Abstract
Facial expression recognition is affected by previously viewed faces. For example, faces with happy expressions impair the recognition of weakly happy expressions viewed subsequently. In this study, we focused on multiple faces leading to an ensemble average of their properties (Haberman & Whitney, 2007) and examined whether the average intensity of facial expressions affected the recognition of expressions subsequently presented. Four prime conditions (ensemble, single 20%, single 40%, and single 60%) were compared to the base, or no-prime, condition. As prime stimuli, two happy facial expressions from the 20% intensity group and two from the 60% intensity group were presented simultaneously in the ensemble condition; their average was 40%. One happy expression from the 20%, 40%, and 60% intensity groups was presented in the single 20%, 40%, and 60% conditions, respectively. The test stimuli were six intensities of happy facial expressions (from 10 to 60%, with increments of 10), which were morphed using 35 Japanese females. Prime stimuli were presented for one second, followed by the mask for one second; test stimuli were presented for 400ms, followed by the mask for 400ms. Participants were asked whether the test stimulus looked happy or not. The results showed that the points of subjective equalities of the ensemble, single 40%, and single 60% conditions were higher than that of the base condition: the prime presentation of four facial expressions made recognition of subsequent facial expressions difficult, and this effect was the same as that of a 40% single face. Additionally, the standard deviation of the psychometric function of the ensemble condition was not significantly different from those of the single prime conditions, suggesting that the participants did not look at one prime stimulus randomly in the ensemble condition but looked at the whole face set and extracted an ensemble average.