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Results for “Contrastive learning”

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PubMed2005

Simulations of a modified SOP model applied to retrospective revaluation of human causal learning.

Dickinson and Burke (1996) proposed a modified version of Wagner's (1981) SOP associative theory to explain retrospective revaluation of human causal judgments. In this modified SOP (MSOP), excitatory learning occurs when cue and outcome representations are either both directly activated or both associatively activated. By contrast, inhibitory learning occurs when one representation is directly activated while the other is associatively activated. Finite node simulations of MSOP yielded simple acquisition, overshadowing, blocking, and inhibitory learning under forward contingencies. Importantly, retrospective revaluation was predicted in the form of unovershadowing and backward inhibitory learning. However, MSOP did not yield backward blocking. These predictions are evaluated against the relevant empirical evidence and contrasted with the predictions of other associative theories that have been applied to retrospective revaluation of human causal and predictive learning.

Forecasting↗

PubMed2005

Frontomedian activation depends on both feedback validity and valence: fMRI evidence for contextual feedback evaluation.

Activation within the posterior frontomedian cortex (pFMC) is suggested to be involved in decision conflict, which typically emerges whenever one does not know which action to choose in order to receive a positive outcome. Decision conflict attenuates due to learning which is often indicated by and therefore confounded with the receipt of increasingly frequent positive and decreasingly frequent negative feedback. The present functional Magnetic Resonance study aimed to disentangle the influence of the factors processing of negative feedback and contextual feedback evaluation on pFMC activation. Participants performed a forced choice paradigm in which they had to decide which one out of two competing stimuli would win in a virtual competition game. In one condition (rule learning, RL), participants were provided with valid feedback so that contextual feedback evaluation had a guiding function for action and thus enabled learning. In contrast, participants received no valid information from feedback in another condition (putative learning, PL) and hence could not learn on the basis of contextual feedback evaluation. However, a learning effect in the latter condition was simulated by gradually increasing the frequency of positive feedback and decreasing the frequency of negative feedback according to a learning model which was derived from pilot data. Importantly, participants were naive with respect to feedback manipulations. Beyond confirming pFMC activation for decision conflicts, a significant interaction between validity and valence of feedback in pFMC revealed the specific contribution of contextual feedback evaluation processes on activation of this area. Not the processing of negative feedback per se, which was found to elicit activation within anterior cingulate cortex, but the evaluation of feedback against the background of the current mental model is suggested to be reflected by pFMC activation.

Adult↗

PubMed1999

Innate and learned components of human visual preference.

BACKGROUND: Recent claims in neuroscience and evolutionary biology suggest that the aesthetic sense reflects preferences for image signals whose characteristics best fit innate brain mechanisms of visual recognition. RESULTS: This hypothesis was tested by behaviourally measuring, for a set of initially unfamiliar images, the effects of category learning on preference judgements by humans, and by relating the observed data to computationally reconstructed internal representations of categorical concepts. Category learning induced complex shifts in preference behaviour. Two distinct factors - complexity and bilateral symmetry - could be identified from the data as determinants of preference judgements. The effect of the complexity factor varied with object knowledge acquired through category learning. In contrast, the impact of the symmetry factor proved to be unaffected by learning experience. Computer simulations suggested that the preference for pattern complexity relies on active (top-down) mechanisms of visual recognition, whereas the preference for pattern symmetry depends on automatic (bottom-up) mechanisms. CONCLUSIONS: Human visual preferences are not fully determined by (objective) structural regularities of image stimuli but also depend on their learned (subjective) interpretation. These two aspects are reflected in distinct complementary factors underlying preference judgements, and may be related to complementary modes of visual processing in the brain.

Adolescent↗

PubMed1990

Learning-induced afterhyperpolarization reductions in hippocampus are specific for cell type and potassium conductance.

