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In the present experiment participants were presented either a serial (F-->T+/T-) or a simultaneous (FT+/T-) feature positive discrimination using a Skinner box for humans. After the participants mastered the discrimination, the associative properties of F were examined using a transfer test and a counterconditioning manipulation. F affected responding to a transfer target less in the Serial than in the Simultaneous condition. However, counterconditioning of F did not affect initial discrimination performance in either condition. These results were discussed in the framework of occasion setting, elemental learning, configural learning, and a neural network model.

The present rat experiment evaluated the validity of two formal accounts of configural learning in the framework of discrimination tasks involving the serial presentation of feature and target stimuli: Rescorla's (1973) modification of the Rescorla-Wagner model (1972) and the Pearce model (1987). The first, ambiguous feature task was of the form X-->A+, Y-->A-, X-->B-, Y-->B+, in which X and Y represent visual features, '-->' signifies a serial arrangement, A and B are auditory target stimuli, and '+' and '-' symbolise food-reinforcement and non-reinforcement, respectively. The second, non-ambiguous feature task was of the form: X-->A+, Y-->A-, X-->B+, Y-->B-. The former task was much more difficult to solve than was the latter task. The Rescorla model is able to account for the observed differences between the two tasks in learning rates and in the associative strength of feature X with more plausible parameter values than is the Pearce model. It is suggested that models acknowledging a role for both elemental and configural learning can better account for discrimination learning in discrimination tasks of the sort presented in this study than do models that exclusively allow for configural learning.

An answer to the question of how the archer fish hits an aerial insect, despite the refraction of light at the surface of the water has not yet been found. The aims of the present studies are to find out: (1) whether the fish applies a learned correction with the virtual image as a point of reference; (2) whether deprivation of practice in squirting affects performance. For the first aim the accuracy of squirts was measured in 30 subjects. Contrary to suggestions from the literature, elevation failures were prominent but the frequencies of over- and under-squirting did not differ, which does not support the idea that the fishes applied a learned correction for refraction by using feedback from the efficacy of squirts. For the second aim, five experimental subjects were deprived of practice, whereas six control subjects got daily practice, during 6 months. The only significant difference, found thereafter, was that during the first session experimental subjects aimed more often before squirting than control subjects did, but hitting was not affected. A number of subjects developed abnormal mandibles which inevitably led to squirting too high. Our findings do not support the hypothesis that the archer fish uses learned corrections for refraction.

Four experiments with human subjects examined the cue-interaction effects using a computer-controlled predictive learning task. In Phase 1, subjects learned that cue P was consistently associated with the occurrence of an outcome (P+), whereas cue N was never followed by the outcome (N-). In Phase 2, two neutral cues, R and I, were compounded with P and N, respectively. Each compound was followed by the outcome (PR+ and NI+). Thus, cue R was compounded with the already predictive cue P, whereas cue I was compounded with the non-predictive cue N. In each phase, subjects rated the contingency between the different cues and the outcome. In experiments 1 and 2, the spatial position of the cues was fixed, whereas it was variable in experiments 3, 4a and 4b. Verbal cues were used in experiments 1-3, whereas the cues consisted of geometrical figures in experiments 4a and 4b. Evidence for cue interaction, as indicated by giving cue I a higher contingency rating than cue R after or during Phase 2, was only found under the conditions of experiments 1 and 2. The results indicate that the use of positional cues facilitates the occurrence of cue-interaction effects. Possible reasons for this finding are discussed.

Three experiments examined spontaneous recovery from extinction of appetitive conditioned responding (CR) as a function of training history. Rats first received reinforced and non-reinforced conditioning trials. Groups of rats were equated for total number of reinforced trials but differed in the number of non-reinforced trials, or in the order of reinforced and non-reinforced trials. CR was then extinguished in all groups. Subsequently, the extent of recovery of CR was assessed in a test session performed either 1 or 17 days after the last extinction session. After a 17-day delay, rats that had received all reinforced trials immediately prior to the first extinction session showed stronger recovery than did rats having received all reinforced trials at the beginning of training, or interspersed among non-reinforced trials. No significant spontaneous recovery was observed after a 1-day test delay. These results, which may be of clinical relevance with respect to relapse after therapy, are explained in terms of the training schedules generating differences in strength of inhibitory associations, and a relatively long, but not a short, test delay attenuating these associations.

