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Results for “Contrastive learning”

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PubMed1991

On the hippocampus and learned conditional responding: effects of aspiration versus ibotenate lesions.

To study the possible involvement of the hippocampus in learned conditional responding, rats with aspiration lesions of the hippocampus and others that had the hippocampus removed with ibotenic acid were trained on concurrent Pavlovian conditional and nonconditional discriminations. In agreement with the results reported by Ross et al. (1984), animals that had the hippocampus removed with aspiration were unable to learn the conditional discrimination, but learned the simple nonconditional discrimination without difficulty. In contrast, rats that had the hippocampus removed with ibotenic acid did not differ from controls in learning either discrimination. Furthermore, transfer test results were consistent with the hypothesis that ibotenate-lesioned rats performed conditional operations to solve the conditional discrimination problem. Histological analysis indicated that the ibotenate lesions resulted in the removal of the hippocampus and dentate gyrus with minimal involvement of other structures. In aspiration hippocampal animals there was less overall damage to the hippocampus, but there was also extensive damage to the axons passing in alveus and fimbria, together with bilateral loss of cells in the subicular complex, the cingulate gyrus, and the cortex. Since rats with ibotenate lesions had more complete removal of the hippocampus, yet learned both discriminations, the impaired conditional responding found in aspiration hippocampals must be due to extrahippocampal damage.

Animals↗

PubMed2000

Perceptual learning for a pattern discrimination task.

Our goal was to differentiate low and mid level perceptual learning. We used a complex grating discrimination task that required observers to combine information across wide ranges of spatial frequency and orientation. Stimuli were 'wicker'-like textures containing two orthogonal signal components of 3 and 9 c/deg. Observers discriminated a 15% spatial frequency shift in these components. Stimuli also contained four noise components, separated from the signal components by at least 45 degrees of orientation or approximately 2 octaves in spatial frequency. In Experiment 1 naive observers were trained for eight sessions with a four-alternative same-different forced choice judgment with feedback. Observers showed significant learning, thresholds dropped to approximately 1/3 of their original value. In Experiment 2 we found that observers showed far less learning when the noise components were not present. Experiment 3 found, unlike many other studies, almost complete transfer of learning across orientation. The results of Experiments 2 and 3 suggest that, unlike many other perceptual learning studies, most learning in Experiment 1 occurs at mid to high levels of processing rather than within low level analyzers tuned for spatial frequency and orientation. Experiment 4 found that performance was more severely impaired by spatial frequency shifts in noise components of the same spatial frequency or orientation as the signal components (though there was significant variability between observers). This suggests that after training observers based their responses on mechanisms tuned for selective regions of Fourier space. Experiment 5 examined transfer of learning from a same-sign task (the two signal components both increased/decreased in spatial frequency) to an opposite-sign task (signal components shifted in opposite directions in frequency space). Transfer of learning from same-sign to opposite-sign tasks and vice versa was complete suggesting that observers combined information from the two signal components independently.

Adult↗

PubMed2004

Experience can change the 'light-from-above' prior.

To interpret complex and ambiguous input, the human visual system uses prior knowledge or assumptions about the world. We show that the 'light-from-above' prior, used to extract information about shape from shading is modified in response to active experience with the scene. The resultant adaptation is not specific to the learned scene but generalizes to a different task, demonstrating that priors are constantly adapted by interactive experience with the environment.

Adaptation, Physiological↗

PubMed2003

Facial recognition using simulated prosthetic pixelized vision.

PURPOSE: To evaluate a model of simulated pixelized prosthetic vision using noncontiguous circular phosphenes, to test the effects of phosphene and grid parameters on facial recognition. METHODS: A video headset was used to view a reference set of four faces, followed by a partially averted image of one of those faces viewed through a square pixelizing grid that contained 10x10 to 32x32 dots separated by gaps. The grid size, dot size, gap width, dot dropout rate, and gray-scale resolution were varied separately about a standard test condition, for a total of 16 conditions. All tests were first performed at 99% contrast and then repeated at 12.5% contrast. RESULTS: Discrimination speed and performance were influenced by all stimulus parameters. The subjects achieved highly significant facial recognition accuracy for all high-contrast tests except for grids with 70% random dot dropout and two gray levels. In low-contrast tests, significant facial recognition accuracy was achieved for all but the most adverse grid parameters: total grid area less than 17% of the target image, 70% dropout, four or fewer gray levels, and a gap of 40.5 arcmin. For difficult test conditions, a pronounced learning effect was noticed during high-contrast trials, and a more subtle practice effect on timing was evident during subsequent low-contrast trials. CONCLUSIONS: These findings suggest that reliable face recognition with crude pixelized grids can be learned and may be possible, even with a crude visual prosthesis.