Hippocampal slices were prepared from rabbits trained in a trace eye-blink conditioning task and from naive and pseudoconditioned controls. Measurements of the post-burst afterhyperpolarization (AHP), action potential, and other cellular properties were obtained from intracellular recordings of CA1 pyramidal (N = 49) and dentate gyrus granule cells (N = 52). A conditioning-specific reduction in the amplitude of the AHP was found in CA1 cells but not in dentate granule cells. This reduction in the AHP was apparent at 50 ms after the end of a depolarizing current pulse, and was maintained for at least 650 ms. Other measured cell characteristics (input resistance, resting membrane potential, action potential shape, inward rectification, spike threshold) were not affected by training, in either CA1 pyramidal or dentate granule cells. Time-course measures indicate that both the medium, Ca2(+)-independent AHP and the slow, Ca2(+)-dependent AHP are reduced by conditioning. The slow AHP largely reflects the Ca2(+)-dependent K+ current, IAHP. Rising and falling slopes, peak amplitude, and width of individual action potentials were not changed by learning. This contrasts with observations from invertebrates in which action potential broadening was reported following learning. We conclude that the reduction in AHP that follows hippocampally-dependent associative learning occurs in specific hippocampal cell types and not others, and is mediated by changes in a Ca2(+)-independent AHP and a particular Ca2(+)-dependent K+ current, IAHP.

Action Potentials↗

PubMed1990

Pentylenetetrazole kindling impairs learning in mice.

Repeated administration of 35 mg/kg body weight pentylenetetrazole (PTZ) induced a kindling phenomenon and an impairment of inhibitory avoidance learning. In contrast, a single administration of the same dose PTZ had no effect on learning. Kindled mice showed impaired habituation of exploratory activity. The results may be of relevance for antiepileptic drug testing.

Animals↗

PubMed1995

Associative learning in degenerative neostriatal disorders: contrasts in explicit and implicit remembering between Parkinson's and Huntington's diseases.

The performances of 12 patients with Parkinson's disease (PD), 16 with Huntington's disease (HD), and young and old healthy controls were assessed on a number of tests of verbal and nonverbal declarative memory, on a test of nonmotor conditional associative learning (words and colors), and on a number of reaction time (RT) tasks. The RT tasks consisted of cued simple and choice reactions. The relationship between the precue and the imperative stimulus in the S1-S2 paradigm was nonarbitrary in the first series and arbitrary in the second series. The series with arbitrary S1-S2 associations was repeated across two successive blocks of trials. The rationale of the study was to investigate the function of the basal ganglia "complex loop," and it was postulated that HD patients would show greater deficits because of greater involvement of the caudate nucleus. The patients with HD had the slowest RTs. Across the two blocks with arbitrary S1-S2 associations, the patients with HD but not PD nevertheless showed evidence of learning in their precued RTs. In contrast, the patients with PD were better able to remember the associations in free recall than were the HD patients. It is concluded that patients with PD have relatively greater deficits in procedural learning, whereas those with HD have relatively more impairments in declarative memory, and the greater level of cognitive impairment in HD overall is interpreted as being due to more serious damage to the caudate loop.

Adult↗

PubMed1999

An evaluation of the concurrent discrimination task as a measure of habit learning: performance of amnesic subjects.

Habit learning has been defined as an association between a stimulus and a response that develops slowly and automatically through repeated reinforcement. Concurrent discrimination (CD) learning, in which subjects learn to choose the rewarded objects in a series of pairs, is believed to be an example of habit learning in monkeys. Studies of human amnesic subjects, however, have produced equivocal results, revealing impaired or absent learning on the same CD tasks that monkeys with medial temporal-lobe (MTL) lesions learn normally. One possible explanation for impaired performance in human amnesic subjects is that, unlike monkeys, human subjects use explicit memory to solve CD problems. To test this hypothesis, we administered a 10-object pair CD learning task to two amnesic subjects, HM and PN, and normal control subjects (NCS). Both amnesic subjects have severe anterograde amnesia with little ability to form explicit memories. On the CD task, they demonstrated little or no learning and acquired no explicit knowledge of the task procedures or reward contingencies. In contrast, NCS learned the task quickly and easily using explicit memory strategies. These results suggest that CD tasks cannot be learned by habit in human subjects, and emphasize the discrepancies between the human and monkey literature on habit learning.

