Effects of number of alternatives on choice in humans.

The present study examined human choice between a task including a single alternative (i.e. a single-alternative task), and a task including multiple alternatives (i.e. a multi-alternative task). The subjects were divided into three groups and were exposed to three conditions. The multi-alternative task included two alternatives in two groups and included three alternatives in one group. An alternative in the single-alternative task was identical to one in the multi-alternative task. Amount of reinforcement for alternatives specific to the multi-alternative tasks was manipulated under three conditions in each group. When the amount of reinforcement was equal to or larger than that in the alternative common to both tasks, the subjects preferred the multi-alternative task over the single-alternative task. When amount of reinforcement was smaller, there was no difference in preference between the multi-alternative and the single-alternative tasks. In addition, the degree of preference for the multi-alternative task depended on the number of alternatives that produced larger reinforcers.