| Research Abstract |
The present study, using humans and nonhuman animals as subjects, deals with issues of self-control and social dilemma in terms of discounting of monetary or non-monetary (food) rewards. For the issue of self-control with humans, we used a new definition of self-control and arranged a procedure in which continuing to choose a smaller reward can maximize the total amount of a reward. To examine the correlation between the number of self-control choices and the rate of temporal discounting, participants were given two types of games in which they chose between "Saving" and "Wallet" options in each trial. In Game 1, a choice of the "Saving" option led to a pair of the poor options (660 yen vs. 500 yen) in the next trial, whereas a choice of the "Wallet" option led to a pair of the rich options (1,200 yen vs. 900 yen) in the next trial. In Game 2, immediate amounts of money subjectively equivalent to the delayed 1,500 yen were estimated under four delay conditions for each participant. As
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a result, some participants developed the choice of "Wallet" option (self-control group), but others didn't (non-self-control group) in Game 1. The number of choices of the "Wallet" option in Game 1 was negatively correlated with the discounting rate eastimated in Game 2 for the self-control group. These findings indicate that the discounting rate is a valid measure for the degree of self-control based on the new definition. For the issue of social dilemma with humans, discounting of a shared reward was examined in a Chicken game-like situation in which participants were given choices between a hypothetical 1,500 yen with sharing ("Saving") and an unshared money of variable amount ("Wallet") for successice 10 trials under each of five conditions of number of other people ranging from 1 to 24. The amount of unshared money was increased or decreased depending on choices in the previous trial. The amount of unshared money after 10th trial was defined as the subjectively equivalent amount money to the shared 1,500 yen. In addition, if a participant and other people chose the "Wallet" option, then they couldn't obtain any money (a "0" yen condition) or they had pay 1,500 yen (a "-1,500" yen condition). As a result, the discounting rate was lower in the "-1,500" yen condition than in Ihe "0" yen condition. The result revealed that the discounting rate was influenced by the loss of money arranged in the pay-off matrix of the game. Taken these results together, it is concluded that the discounting rate obatained in the present procedures may explain the degree of self-control and cooperation in social dilemma. Less
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