ABSTRACT 

When facing a new decision task, decision makers compare the attributes of the feasible options, and can also exhibit sensitivity to the attributes of the surrounding tasks (other tasks in the same experimental session). Previous research highlights two contradictory effects of the surrounding tasks: A contrast effect that implies an increase in risk-taking with a decrease in the attractiveness of the risky options in the surrounding tasks, and an assimilation effect that implies the opposite bias. We present two preregistered web experiments (with a total of 960 participants) that clarify the relative importance of these contradictory effects. The target tasks, in both experiments, involved a choice between the status quo and a fair gamble. Study 1 considered the impact of surrounding tasks that differ from the target task on a single dimension: The probability of gain. The results reveal a strong contrast effect: Decreasing the attractiveness of the risky alternative in the surrounding tasks increased the choice rate of the fair gamble from 53.2% to 79.7%. Study 2 considered the impact of surrounding tasks that differ from the target task in multiple dimensions. The results reveal a strong assimilation effect: Decreasing the attractiveness of the risky alternatives in the surrounding task decreased the choice rate of the fair gamble from 74.7% to 36.5%. These results suggest that the isolated within-task computations assumed by leading descriptive models ignore an important part of the underlying processes.