Questions without Words: A Comparison Between Decision Making Under Risk and Movement Planning Under Risk

This chapter describes speeded movement tasks that are formally equivalent to decision making under risk. In these tasks, subjects attempt to touch reward regions on a touch screen and avoid nearby penalty regions, much as a golfer aims to reach the green while avoiding nearby sand traps. The subject is required to complete the movement within a short time and, like the golfer, cannot completely control the outcome of the planned action. The chapter conjectures that the key difference between the tasks and ordinary decision making under risk is the source of uncertainty, implicit or explicit. In the movement tasks, the probability of each possible outcome is implicit in the subject's own motor uncertainty. In classical decision making, probabilities of outcomes are chosen by the experimenter and explicitly communicated to the subject. An experimental study shows that subjects' optimal performance is disrupted when they are confronted with explicit uncertainty about rewards and penalties.