Aged↗

PubMed1996

Infusion of (+) -MK-801 and memantine -- contrasting effects on radial maze learning in rats with entorhinal cortex lesion.

(+)-5-Methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate ((+)-MK-801) and 1-amino-3,5-dimethyladamantane (memantine), two uncompetitive antagonists of the NMDA receptor were tested in an allocentric version of the radial maze test (with four out of eight arms reinforced) both in normal rats and after quinolinic acid-induced entorhinal cortex lesions. Both agents were infused s.c. using Alzet osmotic minipumps in order to assure steady state drug levels in the serum and brain during the experiment. In non-lesioned rats, (+)-MK-801 (0.312 mg/kg per day) produced disturbances in learning of spatial information dependent on reference memory but not that involving working memory. In contrast, memantine (20 mg/kg per day) had no effect in normal rats. In rats with entorhinal cortex lesions, (+)-MK-801 enhanced the lesion-induced deficit in reference memory. In contrast, memantine reversed the lesion-induced increase in reference memory errors. The divergent effects of those two uncompetitive NMDA receptor antagonists could, at least partially, be due to the differences reported in their channel blocking kinetics and voltage dependence. The results indicate that under conditions of pathological impairment of brain structures such as entorhinal cortex lesion, memantine might produce beneficial effects on cognitive functions.

Animals↗

PubMed2001

Hippocampus and homing in pigeons: left and right hemispheric differences in navigational map learning.

One-month-old, inexperienced homing pigeons, prior to any opportunity to learn a navigational map, were subjected to either right or left unilateral ablation of the hippocampal formation (HF). These pigeons were then held together with a group of age-matched control birds in an outdoor aviary, where they were kept for about 3 months with the opportunity to learn a navigational map. When subsequently tested for navigational map learning at about 4 months of age posthatching, control and right HF-ablated pigeons were equally good at orienting homeward from distant, unfamiliar locations, indicating successful navigational map learning. By contrast, left HF-ablated pigeons were impaired in orienting homeward, indicating a failure to learn a navigational map. Interestingly, both right and left HF-ablated pigeons displayed impaired homing performance relative to controls. These results suggest that different aspects of homing pigeon navigation may be lateralized to different hemispheres, and in particular, the HF of the different hemispheres. The left HF appears critical for navigational map learning, i.e. determining an approximate direction home from distant, unfamiliar locations. The right HF, and possibly the left HF as well, appear to play an important role in local navigation near the loft, which is likely based on familiar landmarks.

Animals↗

PubMedDate not supplied

Selective impairments of object knowledge in a case of acquired cortical blindness.

A patient (N.B.) is described, who displays distinct deficits of object knowledge related to knowledge type (Functional/Associative vs Visual) and also to knowledge category (Animate vs Inanimate). The patient was first given an orally presented forced-choice test devised to assess orthogonal combinations of knowledge type and knowledge category. In the production of this test it was found that normals took longer to respond to Visual questions than to Functional/Associative questions; therefore, sets of questions were compiled that were matched for both accuracy and latency. There were two main findings concerning N.B.'s semantic memory. First, with careful matching of difficulty level, the patient showed selective preservation of Functional/Associative knowledge of Animate objects compared with Visual knowledge of Animate objects and also compared with Functional/Associative knowledge of Inanimate objects. Second, there was a qualitative difference in patterns of knowledge retrieval for Visual compared with Functional/Associative knowledge. Retrieval of Visual knowledge, both Animate and Inanimate, was inconsistent and, in a word-pair recall test, a high degree of connection of a Visual property to an object did not promote paired-associate learning. In contrast, retrieval of Functional/Associative knowledge (both Animate and Inanimate) was consistent and paired-associate learning was influenced by connection strength. This study provides strong evidence to support the validity of both "knowledge type" and "category" based accounts of the organisation of semantic memory.

Adult↗

PubMed1999

Dissociation of dopamine release in the nucleus accumbens from intracranial self-stimulation.

