Similarity and discrimination: A selective review and a connectionist model.

The 1st part of this article evaluates the extent to which 2 elemental theories of conditioning, stimulus sampling theory and the R. A. Rescorla-A. R. Wagner (1972) theory, are able to account for the influence of similarity on discrimination learning. A number of findings are reviewed that are inconsistent with predictions derived from these theories, either in their present form or in various modified forms. The 2nd part of the article is concerned with developing an alternative, configural account for discrimination learning. In contrast to previous configural theories, the present version is set within the framework of a connectionist network. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus similarity and response criterion on successive discrimination reversal learning.

In a study with 30 naive domestic pigeons, 2 levels of stimulus similarity and 2 levels of criterion were factorially combined in a free-operant, successive presentation of stimuli, successive discrimination reversal (SDR) involving chromatic stimuli. Both variables were found to have significant effects on SDR performance. Groups having the less rigorous criterion showed either no improvement or a deterioration in performance, depending on discrimination difficulty. Transfer to a line-angle discrimination revealed no differences between SDR groups and an original-learning control group in time to criterion required to learn this problem. All SDR groups were superior to the control group on the reversal of this problem, but there were no differences between SDR groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of structure: I. Implications for connectionist theories of discrimination learning.

In each of 4 experiments animals were given a structural discrimination task that involved visual patterns composed of identical features, but the spatial relations among the features were different for reinforced and nonreinforced trials. In Experiment 1 the stimuli were pairs of colored circles, and pigeons were required to discriminate between patterns that were the mirror image of each other. A related task was given to rats in Experiment 2. Subjects solved these discriminations. For Experiment 3, some pigeons were given a discrimination similar to that used in Experiment 1, which they solved, whereas others received a comparable task but with 3 colored circles present on every trial, which they failed to solve. The findings from Experiment 3 were replicated in Experiment 4 using different patterns. The results are difficult to explain by certain connectionist theories of discrimination learning, unless they are modified to take account of the way in which compound stimuli are structured. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ALCOVE: An exemplar-based connectionist model of category learning.

ALCOVE (attention learning covering map) is a connectionist model of category learning that incorporates an exemplar-based representation (D. L. Medin and M. M. Schaffer, 1978; R. M. Nosofsky, 1986) with error-driven learning (M. A. Gluck and G. H. Bower, 1988; D. E. Rumelhart et al, 1986). ALCOVE selectively attends to relevant stimulus dimensions, is sensitive to correlated dimensions, can account for a form of base-rate neglect, does not suffer catastrophic forgetting, and can exhibit 3-stage (U-shaped) learning of high-frequency exceptions to rules, whereas such effects are not easily accounted for by models using other combinations of representation and learning method. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of spatial separation and similarity of stimuli on discrimination learning of children and adults.

32 females and 32 males from each of 3 levels-kindergarten, 2nd grade, and college-were given a 2-choice simultaneous discrimination task in which the stimuli were separated either by 6.35 or 25.4 cm. 2 levels of stimulus similarity were used. Increasing the distance between stimuli interfered with the learning of all age groups when the stimuli were highly similar. When stimuli were less similar, however, increasing the interstimulus distance retarded learning in children but not in adults. Results are consistent with findings that spatial separation of task components in a variety of situations interferes more with the performance of children than with that of adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influences of categorization on perceptual discrimination.

Four experiments investigated the influence of categorization training on perceptual discrimination. Ss were trained according to 1 of 4 different categorization regimes. Subsequent to category learning, Ss performed a Same–Different judgment task. Ss' sensitivities (d's) for discriminating between items that varied on category-(ir)relevant dimensions were measured. Evidence for acquired distinctiveness (increased perceptual sensitivity for items that are categorized differently) was obtained. One case of acquired equivalence (decreased perceptual sensitivity for items that are categorized together) was found for separable, but not integral, dimensions. Acquired equivalence within a categorization-relevant dimension was never found for either integral or separable dimensions. The relevance of the results for theories of perceptual learning, dimensional attention, categorical perception, and categorization are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A recurrent connectionist model of group biases.

Major biases and stereotypes in group judgments are reviewed and modeled from a recurrent connectionist perspective. These biases are in the areas of group impression formation (illusory correlation), group differentiation (accentuation), stereotype change (dispersed vs. concentrated distribution of inconsistent information), and group homogeneity. All these phenomena are illustrated with well-known experiments, and simulated with an autoassociative network architecture with linear activation update and delta learning algorithm for adjusting the connection weights. All the biases were successfully reproduced in the simulations. The discussion centers on how the particular simulation specifications compare with other models of group biases and how they may be used to develop novel hypotheses for testing the connectionist modeling approach and, more generally, for improving theorizing in the field of social biases and stereotype change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A connectionist account of asymmetric category learning in early infancy.

