Recent studies have shown that people’s concepts can change due to changes in the prevalence of the relevant information in the environment (Levari, 2018), which is called the Prevalence-Induced Concept Change (PICC). According to PICC, decreasing the prevalence of target stimuli (e.g., blue dots) expands the relevant concept. It makes people judge ambiguous stimuli as the target ones (not quite blue dots as blue). The exact cognitive mechanisms underlying PICC remain unknown. We believe that a metacognitive perspective can reveal new insights about them. For example, confidence judgements can reflect the stability and preciseness of the concepts that drive responses, therefore we can expect PICC to be associated with specific dynamics of confidence judgements. If concepts change, the confidence ratings in judgements driven by new concepts should not be different from the previous judgements driven by the old concepts. Considering that new concepts are skewed towards more ambiguous stimuli they should yield a larger amount of erroneous responses. Hence, the confidence judgements driven by new concepts should be less discriminative between correct and incorrect responses (a decrease in meta d’). We will test these hypotheses by adding metacognitive measurements to the standard PICC procedure. We will compare confidence ratings for the same stimuli that yield different responses during the first and the last 200 trials. Additionally, we will compare meta d’ for the first and the last 200 trials. We will define correct responses as the responses that the majority of people gave in the previous experiments on PICC.