Mesolimbic dopamine-releasing neurons appear to be important in the brain reward system. One behavioural paradigm that supports this hypothesis is intracranial self-stimulation (ICS), during which animals repeatedly press a lever to stimulate their own dopamine-releasing neurons electrically. Here we study dopamine release from dopamine terminals in the nucleus accumbens core and shell in the brain by using rapid-responding voltammetric microsensors during electrical stimulation of dopamine cell bodies in the ventral tegmental area/substantia nigra brain regions. In rats in which stimulating electrode placement failed to elicit dopamine release in the nucleus accumbens, ICS behaviour was not learned. In contrast, ICS was acquired when stimulus trains evoked extracellular dopamine in either the core or the shell of the nucleus accumbens. In animals that could learn ICS, experimenter-delivered stimulation always elicited dopamine release. In contrast, extracellular dopamine was rarely observed during ICS itself. Thus, although activation of mesolimbic dopamine-releasing neurons seems to be a necessary condition for ICS, evoked dopamine release is actually diminished during ICS. Dopamine may therefore be a neural substrate for novelty or reward expectation rather than reward itself.

Animals↗

PubMed2006

Learning to use demonstratives in conversation: what do language specific strategies in Turkish reveal?

Pragmatic development requires the ability to use linguistic forms, along with non-verbal cues, to focus an interlocutor's attention on a referent during conversation. We investigate the development of this ability by examining how the use of demonstratives is learned in Turkish, where a three-way demonstrative system (bu, su, o) obligatorily encodes both distance contrasts (i.e. proximal and distal) and absence or presence of the addressee's visual attention on the referent. A comparison of the demonstrative use by Turkish children (6 four- and 6 six-year-olds) and 6 adults during conversation shows that adultlike use of attention directing demonstrative, su, is not mastered even at the age of six, while the distance contrasts are learned earlier. This language specific development reveals that designing referential forms in consideration of recipient's attentional status during conversation is a pragmatic feat that takes more than six years to develop.

Adult↗

PubMed2006

Qualitative differences between implicit and explicit sequence learning.

Four experiments investigate the differences between implicit and explicit sequence learning concerning their resilience to structural and superficial task changes. A superficial change that embedded the SRT task in the context of a selection task, while maintaining the sequence, did selectively hinder the expression of implicit learning. In contrast, a manipulation that maintained the task surface, but decreased the sequence validity, affected the expression of learning specifically when it was explicit. These results are discussed in the context of a dynamic framework (Cleeremans & Jiménez, 2002), which assumes that implicit knowledge is specially affected by contextual factors and that, as knowledge becomes explicit, it allows for the development of relevant metaknowledge that modulates the expression of explicit knowledge.

Adult↗

PubMed1996

Nitric oxide but not carbon monoxide is involved in spatial learning of mice.

The aim of the present study was to elucidate the role of carbon monoxide (CO) in learning and to compare it with that of nitric oxide (NO). Effects of an inhibitor of heme oxygenase which produces CO, Zn-protoporphyrin IX, on passive avoidance learning and spatial learning in mice were examined using step through, step down and water maze tests. Zn-protoporphyrin IX (10, 20 nmol, i.c.v.) affected neither type of learning. In contrast, N-omega-nitro-L-arginine (40 nmol, i.c.v.), an inhibitor of NO synthase, impaired spatial learning, but not passive avoidance learning. These results suggest that NO but not CO is involved in spatial learning.

Animals↗

PubMed1987

[Effect of intracisternal administration of antisera against neurospecific enolase (protein 14-3-2) on avoidance behavior in rats].

The antisera to three isoenzymes (alpha alpha, alpha gamma, and gamma gamma) of the rat neurospecific enolase were studied. gamma gamma-antiserum administered into the brain cistern (8 microliters) prior to learning, in contrast to two other antisera, impaired the retrieval of passive avoidance response within 1-28 days after learning. Maximal amnestic effect occurred in the first 3 days. Probable mechanisms of the neurospecific enolase participation in the formation of memory traces, are discussed.