Young infants show unexplained asymmetries in the exclusivity of categories formed on the basis of visually presented stimuli. A connectionist model is described that shows similar exclusivity asymmetries when categorizing the same stimuli presented to infants. The asymmetries can be explained in terms of an associative learning mechanism, distributed internal representations, and the statistics of the feature distributions in the stimuli. The model was used to explore the robustness of this asymmetry. The model predicts that the asymmetry will persist when a category is acquired in the presence of mixed category exemplars. An experiment with 3–4-month-olds showed that asymmetric exclusivity persisted in the presence of mixed-exemplar familiarization, thereby confirming the model's prediction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of extraversion and self-report arousal on semantic priming: A connectionist approach.

Simulation and experimental data were used to test the hypothesis that extraversion and self-report arousal affect the spread of activation in a connectionist semantic network, assessed by priming of lexical decision. A simulation of network activation processes showed that individual differences in different network parameters predict different patterns of observable individual differences in response time. Two experiments using undergraduate Ss showed that extraversion and arousal interactively affect priming magnitude, irrespective of the time lag between prime and target word and of prime stimulus quality. The simulation data suggest that the personality effects obtained experimentally may be governed by a specific network parameter: individual differences in the level of random noise. Connectionist models may provide a general framework for explaining arousal-dependent effects of extraversion on cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overconfidence effects in category learning: A comparison of connectionist and exemplar memory models.

Exemplar and connectionist models were compared on their ability to predict overconfidence effects in category learning data. In the standard task, participants learned to classify hypothetical patients with particular symptom patterns into disease categories and reported confidence judgments in the form of probabilities. The connectionist model asserts that classifications and confidence are based on the strength of learned associations between symptoms and diseases. The exemplar retrieval model (ERM) proposes that people learn by storing examples and that their judgments are often based on the first example they happen to retrieve. Experiments 1 and 2 established that overconfidence increases when the classification step of the process is bypassed. Experiments 2 and 3 showed that a direct instruction to retrieve many exemplars reduces overconfidence. Only the ERM predicted the major qualitative phenomena exhibited in these experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A connectionist model of complacency and adaptive recovery under automation.

Automation is intended to reduce the demands on operators in complex environments, thereby enhancing overall system performance. Although automation usually reduces workload, it is often accompanied by a decline in monitoring performance, an effect known as complacency. The circumstances under which complacency occurs and how it can be prevented, for example by intermittently returning control to the operator, are empirically well understood. To date, that empirical knowledge has not been accompanied by strong psychological theory. This article presents a computational model of human performance under automation based on connectionist principles. The model is shown to explain several benchmark findings, among them the basic complacency effect; the effect of the variability of automation reliability on complacency; the effect of task complexity; and the effect of intermittently returning control to the operator. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combining exemplar-based category representations and connectionist learning rules.

Adaptive network and exemplar-similarity models were compared on their ability to predict category learning and transfer data. An exemplar-based network (J. K. Kruschke, 1990, 1992) that combines key aspects of both modeling approaches was also tested. The exemplar-based network incorporates an exemplar-based category representation in which exemplars become associated to categories through the same error-driven, interactive learning rules that are assumed in standard adaptive networks. Exp 1, which partially replicated and extended the probabilistic classification learning paradigm of M. A. Gluck and G. H. Bower (1988), demonstrated the importance of an error-driven learning rule. Exp 2, which extended the classification learning paradigm of D. L. Medin and M. M. Schaffer (1978) that discriminated between exemplar and prototype models, demonstrated the importance of an exemplar-based category representation. Only the exemplar-based network accounted for all the major qualitative phenomena; it also achieved good quantitative predictions of the learning and transfer data in both experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of labels on the perception and discrimination learning of retardates.

Assessed the role of labels in perception in 54 familial retardates and 48 normal IQ children at 2 matched MA levels. 3 experimental manipulations were employed at each level in a factorial design. 1 group learned to associate a common label to random visual forms; a 2nd group learned distinctive labels to the same forms; finally, a 3rd group viewed the forms without labels. Following verbal training, all Ss received perceptual judgment and discrimination-learning tasks. No significant differences emerged between the retarded and normal Ss on paired-associate learning, discrimination learning, or perceptual accuracy without labels. In contrast to the normal children, however, the retardates' perceptual and learning processes were relatively unaffected by the learning of verbal levels. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A connectionist model of septohippocampal dynamics during conditioning: Closing the loop.

Septohippocampal interactions determine how stimuli are encoded during conditioning. This study extends a previous neurocomputational model of corticohippocampal processing to incorporate hippocamposeptal feedback and examines how the presence or absence of such feedback affects learning in the model. The effects of septal modulation in conditioning were simulated by dynamically adjusting the hippocampal learning rate on the basis of how well the hippocampal system encoded stimuli. The model successfully accounts for changes in behavior and septohippocampal activity observed in studies of the acquisition, retention, and generalization of conditioned responses and accounts for the effects of septal disruption on conditioning. The model provides a computational, neurally based synthesis of prior learning theories that predicts changes in medial septal activity based on the novelty of stimulus events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of similarity and repetition on memory: Registration without learning?