The present experiment contributes to the identification of factors affecting magnitude of context specificity of simple appetitive conditioned responding. Rats were first trained to associate an auditory and a visual stimulus with food. Each of these stimuli was consistently presented in a distinctive environmental context. Groups of rats differed only in the number of conditioning trials. At test, all groups received trials on which each of the stimuli was presented either in the same context as used during training, or in the different context. Rats made significantly fewer food-magazine visits on different-context trials than on same-context trials only under the conditions that the stimulus tested was the auditory stimulus, which generally elicited a stronger conditioned response (CR) than did the visual stimulus, and the animals had received a relatively small number of conditioning trials. Apparently, magnitude of context specificity is affected by factors determining the strength of the appetitive conditioned response to the target stimulus.

Filial imprinting has been studied extensively in precocial birds. In these studies, inanimate objects were used as imprinting objects. Although attachment to the parents is common in mammals, experiments with inanimate objects are rare and mostly restricted to guinea pigs (Cavia porcellus). The results of these studies are inconclusive. The aim of the present experiment was to assess whether guinea pigs can develop an attachment to inanimate objects. For this purpose, 11 young guinea pig pups were taken from their mothers within 16 h after birth, and subsequently reared individually in the presence of an inanimate object. Between 2 and 35 days of age, the pups were submitted to preference tests as well as separation tests. Neither test provided evidence of attachment: during separation, the pups did not increase their distress calling; moreover, pups preferred a novel object to their rearing object in the preference tests.

Two experiments with rats examined behavioural control by feature stimuli in appetitive conditioning using latency of food-magazine visits as the dependent measure. In experiment 1, a feature-positive (FP) discrimination was presented in which a target stimulus was consistently followed by food when preceded by a serial feature and accompanied by a simultaneous feature, and not followed by food when presented alone. The reverse condition, a feature-negative (FN) discrimination procedure, was in effect in experiment 2. Groups of rats differed in the physical identity of the stimuli used as target and features. In the FP discrimination, all groups came to respond faster on reinforced than on nonreinforced trials. Subsequent tests revealed that the serial feature was responsible for this performance in all groups, whereas the simultaneous feature had not acquired significant control in all groups. Only one half of the groups solved the FN discrimination and they did this on the basis of only the simultaneous feature, which was a relatively intense stimulus in these groups. These results suggest a propensity to use the serial feature in FP discriminations and the simultaneous feature in FN discriminations.

Rats were reared from weaning onwards in impoverished (IC), social (SC) or enriched (EC) environments. In addition, some groups were moved from an enriched to an impoverished environment, or vice versa, either once or three times during rearing. After 2 months of differential rearing, animals were tested in a multidimensional discrimination procedure in an operant chamber, where reinforcements were given on a random schedule, that is, uncorrelated with the choices made by the animals. It was found that eventually all rats took up alternating place. However, enriched subjects did so more consistently than impoverished or socially reared subjects. Animals shifted three times, behaved more routine-like than did animals never changed or changed only once; such animals did so to a greater degree than did the enriched animals. In comparison, impoverished animals, and those never changed or changed once, more often kept responding to the environmental cues. The results are discussed in relation to general interpretations of the effects of impoverishment and enrichment in terms of behavioural flexibility, over-attention, and in relation to styles of coping. It is argued that, contrary to welfare people's claims, the behavioural differences found are well within the range of normal individual variation.

The primary purpose of this article is to present some empirical data concerning three different potential time of day effects on conditioned freezing in a commonly-used aversive context-conditioning procedure with an unsignalled electric footshock as the unconditioned stimulus. In Experiment 1, rats were repeatedly placed in a conditioning box in which they received a shock. For one group of rats, these sessions consistently occurred in the morning; for another group in the afternoon. In Experiments 2 and 3, rats received two training sessions per day. One group was consistently shocked in a training box on morning sessions but not on afternoon or evening sessions, whereas another group received the reverse treatment. The pattern of freezing observed during repeated non-shock morning and afternoon/evening test sessions reflected an effect of time of shock delivery on the acquisition of a context-shock association in Experiments 1 and 2, and a time of testing, or non-specific performance, effect in Experiments 1 and 3. In none of the experiments was there an effect that would reflect differential retrieval of a context-shock association by time cues. These results were discussed in the light of data from previous experiments.

