Biased belief in the Bayesian brain: A deeper look at the evidence

•Bayesian models of delusion assume healthy belief formation approximates Bayes.•A recent critique of such models argues that healthy belief formation is non-Bayesian.•We provide a deeper examination of the empirical evidence underlying this critique.•We argue this evidence fails to reveal convincing violations of Bayesian inference.•This evidence does not therefore undermine assumptions of Bayesian models of delusion. A recent critique of hierarchical Bayesian models of delusion argues that, contrary to a key assumption of these models, belief formation in the healthy (i.e., neurotypical) mind is manifestly non-Bayesian. Here we provide a deeper examination of the empirical evidence underlying this critique. We argue that this evidence does not convincingly refute the assumption that belief formation in the neurotypical mind approximates Bayesian inference. Our argument rests on two key points. First, evidence that purports to reveal the most damning violation of Bayesian updating in human belief formation is counterweighted by substantial evidence that indicates such violations are the rare exception—not a common occurrence. Second, the remaining evidence does not demonstrate convincing violations of Bayesian inference in human belief updating; primarily because this evidence derives from study designs that produce results that are not obviously inconsistent with Bayesian principles.