Magnitudes of score differences produced within sessions in a cooperative exchange procedure.

Interest centered on maximal score differences produced within sessions during two-party exchange. Subjects chose between earning money independently or through potentially higher-paying exchange. In the exchange option, only one person could produce points for the other on a trial. Because each exchange response ("give") required the giver to forego earning points independently, the larger the score difference produced (i.e., the further ahead in earnings the other person was put), the greater the reduction in the giver's earnings if the other person did not reciprocate. Results showed that scores were usually equal at the end of each session, and that subjects maintained close equality of scores throughout each session. When a response-cost contingency that punished the alternation of giving was introduced, however, large within-session score differences developed. These large differences continued to be produced after the response-cost contingency was removed. Finally, when subjects were told that the session could end at any moment, score differences were sharply reduced, indicating that production of score differences remained under the control of discriminative stimuli associated with the likelihood of reciprocation. The study suggests that with appropriate procedures, an experimental analysis of behavioral phenomena associated with the concept of "trust" may be possible.