Happy faces are preferred regardless of familiarity—sad faces are preferred only when familiar.

Familiarity leads to preference (e.g., the mere exposure effect), yet it remains unknown whether it is objective familiarity, that is, repetitive exposure, or subjective familiarity that contributes to preference. In addition, it is unexplored whether and how different emotions influence familiarity-related preference. The authors investigated whether happy or sad faces are preferred or perceived as more familiar and whether this subjective familiarity judgment correlates with preference for different emotional faces. An emotional face--happy or sad--was paired with a neutral face, and participants rated the relative preference and familiarity of each of the paired faces. For preference judgment, happy faces were preferred and sad faces were less preferred, compared with neutral faces. For familiarity judgment, happy faces did not show any bias, but sad faces were perceived as less familiar than neutral faces. Item-by-item correlational analyses show preference for sad faces--but not happy faces--positively correlate with familiarity. These results suggest a direct link between positive emotion and preference, and argue at least partly against a common cause for familiarity and preference. Instead, facial expression of different emotional valence modulates the link between familiarity and preference.