Probability-reward preferences of rhesus monkeys

• Published in: The American journal of psychology Vol. 98; no. 1; p. 77
• Main Authors: Hill, C W, Riopelle, A J
• Format: Journal Article
• Language: English
• Published: United States 01.01.1985
• Subjects: Animals; Discrimination Learning; Female; Gambling - psychology; Humans; Macaca mulatta; Male; Probability; Reinforcement Schedule; Reward
• ISSN: 0002-9556
• DOI: 10.2307/1422768

The relative preferences of rhesus monkeys for reward probability versus amount were investigated with procedures which contrasted general experience with specific instructions, and evaluated the relationship between probability-amount combinations and preference strength. Four stimulus objects, each signifying a different combination of reward frequency and amount (100% with one unit; 50% with two units; 33% with three units; or 25% with four units), were presented in pairs, one pair per daily session, with trial schedules providing the same amount of reward within each set of 12 trials. In Phase A, 4 monkeys (Group 1) were tested on the six choice-pairs with no preliminary training. In Phase B, Group 1 was joined by an additional 4 monkeys (Group 2), and each of the tasks was preceded by a demonstration of the relevant stimuli, one at a time, together with their associated probabilities and amounts. Group 1 animals developed preferences during Phase A for the more frequently rewarded objects, which persisted into Phase B, whereas Group 2 animals showed no preferences. This result indicates that preliminary instructions concerning the reward combinations associated with stimulus objects can prevent the development of a preference for greater probability over greater amount of reward, but cannot extinguish it once it has been formed or reestablished within the context of a particular task.