A Brain Imaging Study of Procedural Choice

We study the behavior of subjects facing choices between certain, risky, partially ambiguous, and ambiguous lotteries in an experimentally controlled environment. Our observations are the choice behavior, the response time, and the brain activations of the subjects. Choices were simple enough to insure consistent behavior with small amount of noise. The behavioral evidence supports the idea that subjects face the choice task as an estimation of the value of the two lotteries and that some measure of the difficulty of the choice provides an important explanatory variable (together with risk and ambiguity aversion) for the observed behavior. The Neuro-imaging data suggest that the estimation is of approximate nature, and involves mental faculties that are independent of language and shared by all mammals. The regions in the brain that are activated are not located in frontal structures, which are known to be involved in planning, but in parietal regions typically involved in approximate calculations. The time to decide is shorter for seemingly harder choices, a Þnding that suggests the need for new models of the allocation of effort in the choice process. Emotional factors seem to play a minor role in the choice.