DISCOUNTING OF DELAYED FOOD REWARDS IN PIGEONS AND RATS: IS THERE A MAGNITUDE EFFECT?

Temporal discounting refers to the decrease in the present, subjective value of a reward as the time to its receipt increases. Results from humans have shown that a hyperbola‐like function describes the form of the discounting function when choices involve hypothetical monetary rewards. In addition,...

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Bibliographic Details
Published in:Journal of the experimental analysis of behavior 2004-01, Vol.81 (1), p.39-50
Main Authors: Green, Leonard, Myerson, Joel, Holt, Daniel D., Slevin, John R., Estle, Sara J.
Format: Article
Language:English
Subjects:
adjusting-amount
Animal Behavior
Animals
Behavior, Animal - physiology
Behavioral Science Research
Birds
choice
Choice Behavior
Columbidae
delay
Delay of Gratification
discounting
Female
Food
key peck
lever press
magnitude effect
Mathematical Models
pigeons
Rats
Reinforcement
Reward
Rewards
Rodents
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Summary:Temporal discounting refers to the decrease in the present, subjective value of a reward as the time to its receipt increases. Results from humans have shown that a hyperbola‐like function describes the form of the discounting function when choices involve hypothetical monetary rewards. In addition, magnitude effects have been reported in which smaller reward amounts are discounted more steeply than larger amounts. The present research examines the cross‐species generality of these findings using real rewards, namely food pellets, with both pigeons and rats. As with humans, an adjusting amount procedure was used to estimate the amount of immediate reward judged equal in value to a delayed reward. Different amounts of delayed food rewards (ranging from 5 to 32 pellets in pigeons and from 5 to 20 pellets in rats) were studied at delays varying from 1 s to 32 s. A simple hyperbola, similar to the hyperbola‐like mathematical function that describes the discounting of hypothetical monetary rewards in humans, described the discounting of food rewards in both pigeons and rats. These results extend the generality of the mathematical model of discounting. Rates of discounting delayed food rewards were higher for pigeons than for rats. Unlike humans, however, neither pigeons nor rats showed a reliable magnitude effect: Rate of discounting did not vary systematically as a function of the amount of the delayed reward.
ISSN:0022-5002
1938-3711
DOI:10.1901/jeab.2004.81-39