Motivational artifact in standard food-deprivation schedules.

Abstract

5 albino rats (adjusted percentage: AP) held at 80% of normal body weight of 2b Ss maintained on adlib 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.