EXPRESS: Familiarity with non-famous faces increases 'person misidentification'.

People sometimes mistakenly identify an unknown person they encounter as a known person. Previous studies have elucidated this phenomenon and revealed that it is a common experience. However, no experimental study has identified factors associated with its occurrence. We termed this relatively under-examined phenomenon as 'person misidentification' and examined its factors. Specifically, we focused on (1) establishing experimental procedures to detect person misidentification in a laboratory context, and (2) investigating the mechanism by which visual familiarity with the encountered unknown faces contributes to person misidentification. The results indicated that the developed procedure measured 247 misidentifications in 72 of 106 participants in all experiments. Although the effect of familiarity on person misidentification was not observed in Experiment 1, this effect was detected in Experiment 2, where the manipulation of familiarity was enhanced and confirmed. Concretely, unknown faces with familiarity enhanced by subliminal exposure were more frequently misidentified as another known person. This indicates that familiarity with an encountered face contributes to and induces person misidentification. In addition, the results demonstrated that similarities, especially in terms of hairstyle, between the encountered face and the misidentified known person might be related to its occurrence. These results have rich implications and expand the literature on face processing.