Implicitly learned bias impacts decision-making but not metacognition

People can implicitly learn biases that affect decisions. It is unclear if implicit and explicit learning of priors differentially influenced performance. Participants judged the orientation of moving dot patterns with stimuli occurring more frequently in one of the orientations depending on the color. Participants were or were not told about the base-rate differences. The explicitly informed group showed a greater application of the prior, although participants who were not aware of the two priors also showed a response bias. For participants who learned the priors implicitly there was only an effect of the prior when no diagnostic sensory information was available. Those who were instructed of the priors were more confident for prior-consistent stimuli while this was not seen in participants who merely experienced the priors.These results suggest that base-rate priors can be learned implicitly and can bias perceptual decisions, but this bias does not appear to affect confidence.