Abstract
Emotional contents of faces would pose ambiguity when each facial feature varies in a subtle manner. Here we propose that such ambiguity may not solely arise from visual similarity in facial expressions but also from the way the expressions are interpreted in our daily life. In the present experiments, we asked participants to search for a target face with no facial expression (i.e., neutral) either (1) among a set of faces with smiles (i.e., pleasant) or (2) among faces with an angry frown (i.e., unpleasant). The face stimuli were either photographs taken from real faces or simple line drawings. The participants were asked to report target presence or absence as fast as possible. In the target-present trials, mean search response time was faster if distractors were all pleasant faces, whereas it was rather delayed if the distractors were all unpleasant faces. Further, the overall response times in the target-absent trials were slower than the target-present trials, and the pattern of the delay was more evident if the distractors were all unpleasant faces than all pleasant faces. The results indicate that the neutral target face among unpleasant faces is difficult to be searched after, whereas it is relatively easy among pleasant faces. The results also suggest that what determines emotional contents of faces is not only the visual similarity across facial expressions but also what the expressions do stand for in our daily life.