Transcranial stimulation over right inferior frontal gyrus increases the weight given to private information during sequential decision-making.

Decision makers often follow other similarly situated people in making decisions, creating a sequential decision-making context. Although rational behavior is often to make the same choice as previous decision makers, which can result in an information cascade, people may assign inappropriately higher weight to their own private information and discount public information about predecessors' choices. Recent findings suggest that overweighting private information may be associated with increased activities in the inferior frontal gyrus (IFG). In the present study, we employed transcranial direct current stimulation (tDCS) and developed a computational model to examine the causal relationship between right IFG (rIFG) and overweighting private information. Specifically, we applied three types of tDCS over rIFG while participants were completing a sequential decision-making task. Our results showed that anodal stimulation significantly increased the weight given to private information and decreased the response time in making a decision when private information conflicted with public information, but cathodal stimulation did not have such impacts. Importantly, the effect of anodal stimulation was significant in some conditions when information conflict or task difficulty reached a threshold that might trigger cognitive control-related processes. Our findings revealed the important role of rIFG in trade-off between considering private and public information during sequential decision-making.

Normative and Descriptive Analyses of Simpson's Paradox in Decision Making.

Suppose that you are evaluating two delivery companies. Your investigation shows that Company B has a better on-time rate for small packages and also for large packages. Despite Company B's performance, however, Company A has a better overall on-time rate. This situation exemplifies Simpson's Paradox, in which the judged relationship between two variables (e.g., company and performance) differs depending on whether that relationship is viewed within subcategories of a third variable (e.g., package size) or in the aggregate. A normative analysis is presented arguing that the reasonableness of using the third variable depends upon the sample size as well as the separation between and variability within categories. To test subjects' abilities to behave appropriately in Simpson's Paradox situations, we examined responses to variations in these factors in five studies. Results showed that subjects had little or no sensitivity to differing stimulus set sizes. Also, subjects were sensitive to relationship strength and the variability within and between groups, and in nonnormative ways. Subjects' judgment behavior is related to a broader perspective concerning selection among multiple available levels of analysis based on a consideration of argument strength. Copyright 2000 Academic Press.