrew/GmGM-Bioinformatics) and Zenodo (10.5281/zenodo.20384566).

Gene Regulatory Networks↗

PubMed2003

Transfer of spatial context from visual to haptic search.

Under incidental learning conditions, spatial layouts can be acquired implicitly and facilitate visual search (contextual-cueing effect). We examined whether the contextual-cueing effect is specific to the visual modality or transfers to the haptic modality. The participants performed 320 (experiment 1) or 192 (experiment 2) visual search trials based on a typical contextual-cueing paradigm, followed by haptic search trials in which half of the trials had layouts used in the previous visual search trials. The visual contextual-cueing effect was obtained in the learning phase. More importantly, the effect was transferred from visual to haptic searches; there was greater facilitation of haptic search trials when the spatial layout was the same as in the previous visual search trials, compared with trials in which the spatial layout differed from those in the visual search. This suggests the commonality of spatial memory to allocate focused attention in both visual and haptic modalities.

Adult↗

PubMed2006

Sweep visual evoked potential grating acuity thresholds paradoxically improve in low-luminance conditions in children with cortical visual impairment.

PURPOSE: Children with cortical or cerebral visual impairment (CVI) often experience photophobia. In a study conducted to test whether this clinical phenomenon affects visual function, the sweep visual evoked potential (VEP) was used to evaluate cortical responses to grating stimuli in two luminance conditions: low and normal. METHODS: Twenty children (age range, 7 months to 4 years 10 months) with CVI and 17 age-matched control subjects were examined. Testing conditions consisted of a swept grating stimulus shown against a normal background luminance (109 cd/m2) and against a low-luminance background (20 cd/m2). Thresholds in these two luminance conditions were compared. Response amplitudes across the spatial frequency domain were also compared. RESULTS: Children with CVI paradoxically have improved grating acuity thresholds when the stimulus is shown using a low-luminance background (P=0.006). Response amplitudes are also increased in low luminance. In control children, luminance had no significant effect on response amplitudes or thresholds. CONCLUSIONS: Increased luminance causes a worsening of acuity thresholds in children with CVI. Response amplitudes are also diminished in normal luminance. This finding has implications for optimal viewing and learning conditions for children with CVI.

Blindness, Cortical↗

PubMed1969

A theory of cerebellar cortex.

1. A detailed theory of cerebellar cortex is proposed whose consequence is that the cerebellum learns to perform motor skills. Two forms of input-output relation are described, both consistent with the cortical theory. One is suitable for learning movements (actions), and the other for learning to maintain posture and balance (maintenance reflexes).2. It is known that the cells of the inferior olive and the cerebellar Purkinje cells have a special one-to-one relationship induced by the climbing fibre input. For learning actions, it is assumed that:(a) each olivary cell responds to a cerebral instruction for an elemental movement. Any action has a defining representation in terms of elemental movements, and this representation has a neural expression as a sequence of firing patterns in the inferior olive; and(b) in the correct state of the nervous system, a Purkinje cell can initiate the elemental movement to which its corresponding olivary cell responds.3. Whenever an olivary cell fires, it sends an impulse (via the climbing fibre input) to its corresponding Purkinje cell. This Purkinje cell is also exposed (via the mossy fibre input) to information about the context in which its olivary cell fired; and it is shown how, during rehearsal of an action, each Purkinje cell can learn to recognize such contexts. Later, when the action has been learnt, occurrence of the context alone is enough to fire the Purkinje cell, which then causes the next elemental movement. The action thus progresses as it did during rehearsal.4. It is shown that an interpretation of cerebellar cortex as a structure which allows each Purkinje cell to learn a number of contexts is consistent both with the distributions of the various types of cell, and with their known excitatory or inhibitory natures. It is demonstrated that the mossy fibre-granule cell arrangement provides the required pattern discrimination capability.5. The following predictions are made.(a) The synapses from parallel fibres to Purkinje cells are facilitated by the conjunction of presynaptic and climbing fibre (or post-synaptic) activity.(b) No other cerebellar synapses are modifiable.(c) Golgi cells are driven by the greater of the inputs from their upper and lower dendritic fields.6. For learning maintenance reflexes, 2(a) and 2(b) are replaced by2'. Each olivary cell is stimulated by one or more receptors, all of whose activities are usually reduced by the results of stimulating the corresponding Purkinje cell.7. It is shown that if (2') is satisfied, the circuit receptor --> olivary cell --> Purkinje cell --> effector may be regarded as a stabilizing reflex circuit which is activated by learned mossy fibre inputs. This type of reflex has been called a learned conditional reflex, and it is shown how such reflexes can solve problems of maintaining posture and balance.8. 5(a), and either (2) or (2') are essential to the theory: 5(b) and 5(c) are not absolutely essential, and parts of the theory could survive the disproof of either.