The present experiments examined whether external contextual stimuli can acquire inhibitory properties through a simple differential context-reinforcement procedure. Rats first received discrimination training sessions in which an electric footshock was consistently delivered in one context, but not in a second, different context. In Experiments 1A and 1B, summation and retardation tests were subsequently performed using the non-reinforced context. Each of these tests failed to reveal contextual conditioned inhibition. In Experiment 2, a summation and retardation test were performed using a contextual stimulus that was unique to the non-reinforced context. Weak but significant contextual inhibition was found. It was suggested that contextual stimuli that are unique to the non-reinforced context did acquire inhibitory strength in each experiment, but that in Experiments 1A and 1B, expression of this inhibition during testing had been masked by the concurrent presence of excitation from elements that the non-reinforced context had in common with the reinforced context.

Rats were subjected to a Pavlovian discrimination procedure in which a target stimulus was followed by food in Context X and followed by nothing in a distinctively different Context Y. Two experiments sought to determine the effect of postacquisition manipulations regarding Context Y, on responding to the target in that context. In Experiment 1A, the effect of separate nonreinforced exposures to Context Y was examined and in Experiment 1B, the effect of a separate reinforced exposure was assessed in four groups of rats receiving different amounts of deliveries of the reinforcer in Context Y. It was found that both nonreinforced and reinforced exposures to Context Y had an adverse effect on the attenuation of responding to the target that was originally observed in that context at the end of discrimination training. The results were discussed in view of an occasion-setting account and of more traditional models of associative learning., (Copyright © 1994. Published by Elsevier B.V.)

Studies on the effects of rearing conditions on behavioural development showed that most monkeys reared with surrogate mothers persistently avoided a big novel object (paper bag) whereas most monkeys reared by natural mothers would approach it. Conditioned fear and conditioned avoidance, observational learning, and lack of support by the mothers' presence could be excluded as possible causes; we established that the high incidence of phobic behaviour in surrogate-reared groups was caused by deprivation of maternal care. Results of further studies showed that the avoidance was not restricted to the object the Ss had been exposed to in infancy; monkeys still avoiding the bag at 2 years also avoided other big novel objects. Some researchers have found differences in the neurobiological status between surrogate-reared monkeys and mother-reared monkeys. However, the results of our experiments showed that both types of rearing condition produced avoiders as well as non-avoiders. The question under discussion here is whether avoidance of novelty is a habit or a trait. The relative importance of features of surrogates versus real mothers, characteristics of infants and differences in mothering style is discussed., (Copyright © 1994. Published by Elsevier B.V.)

Preexposures to a punctate stimulus or to an external context were examined for their effect on the competition for associative strength between context and stimulus in subsequent aversive classical conditioning. Using rats as subjects and freezing as the index of conditioned responding, Experiment 1 showed that preexposure to a tone retarded the subsequent acquisition of responding to the tone, but enhanced the acquisition of freezing to the conditioning context. Experiment 2 examined whether the enhanced contextual freezing in Experiment 1 was based on the formation of an association between the preexposure context and the tone. A tone was preexposed in one context and conditioned in another. A subsequent of fear for the preexposure context failed to support the notion of an association between context and tone. In Experiment 3, context preexposure was given prior to tone conditioning in that context. The acquisition of contextual freezing was impaired but the exposure treatment had no augmenting effect on freezing to the tone. Collectively, the results suggest that preexposure reduced the associability of both the punctate stimulus and contextual stimuli. More importantly, the reduced associability of the punctate stimulus resulted in a reduced overshadowing of contextual stimuli by the punctate stimulus, whereas the reduced associability of the context did not result in a reduced overshadowing of the punctate stimulus by the context., (Copyright © 1993. Published by Elsevier B.V.)

When confronted with a novel situation rats show a tendency either to stay in a dark place or to retreat to a familiar place, if available. To produce a conflict between these two tendencies the rat's home cage was connected by a runway to a dark but unfamiliar compartment. Three groups of rats were tested in this apparatus with different levels of illumination in the home cage. Tryon Maze Bright rats showed a strong preference for the home cage which was independent of the illumination level. This preference was also found in Wistar rats. With a very high level of illumination in the home cage, however, Wistar rats showed a preference for the home cage only in the first few trials or a series of repeated trials. In later trials they spent more time in the dark part of the apparatus. The results were regarded as an indication that in a novel situation rats primarily search for a familiar place. When such a place is available they tolerate aversive stimulation present in this place., (Copyright © 1978. Published by Elsevier B.V.)