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PubMed2002

Perceptual learning of luminance contrast detection: specific for spatial frequency and retinal location but not orientation.

Performance of a wide range of simple visual tasks improves with practice. Here we ask whether such learning occurs for the fundamental visual task of luminance contrast detection. In two experiments we find that contrast sensitivity increases following extensive practice at detecting briefly presented sinusoidal luminance gratings and that learning is maintained after six months. Learning is spatial frequency tuned, specific to retinal location and can be specific to one eye, but is not selective for orientation. The selectivity of learning implies that it is based on plasticity in early visual, as opposed to central cognitive, processing mechanisms.

Contrast Sensitivity↗
PubMed1966

Two types of behavioral contrast in discrimination learning.

Two groups of pigeons received daily discrimination training at two values on a line-tilt continuum. S+ (VI 1) and S- (EXT) intervals alternated, and a 30-sec criterion of no responding to S- was required before S+ returned. Rates of responding to S+ showed two separate contrast effects: at an intermediate stage of training a high peak rate appeared which declined, later in training, to a stable level still in excess of the VI baseline rate. The peak rate was correlated with the total number of responses to S-, while the final rate was not; suggesting that the peak rate and final rate may not be functions of the same variable. These results were compared with performance on a red-green discrimination where the two stages were not so clear. A line-tilt discrimination was repeated with fixed length S- intervals terminated by TO, and showed the same contrast magnitude in the final rate without any peak. The peak rate was interpreted as an effect of the ;punishment' contingency where responding to S- prolongs S- for 30 sec, while the final rate was taken to be analogous to previous demonstrations of contrast.

Animals↗
PubMed1989

Contrast effects in flavour preference learning.

In four experiments the role of contrast effects in producing learned flavour preferences was examined. The experiments showed that contrast effects are pervasive in flavour preference learning, producing results that are often paradoxical from a traditional reinforcement point of view. In Experiment 1, rats preferred a reinforced flavour over a nonreinforced flavour more if the reinforcer was 1% sucrose than if the reinforcer was 8% sucrose. Because the cue flavour was dissolved in 8% sucrose, this represents an anticipatory positive contrast effect. In Experiment 2, the relationship between cue and consequence was shown to be important in flavour preference learning, as expected if contrast effects are involved. In Experiment 3, rats preferred a flavour that was reinforced 4 times, and they preferred this flavour more than one reinforced 8 times, presumably because the greater the expectancy of the consequence, the greater the anticipatory negative contrast. In Experiment 4, rats consumed less of 0.15% saccharin if they received 32% sucrose randomly 90 min either before or after the 0.15% saccharin than if they received only 0.15% saccharin, a simultaneous negative contrast effect.

Animals↗
PubMed1987

Training and testing determinants of short-term associative suppression of phototaxic behavior in Hermissenda.

Hermissenda crassicornis shows both short- and long-term retention of conditioning following light-rotation pairings. Previous research has shown that prolonged training (50 trials per session, three consecutive daily sessions) produces a suppression of phototaxis lasting for days. This long-term retention reflects associative learning processes, with little or no contribution of nonassociative learning. In contrast, both associative learning and nonassociative behavioral modification contribute to short-term retention following a single session of five pairing trials. In this paper, we describe important associative and nonassociative determinants of short-term changes in phototaxis. In Experiment 1, animals received successive hourly tests for phototaxis in either a horizontal or a vertical orientation. Repeated testing resulted in decreased phototaxis which was especially pronounced for animals tested horizontally. Experiments 2-4 demonstrated that both repeated handling of animals and repeated periods of dark adaptation prior to each phototaxic test contributed to the development of phototaxic suppression with repeated testing. These nonassociative influences on phototaxis interacted with the gravitational orientation employed during behavioral testing, being most pronounced for testing in the horizontal orientation. An implication of these findings is that attempts to demonstrate short-term pairing-specific suppression will be most successful when nonassociative contributions are minimized (by testing animals vertically). Experiment 5 tested this prediction. We also tested the influence of training light intensity and the stimulus specificity of conditioned suppression. Animals received either five paired or five random presentations of light and rotation. Training light intensity was either moderate or bright. Following training, animals were tested for either suppression of phototaxis or suppression of negative geotaxis, using either a horizontal or a vertical testing orientation. Consistent with previous results, horizontally tested animals exhibited pronounced nonassociative suppression following training. The use of a bright training light also produced nonassociative suppression. However, when trained with a light of moderate intensity and tested vertically, Hermissenda showed associative suppression of phototaxis (significant paired--random difference) but not geotaxis (no paired--random difference). In a final experiment we observed that the longer the period of dark adaptation (prior to testing) the longer the phototaxic latency.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

