Base rate neglect, an important bias in estimating probability of uncertain events, describes humans’ tendency to underweight base rate (prior) relative to individuating information (likelihood). However, the neural mechanisms that give rise to this bias remain elusive. In this study, subjects chose between uncertain prospects where estimating reward probability was essential. We found that when the variability of prior and likelihood information about reward probability were systematically manipulated, prior variability significantly affected the degree to which subjects underweight the base rate of reward probability. Activity in the orbitofrontal cortex, medial prefrontal cortex, and putamen represented the relative subjective weight that reflected such bias. Further, sensitivity to likelihood relative to prior variability in the putamen correlated with individuals’ overall tendency to underweight base rate. These findings suggest that in combining prior and likelihood, relative sensitivity to information variability and subjective-weight computations critically contribute to the individual heterogeneity in base rate neglect.

基本率忽略是估计不确定事件概率的重要偏差，它描述了人类相对于个性化信息（可能性）而言偏低基本率（先前）的趋势。但是，引起这种偏见的神经机制仍然难以捉摸。在这项研究中，受试者在不确定的前景之间进行选择，在这些前景中，估计奖励概率至关重要。我们发现，当系统地操纵关于奖励概率的先验和可能性信息的变异性时，先验变异性会显着影响受试者偏低奖励概率基本率的程度。眶额皮质，前额内侧皮质和壳壳中的活性代表反映这种偏见的相对主观权重。进一步，相对于壳核先前变异的可能性的敏感性与个体总体上体重过轻的趋势有关。这些发现表明，结合先验和可能性，对信息变异性和主观权重计算的相对敏感性对忽略基准利率的个体异质性至关重要。