2.3.1. Materials
The stimuli for the EEG experiment were taken with permission from the face database of Xi’an Jiaotong University (http://www.aiar.xjtu.edu.cn/info/1015/1639.htm). The faces were selected based on an initial distinctiveness rating. A total of 35 female face pictures were rated by 21 female students of Zhejiang Normal University, different from the participants of the EEG experiment. The instructions for the distinctiveness ratings were: “Imagine that you are in a dining hall, and this person is in the crowd. How hard is it for you to notice the person?” Ratings were on a 5-point scale from (1) very easy to (5) very hard. In addition, the faces were rated on attractiveness (“In your opinion, how attractive is this face?”) on a 5-point scale from (1) very attractive to (5) very unattractive, and emotionality of facial expression (“In your opinion, what expression does this face show?”), also on a 5-point scale from (1) very negative to (5) very positive.
On the basis of these ratings, we selected a low-distinctive face as the target face; this was done to increase the difficulty of target face recognition. According to these ratings the target face was hard to notice, M = 3.90 (SD = 0.97), attractiveness was average,M = 2.33 (SD = 0.89), and emotionality was slightly positive, M = 3.14 (SD = 0.47).
From the other faces, we selected a set of 6 easy-to-notice (high-distinctive) faces and 4 hard-to-notice (low-distinctive, typical) faces. High- and low-distinctive faces differed in distinctiveness as intended, M = 2.80 (SD = 0.98) vs. M = 3.99 (SD = 0.85), facial expressions were rated as more positive in more distinctive than in more typical faces, M = 3.48 (SD= 0.69) vs. M = 2.63 (SD = 0.69), and attractiveness was rated lower in more distinctive than in more typical faces, M = 2.90 (SD = 0.95) vs. M = 2.13 (SD = 0.87). According to a permutation test, the differences in all three dimensions were significant, p = .005, .019, and .007, respectively. The confound of distinctiveness with attractiveness was to be expected because faces close to the average of faces are usually considered more attractive and it is also not surprising that more attractive faces are perceived as showing a more positive expression.