The principles of conventionality and contrast in word learning: an empirical examination.

In Study 1, 4-year-olds avoided 2 names for an object when exposed to a common or a proper noun in a puppet's presence or to a common noun in a puppet's absence, but not when exposed to a proper noun in a puppet's absence. In Study 2, 3-year-olds avoided 2 names for an object when the requester for the referent of a second label in a different language was bilingual and present during naming, but not when the speaker was bilingual but absent or monolingual. Study 3 followed up on the results of the first 2 studies. When children could assume that the puppet knew the name the experimenter used, they inferred that the puppet's use of a different name implied a different referential intent.

Child, Preschool↗
PubMed2007

Psychometric intelligence dissociates implicit and explicit learning.

The hypothesis that performance on implicit learning tasks is unrelated to psychometric intelligence was examined in a sample of 605 German pupils. Performance in artificial grammar learning, process control, and serial learning did not correlate with various measures of intelligence when participants were given standard implicit instructions. Under an explicit rule discovery instruction, however, a significant relationship between performance on the learning tasks and intelligence appeared. This finding provides support for Reber's hypothesis that implicit learning, in contrast to explicit learning, is independent of intelligence, and confirms thereby the distinction between the 2 modes of learning. However, because there were virtually no correlations among the 3 learning tasks, the assumption of a unitary ability of implicit learning was not supported.

Adolescent↗
PubMed2003

GABAergic mechanisms gate tactile discrimination learning.

In contrast to mechanisms mediating synaptic plasticity, the pharmacological basis of perceptual learning remains to be clarified. Here we report that a specific form of perceptual learning is influenced by GABAergic mechanisms. We induced perceptual learning by Hebbian co-activation of the skin of the tip of the right index fingers in human subjects. Under placebo conditions, tactile 2-point discrimination was improved on the co-activated, but not on the left, index finger. This augmentation was completely eliminated by lorazepam, a GABAA receptor agonist. No drug effects were found on the left index finger indicating that the drugs had no effect per se on performance. The results demonstrate that perceptual learning is subject to pharmacological gating by basic mechanisms known to mediate and modulate synaptic plasticity.

Adult↗
PubMed2003

A knowledge-resonance (KRES) model of category learning.

This article introduces a connectionist model of category learning that takes into account the prior knowledge that people bring to new learning situations. In contrast to connectionist learning models that assume a feedforward network and learn by the delta rule or backpropagation, this model, the knowledge-resonance model, or KRES, employs a recurrent network with bidirectional symmetric connection whose weights are updated according to a contrastive Hebbian learning rule. We demonstrate that when prior knowledge is represented in the network, KRES accounts for a considerable range of empirical results regarding the effects of prior knowledge on category learning, including (1) the accelerated learning that occurs in the presence of knowledge, (2) the better learning in the presence of knowledge of category features that are not related to prior knowledge, (3) the reinterpretation of features with ambiguous interpretations in light of error-corrective feedback, and (4) the unlearning of prior knowledge when that knowledge is inappropriate in the context of a particular category.

Animals↗
PubMed2006

Category dimensionality and feature knowledge: when more features are learned as easily as fewer.

