Visual discrimination learning in the fire-bellied toad Bombina orientalis

This study explored the visual discrimination learning ability of fire-bellied toads (Bombina orientalis). Two groups of toads were trained in a simultaneous visual discrimination task involving video footage of either black crickets on a white background (black-cricket toads) or white crickets on a black background (white-cricket toads). Fifteen widely spaced acquisition trials were followed by 12 reversal trials. Successful learning was observed by decreased incorrect snapping and reduced latency to snap at the correct stimulus (S+) during acquisition; however, white-cricket toads executed significantly more incorrect snaps than did black-cricket toads. Both groups of toads could master the reversal task as measured by latency to snap at S+, but not as measured by the proportion of incorrect snaps. Despite the stronger potency of the black-cricket stimulus, the results showed that toads can learn a simultaneous discrimination task and a reversal of its contingency. This elaborate form of learning appears to be conserved among vertebrates.     

Visual discrimination learning of random figure problems by rhesus monkeys

In a two-choice discrimination learning paradigm, a U-shaped function was found between trials to criterion and the number of sides comprising the random figure discriminanda. These data are consistent with results from human Ss and suggest similar information processing capabilities in the two species. Changing the orientation of the stimulus figures after the discrimination had been learned only partially disrupted subsequent discrimination performance. Any single difference in selected form attributes between the two figures comprising a problem was not a good predictor of learning speed, suggesting that monkeys use a combination of such factors.     

Visual discrimination of letter-like forms and its relationship to achievement over time in children with learning disabilities

The purpose of this study was to better understand whether visual discrimination abilities are related to reading intelligence and other achievement areas in children with learning disabilities and normally achieving children. Children with visual discrimination problems were identified using the Gibson letter-like visual discrimination task. This task was given to a large sample of children with learning disabilities as well as a sample of normally achieving children. All children were followed throughout elementary school. Results indicated that children with learning disabilities who had visual discrimination problems at 6 or 7 years of age performed more poorly in reading and general achievement over the elementary school years in comparison to the other children with learning disabilities and compared to normally achieving children. Discussion centers around the importance of this skill for reading.     

Reward pretraining and discrimination learning set

Pigtailed monkeys were trained on discrimination problems involving objects that had been previously paired with reward, previously paired with nonreward, or objects not associated with any pretraining. In two separate studies, no differences on these various problem formats were observed, but performance improved considerably with practice. These results are contrary to the theories for learning set formation of Spence and Medin.     

Contrast effects in simultaneous discrimination learning

Pigeons were trained on a form discrimination that alternated across trials with an already-learned color discrimination, which was associated with different probabilities of reinforcement for different groups. The rate of acquisition of the form discrimination varied inversely with the rate of reinforcement for the color discrimination, thus demonstrating a “contrast effect” in simultaneous discrimination learning.     

Visual discrimination of real objects and pictures in pigeons

Pigeons were trained on two visual discrimination tasks. One task was discrimination between real objects and their photographs. Training stimuli consisted of real food (grains), photographs of food, and nonedible junk objects and their photographs. The other task was discrimination between food and nonfood using the same stimuli as those in the first task. The pigeons learned either task and showed generalization of these classifications to novel stimuli. These results suggest that pigeons can either discriminate or integrate real stimuli and their photographs. Bilateral ectostriatal lesions caused deficits in food versus nonfood discrimination, but not in object versus picture discrimination. This dissociation suggests different brain mechanisms between the two visual discriminations using the same stimuli.     

学习与记忆的研究进展

学习与记忆是脑的最重要生理功能,是现代生命科学研究的前沿。本文就学习记忆有关的脑区、学习记忆的长时程增强模型以及长时程增强的分子生物学机制方面近年来的研究进展作一综述。     

Visual recognition memory in squirrel monkeys

Squirrel monkeys (Saimiri sciureus) were trained on visual recognition memory tasks in a Wisconsin General Testing Apparatus with a trial-unique procedure that used 250 objects as stimuli. In Experiment 1, acquisition of a trial-unique delayed non-match-to-sample task (DNMS) was compared with acquisition of a trial-unique delayed match-to-sample (DMS) task. The DNMS task was learned in significantly fewer trials and with significantly fewer errors. Two animals in the DNMS group demonstrated highly accurate retention of the DNMS strategy despite an 11-month hiatus in experimental testing. In Experiment 2, the same procedures were used to study the learning of lists of 3, 5, 10, or 20 serially presented items. Although the animals were able to accurately remember lists of up to 20 items, there was no evidence of serial position effects.     

The nature of discrimination learning in pigeons

The results from five experiments are considered in relation to two of Spence's (1937, 1938) proposals concerning discrimination learning. In Experiments 1 and 2, we investigated whether his ideas about the interaction between excitatory and inhibitory generalization gradients can be used to understand how animals solve a complex patterning discrimination. The results supported a development of his proposals as put forward by Pearce (1994), provided a modification was made to Pearce's rulefor determining the shape ofthe generalization gradient. In Experiments 3, 4, and 5, we examined whether animals would pay more attention to stimuli that are relevant, rather than irrelevant, to the solution of a discrimination. The results supported this proposal for stimuli comprising visual patterns, but not for those comprising plain colors. The results also indicated that change of attention was a consequence of preliminary receptor-exposure acts, as envisaged by Spence, and not of more central changes in attention.     

