Partial reinforcement effects in instrumental escape conditioning

In Experiment I acquisition and extinction of instrumental escape conditioning with rats (N = 64) were studied as a function of reinforcement magnitude under conditions of partial and continuous reinforcement. In Experiment II the effects of partial and continuous reinforcement were studied in rats (N = 96) during acquisition followed by small, medium, and large reductions in reinforcement magnitude. A water-tank escape apparatus was used with temperature as the relevant variable. It was found that (1) with large reinforcement magnitude a continuously reinforced group was superior in acquisition to one that was partially reinforced; there were no differences with small reinforcement; (2) disruptive effects of a nonreinforced trial (a) appear early in learning, (b) are quite strong after each nonreinforced trial, and (c) persist through several succeeding reinforced trials; (3) major competing behaviors persist throughout acquisition for small reinforcement magnitude regardless of schedule, decline with large reinforcement (more so with continuous than with partial), and return to a high level in extinction for all conditions; (4) the partial reinforcement extinction effect occurs after large reinforcement but not after small, and it appears only with large reductions in reinforcement magnitude which approach extinction conditions. Only the first part of the last finding appears to be consistent with the appetitive conditioning literature.     

Caffeine,impulsivity, and memory scanning: A comparison of two explanations for the Yerkes-Dodson Effect

Two explanations for the Yerkes-Dodson Effect (1908) were tested. Easterbrook (1959) proposed that arousal reduces the range of cue utilization. Thus, arousal should interfere with the capacity for simultaneous (dual) memory scans. In contrast, Humphreys and Revelle (1984) proposed that arousal facilitates sustained information transfer but interferes with short-term memory. Arousal should thus reduce the time needed to prepare to respond but increase the time needed to scan memory. Either caffeine or placebo was given to 78 subjects who differed in impulsivity. They completed three versions of a memory-scanning task: two single-task versions (physical and category matches) and one dual-task version (either type of match). As predicted by Humphreys and Revelle, relative to placebo, caffeine lowered the intercept (p<.01), suggesting facilitation of sustained information transfer, but increased the slope (p<.05), suggesting impairment of access to short-term memory, of the regression of reaction time on log-transformed memory-set size. That caffeine had a main effect on slopes and on intercepts but did not interact with type of task suggests that arousal does not necessarily disrupt dual-task performance.     

Overtraining in classical conditioning: A comparison of motor and cardiac systems in dogs

Data from the analysis of the Overlearning Reversal Effect (ORE) noted in a simultaneous, visual discrimination task, and the lack of this effect in a position habit discrimination, led to the prediction that the ORE would not be noted in classical conditioning. It was further noted that very little work on discrimination learning had been reported in Pavlovian conditioning. The idea of schizokinesis, as observed by Gantt and others in classical conditioning, has been elaborated using the simple conditioning paradigm, and no data were available to test whether this same split would occur on a more complex level of conditioning, such as a discrimination task. To test these ideas, nine dogs were trained to a criterion of minimum discrimination, and then divided into three groups and given varying amounts of overtraining (OT). The discrimination task given the animal was to flex its paw during the CS+ signalling the onset of a brief shock. After the varying amounts of OT all groups were placed in extinction, followed by reversal training until each dog reached a criterion of minimum reversal. The results indicated 1) that the cardiac discrimination did not form before the motor discrimination; 2) extinction of differentiation was not significantly affected by the amount of OT given; 3) the mean level of responding in the motor system during extinction was highly correlated with the mean level of responding during the initial discrimination training; 4) OT had no effect on the speed of reversal of either the motor or the cardiac systems; 5) the speed of reversal learning in the motor system was highly correlated with the speed of initial discrimination.     

A quantitative description of the stimulus

A formula for the stimulus is derived. The essential postulates and assumptions are based on Gestalt theory.     

Tall is typical: Central tendency, ideal dimensions, and graded category structure among tree experts and novices

Many accounts of categorization equate goodness-of-example with central tendency for common taxonomic categories; the best examples of a category are average members--those that are most similar to most other category members. In the present study, we asked 24 tree experts and 20 novices to rate goodness-of-example for a sample of 48 trees and found (1) that the internal structure of the category tree differed between novices and experts and (2) that central tendency did not determine goodness-of-example ratings for either group. For novices, familiarity determined goodness-of-example ratings. For experts, the "ideal" dimensions of height and weediness, rather than average similarity to other trees, were the primary predictors of goodness-of-example ratings for experts. The best examples of tree were not species of average height, but of extreme height. The worst examples were the weediest trees. We also found systematic differences in predictors of goodness-of-example as a function of type of expertise. We argue that the internal structure of taxonomic categories can be shaped by goal-related experience and is not necessarily a reflection of the attributional structure of the environment. Implications for models of category structure and category learning are discussed.     

Predictive Testing of Eighteen Year Olds: Counseling Challenges

Genetic counseling of teenagers is challenging and complex. The ability to think abstractly, a sense of self and independence from family all develop during adolescence. Predictive genetic testing counseling protocols presuppose that these qualities exist, requiring the at-risk individual to consider the short and long term consequences of testing as well as their motivations. Eighteen year olds are in transition from adolescence to adulthood; eligible for predictive genetic testing, they may not yet be independent of their family or able to articulate their feelings. This paper presents case studies from the authors' clinical practice to illustrate some of the difficulties faced by genetic counselors when 18 year olds request predictive testing for Hereditary Non-Polyposis Colorectal Cancer. By reflecting upon their experiences with these young adults and their families, the authors' intention is to generate discussion about genetic counseling strategies, particularly for predictive genetic testing, that are both age-appropriate and family-sensitive.