Document Type



Three adult humans were presented with choices between fixed and variable (probabilistic) numbers of points exchangeable for money. The mean number of points per trial was held constant across fixed and variable outcomes while the form of the distribution of outcomes on the variable option was manipulated. Across conditions, choice was assessed across bivalued, rectangular, reverse exponential, and approximately normal probability distributions. To more closely approximate procedures used with nonhumans, contingencies were experienced directly across repeated trials under steady-state conditions, and potential verbal influences were minimized. Subjects strongly preferred the fixed option across most conditions regardless of distribution type. The results replicate and extend those obtained with humans' choices involving verbal/hypothetical outcomes and with nonhumans' choices involving food reinforcers, and they illustrate a potentially useful procedure for cross-species comparisons in risky choice.