Partial reinforcement effects on discrimination learning

Rats were trained on a series of reversals of a successive discrimination in which the percentage of S+ trials ending in food was varied. Changes in the discrimination index occurred more slowly with 50% reinforcement than with 100% reinforcement when the number of training trials was equated across conditions, but were approximately invariant when the conditions were equated with respect to the number of obtained reinforcements. Presentation of free reinforcement during the intertrial intervals reduced the overall rate of discrimination acquisition, but left this invariance unaffected. Invariance in reinforcements necessary to attain acquisition also occurred when different discriminations correlated with different percentages of reinforcement were intermixed within experimental sessions. The failure of the invariance effect to be disrupted by either manipulation suggests that previous accounts of the invariance effect in terms of “comparator” models of conditioning (e.g., Gibbon & Balsam, 1981) are inadequate.     

Simultaneous discrimination learning: Stimulus interactions

Although considerable attention has been given to interactions between events serving as the positive (S+) and negative (S−) stimuli in successive discriminations, there has been little study of similar interactions in simultaneous discriminations. We propose that in a simultaneous discrimination, given what is typically relatively little experience with the consequences of responding to the S−, some of the value of the S+ transfers to the S− with which it was paired. Furthermore, the mechanisms responsible for this transfer of value appear to be the higher order Pavlovian association between the S− and the S+, as well as within-event associations between them. Although in typical simultaneous discriminations, negative value does not appear to transfer from the S− to the S+, when adequate experience is provided with the S−, contrast typically develops, reducing the value of the S− (negative contrast) and enhancing the value of the S+ (positive contrast). This model of stimulus interactions has implications not only for simple simultaneous discrimination learning, but also for research using combinations of discriminations (e.g., transitive inference in animals and humans). This model may also have implications for a number of human social psychological phenomena.     

Pretraining and discrimination reversal learning by rhesus monkeys

Groups of five to seven macaques were trained on repeated reversals of a visual (or spatial) discrimination habit after no pretraining, extended discrimination training, or repeated reversal training on spatial (or visual) cues. Neither sort of pretraining had a significant effect on reversal learning on the second cue. These results indicate that monkeys’ capacity to develop generalized “win-stay, lose-shift” hypotheses may have been exaggerated in previous experiments.     

Irrelevant cues and shape discrimination learning by cats

Experimentally naive eats learned to discriminate a pair of objects (circle and triangle) that differed in external contour, with no irrelevant cues (N = 30), with irrelevant brightness cues (N = 26), and with irrelevant size and brightness cues (N = 26). In a second experiment, naive cats were trained to discriminate bidimensional patterns (circle and triangle) with no irrelevant visual cues (N = 24) or with irrelevant size and brightness cues (N = 26). Irrelevant cues did not significantly affect the rate of shape discrimination learning in either experiment. The findings disagree with the results of several similar experiments with rats.     

“Thinking ahead” in rat discrimination learning

If rats chose S+ in a brightness discrimination in a T-maze, they experienced, on that run and over four forced runs to S+ which followed, a pattern of reinforcement in which quantity of reward in the goalbox increased from 0 to 14 food pellets, decreased from 14 to 0 food pellets, or varied randomly. If the rats erred and chose S?, reinforcement was withheld, and they were forced a second time to 0 reward in the S? goalbox. The results indicate that rats readily learn the brightness discrimination under these conditions, the animals exposed to the sequentially increasing pattern learning somewhat slower than the others. This was true in spite of substantial delay of reward. Theoretical accounts based on perseverative inhibitory or facilitatory tendencies, or upon frustration, fail to describe the data accurately. Instead, analysis of the data shows that the animals were accurately anticipating the quantity of reward to be obtained on each run, running fast for large quantities and slowly for small.

     

Metaphorical graphics aid learning and memory

The present investigation was designed to determine the effects of metaphorical graphics on learning from an expository text. The graphics were designed to function as metaphorical representations of the semantic elements inherent in the passage, with the level of correspondence between the graphics and text varied as weak or strong. In study 1, participants (N = 168) were randomly assigned to one of three graphic/text conditions (strong, weak, or none). Learning was measured immediately after the presentation of learning materials and again a week later. In study 2, participants (N = 98) followed the same procedure as study 1, but they were allowed to view the experimental materials online, rather than in a lab setting. Results from both studies revealed that, while decorative graphics may appear benign or detrimental to learning outcomes immediately after exposure under experimental lab conditions, further analysis indicated that graphics designed to metaphorically correspond to text content functioned to preserve learning across a one-week delay. In addition, when participants viewed the materials online, the decorative graphics improved learning, not just prevented decay. The online effect was mediated by the level of metaphorical correspondence between the passage and the graphic.     

Employer learning,statistical discrimination and university prestige

This paper investigates whether employers use university prestige as a signal of workers’ unobservable productivity. Our test is based on employer learning-statistical discrimination models, which suggest that if employers use university reputation to predict a worker’s unobservable quality, then college prestige should become less important for earnings as a worker gains labor market experience. In this framework, we use a regression discontinuity design to estimate a 13% wage premium for college graduates in their first year of the labor market who were barely accepted by one of the two most prestigious universities in Chile compared with those barely rejected by these two schools. However, we find that this premium decreases to 4% for workers with 6 or more years of labor market experience. This result suggests that college prestige becomes less important for employers as workers reveal their quality throughout their careers.