Have you really seen this illusory face before? Illusory faces bias recognition memory reports.

Visual memory is known to be influenced by objective image properties, including image size and contrast, as well as visual category. However, the influence of illusory perceptual experience on memory remains less understood. Here we investigated whether face pareidolia, a robust illusory phenomenon where certain stimuli elicit a face-like percept despite not being real faces, influences memory. While we assumed illusory faces would be remembered better than matched control images since they are surprising, interesting, draw more attention and may be associated with longer observation times, old-new recognition memory sensitivity was not consistently influenced by the face illusion. Surprisingly, decision criterion was more liberal for illusory faces than for other categories, and this effect scaled with illusory strength such that participants were more likely to report having seen illusory faces for stronger illusory face percepts. In a two-alternative-forced-choice recognition memory paradigm that minimizes criterion influence, we found that the tendency to report having seen illusory faces is present even for unseen images. Further analyses, involving confidence ratings indicated our findings probably reflect a heightened sense of familiarity for illusory faces and not genuine false memory. Our results suggest that during retrieval, illusory faces influence decisions independently of the actual memory trace.