Adult↗

PubMedDate not supplied

The effects of telencephalic pallial lesions on spatial, temporal, and emotional learning in goldfish.

In mammals, the pallial amygdala is implicated in emotional learning and memory, whereas the hippocampus is involved in spatial, contextual, or relational memory. This review presents a set of experiments aimed to study the involvement of the dorsomedial and dorsolateral telencephalon of goldfish in spatial and active avoidance learning. Results showed that (1) medial lesions impaired both acquisition and retention of conditioned avoidance response in two-way active avoidance learning experiments with stimuli overlapping (emotional factor) and with an interstimuli gap (temporal and emotional factors), and (2) the medial lesion did not affect spatial learning (spatial, contextual, or relational factors). In contrast, lateral lesions did not impair conditioned avoidance response with stimuli overlapping, but affected conditioned avoidance response with an interstimuli gap and spatial learning. These results support the presence of two differentiated memory systems in teleost fish based on discrete pallial regions: emotional (dorsomedial telencephalon) and spatial/temporal or relational (dorsolateral telencephalon). Furthermore, these functional data support the homology between the medial pallium of the teleost and the pallial amygdala of land vertebrates, and between the teleost lateral pallium and the mammalian hippocampus.

Amygdala↗

PubMed2001

Dissociation between intentional and incidental sequence learning in Huntington's disease.

The ability to acquire and act upon serial order information is fundamental to almost all forms of adaptive behaviour. There is growing evidence that such knowledge may be acquired through a number of different means, each perhaps with its own neuronal substrate. One major distinction is between serial order information acquired intentionally and leading to explicit conscious knowledge of the sequence structure, and information acquired incidentally through experience. While this latter form of knowledge influences behaviour, it may do so without the participant being aware of the sequential information, i.e. it is acquired implicitly. Evidence from physiological and lesion studies in animals and imaging studies in humans suggests that these two forms of learning may have dissociable neuronal substrates. Specifically, the striato-thalamo-cortical circuit centred on the caudate nucleus is proposed to be involved in intentional sequence learning and that based on the putamen on incidental learning. The present study tested one part of this proposed dissociation by assessing patients with Huntington's disease on tasks of the two forms of learning. On the test of trial-and-error intentional learning there were marked deficits, which were closely related to disease progression and to measures of executive cognitive dysfunction. This finding was in contrast to the finding from the incidental learning task. Performance of the Huntington's disease group was essentially normal and unrelated to measures of disease progression and cognitive status. The results, although supportive of the proposed dual-system hypothesis, offer only partial confirmation. Further direct study is required using similar tasks in patients with putamenal disorder or lesions within the skeletomotor striato-thalamo-cortical circuit.

Adult↗

PubMed2002

Firsthand learning through intent participation.

This article examines how people learn by actively observing and "listening-in" on ongoing activities as they participate in shared endeavors. Keen observation and listening-in are especially valued and used in some cultural communities in which children are part of mature community activities. This intent participation also occurs in some settings (such as early language learning in the family) in communities that routinely segregate children from the full range of adult activities. However, in the past century some industrial societies have relied on a specialized form of instruction that seems to accompany segregation of children from adult settings, in which adults "transmit" information to children. We contrast these two traditions of organizing learning in terms of their participation structure, the roles of more- and less-experienced people, distinctions in motivation and purpose, sources of learning (observation in ongoing activity versus lessons), forms of communication, and the role of assessment.

Adult↗

PubMed2003

Different mechanisms involved in adaptation to stable and unstable dynamics.