Investigated judgments of the frequency of test items (Y) that were highly similar to studied items (X) to test a prediction made by several memory models: that the judged frequency of Y should be proportional to the judged frequency of X. Whether stimuli were pictures or words, judged frequency of Y was bimodally distributed with 1 mode at zero, suggesting that frequency judgments involve a 2-stage process in which a zero judgment is made if there is a mismatch between retrieved information and the test item. Nonzero judgments, taken by themselves, were consistent with the prediction of proportionality. In 2 experiments, the percentage of zero judgments made to Y increased with repetition of X, but in 2 others the percentage did not change beyond frequency?=?1. The percentage of "new" judgments in recognition memory followed this same pattern. Because the judged frequency of X increased even as X–Y discrimination showed no improvement, the result is characterized as "registration without learning." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ventral putamen lesions on discrimination learning by monkeys.

Studied the effect of caudoventral putamen lesions on the postoperative retention of visual and auditory discriminations and on the postoperative acquisition of delayed alternation in 19 adolescent rhesus monkeys. Lesions in the caudoventral putamen and the adjacent white matter impaired performance of the visual but not the auditory and alternation tasks, indicating that this area is part of the neural circuitry underlying visual discrimination. However, the relative contribution to the deficit of the putamen damage and of the white matter damage could not be ascertained. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of brightness preferences in young chicks: Effects on brightness discrimination learning.

Conducted 7 experiments with a total of 256 1-3 day old Vantress * Arbor Acre chicks to investigate the effects of interactions between the S and its sensory environment on both emergence of brightness preferences and modification by conditioning. In a simultaneous brightness discrimination, Ss were rewarded with heat for approaching either a bright or dim stimulus. Results indicate (a) brightness preference was so stable that it could not be eliminated by incubating, hatching, and rearing in the dark; (b) light experience significantly increased this preference; and (c) modification of this preference by heat reinforcement depended on age of S, prior rearing condition, sensory stimulation between testing sessions, and the length of interval between testing sessions. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationship between overinclusive thinking, perceptual rigidity, and the discrimination learning of new concepts.

Compared 19 newly admitted psychiatric inpatients who showed overinclusive thinking on the Payne Object Classification Test with 24 patients matched for age, IQ, and abstraction ability who were not overinclusive. In a concept-attainment experiment, contrary to prediction, overinclusive Ss did not learn overinclusive concepts. There were no significant differences between the groups. However, overinclusive Ss, as predicted, showed an abnormal lack of "Einstellung" rigidity as measured by a flexibility score from the Brengelmann Picture Recognition Test. The overinclusion score of the object classification test correlated highly (.90) with this flexibility score. (French summary) (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of power enhances visual perceptual discrimination.

Powerless individuals face much challenge and uncertainty. As a consequence, they are highly vigilant and closely scrutinize their social environments. The aim of the present research was to determine whether these qualities enhance performance in more basic cognitive tasks involving simple visual feature discrimination. To test this hypothesis, participants performed a series of perceptual matching and search tasks involving colour, texture, and size discrimination. As predicted, those primed with powerlessness generated shorter reaction times and made fewer eye movements than either powerful or control participants. The results indicate that the heightened vigilance shown by powerless individuals is associated with an advantage in performing simple types of psychophysical discrimination. These findings highlight, for the first time, an underlying competency in perceptual cognition that sets powerless individuals above their powerful counterparts, an advantage that may reflect functional adaptation to the environmental challenge and uncertainty that they face. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Spatial EEG correlates of nonassociative and associative olfactory learning in rabbits.

Recent studies have shown that spatially distributed olfactory bulbar activity correlates with odor-specific behavioral responding (e.g., W. J. Freeman and K. A. Grajski [see PA, Vol 75:28775]; Freeman and W. Schneider [see PA, Vol 68:5257]). The present studies established olfactory bulbar spatial EEG correlates of nonassociative and associative learning in odorant stimulation in rabbits. Behavior was quantified by measuring magnitude and probability of the sniff response. It was shown that (a) olfactory bulbar spatial EEG amplitude patterns do not simply reflect odor (peripheral) stimulation, (b) repeated presentations of a nonreinforced odor initially reveal a transient EEG pattern change but the pattern change does not recur after the subject has habituated to the odor, and (c) repeated presentations of a reinforced odor (mild cutaneous shock), with a second nonreinforced odor serving as a control, reveal that coexisting, odorspecific spatial EEG amplitude patterns emerge with the acquisition of differential behavioral responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)