The neurobiology of opinions : can judges and juries be impartial ? ∗

In this article we build on neuroscience evidence to model belief formation and study decision-making by judges and juries. We show that physiological constraints generate posterior beliefs with properties that are qualitatively different from traditional Bayesian theory. In particular, a decision-maker will tend to reinforce his prior beliefs and to hold posteriors influenced by his preferences. We study the implications of the theory for decisions rendered by judges and juries. We show that early cases in a judge’s career may affect his decisions later on, and that early evidence produced in a trial may matter more than late evidence. In the case of juries, we show that the well-known polarization effect is a direct consequences of physiological constraints. It is more likely to be observed when information is mixed, as behavioral evidence suggests, and when prior beliefs and preferences are initially more divergent across jurors.