Motivational artifact in standard food-deprivation schedules.

Abstract

5 albino rats (adjusted percentage: AP) held at 80% of normal body weight of 25 Ss maintained on ad-lib, food and water (criterion) were compared with 5 Ss maintained at 80% of their individual predeprivation weight (fixed percentage: FP) and 5 Ss fed for 30 min. every 24 hr. (fixed interval: FI). Predictions based on an assumed artifact due to failure to account for normal body growth under FP and FI were confirmed. Lever-press rates under a VI-2-min. reinforcement schedule gradually increased under FP and FI as body weight (percentage of criterion Ss) decreased, whereas AP Ss maintained constant-response rates. Interchanging AP and FP deprivation schedules resulted in response rates consistent with weight levels assumed under new schedules.

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

“…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.…”

“…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 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).…”

“…One purpose of the present study (Davenport & 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.…”

“…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).…”