Recently, we demonstrated that humans can learn to make accurate movements in an unstable environment by controlling magnitude, shape, and orientation of the endpoint impedance. Although previous studies of human motor learning suggest that the brain acquires an inverse dynamics model of the novel environment, it is not known whether this control mechanism is operative in unstable environments. We compared learning of multijoint arm movements in a "velocity-dependent force field" (VF), which interacted with the arm in a stable manner, and learning in a "divergent force field" (DF), where the interaction was unstable. The characteristics of error evolution were markedly different in the 2 fields. The direction of trajectory error in the DF alternated to the left and right during the early stage of learning; that is, signed error was inconsistent from movement to movement and could not have guided learning of an inverse dynamics model. This contrasted sharply with trajectory error in the VF, which was initially biased and decayed in a manner that was consistent with rapid feedback error learning. EMG recorded before and after learning in the DF and VF are also consistent with different learning and control mechanisms for adapting to stable and unstable dynamics, that is, inverse dynamics model formation and impedance control. We also investigated adaptation to a rotated DF to examine the interplay between inverse dynamics model formation and impedance control. Our results suggest that an inverse dynamics model can function in parallel with an impedance controller to compensate for consistent perturbing force in unstable environments.

Adaptation, Physiological↗

PubMed2002

Area postrema lesions impair flavor-toxin aversion learning but not flavor-nutrient preference learning.

Rats with lesions of the area postrema (APX) or sham lesions were trained to associate flavored solutions with positive or negative postingestive consequences. The APX rats were similar to controls in learning preferences for flavors paired with concurrent intragastric infusions of maltodextrin or corn oil and for a flavor paired with delayed maltodextrin infusions. In contrast, the APX rats displayed impaired aversion learning for flavors paired with toxic drug treatments (lithium chloride infusion or methylscopolamine injection). The aversion learning deficit ranged from mild to total, depending on training procedures. These findings confirm the important role of the area postrema in flavor-toxin learning but provide no evidence for its involvement in flavor-nutrient conditioning.

Animals↗

PubMed2004

[Neurobiology of learning--the basis of an alteration process].

In contrast to the opinion that prevailed in the 1980es, there is now increasing evidence that the plasticity of the human brain, i. e. its remarkable ability to adapt to and change with experience, is, under normal conditions, a lifelong phenomenon. Representations of the environment are associated with activations and biochemical modifications in neuronal networks, which will be stabilized, modified or will wither in the course of cumulated experience. The capability to modify the biochemistry of synapses as well as the growth and change in terms of rewiring of synapses, dendritic branching and glial cell proliferation via the dialogue of synapses and genes, results in specific changes in neuronal connectivity and function. On the neurotransmitter level, glutamate and gamma-amino-butyric acid (GABA) as well as dopamine and serotonin, but also endorphin and encephalin, have a key position in this context. These neurotransmitter systems modulate neuronal plasticity on the neuronal level; on the behavioural level they influence affect, emotion, positive motivation and the correct evaluation of environmental stimuli. Experience, action as well as learning and memory are influenced by these systems. A basic thesis of this paper is that these mechanisms are involved in neuronal plasticity and that learning and memory are thus not only used and reused in structuring the CNS during the initial establishment of connections in the immature brain, in lifelong memory consolidation or the rewiring after brain damage, but can also be used to mould experience, learning und behaviour during psychotherapy and rehabilitation in adults.

Brain↗

PubMed2004

Effects of NMDA receptor-related agonists on learning and memory impairment in olfactory bulbectomized mice.

A significant impairment of learning and memory-related behavior was induced in mice on the 7th and 14th days after olfactory bulbectomy (OBX), as measured by a passive avoidance task. The involvement of the N-methyl-D-aspartate (NMDA) receptor ion-channel complex for learning and memory-related behavior impairment was examined by the intracerebroventricular administration of several NMDA receptor-related agonists and in combination with antagonists. The NMDA receptor agonist NMDA (1 ng/mouse) and the polyamine site agonist spermidine (1 micro g/mouse) improved learning and memory-related behavior impairment. In contrast, the glycine agonist D-cycloserine (0.2, 1 and 5 micro g/mouse) had no effect on learning and memory-related behavior impairment. The improved effects by NMDA and spermidine were reversed by the coadministration of D-APV, a competitive NMDA receptor antagonist, MK-801, an NMDA ion-channel blocker and ifenprodil, a polyamine site antagonist, respectively. These results suggest that the degeneration of NMDA receptors and polyamine sites in the NMDA receptor ion-channel complex may be involved in the OBX-induced impairment of learning and memory-related behavior.

