Stimuli
The CS were two pictures of female faces with a neutral facial
expression from the NimStim Set of Facial Expressions (03F_NE_C,
10F_NE_C; Tottenham et al., 2009). The images were converted to gray
scale and luminance and brightness were kept constant. Four GSs were
morphed from the CS pictures in steps of 20% with a face-morphing
software shown in Figure 1 (Sqirlz Morph; Xiberpix, Solihull, UK). Each
picture was presented on a gray background (R: 133, G: 133, B:133)
flickering at 15 Hz. The US was a female scream combined with a white
noise of 90 dB which lasted for 1 s and was presented through four field
speakers.