Three experiments compared the learning of lower-dimensional family resemblance categories (4 dimensions) with the learning of higher-dimensional ones (8 dimensions). Category-learning models incorporating error-driven learning, hypothesis testing, or limited capacity attention predict that additional dimensions should either increase learning difficulty or decrease learning of individual features. Contrary to these predictions, the experiments showed no slower learning of high-dimensional categories; instead, subjects learned more features from high-dimensional categories than from low-dimensional categories. This result obtained both in standard learning with feedback and in noncontingent, observational learning. These results show that rather than interfering with learning, categories with more dimensions cause individuals to learn more. The authors contrast the learning of family resemblance categories with learning in classical conditioning and probability learning paradigms, in which competition among features is well documented.

Concept Formation↗
PubMed2003

The dynamics of learning and allocation of study time to a region of proximal learning.

In contrast to the dominant discrepancy reduction model, which favors the most difficult items, people, given free choice, devoted most time to medium-difficulty items and studied the easiest items first. When study time was experimentally manipulated, best performance resulted when most time was given to the medium-difficulty items. Empirically determined information uptake functions revealed steep initial learning for easy items with little subsequent increase. For medium-difficulty items, initial gains were smaller but more sustained, suggesting that the strategy people had used, when given free choice, was largely appropriate. On the basis of the information uptake functions, a negative spacing effect was predicted and observed in the final experiment. Overall, the results favored the region of proximal learning framework.

Humans↗
PubMed2005

Tumor feature visualization with unsupervised learning.

Dynamic contrast enhanced magnetic resonance imaging (DCE MRI) is applied for diagnosis and therapy control of breast cancer. The malignancy of a lesion is expressed in the average signal kinetics of selected regions of interest (ROI) representing the lesion. The technique is reported to characterize malignant tumors with high sensitivity and highly variable specificity. Computer-based diagnosis (CAD) systems have been proposed to analyze and classify signal time curve data, extracted from hand selected ROI in the DCE MRI data. In this paper, we apply the self-organizing map (SOM) to a set of time curve feature vectors of single voxels from seven benign lesions and seven malignant tumors. Applying the SOM we are able to project the time curve values of each voxel on a two-dimensional map. The results show, that the SOM is able to visualize the hidden two-dimensional structure of the six-dimensional signal space. Using the trained SOM, we are able to identify voxels with benign or malignant signal characteristics and to visualize lesion cross-sections with pseudo-colors. A comparison with the established three time points method shows that the SOM has clear potential for deriving visualization parameters in DCE MRI analysis.

Breast Neoplasms↗
PubMedDate not supplied

Learning and self-regulation of slow cortical potentials in older adults.

Two groups of subjects, aged 20-28 and 50-64, respectively, matched for health status and verbal abilities, learned to control their slow cortical potentials (SCP) in a feedback paradigm by producing, on command, SCP shifts in either positive or negative direction. Both groups were able to differentiate significantly between the positivity task and the negativity task, with the differentiation score being only slightly (and not significantly) lower in older than in younger subjects. In all conditions, however, significantly more negative brain responses were obtained in older than in younger subjects. This effect was larger in the positivity task versus negativity task, and larger in trials without continuous SCP feedback versus trials with feedback. Additionally four learning tasks were carried out with all subjects. The older group demonstrated substantial performance deficits in two tasks with explicit learning (verbal and visual). In contrast, implicit learning (perceptual learning and skill acquisition) was not impaired with age. The results are at odds with the idea of general age-related learning deficit and concur with the hypothesis that only explicit, but not implicit, learning processes are compromised in older subjects. The pattern of consistently more negative SCP shifts produced by elderly subjects may indicate their impaired cortical inhibition. Another interpretation, which does not exclude the inhibitory deficit hypothesis but seems to better agree with other psychophysiological data, may be that older subjects have disturbance in the system controlling arousal and effort.

