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.