In 5 experiments rats were required to escape from a triangular shaped pool by swimming to a submerged platform. The principal group of interest in each experiment received training with a beacon attached to the platform. The purpose of the experiments was to assess if the beacon overshadowed (Experiments 1-4) or blocked (Experiment 5) learning about the position of the platform with reference to the shape of the pool. The platform was located in the center of the pool for the first 2 experiments and in a corner for the remaining experiments. Although there was an overshadowing effect in Experiment 1, the remaining experiments failed to reveal any disruptive influence of the beacon on learning based on the shape of the pool. Moreover, in Experiments 3-5 there was an indication that the beacon facilitated such learning. The results suggest that spatial learning based on the shape of a test environment may not take place in the same way as that based on more discrete landmarks.

In 4 experiments rats received appetitive Pavlovian conditioning followed by extinction. Food accompanied every trial with the conditioned stimulus (CS) for the continuously reinforced groups and only half of the trials for the partially reinforced groups. In contrast to previous experiments that have compared the effects of partial and continuous reinforcement, the rate at which food was delivered during the CS was the same for both groups. The strength of the conditioned response during extinction weakened more rapidly in the continuously than in the partially reinforced groups. The results demonstrate that the partial reinforcement extinction effect is a consequence of the nonreinforced trials with the CS, rather than the rate at which the unconditioned stimulus is delivered during the CS.For many years the partial reinforcement extinction effect (PREE) was a mainstay of research in the field of animal learning and behavior. Within the context of instrumental conditioning, the PREE can be defined as a resistance to the detrimental effects of extinction following trials in which responding is intermittently rather than consistently paired with reinforcement (for a review see Mackintosh, 1974). So widespread was the PREE in studies of instrumental conditioning-and such was the paucity of evidence for the effect within Pavlovian conditioning-that for some time the PREE was thought to differentiate these two forms of conditioning (Kimble, 1961). However, the possibility that the PREE contradicted the single-process rule of learning (Guthrie, 1935;Hull, 1943) has not stood the test of time. Many studies of Pavlovian conditioning have now demonstrated that a conditioned stimulus (CS) that is intermittently paired with an unconditioned stimulus (US) will show a resistance to extinction relative to a CS that is consistently paired with a

In 4 experiments, pigeons received autosbaping with various combinations of three stimuli, A, B, and C, before test trials in which responding during all three stimuli, ABC, was compared with that during a three-element control compound, DEF, which had been consistently paired with food. Pairing A, B, and C individually with food resulted in similar rates of responding during ABC and DEF (Experiments 1 and 2). Responding was faster, however, during ABC than during DEF after training in which food was signaled by the pairs of stimuli (AB, AC, and BC; Experiment 1). Responding was also faster during ABC than during DEF after training involving reinforced ( + ) and nonreinforced (°) trials of the form ABC + A° BC°, followed by A* BC + (Experiment 2), or AB + BC 4 " B° (Experiments 3 and 4). The results are consistent with those of a configural analysis of summation.

No abstract

In 4 experiments pigeons received a categorization task involving 6 simultaneous compounds in which the elements A, B, and C were more frequently paired with food than were the elements D, E, and F. Food was delivered after compounds ABF, AEC, and DEC but not after DEC, DBF, and AEF. Subsequent testing revealed a higher rate of responding during ABC than during any of the compounds that had signaled food and a lower rate of responding during DBF than during any of the compounds that had not signaled food. Experiments 2, 3, and 4 further demonstrated that the rate of responding during test trials with ABC was faster than during a compound composed of 3 elements that had individually been paired with food. The results are more consistent with a configural than an elemental analysis of discrimination and categorization. A frequent finding from studies of categorization with humans is that exemplars that can be said to represent the central tendency of a category are the easiest to classify correctly. Reed (1972) described one example of such a prototype effect; Reed showed students cartoon drawings of faces that belonged to two categories. The faces for one category had, on average, smaller foreheads, more closely spaced eyes, and shorter noses than those in the other category. Once the subjects were able to sort the faces correctly, test trials with novel patterns were given. The test patterns that were most accurately classified were those that corresponded to the averages of the faces belonging to the two categories, that is, the prototypes. In a rather different study, Posner and Keele (1968) generated four prototypical patterns from a number of dots. They then distorted these patterns to some extent by moving the dots, and the resultant figures were used for a catego-rization study. Once subjects were able to sort the distorted patterns into groups on the basis of their prototypes, they were required to sort a number of novel patterns, including the prototypes. The more similar a novel pattern was to a category prototype, the easier it was to classify. For the above-mentioned experiments, the prototypes were based on the mean values of the various dimensions from which the exemplars of the respective categories had been constructed. Prototype effects can also be observed when the test stimulus is based on a rather different measure of central tendency. Goldman and Homa (1977) conducted a study based on cartoon drawings of faces, in which the prototypical faces were composed of the features that most frequently appeared in the training faces. Such modal faces were classified more efficiently than any other faces, in