Effect on rats’ straight alley performance of shifts in body weight as a function of method of weight maintenance

Abstract

Rats were maintained at either 80% or 95% of their initial ad lib weights or their expected weights. Weights were then shifted from 80% to 95%. The effects of level of percentage body weight loss and the effects of shifting percentage body weight loss on straight alley performance were independent of method of weight maintenance.An increasinglY favored method of manipulating motivation in the rat is to vary percentage body weight loss. One question concerning the use of this measure is whether the loss should be measured from the animal's pre deprivation weight (fixed percentage, FP) or whether adjustment should be made for the growth which would be expected to occur during the deprivation period (adjusted percentage, AP). Direct comparisons of the effects of FP and AP methods on performance have been made in the activity wheel (Moskowiiz, 1959) and in the barpressing situation (Davenport & Goulet. 1964;Marwine & Collier, 1971). The main purpose of these studies was to determine which method of weight maintenance produces a more nearly constant motivational level. When an FP method has been employed, an increasing rate of performance over days, suggesting increasing motivation, has been obtained in the barpressing situation (Davenport & Goulet, 1964; ~1arwine & Collier, 1971), in the activity wheel (Moskowitz, 1959), and in the straight alley in some cases (Ehrenfreund, 1960, Figs. 2 and 3), but not in other cases (Ehrenfreund, 1960, Fig.1; Ehrenfreund, 1971). When an AP method has been employed, a decreasing rate of performance over days, suggesting decreasing motivation, has been obtained in the barpressing situation (Davenport & Goulet, 1964;Marwine & Collier, 1971), but not in the activity wheel (Moskowitz, 1959) or the straight alley (Traupmann, 1971). Thus, the question of which method produces a more nearly constant motivational level appears open, but this question was not of major concern here.One purpose of the present study Goulet, 1964, Marwine & Collier, 1971) have compared FP and AP methods at only one level of percentage body weight loss. The present study compared FP and AP methods at two levels of percentage body weight loss. The second purpose of the present study was to evaluate the effects of shifting percentage body weight loss under the two different techniques. It has been reported that animals shifted from a high to a low deprivation run faster in the straight allev than animals trained only under iow' deprivation (e.g., Zaretsky, 1966). It is possible that this effect may be influenced by method of weight maintenance. Specifically, if an FP method is employed, it is possible that in the second phase of such a study, when all groups are run under low percentage body weight loss, this low percentage body weight lass i5 actually a fairly high motivation al level, if motivation increases over days with the FP method. Thus, animals trained previously under high percentage body weight loss could be expected to run faster than animals previously trained under low, because the testing situat...

The interaction of deprivation and delay of reinforcement under a fixed-ratio schedule of responding

“…The rats were fed ad lib for 150 days, after which time six of the rats were allowed to continue ad lib and the other four rats were deprived to 80% of their weight. Deprived weights were adjusted according to the weight gain of the six rats that were fed ad lib throughout the experiment (Capaldi, 1972). …”