Do monkeys choose to choose?

Abstract

Both empirical and anecdotal evidence supports the idea that choice is preferred by humans. Previous research has demonstrated that this preference extends to nonhuman animals, but it remains largely unknown whether animals will actively seek out or prefer opportunities to choose. Here we explored the issue of whether capuchin and rhesus monkeys choose to choose. We used a modified version of the SELECT task-a computer program in which monkeys can choose the order of completion of various psychomotor and cognitive tasks. In the present experiments, each trial began with a choice between two icons, one of which allowed the monkey to select the order of task completion, and the other of which led to the assignment of a task order by the computer. In either case, subjects still had to complete the same number of tasks and the same number of task trials. The tasks were relatively easy, and the monkeys responded correctly on most trials. Thus, global reinforcement rates were approximately equated across conditions. The only difference was whether the monkey chose the task order or it was assigned, thus isolating the act of choosing. Given sufficient experience with the task icons, all monkeys showed a significant preference for choice when the alternative was a randomly assigned order of tasks. To a lesser extent, some of the monkeys maintained a preference for choice over a preferred, but computer-assigned, task order that was yoked to their own previous choice selection. The results indicated that monkeys prefer to choose when all other aspects of the task are equated.

Figure 1

An example test block. This illustration shows the sequence of responses involved in a block in which a monkey moves the cursor (small red dot) into contact with the Free Choice icon (black and red icon - panel a), and then chooses to contact the four SELECT icons in the following order: CHASE (green and black icon - panel b; CHASE task itself; panel c), LS (pink and black icon - panel d; LS task itself – panel e), DMTS (yellow and black icon - panel f; DMTS task – panel g), and MTS (blue and black icon - panel h; MTS task – panel i).

Figure 2

Capuchin monkey performance across 40-block intervals for the 1^st, 2^nd and 3^rd sets of Free Choice and Random icons (±SE).

Figure 3

Rhesus monkey performance across 40-block intervals for the 1^st, 2^nd and 3^rd sets of Free Choice and Random icons (±SE).