Handling time and choice in pigeons

According to optimal foraging theory, animals should prefer food items with the highest ratios of energy intake to handling time. When single items have negligible handling times, one large item should be preferred to a collection of small ones of equivalent total weight. However, when pigeons were offered such a choice on equal concurrent variable-interval schedules in a shuttlebox, they preferred the side offering many small items per reinforcement to that offering one or a few relatively large items. This preference was still evident on concurrent fixed-cumulative-duration schedules in which choosing the alternative with longer handling time substantially lowered the rate of food intake.     

Temporal proximity and reinforcement sensitivity in multiple schedules

Distributions of reinforcers between two components of multiple variable-interval schedules were varied over a number of conditions. Sensitivity to reinforcement, measured by the exponent of the power function relating ratios of responses in the two components to ratios of reinforcers obtained in the components, did not differ between conditions with 15-s or 60-s component durations. The failure to demonstrate the “short-component effect,” where sensitivity is high for short components, was consistent with reanalysis of previous data. With 60-s components, sensitivity to reinforcement decreased systematically with time since component alternation, and was higher in the first 15-s subinterval of the 60-s component than for the component whose total duration was 15 s. Varying component duration and sampling behavior at different times since component transition may not be equivalent ways of examining the effects of average temporal distance between components.     

Representation and retention of three-event sequences in pigeons

The present experiments studied a three-event delayed sequence-discrimination (DSD) task: one arrangement (order) of two stimuli (red and yellow overhead lights) taken three in succession (e.g., red, yellow, red) was the positive sequence and the remaining seven arrangements were the negative sequences for responding and reward during the subsequent test stimulus. In Experiment 1, the final stimulus (recency) and the order of stimuli in the positive sequence controlled acquisition of discrimination. In Experiment 2, increasing the duration of memory intervals between stimuli reduced the discriminability of those negative sequences identical to the positive sequence after the delay. Three-event DSD performance in Experiments 1 and 2 was similar to two-event DSD performance in comparable published experiments. Models developed to explain pigeon performance in two-event DSD were extended to the three-event task. Results from both two- and three-event versions of the DSD task falsified a noncumulative model and several cumulative integration models (i.e., adding, averging, and some multiplying models), but corroborated one cumulative, multiplying model.     

Induction of depressive affect after prolonged exposure to a mildly depressed individual

Scores on the Beck Depression Inventory (BDI) were periodically obtained from the roommates of college students who exhibited a persistent mild depression over a 3-month period. For comparative purposes, BDI scores were also obtained from roommates of individuals who were transiently depressed and from subjects with nondepressed roommates. In comparison with control subjects, the roommates of persistently depressed persons displayed a progressive increase in BDI score over the course of the study.     

Biomagnetism from the neuropsychiatric viewpoint--principles of recent developments in diagnostic procedure

The following survey is intended to demonstrate and discuss some principle problems of biomagnetism and the application in clinical fields. The development of special technical parameters especially by the SQUID method is initiating new possibilities of research and completing the neurobiologically determinated basis and conditions of neuropsychiatric disorders. The Magnetoencephalography (MEG) will be represent an important role of a new functional diagnostic method.