The subjective feeling of a gap between conceptual and perceptual fluency is interpreted as a metacognitive signal of pastness

The present study aimed to address the following question: does the discrepancy between an expected word and its readability enhances or impair its memorability? We used an adaptation of the sentence stem paradigm (Whittlesea in J Exp Psycol 19:1235–1253, 1993) and manipulated the perceptual clarity of the words by introducing some Gaussian noise (Reber in Psycol Sci 9:45–48, 1998). The target words were semantically predictable or otherwise (conceptual fluency) or were easy or difficult to read (perceptual fluency). The first experiment was conducted to ensure that the two manipulated factors had an impact on the readability of the words. In particular, results showed that when the words were written against a noisy background their predictability enhanced the judgement of readability. The second experiment aimed to test the hypothesis that recognition would be influenced by the discrepancy between conceptual and perceptual fluency. The results showed that with a noisy background, the predictability of the target words had an impact on recognition judgement; with a clear background, the effect on the recognition judgement was caused by the non-predictability of the target words. Conversely, confidence in judgement increased when the two factors went in the same direction, that is, predictability with clarity and non-predictability with low clarity. The results showed that (a) depending on the task, the effects of conceptual and perceptual fluency did not go in the same direction; (b) the kinds of fluency (conceptual and perceptual) were not independent; and (c) recognition judgements were affected by the gap between conceptual and perceptual fluency.