A series of experiments was designed to evaluate the applicability of Capaldi's sequential hypothesis for describing human partial reinforcement-extinction effects (PREEs). The 5s were required to make a decision about whether or not to gamble on an uncertain outcome. Experiment I was designed to determine whether the experimental context would result in a usual PREE. Experiment II evaluated the memory trace assumptions of the theory via the use of intertrial reinforcements. The third, fourth, and fifth experiments were designed to evaluate assumptions concerning the effects of patterns of reinforcements and nonreinforcements on the PREE. Similarities between Capaldi's sequential hypothesis of instrumental learning and other sequential theories of human choice behavior were noted. The results were in general agreement with predictions from sequential theory. It was suggested that human choice behavior can be best described as a situation where 5s process information for the purpose of developing sequential response strategies.

2The integration of information model ofsignal detection theory (SDT) was tested in a multiple observation tilt-discrimination task. Improvement in discriminability with additional observations was consonant with theory over two observations, but observations beyond the second yielded less improvement than predicted by the integration model. Analyses of operating characteristics lent some support to the applicability of SDr to the tilt-discrimination task.This paper describes two experiments designed to test the integration model of signal detection theory (SOT) in a multiple observation task (cf. Green & Swets, 1966). In opposition to traditional threshold theory which posits an all-or-nothing informing effect of stimuli, SOT states that the informing effects range along a continuum from determinate information favoring one stimulus alternative through no information to determinate information favoring the other alternative. A stimulus is evaluated by comparing its informing effect with an internal standard or criterion. The probability density function of the informing effects yielded by a given stimulus source is assumed to be normal. In a two-alternative discrimination task, the informing effects density functions associated with the alternative stimuli would differ in location, but, for the sake of simplicity, can be assumed to be equal in variance. The difference between the means of the probability density functions, in units of the density function standard deviation, is labeled the index of signal detectability (d') and constitutes the SOT measure of discriminability-sensitivity.In order to derive predictions of discriminability when multiple observations of the stimulus are furnished on each trial, it is assumed that the informing effect associated with a set of independent observations is the mean of the informing effects of the component observations. Thus, the probability density function for a set of n observations should possess the same location on the informing effects continuum as the density function for single observations. However, the standard deviation should be only If./ii (n being the number of observations) of the standard deviation of the single observation density function. Because d' is the ratio of the difference in location to the standard deviation of the density functions, reduction in the standard deviation yields a proportional increase in d'. Thus, the d' based on n observations per trial is predicted by the SOT integration model to be v'n times the d' based on one observation per trial. The v'nprediction requires the assumption that the multiple stimulus observations are mutually independent. If dependence should exist, the predicted improvement would be less than v'n. It may be noted that the same predictions can be derived if one assumes that S bases his judgment on the likelihood ratio of the informing effects, and that the likelihood ratio of a set of stimulus observations is the product of the likelihood ratios of the individual observations (Green & Swets, 1966).In an a...

2 experiments investigating concurrent simultaneous and successive contrast effects with human 5s in a probability learning task are reported. Successive and simultaneous negative contrast effects were noted with 2 nonzero levels of incentives. These effects were not obtained with a paired zero and nonzero incentive level. An absolute magnitude hypothesis for the latter condition was proposed.

Human 5s received 10 acquisition trials under conditions of partial reinforcement in a modified gambling task. Groups differed as a function of percentage of reinforcement and number of N-R transitions. In addition to the demonstration of a small-trials FREE, the results were in agreement with predictions made from sequential theory. Alternative theories developed from frustration models are also discussed.

In three separate experiments, Ss were provided with auditory, visual, or simultaneous auditory and visual information in a classification task. Difficulty of classification was manipulated by varying the stimulus exposure duration. Consistent bisensory facilitation effects were noted for later trials, with interference evident on earlier trials. Exposure duration influenced rate and not amount of learning, with bisensory performance being most affected by duration. A transfer paradigm was used in Experiment III, and little if any transfer was noted between unisensory and bisensory stimulus conditions. It was concludedthat Ss were extracting the most salient bisensory stimulus components from the auditory and visual modes of information into a unidimensional information configuration.Studies of intersensory processes are, for the most part, designed to determine whether, and/or how, organisms utilize information that is presentd to more than one sensory modality. Typically, a bisensory task is used where stimulus information is provided to the visual and auditory modalities, either simultaneously or separated by some short interval. The design frequently involves three groups, one of which receives combined visual and auditory information, the other two groups experiencing either the auditory or visual stimuli only. An intersensory facilitation effect is noted when the performance of the bisensory group is superior to the performance of each of the other two groups. Intersensory interference refers to circumstances where bisensory performance is inferior to the performance of either of the unisensory groups. While both facilitation and interference have been obtained (as well as the absence of intersensory effects), the most typical result is facilitation, particularly in situations where the stimuli are difficult to detect or discriminate. Excellent reviews of the "intersensory" literature have been provided by Loveless, Brebner, and Hamilton (1970) and Nickerson (1973), with the latter being largely limited to experiments which emphasize a response time (RT) dependent measure.With few exceptions, data on intersensory processes come from experimenal contexts which have used either a detection or discrimination paradigm along with short-duration stimulus exposures. Although there has not been a considerable effort directed toward theoretical development, two different. but not opposing, theories have been proposed. These are the energy summation hypothesis (e.g., Bernstein, 1970) and the preparation-enhancement model (e.g. • Nickerson, 1973). Very briefly, the former attributes bisensory facilitation to the cross-modal summation of stimulus energy, while the latter treats one of the two sources of bisensory information as an accessory which serves primarily to "set." "orient." or prepare the S for the other source of information.At a strictly intuitive level, it would appear that the ability to effectively utilize two sources of simultaneous or near-simultaneous bisensory information would develop as a result of...