2-Amino-5-phosphonovalerate↗

PubMed2005

Independent perceptual learning in monocular and binocular motion systems.

Eye-transfer tests, external noise manipulations, and observer models were used to systematically characterize learning mechanisms in judging motion direction of moving objects in visual periphery (Experiment 1) and fovea (Experiment 2) and to investigate the degree of transfer of the learning mechanisms from trained to untrained eyes. Perceptual learning in one eye was measured over 10 practice sessions. Subsequent learning in the untrained eye was assessed in five transfer sessions. We characterized the magnitude of transfer of each learning mechanism to the untrained eye by separately analyzing the magnitude of subsequent learning in low and high external noise conditions. In both experiments, we found that learning in the trained eye reduced contrast thresholds uniformly across all of the external noise levels: 47 +/- 10% and 62 +/- 8% in experiments 1 and 2, respectively. Two mechanisms, stimulus enhancement and template retuning, accounted for the observed performance improvements. The degree of transfer to the untrained eye depended on the amount of external noise added to the signal stimuli: In high external noise conditions, learning transferred completely to the untrained eye in both experiments. In low external noise conditions, there was only partial transfer of learning: 63% in experiment 1 and 54% in experiment 2. The results suggest that template retuning, which is effective in high external noise conditions, is mostly binocular, whereas stimulus enhancement, which is effective in low external noise displays, is largely monocular. The two independent mechanisms underlie perceptual learning of motion direction identification in monocular and binocular motion systems.

Fixation, Ocular↗

PubMed2006

Differential hippocampal and prefrontal-striatal contributions to instance-based and rule-based learning.

It is a topic of current interest whether learning in humans relies on the acquisition of abstract rule knowledge (rule-based learning) or whether it depends on superficial item-specific information (instance-based learning). Here, we identified brain regions that mediate either of the two learning mechanisms by combining fMRI with an experimental protocol shown to be able to dissociate both learning mechanisms. Subjects had to learn object-position conjunctions in several trials and blocks. In a learning condition, either objects (Experiment 1) or positions (Experiment 2) were held constant within-blocks. In contrast to a control condition in which object-position conjunctions were trial-unique, a performance increase within and across-blocks was observed in the learning condition of both experiments. We hypothesized that within-block learning mainly relies on instance-based processes, whereas across-block learning might depend on rule-based mechanisms. A within-block parametric fMRI analysis revealed a learning-related increase of lateral prefrontal and striatal activity and a learning-related decrease of hippocampal activity in both experiments. By contrast, across-block learning was associated with an activation modulation in distinct prefrontal-striatal brain regions, but not in the hippocampus. These data indicate that hippocampal and prefrontal-striatal brain regions differentially contribute to instance-based and rule-based learning.

Adult↗

PubMed2003

Impairment of reward-related learning by cholinergic cell ablation in the striatum.

The striatum in the basal ganglia-thalamocortical circuitry is a key neural substrate that is implicated in motor balance and procedural learning. The projection neurons in the striatum are dynamically modulated by nigrostriatal dopaminergic input and intrastriatal cholinergic input. The role of intrastriatal acetylcholine (ACh) in learning behaviors, however, remains to be fully clarified. In this investigation, we examine the involvement of intrastriatal ACh in different categories of learning by selectively ablating the striatal cholinergic neurons with use of immunotoxin-mediated cell targeting. We show that selective ablation of cholinergic neurons in the striatum impairs procedural learning in the tone-cued T-maze memory task. Spatial delayed alternation in the T-maze learning test is also impaired by cholinergic cell elimination. In contrast, the deficit in striatal ACh transmission has no effect on motor learning in the rota-rod test or spatial learning in the Morris water-maze test or on contextual- and tone-cued conditioning fear responses. We also report that cholinergic cell elimination adaptively up-regulates nicotinic ACh receptors not only within the striatum but also in the cerebral cortex and substantia nigra. The present investigation indicates that cholinergic modulation in the local striatal circuit plays a pivotal role in regulation of neural circuitry involving reward-related procedural learning and working memory.