Adult↗
PubMed2004

The neurobiology of adaptive learning in reading: a contrast of different training conditions.

fMRI was used to investigate the separate influences of orthographic, phonological, and semantic processing on the ability to learn new words and the cortical circuitry recruited to subsequently read those words. In a behavioral session, subjects acquired familiarity for three sets of pseudowords, attending to orthographic, phonological, or (learned) semantic features. Transfer effects were measured in an event-related fMRI session as the subjects named trained pseudowords, untrained pseudowords, and real words. Behaviorally, phonological and semantic training resulted in better learning than did orthographic training. Neurobiologically, orthographic training did not modulate activation in the main reading regions. Phonological and semantic training yielded equivalent behavioral facilitation but distinct functional activation patterns, suggesting that the learning resulting from these two training conditions was driven by different underlying processes. The findings indicate that the putative ventral visual word form area is sensitive to the phonological structure of words, with phonologically analytic processing contributing to the specialization of this region.

Adaptation, Psychological↗
PubMed2006

Texture segregation on the basis of contrast polarity of odd-symmetric filters.

This is the first study to demonstrate the selectivity of learning for contrast polarity. The finding is the main result of an investigation into the existence of central and peripheral vision mechanisms selective for contrast polarity within the texture-segregation process, using the perceptual learning paradigm in a detection task. Energy models (Malik & Perona, 1990) exclude segregation of textures composed of elements of odd-symmetric luminance profile by contrast polarity differences. Here the target was a Gabor patch (0.8 deg) of 1 cyc/deg in sine phase (odd-symmetry) embedded in a background of mirror-image elements. Our results showed that, in fovea, segregation on the basis of contrast polarity was above threshold from the first session. After learning, the target popped-out in both central and peripheral vision for durations over 10 ms. Our major result is that learning is selective for contrast polarity; it is also selective for orientation and position, all characteristics distinctive of early processing. Since the learning effects were obtained with texture composed of odd-symmetric mirror-image elements, they indicate that the output from odd-symmetric filters was not excluded or inhibited in texture segmentation, but instead played an active role. Our data support models of texture segmentation, in which detection of texture gradient is achieved on the basis of early cortical process, before the non-linear transformation of their output.

Adult↗
PubMed1992

Effect of diazepam on successive negative contrast in one-way avoidance learning.

The effect of administration of diazepam on successive negative contrast in one-way avoidance learning was examined in rats. Contrast was induced by shifting rats from a large reward, 30 s spent in the safe compartment, to a small reward, 1 s spent in the safe compartment. IP administration of 2 mg/kg diazepam eliminated this negative contrast. Moreover, this effect is dose dependent, with doses of 2 and 2.5 mg/kg, but not 0.5 mg/kg, effective in reliably reducing contrast. These results suggest the existence of similar or common underlying mechanisms in both aversive and appetitive contrast effects; they are discussed in light of the current theories of frustrative nonreward and as a mean of studying the behavioral and biological mechanisms of anxiety.

Animals↗
PubMed1998

Developing musculoskeletal education programs for physicians and the general public: findings from a needs assessment.

OBJECTIVE: To assess the educational needs and learning preferences of primary care physicians and the general public in receiving musculoskeletal health education. METHODS: Prospective surveys were mailed simultaneously to 2,250 primary care physicians and 2,250 members of the general public. The surveys included questions about demographics, motivation for attending programs, and preferred education program formats. RESULTS: The 68 responding physicians attend continuing medical education programs mainly based on topics, speakers, and timing. They prefer lectures and find question and answer sessions least helpful in supporting learning. The 96 responding members of the general public attend programs mainly based on topics, speakers, and fees. The general public stated that question and answer sessions best support learning in programs. A large percentage of responding physicians provide health education to their patients, but a small percentage of the general public respondents stated that they receive health education from physicians. DISCUSSION: Responses from physicians and the general public were generally not surprising but revealed interesting contrasts between learning preferences. While physicians and the general public both value speakers and topics, the physicians want to increase their knowledge about disease, whereas the general public wants practical information. Physicians and the general public also appear to take different approaches to learning. The contrast between availability and provision of health education is also striking. We cannot generalize our results with absolute confidence because the return rates for the surveys were so low. Nonetheless, we support the need to educate physicians and the general public in ways that match their preferred learning methods and educational needs.

Adult↗