Differential reinforcement of interresponse times with controlled probability of reinforcement per response

Pigeons were presented food after interresponse times (IRTs) longer or shorter than a fixed percentage of their most recent IRTs. This procedure controlled probability of reinforcement per response while still allowing different classes of IRTs to be reinforced differentially. Support was found for IRT-reinforcement theory in that response rates were determined by the degree and direction of differential reinforcement of IRTs, but were relatively independent of probability of reinforcement per response and of the length of the control system's IRT memory. Stimulus control of these differential response rates was also demonstrated.     

Between-chains and within-chain speed gradients as functions of length

Two experiments examined between-chains and within-chain speed gradients as functions of length. The first, involving straight runways, revealed hyperbolic gradients within chains for each of three lengths, .61, 1.22, and 2.44 m. Between-chains comparisons showed a goal gradient effect confined to the start box segment and a long-chain depression effect in the last two segments. The second experiment, involving discrete-trial fixed-ratio bar-pressing schedules of FR(1 + 4), FR(1 + 8), and FR(1 + 16), showed goal gradient effects for starting speeds and for speeds across the first segment beyond start. Also, confounding effects apparent in the runway, of acceleration, deceleration, and long-chain depression, were diminished or absent in the bar-pressing situation.     

Effects of prefeeding on performance with body weight held constant

Two experiments are reported in which rats received either no prefeeding, nutritive substance prefeeding, or nonnutritive substance prefeeding prior to running in a straight alley. The running-speed data supported body weight as an overall measure of hunger drive. Performance was a function of body weight but not stomach weight or associated stomach bulk.     

Interactive effects of deprivation in the albino rat

The interactive effects of feeding and drinking schedules were investigated in three experiments. Twenty-four hour water-deprived rats consumed their entire obligatory water intake prior to feeding, whereas 24-hr food-deprived rats consumed only small quantities of food prior to drinking. This drinking was apparently due to a shift of water stores rather than an actual negative water balance. Experiment 3 investigated the effects of 24, 48, or 72 hr of water, food, or total deprivation. Water-deprived rats did not adequately suppress food intake and became thirstier than totally deprived rats. The effects of total deprivation were essentially identical to those of food deprivation. These experiments indicate the degree to which deprivation schedules impose restrictions on the reinforcement parameters of behavioral experiments.     

Aversive properties of the negative stimulus during learning with and without errors

In a successive discrimination four groups of pigeons were trained to discriminate between red and green. The groups differed with respect to the procedure used to introduce S?: Early-Progressive, Early-Constant, Late-Progressive, and Late-Constant. The aversive properties of S? were measured by an escape response in which a single peck at a second key terminated S? for 10 sec and darkened the chamber. The correlation between the aversive and error-producing properties of extinction was zero. More errors occurred when S? was introduced abruptly at a constant intensity while more timeouts from S? occurred when S? was introduced late. The procedure for introducing S? rather than the number of responses to S? appears crucial in determining how aversive S? becomes.     

A two-phase model account of aversive classical conditioning performance in humans and rabbits

A two-phase model was applied to classical conditioning performance in man and rabbits. During phase 1, response probability remained constant. During phase 2, response probability generally increased, although one operator was sufficient for a majority of Ss and two operators were required for a minority of Ss. The latter Ss exhibited increases in responding after a CR trial and decreases in responding after a non-CR trial. The pattern of parameters was similar for man and rabbits. In man, increases in UCS intensity resulted in a decrease in the duration of phase 1 and an increase in the limit of the operators for those Ss requiring more than a single operator to describe performance during phase 2. The value of employing a model to describe the data and understand the effects of independent variable manipulation was discussed.     

Performance expectancies and affect associated with outcomes as a function of time perspective

An experiment was conducted to investigate the effects of time perspective on performance expectancies and the subjective evaluation of outcomes in regard to a task at which subjects had previously succeeded or failed. Prior research has produced conflicting findings on the subjective evaluation of positive and negative outcomes, but some of the research has dealt with tangible rewards and punishments while other work has been concerned with performance outcomes involving tasks with which subjects were unfamiliar. In the current study subjects first succeeded or failed on either an easy or difficult task. They then stated performance expectancies and made evaluations of the affect associated with success and failure in regard to performing the task again immediately, in 3 wk, or in 21 wk. Results indicated a significant decrease over time for both the satisfaction associated with passing and the dissatisfaction associated with failure. Performance expectancies were significantly higher for the testing period of 21 wk in the future than for either the immediate or 3-wk testing period, but this difference was evidenced only for subjects who initially passed the test.     

Modeling strategy shifts in a problem-solving task

A computer simulation model was fitted to human laboratory data for the Missionaries and Cannibals task to explain (1) the effects upon problem performance of giving a hint, and (2) the effects of solving the problem a second time after one successful solution had been achieved. Most of the variance in the relative frequencies of different moves can be explained by positing that the effect of the hint, or of previous experience in solving the problem, is to cause subjects to switch more promptly from a strategy of balancing the numbers of missionaries and cannibals on both sides of the river, to a means-ends strategy.     

Structural ambiguity in serial pattern learning

Four experiments on serial anticipation learning of lights by college students show that (a) the operations of transposing and taking the mirror image are used, (b) temporal inversion is not used, (c) a sequence made of two contrasting halves may be as easy to learn as a sequence having a single homogeneous hierarchical structure. Data revealed intrasequence confusion errors made by importing an operation from one part of the sequence to another. In homogeneous sequences, subjects appear to lose track of where they are in a sequence, and therefore repeat an operation already performed. The evidence supports the idea of an hierarchical cognitive structure, but shows that learning is not a simple function of that structure. Errors and difficulties arise from structural ambiguities, substrings of events that can be reconciled with more than one possible cognitive structure.     

Basic objects in natural categories

Categorizations which humans make of the concrete world are not arbitrary but highly determined. In taxonomies of concrete objects, there is one level of abstraction at which the most basic category cuts are made. Basic categories are those which carry the most information, possess the highest category cue validity, and are, thus, the most differentiated from one another. The four experiments of Part I define basic objects by demonstrating that in taxonomies of common concrete nouns in English based on class inclusion, basic objects are the most inclusive categories whose members: (a) possess significant numbers of attributes in common, (b) have motor programs which are similar to one another, (c) have similar shapes, and (d) can be identified from averaged shapes of members of the class. The eight experiments of Part II explore implications of the structure of categories. Basic objects are shown to be the most inclusive categories for which a concrete image of the category as a whole can be formed, to be the first categorizations made during perception of the environment, to be the earliest categories sorted and earliest named by children, and to be the categories most codable, most coded, and most necessary in language.