Acetylcholine↗

PubMed2003

Infants' learning, memory, and generalization of learning for bimodal events.

Study 1 investigated whether infants 3 and 7 months of age show differential learning of and memory for sight-sound pairs depending on whether or not temporal synchrony was present; memory was assessed after a 10-min and 1-week interval. Study 2 examined whether 7-month-olds show generalization of learning when they encounter novel bimodal events that are similar (changes in size, orientation, or color, and spectral sound properties) to the sight-sound pairs learned 1 week earlier based on temporal synchrony. For Study 1, infants received a familiarization phase followed by a paired-comparison preference procedure to assess for learning of the sight-sound pairs. One week later a memory test was given. Results confirmed that 7-month-olds had no difficulty learning auditory-visual pairings regardless of whether or not events were temporally synchronous, and they remembered these 10 min and 1 week later. In contrast, 3-month-olds showed poorer learning of sight-sound associations in the no-synchrony than synchrony conditions, and memory for sight-sound pairs 1 week later was shown only for the synchrony conditions. Results for Study 2 revealed generalization of learning of bimodal pairings under all stimulus conditions after a 1-week interval at 7 months of age. Implications of these findings for development of intersensory knowledge are discussed.

Discrimination Learning↗

PubMed2004

Image fusion for dynamic contrast enhanced magnetic resonance imaging.

BACKGROUND: Multivariate imaging techniques such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) have been shown to provide valuable information for medical diagnosis. Even though these techniques provide new information, integrating and evaluating the much wider range of information is a challenging task for the human observer. This task may be assisted with the use of image fusion algorithms. METHODS: In this paper, image fusion based on Kernel Principal Component Analysis (KPCA) is proposed for the first time. It is demonstrated that a priori knowledge about the data domain can be easily incorporated into the parametrisation of the KPCA, leading to task-oriented visualisations of the multivariate data. The results of the fusion process are compared with those of the well-known and established standard linear Principal Component Analysis (PCA) by means of temporal sequences of 3D MRI volumes from six patients who took part in a breast cancer screening study. RESULTS: The PCA and KPCA algorithms are able to integrate information from a sequence of MRI volumes into informative gray value or colour images. By incorporating a priori knowledge, the fusion process can be automated and optimised in order to visualise suspicious lesions with high contrast to normal tissue. CONCLUSION: Our machine learning based image fusion approach maps the full signal space of a temporal DCE-MRI sequence to a single meaningful visualisation with good tissue/lesion contrast and thus supports the radiologist during manual image evaluation.

Algorithms↗

PubMed2006

Recency effects as a window to generalization: separating decisional and perceptual sequential effects in category learning.

Accounts of learning and generalization typically focus on factors related to lasting changes in representation (i.e., long-term memory). The authors present evidence that shorter term effects also play a critical role in determining performance and that these recency effects can be subdivided into perceptual and decisional components. Experimental results based on a probabilistic category structure show that the previous stimulus exerts a contrastive effect on the current percept (perceptual recency) and that responses are biased toward or away from the previous feedback, depending on the similarity between successive stimuli (decisional recency). A method for assessing these recency effects is presented that clarifies open questions regarding stimulus generalization and perceptual contrast effects in categorization and in other domains.

Attention↗

PubMed1987

[The effects of self-evaluative responses with feedback in learning].

This study was designed to investigate the effects of self-evaluative responses with feedback in a nonsense syllable recognition task (Experiment I) and a concept learning task (Experiment II). Subjects were 143 fifth graders who were first asked to identify each item in the task before being exposed to the experimental procedures. Following the actual learning trials, all subjects were given the post-test. The experimental procedures were as follows: SF--in the process of identification, subjects evaluated their answers and feedback was provided on their evaluations. EF--in the process of identification, subjects were given feedback on their answers. NF--subjects evaluated their answers but no feedback was provided. PF--EF and NF procedures alternated from trial to trial. In both experiments, SF and EF groups learned more effectively than NF and PF groups. In contrast to experiment I, many subjects in SF group were successful in the concept learning task. These results suggested that self-evaluative responses with feedback had positive effects on learning, especially on concept learning.

Child↗