The ecological rationality of state-dependent valuation

Laboratory studies on a range of animals have identified a bias that seems to violate basic principles of rational behavior: a preference is shown for feeding options that previously provided food when reserves were low, even though another option had been found to give the same reward with less delay. The bias presents a challenge to normative models of decision making (which only take account of expected rewards and the state of the animal at the decision time). To understand the behavior, we take a broad ecological perspective and consider how valuation mechanisms evolve when the best action depends upon the environment being faced. We show that in a changing and uncertain environment, state-dependent valuation can be favored by natural selection: Individuals should allow their hunger to affect learning for future decisions. The valuation mechanism that typically evolves produces the kind of behavior seen in standard laboratory tests. By providing an insight into why learning should be affected by the state of an individual, we provide a basis for understanding psychological principles in terms of an animal's ecology.     

Memory for event frequency as a function of depression, age, intentionality, and level of processing

In two experiments, we examined memory for event frequency among depressed and/or elderly subjects (depression was either naturally occurring or induced by the Velten technique). We also manipulated level of processing and instructional set to test the notion that memory for event frequency is relatively invariant across a variety of tasks. Results supported the proposal that memory for frequency is robust in the face of depression and old age. Memory for frequency was enhanced, however, by semantic processing and by an intentional learning instructional set. Finally, the results suggest that the Velten technique not only induced variation in mood but also may have induced a semantic processing strategy in our depressed and elated subjects.     

The maximization of overall reinforcement rate on concurrent chains

We model behavioral allocation on concurrent chains in which the initial links are independent variable-interval schedules. We also quantify the relationship between behavior during the initial links and the probability of entering a terminal link. The behavior that maximizes overall reinforcement rate is then considered and compared with published experimental data. Although all the trends in the data are predicted by rate maximization, there are considerable deviations from the predictions of rate maximization when reward magnitudes are unequal. We argue from our results that optimal allocation on concurrent chains, and prey choice as used in the theory of optimal diets, are distinct concepts. We show that the maximization of overall rate can lead to apparent violations of stochastic transitivity.     

Evaluation of a sound-generator chip: The AY 3-8910

Despite the continuing decrease in computer prices, psychoacoustic research is still expensive because of the high cost of sound-generation equipment and software. A single-chip sound generator was evaluated as an inexpensive tone/noise generator, amplitude attenuator, envelope modulator, and sound mixer. Although the chip has some limitations, it offers important advantages for pilot research and laboratory demonstrations.