Animals↗

PubMed1978

Heart rate, recall, and reaction-time measures of levels of processing.

A problem of circularity emerges in any attempt to index depth by retention alone. In the present study, reaction time (RT), and heart-rate response were used to index the three qualitatively distinct levels of physical, phonemic, and semantic processing. An additional objective was to distinguish between the three levels under incidental vs intentional learning conditions. Subjects were 46 male undergraduates who were given 30 trials. A trial consisted of the presentation of an orienting question and an imperative word-stimulus separated by a 6-sec. interval. There were three types of questions in order to induce processing to one of the three target levels. The results indicated that recall as well as heart-rate acceleration distinguished between two (physical vs phonemic and semantic) rather than three levels of processing in the incidental condition. Heart-rate change differentiated between incidental and intentional, the intentional condition showing a smaller change. Semantic and phonemic RTs were faster than physical RT, but there were no differences between semantic and phonemic RTs. Intentional recall was superior to incidental recall. It is suggested that psychophysiological indices can provide independent evidence for 'levels of processing.'

Adolescent↗

PubMed1997

Encoding activity and face recognition.

A series of studies conducted over the past 20 years have explored the effects of various tasks on recognition memory for faces. Memory for faces appears better when the study task involves judgements about an abstract trait rather than a physical feature. The various situations in which these results were obtained raise important methodological questions regarding the learning conditions, whether incidental or intentional, and the duration of exposure to the stimulus during the study phase. We consider here two alternative explanations for the reported results. One concerns depth of processing and the other the opposition between component and holistic processing. Possible strategies for improving face recognition performance are considered.

Face↗

PubMed1999

The acquisition of category structure in unsupervised learning.

Four experiments examined the extent to which prior knowledge influences the acquisition of category structure in unsupervised learning conditions. Prior knowledge is general knowledge about a broad domain that explains why an object has the features it does. Category structure refers to the statistical regularities of features within and across categories. Subjects viewed items and then divided them up into the categories that seemed most natural. Each item had one feature that was related to prior knowledge and five features that were not. The results showed that even this small amount of prior knowledge helped subjects to discover the category structure. In addition, prior knowledge enhanced the learning of many of the category's features, and not just the features that were directly relevant to the knowledge. The results suggest that prior knowledge may help to integrate the features of a category, thereby improving the acquisition of category structure.

Adult↗

PubMed2006

What is the locus of the errorless-learning advantage?

In two experiments involving word-stem completion, an advantage was found for errorless over errorful-learning conditions, for both severely and moderately memory-impaired participants. This advantage did not depend on the implicit/explicit nature of the question asked. Additional tests showed that subsequent recognition of target items was good for both groups, but only in the absence of lures derived from participants' prior errors. Source-memory was shown to be virtually absent in the severely impaired group and only weakly present in the moderately impaired group. This combination of results suggests that preserved implicit memory, in the absence of explicit memory, is sufficient for an errorless-learning advantage to accrue.

Adult↗

PubMed2004

The psychological behaviorism theory of pain and the placebo: its principles and results of research application.

The psychological behaviorism theory of pain unifies biological, behavioral, and cognitive-behavioral theories of pain and facilitates development of a common vocabulary for pain research across disciplines. Pain investigation proceeds in seven interacting realms: basic biology, conditioned learning, language cognition, personality differences, pain behavior, the social environment, and emotions. Because pain is an emotional response, examining the bidirectional impact of emotion is pivotal to understanding pain. Emotion influences each of the other areas of interest and causes the impact of each factor to amplify or diminish in an additive fashion. Research based on this theory of pain has revealed the ameliorating impact on pain of (1) improving mood by engaging in pleasant sexual fantasies, (2) reducing anxiety, and (3) reducing anger through various techniques. Application of the theory to therapy improved the results of treatment of osteoarthritic pain. The psychological behaviorism theory of the placebo considers the placebo a stimulus conditioned to elicit a positive emotional response. This response is most powerful if it is elicited by conditioned language. Research based on this theory of the placebo that pain is ameliorated by a placebo suggestion and augmented by a nocebo suggestion and that pain sensitivity and pain anxiety increase susceptibility to a placebo.

Affect↗

PubMed1999

On the whats and hows of retrieval in the acquisition of a simple skill.

Two general views on the role of memory in cognitive skills--an instance-based theory and an associative perspective--were compared with respect to their general assumptions about the information involved and the processes that operate on that information. Characteristics of memory information were examined in terms of predictions for transfer to various stimulus forms as a function of 2 types of learning conditions. Characteristics of memory processes were examined using a set of general process models. Results of 4 experiments indicate that (a) neither theoretical perspective was capable of accounting for all the observed transfer effects, indicating needed refinements to informational assumptions, and that (b) 1 class of process assumptions was consistently supported, whereas other classes were consistently contradicted, indicating a general set of process characteristics that can be used in further model development.

Humans↗