[What factors of prosocial behavior evoke recipients’ gratitude and indebtedness? An experimental examination].

We examined two psychological processes of prosocial behavior: feeling gratitude and indebtedness. First, we asked if the value of the behavior for the receiver promotes gratitude; and second if the cost of the behavior for the giver promotes indebtedness. Gratitude and indebtedness were measured as behavioral indices of a quid pro quo (indirect reciprocity and direct reciprocity) to avoid social desirability effects in self-report measures. In Study 1, 119 undergraduates recalled a past experience in which they had been the recipients of prosocial behavior while emphasizing the value, cost, or situation (control) of the event. The level of gratitude was higher, and indirect reciprocity was observed more frequently, in the value condition than in the cost and control conditions. Indebtedness, however, did not differ across the conditions. In Study 2, 59 participants received a gift (the value and cost of which were manipulated) from an imaginary confederate. The value manipulation promoted indirect reciprocity, and both value and cost manipulations encouraged direct reciprocity. Implications for adaptive functions of gratitude in social selection processes are discussed.