Animals↗

PubMed2005

Alternative use of chromatic and achromatic cues in a hawkmoth.

The diurnal hummingbird hawkmoth Macroglossum stellatarum can learn the achromatic (intensity-related) and the chromatic (wavelength-related) aspect of a spectral colour. Free-flying moths learn to discriminate two colours differing in the chromatic aspect of colour fast and with high precision. In contrast, they learn the discrimination of two stimuli differing in the achromatic aspect more slowly and less reliably. When trained to use the chromatic aspect, they disregard the achromatic aspect, and when trained to use the achromatic aspect, they disregard the chromatic aspect, at least to some degree. In a conflicting situation, hummingbird hawkmoths clearly rely on the chromatic aspect of colour. Generally, the moths pay attention to the most reliable cue that allows them to discriminate colours in the learning situation. This is usually the chromatic aspect of the colour but they can learn to attend to the achromatic aspect instead. There is no evidence for relative colour learning, i.e. moths do not learn to choose the longer or shorter of two wavelengths, but it is possible that they learn to choose the darker or brighter shade of a colour, and thereby its relative intensities.

Animals↗

PubMed2004

The effect of learning on experimental evolution of resource preference in Drosophila melanogaster.

Learning is thought to be adaptive in variable environments, whereas constant, predictable environments are supposed to favor unconditional, genetically fixed responses. A dichotomous view of behavior as either learned or innate ignores a potential evolutionary interaction between the learned and innate components of a behavioral response. We addressed this interaction in the context of oviposition substrate choice in Drosophila melanogaster, asking two main questions. First, will learning also evolve in a constant environment in which it always pays to show the same choice? Second, how does an opportunity to learn affect the evolution of the innate (genetic) component of oviposition substrate choice? We exposed experimental populations to four selection regimes, involving selection on oviposition substrate preference (an orange versus a pineapple medium). In two selection regimes the flies were selected for preference either for the orange medium, or for the pineapple medium. In the remaining two selection regimes the flies were also selected for preference for either orange or pineapple, but additionally could use past experience (aversion learning) to decide which medium it paid to avoid. Lines exposed to the latter selection regimes evolved improved learning ability, indicating that learning may be advantageous even if the same behavioral response is favored every generation. Furthermore, of the two selection regimes that favored oviposition on the pineapple medium, the regime that allowed for learning led to the evolution of a stronger innate preference for pineapple, than the regime that did not allow for learning. In contrast, of the two regimes that selected for oviposition on the orange medium, the one that allowed for learning led to a smaller evolutionary change of the innate preference. Thus, an opportunity to learn facilitated the evolution of innate preference under selection for preference for pineapple, but hindered it under selection for preference for orange. We discuss possible mechanisms for this effect.

Analysis of Variance↗

PubMed1992

Inferotemporal-frontal Disconnection: The Uncinate Fascicle and Visual Associative Learning in Monkeys.

We report a series of six experiments in which we examined the behavioural effects of disconnecting the inferior temporal cortex from the prefrontal cortex in cynomolgus monkeys by sectioning the direct cortico-cortical pathway between them, the uncinate fascicle. In experiment 1, monkeys with bilateral section of the uncinate fascicle showed a marked deficit in learning visuomotor conditional problems. Experiments 2 and 3 demonstrated that this deficit was not the result of a mild motor impairment, nor of a visual discrimination impairment. However, experiment 4 showed that the impairment extended to visual - visual conditional learning. In contrast, following bilateral section of the uncinate fascicle monkeys were unimpaired at two other tasks of visual associative learning: a reward - visual associative task (experiment 5), in which the presence or absence of a food reward served as a cue to the correct choice between two visual stimuli, and a time - visual associative task (experiment 6), in which the cue to the correct choice was the length of the intertrial interval. Thus, animals with uncinate fascicle section showed no impairment in learning to choose between visual stimuli based on their differential association with food reward or other non-visual cues, but were unable to learn to choose between visual stimuli based on their differential association with another visual stimulus. They were equally unable to choose between two motor responses on the basis of the visual cue.

Journal Article↗