DO ELEPHANTS EVER FORGET?1

Three adult female elephants (Elephas maximus) were tested on a light-dark discrimination problem with an 8-yr intertrial interval. The first subject took only 6 min to reach criterion and made only two errors, suggesting remarkable retention. The other two subjects were found to have visual anomalies that would have gone undetected without this research.     

Conditioned inhibition is not the symmetrical opposite of conditioned excitation: A test of the Rescorla-Wagner model

Rescorla and Wagner's (1972) linear associative model of learning predicts that a neutral stimulus will become weakly excitatory if it is paired with a conditioned inhibitor and the compound is not reinforced. If the inhibitor is not allowed to extinguish during these pairings, the model predicts that the neutral stimulus will become strongly excitatory. Rescorla (1971) has presented some evidence to support the former prediction of a weak effect. Experiment I tested the latter prediction of a strong effect using rats in a conditioned emotional response paradigm, and found no evidence that the pairings made the neutral stimulus excitatory. Experiment II replicated Rescorla's results, but showed that even on a relearning test the experimental group learned no faster than a novel stimulus control group.     

Concomitant changes in classically conditioned heart rate and corneoretinal potential discrimination in the rabbit (Oryctolagus cuniculus)

Corneoretinal Potential (CRP) and heart rate changes were measured in a series of differential classical conditioning experiments in which the directionality of the heart rate response was related to (a) CRP acquisition, and (b) the certainty or uncertainty of the stimulus situation. The results suggested that heart rate decelerations were associated with stimuli that predict upcoming aversive events, while heart rate accelerations were associated with asymptotic CRP responding late in conditioning. These findings were interpreted in terms of (a) changes in general somatic activity, and (b) the cue properties associated with CSs which predict aversive events.     

Eliminating nail-biting by the habit reversal procedure

Fingernail-biting is prevalent among children and adults alike. About 43% of children bite their nails during the puberty ages (Wechsler, 1931); 25% of college students are nail-biters (Coleman and McCalley, 1948), and 10% of adults bite their nails (Pennington, 1945).A variety of treatments including negative practice, operant procedures and psychotherapy have been used in treating nail-biting but no single treatment has been generally effective in eliminating nail-biting. Smith (1957) using negative practice reported that 21 of 57 (39%) of his nail-biting clients were cured. 9 improved and 27 (47%) were unimproved. Bucher (1968) reported that 13 of 20 (65%) college students stopped nail-biting by using a self-administered operant shock procedure. However, he reported many relapses after the withdrawal of shock for nail-biting. No evaluation of psychoanalytic treatment for nail-biting appears to have been made.     

Using conjoint-measurement models to investigate a theory about probabilistic information processing

A theory of how opinions are formed and revised on the basis of probabilistic evidence is presented. The decision maker is viewed as a limited information processor who attends to the dimensions of a sample of equivocal information in a sequential fashion, beginning with the most salient dimension and continuing in decreasing order of salience. The contribution of each dimension level to the final opinion depends on the strength of association between that level and each of the two hypotheses under consideration. This theory is represented formally as an additive-difference model, various special cases of which correspond to other algebraic models in the literature. Two of the special cases were empirically investigated under varying levels of experience and payoffs, using the techniques of conjoint-measurement theory and ordinal data from individual subjects. The data provided reasonably good support for the models under all conditions investigated, and in addition showed interesting effects on salience and on processing of the independent variables.     

Age trends in children's time-sharing performance

To investigate developmental differences in time-sharing performance, 60 boys, 20 in each of three age groups (7-, 10-, and 13-year-olds) performed an auditory matching task and a tracking task alone and concurrently, the latter under two sets of instructions. Decrements produced by concurrent performance were compared for the three age groups. When the time-shared tasks were presented as equally important, time-sharing produced significantly greater proportional decrements in the tracking performance of the younger children and for all age groups tracking task decrements were directly related to matching task difficulty. Subsequently, the children were instructed that one or the other of the tasks was more important and that they were to improve their performance on that task. All three age groups showed a significant improvement on the task emphasized by instructions. The relationship of the results to two models of information processing is discussed.     

Structure in semantic memory: A probabilistic approach using a continuous response task

In the continuous response (CR) task, the subject is given the name of a familiar category and must respond with category examples within a fixed time limit. The response sequence and the interresponse times are the measured variables. A general model is proposed for performance in the CR task. The time taken to generate a response is identified with the shortest search time from among a set of simultaneous search processes. Each response has a generation probability that is a function of the parameters governing the search process durations. Data involving the category states in the United States are used to test the model. The model accounts for the performance of nearly all individuals in these data.This article is based on a dissertation completed at the University of California-Berkeley in partial fullfillment of the requirements for the Ph.D. degree in psychology. Portions of the article were presented at the joint meeting of the Psychometric and Classification Societies (June 1984) and at the meeting of the Society for Mathematical Psychology (August 1984). The authors wish to thank Barbara Mellers, Juliet Schaffer, Steve Palmer, and Eleanor Rosch for helpful comments.     

Quantification of the effects of chlorpromazine on performance under delayed matching to sample in pigeons.

The effects of four doses of chlorpromazine (dose range 0.5 to 12.5 mg/kg) on performance under a delayed matching-to-sample procedure in pigeons was investigated, using the exponential model of memory (White, 1985). Performance was measured using a bias-free measure of discriminability, log d (Davison & Tustin, 1978), and negative exponential functions were fitted to individual-subject and group data at each dose level. A decrease in matching accuracy was found to be caused by an increase in the rate of forgetting, b, and a decrease in the initial discriminability, log d0. Changes in rate of forgetting and discriminability occurred at doses that had no statistically significant effect on response latency. The exponential model of memory accounted well for the data and provided a useful way of quantifying the effects of chlorpromazine on the processes involved in delayed matching-to-sample performance.