Pigeons prefer a low-probability, high-payoff but suboptimal alternative over a reliable low-payoff optimal alternative (i.e., one that results in more food). This finding is analogous to suboptimal human monetary gambling because in both cases there appears to be an overemphasis of the occurrence of the winning event (a jackpot) and an underemphasis of losing events. In the present research we found that pigeons chose suboptimally to the degree that they were impulsive as indexed by the steeper slope of the hyperbolic delay-discounting function (i.e., the shorter the delay they would accept in a smaller-sooner/larger-later procedure). These correlational findings have implications for the mechanisms underlying suboptimal choice by humans (e.g., problem gamblers) and they suggest that high baseline levels of impulsivity can enhance acquisition of a gambling habit.

The distribution of latencies and interresponse times (IRTs) of rats was compared between two fixedinterval (FI) schedules of food reinforcement (FI 30 s and FI 90 s), and between two levels of food deprivation. Computational modeling revealed that latencies and IRTs were well described by mixture probability distributions embodying two-state Markov chains. Analysis of these models revealed that only a subset of latencies is sensitive to the periodicity of reinforcement, and prefeeding only reduces the size of this subset. The distribution of IRTs suggests that behavior in FI schedules is organized in bouts that lengthen and ramp up in frequency with proximity to reinforcement. Prefeeding slowed down the lengthening of bouts and increased the time between bouts. When concatenated, latency and IRT models adequately reproduced sigmoidal FI response functions. These findings suggest that behavior in FI schedules fluctuates in and out of schedule control; an account of such fluctuation suggests that timing and motivation are dissociable components of FI performance. These mixturedistribution models also provide novel insights on the motivational, associative, and timing processes expressed in FI performance. These processes may be obscured, however, when performance in timing tasks is analyzed in terms of mean response rates.

Paradoxical choices in human and nonhuman animals represent substantial deviations from rational models of behavior; such deviations often demand models that incorporate multiple perspectives, including psychology, biology, and economics. The past couple of decades have seen an increased interest in the paradoxical choice of pigeons in 2-armed bandit tasks (2ABT) developed by Zentall and colleagues. In these 2ABTs, pigeons, but not rats, systematically choose an alternative that yields less reward over multiple trials but provides more information on events within a trial, over an alternative that yields more reward over trials but provides less information on events within a trial. Although current computational models account for much of the extant data generated in studies on 2ABT choice, they do not explain, in a trial-by-trial basis, how pigeons learn to ignore some stimuli and not others in 2ABTs. To address the provenance of this differential allocation of attention, a simple model composed of Bush-Mosteller linear operators and a Pearce-Hall-like associability mechanism is proposed. This model, referred to as the Associability Decay Model (ADM) of paradoxical choice, adequately accounts for the performance of pigeons and rats in 2ABTs. The ADM yields an untested prediction that is inconsistent with other computational models of 2ABT performance, and offers potential explanations for why differences in motivation, social enrichment, and impulsivity alter the degree to which pigeons systematically choose information despite earning fewer rewards. The success of the ADM shows that a relatively simple dynamic trial-by-trial model can account for much of the extant paradoxical-choice data while identifying opportunities for further study and refinement of models of 2ABT performance. (PsycINFO Database Record

When humans are asked to judge the value of a set of objects of excellent quality, they often give this set higher value than those same objects with the addition of some of lesser quality. This is an example of the affect heuristic, often referred to as the less-is-more effect. Monkeys and dogs, too, have shown this suboptimal effect. But in the present experiments, normally hungry pigeons chose optimally: a preferred food plus a less-preferred food over a more-preferred food alone. In Experiment 2, however, pigeons on a less-restricted diet showed the suboptimal less-is-more effect. Choice on control trials indicated that the effect did not result from the novelty of two food items versus one. The effect in the less-food-restricted pigeons appears to result from the devaluation of the combination of the food items by the presence of the less-preferred food item. The reversal of the effect under greater food restriction may occur because, as motivation increases, the value of the less-preferred food increases faster than the value of the more-preferred food, thus decreasing the difference in value between the two foods.

According to the biexponential refractory model (BERM) of variable-interval (VI) performance, operant behavior is organized in bouts, described by 3 dissociable components: between-bout interresponse times (IRTs), within-bout IRTs, and bout lengths. Research has shown that between-bout IRTs are sensitive to changes in rate of reinforcement and reinforcer efficacy, the length of some bouts is selectively sensitive to changes in response-reinforcer contingencies, and within-bout IRTs are relatively insensitive to both manipulations. BERM assumes that within- and between-bout IRTs are exponentially distributed, and bout lengths are described by a mixture of negative binomial and geometric distributions. To assess BERM assumptions and the interpretation of associated findings, Fischer 344/DuCrl rats were trained on a heterogeneous tandem VI fixed-ratio (FR) schedule of reinforcement intended to dissociate the components of operant behavior. Initial (VI) and terminal (FR) links were programmed on separate levers; no stimulus signaled the completion of the initial link. FR requirement, VI requirement, and deprivation level were varied. Typical performance consisted of single responses on the VI lever separated by response runs on the FR lever. It was hypothesized that (a) the interval between the end of each FR run and the first subsequent VI response (FR-VI IRTs) would constitute between-bout IRTs, and would be sensitive to changes in VI requirement and deprivation level, (b) FR runs would constitute response bouts, so the length of a fraction of them would be selectively sensitive to changes in FR requirement, and (c) intervals between consecutive FR responses (FR-FR IRTs) would constitute within-bout IRTs, and would be relatively robust to all manipulations. Findings were consistent with these expectations. The underlying distributions of FR-FR IRTs, FR-VI IRTs, and FR run lengths, however, were inconsistent with BERM assumptions. These data support the distinct components of operant performance, but challenge the simple processes assumed to underlie their generation. (PsycINFO Database Record