Humans exhibit substantial biases in their decision making even in simple two-choice tasks, but the origin of these biases remains unclear. I hypothesized that one source of bias could be individual differences in sensory encoding. Specifically, if one stimulus category gives rise to an internal-evidence distribution with higher variability, then responses should optimally be biased against that stimulus category. Therefore, response bias may reflect a previously unappreciated subject-to-subject difference in the variance of the internal-evidence distributions. I tested this possibility by analyzing data from three different two-choice tasks (ns = 443, 443, and 498). For all three tasks, response bias moved in the direction of the optimal criterion determined by each subject’s idiosyncratic internal-evidence variability. These results demonstrate that seemingly random variations in response bias can be driven by individual differences in sensory encoding and are thus partly explained by normative strategies.

即使在简单的二选一任务中，人类的决策也会表现出很大的偏见，但这些偏见的根源仍不清楚。我假设偏差的来源之一可能是感觉编码的个体差异。具体来说，如果一种刺激类别产生具有较高变异性的内部证据分布，那么反应最好应该偏向于该刺激类别。因此，反应偏差可能反映了先前未意识到的内部证据分布方差中的受试者之间的差异。我通过分析来自三个不同的二选任务的数据（ n s = 443、443 和 498）来测试这种可能性。对于所有三项任务，反应偏差都朝着由每个受试者特殊的内部证据变异性确定的最佳标准的方向移动。这些结果表明，看似随机的反应偏差变化可能是由感觉编码的个体差异驱动的，因此可以部分地用规范策略来解释。