Abstract
There is accumulating evidence that humans distort information about probability when making visual, motor, and economic decisions under risk. When probability was stated explicitly (decision from description), subjects typically overweight small probabilities but underweight moderate to large probabilities. In contrast, when information about probability distributions over monetary outcomes was acquired through experience (decision from experience), people tended to exhibit the opposite distortion pattern. However, it is not clear to what extent such contrast was due to experience-dependent knowledge of probability per se because probabilities were never learned independently of monetary outcomes in those tasks. In this study we intended to resolve this issue. There were 2 sessions in the experiment. In Session 1, subjects repeatedly sampled from 4 decks of cards each having a unique probability distribution over two possible events that did not carry monetary consequences. After obtaining the sampled result, on each trial, subjects were asked to provide probability estimates. In Session 2, we associated events with monetary rewards in all cards. On each trial, the subjects were presented with 2 decks of cards and asked to choose the one s/he preferred. To prevent any further learning about probability, no feedback on winning was provided during the course of the session. The subjects were instructed that two of the chosen options would be selected at random after the session was completed and executed to determine his/her payoffs. Four subjects participated in the experiment. Subjects showed accurate estimates of probabilities after Session 1. To our surprise, all subjects exhibited a pattern of probability distortion consistent with previous results in decision from description, but not decision from experience. This suggests that when probabilistic knowledge acquired through experience was independent of monetary outcomes, subsequent distortion pattern follows that typically found in decision from description.
Meeting abstract presented at VSS 2012