Learning of a Discrimination by Satiated and Deprived Rats with Sucrose as Incentive

Abstract

Previous studies have shown that sucrose, when used as an incentive, provides motivation for the learning by rats of rather simple responses, such as, running to sucrose in a preference apparatus, a straight alley, a T-maze, and making a simple black-white discrimination.1 The present study used a more difficult discrimination, as judged by previous studies, involving high and low hurdles.2 In addition the design of this study makes possible a direct comparison of the rates of learning between food-motivated and sucrose-motivated rats, a contrast appearing in only one previous study,3 as well as throwing some light on the interaction of these motivations with each other and with food and sucrose rewards. Procedure. A 2 X 2 X 2 factorial design was employed. Four groups were maintained on four different schedules, as follows: (1) Group FDSD was deprived of both food and sucrose; (2) Group FDSs was deprived of food but satiated on sucrose; (3) Group FsSD was satiated on food but deprived of sucrose; and (4) Group FsSs was satiated on both food and sucrose. Half the rats in each of these groups ran for food (F) as reward and half for sucrose (S), thus making eight groups. The groups will be referred to by the capital letters designating their treatment, thus group FDSD-F is deprived of food (FD), deprived of sucrose (SD), and received food as reward (F). An apparatus requiring the discrimination between goal-boxes having a highhurdle and a low-hurdle was employed.4 It consisted of a starting box opening into a choice-alley which led in turn to the entrances of two goal-boxes placed side by side. Guillotine-type doors at the starting box and at the entrances to the goal-boxes prevented retracing. Within the high-hurdle goal-box were four equidistant 1-in. high, plywood hurdles, and in the low-hurdle goal-box were four equidistant ?-in. high hurdles. Thus after making a choice the rat had to run over the hurdles to get the reward. Each box had a countersunk food-well at the far end sufficiently deep so that the reward could not be seen until the S was directly over it. The apparatus was painted a flat gray except for the goal-boxes and hurdles which were black. The Ss were 40 naive, male albino rats between 45 and 60 days old at the beginning of the experiment. Eight groups were formed, each of five rats matched