When making discrimination decisions between two stimulus categories, subjective confidence judgments are more positively affected by evidence in support of a decision than negatively affected by evidence against it. Recent theoretical proposals suggest that this “positive evidence bias” may be due to observers adopting a detection-like strategy when rating their confidence—one that has functional benefits for metacognition in real-world settings where detectability and discriminability often go hand in hand. However, it is unknown whether, or how, this evidence-weighting asymmetry affects detection decisions about the presence or absence of a stimulus. In four experiments, we first successfully replicate a positive evidence bias in discrimination confidence. We then show that detection decisions and confidence ratings paradoxically suffer from an opposite “negative evidence bias” to negatively weigh evidence even when it is optimal to assign it a positive weight. We show that the two effects are uncorrelated and discuss our findings in relation to models that account for a positive evidence bias as emerging from a confidence-specific heuristic, and alternative models where decision and confidence are generated by the same, Bayes-rational process.

当在两个刺激类别之间做出区分决策时，主观置信度判断更容易受到支持决策的证据的积极影响，而不是受到反对决策的证据的负面影响。最近的理论建议表明，这种“积极证据偏差”可能是由于观察者在评估自己的信心时采用了类似检测的策略，这种策略对于现实世界中的元认知具有功能性好处，在现实世界中，可检测性和可辨别性往往是齐头并进的。然而，尚不清楚这种证据加权不对称是否或如何影响有关刺激存在或不存在的检测决策。在四个实验中，我们首先成功地复制了歧视信心中的积极证据偏差。然后，我们表明，检测决策和置信度自相矛盾地遭受相反的“负面证据偏见”，即使在分配正面权重是最佳的情况下，也会对证据进行负面权衡。我们证明这两种效应是不相关的，并讨论了我们的研究结果，这些模型解释了从特定置信度启发式中出现的积极证据偏差，以及决策和置信度由相同的贝叶斯理性过程生成的替代模型。