Determinants of reinforcer accumulation during an operant task.

Responses by rats on an earn lever made available food pellets that were delivered to a food cup by responses on a second, collect, lever. The rats could either collect and immediately consume or accumulate (defined as the percentage of multiple earn responses and as the number of pellets earned before a collect response) earned pellets. In Experiment 1, accumulation varied as a function of variations in the earn or collect response requirements and whether the earn and collect levers were proximal (31 cm) or distal (248 cm) to one another. Some accumulation occurred under all but one of the conditions, but generally was higher when the earn and collect levers were distal to one another, particularly when the earn response requirement was fixed-ratio (FR) 1. In Experiment 2, the contributions of responses and time to accumulation were assessed by comparing an FR 20 earn response requirement to a condition in which only a single earn response was required at the end of a time interval nominally yoked to the FR interval. When 248 cm separated the earn and collect levers, accumulation was always greater in the FR condition, and it was not systematically related to reinforcement rate. In Experiment 3, increasing the earn response requirement with a progressive-ratio schedule that reset only with a collect response increased the likelihood of accumulation when the collect and earn levers were 248 cm apart, even though such accumulation increased the next earn response requirement. Reinforcer accumulation is an understudied dimension of operant behavior that relates to the analysis of such phenomena as hoarding and self-control, in that they too involve accumulating versus immediately collecting or consuming reinforcers.

Effect of preoperative biofeedback/pelvic floor training on continence in men undergoing radical prostatectomy.

OBJECTIVES: To determine whether preoperative biofeedback training improves urinary continence overall or the rate of return of continence in men undergoing radical prostatectomy. METHODS: One hundred men scheduled to undergo radical prostatectomy were randomized to receive graded pelvic muscle exercise training with biofeedback 2 to 4 weeks before surgery or to a control group performing pelvic muscle exercises without biofeedback. The biofeedback group was instructed to continue exercises four times per day until surgery and to resume exercises when the urethral catheter was removed following surgery. The control group received written and brief verbal instructions in pelvic muscle exercises before surgery and again after catheter removal. Urinary continence was assessed by personal or phone interviews. RESULTS: Six months following surgery, the continence rates, as defined by the use of one pad or less per day, were 94% (44 of 47) and 96% (48 of 50) in the biofeedback and control groups, respectively (P = 0.596). Also, the rate of return as determined at time points 1, 2, 3, and 4 months after surgery was not significantly different between the two groups. CONCLUSIONS: Preoperative biofeedback training did not improve the outcome of pelvic muscle exercises on overall continence or the rate of return of urinary control in men undergoing radical prostatectomy.

Imported yellow fever in a United States citizen.

The last imported case of yellow fever seen in this country was in 1924. We report a case of yellow fever acquired by an American tourist who visited the jungles of Brazil along the Rio Negro and Amazon Rivers. The patient died 6 days after hospital admission and 10 days after his first symptoms appeared. Yellow fever virus was recovered from clinical specimens, and the isolate was genetically similar to the E genotype IIB of South American yellow fever viruses. This patient's illness represents a case of vaccine-preventable death since he failed to be immunized with a recommended preexposure yellow fever vaccine.

What is happening in psychology of learning courses?

Current practices in the undergraduate Psychology of Learning course were assessed through a survey in which a questionnaire probing the teaching of the course was sent to 238 4-year colleges and universities in the United States. Fifty-four percent of the questionnaires were returned. Learning courses were taught at all but 10 of the schools that responded. The course typically is one of several that can be selected to fulfill requirements for the major in psychology. The course orientation and content varied widely from cognitive to eclectic to behavioral, and laboratory requirements existed in less than half of the courses. The effects of these practices on behavior analysis are considered and several suggestions are made for teaching behavior analysis in the Learning course and elsewhere to undergraduates.

Comparative toxicology of tetrachlorobiphenyls in mink and rats. I. Changes in hepatic enzyme activity and smooth endoplasmic reticulum volume.

Mink have been shown previously to be extraordinarily sensitive to polychlorinated biphenyls (PCBs) and related classes of halogenated hydrocarbons. This study explored several aspects of the acute response of mink to two purified tetrachlorobiphenyl (TCB) congeners and compared their response with that of the rat, a less sensitive and more thoroughly studied species. Young female pastel mink and young female Sprague-Dawley rats received three daily intraperitoneal injections with equimolar doses of either 2,4,2',4'-TCB or 3,4,3',4'-TCB, and were sacrificed after 7 days. Two control groups were used for each species; one was allowed free access to food and the other was pair-fed to the 3,4,3',4'-TCB treatment group. Rats remained clinically normal, while mink treated with 3,4,3',4'-TCB developed severe anorexia, diarrhea, and melena. Both species had significant increases in hepatic cytochrome P-450 content and the characteristic shift in the spectral maxima from 450 to 448 nm in the 3,4,3',4'-TCB- but not in the 2,4,2',4'-TCB-treated animals. Rats but not mink had increased activities of several hepatic monooxygenases in response to both congeners while microsomal epoxide hydrolase was increased in rats after 2,4,2',4'-TCB and in mink after 3,4,3',4'-TCB. Significant increases in the relative volume of smooth endoplasmic reticulum within hepatocytes of 2,4,2',4'-TCB-treated rats but not mink were confirmed by ultrastructural morphometry. Accumulation of both congeners was greater in adipose tissue than in the liver of either species. In both species, concentrations in adipose tissue were much greater for 2,4,2',4'-TCB than for 3,4,3',4'-TCB. PCB toxicosis in mink, as in other species, appeared to be dependent on isomeric arrangement of chlorine substituents. However, unlike other species, the toxicosis was not associated with biochemical or morphological evidence of hepatic enzyme induction. Moreover, the target organ of 3,4,3',4'-TCB toxicosis in mink was the small intestinal mucosa.