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CHAPTER 2 38 METHOD Participants Participants were 64 student volunteers ( M age = 22.63, SD = 5.12, 41 women, 23 men). They gave written informed consent and received money or course credit for their cooperation. The study was approved by the Ethics Review Board of the Faculty of Social and Behavioural Sciences of Utrecht University. Participants were randomly allocated to the Full avoidance or Control condition. Apparatus, stimuli, and measures State-trait anxiety inventory (STAI) The STAI (Spielberger, Gorusch, & Lushene, 1970) was included to measure state and trait anxiety, because they may affect fear learning (Grillon et al., 2006; Lissek et al., 2005). Each scale contained 20 items, rated on a scale from 1 ( not at all ) to 4 ( severely ). In this study, Cronbach’s α = .87 and .86 for state and trait anxiety, respectively. Experimental task The experimental task was programmed in Python (Python Software Foundation) using the PyGaze toolbox (Dalmaijer, Mathôt & van der Stigchel, 2014) and presented on a 21 inch ViewSonic P227f CRT monitor (1024 x 768 px, 100 Hz) at a distance of 67 cm from the participant. The US was 1 s of 100 dB white noise presented through headphones (cf. Leer & Engelhard, 2015) that were connected to the computer with a sound amplifier. CS were a black (0.24 cd/m 2 ) circle, square, and triangle presented on a light grey (6.41 dc/m 2 ) background. CS were equiluminant and of the same surface area. Threat expectancy Immediately after each CS presentation, but before (possible) presentation of the aversive loud noise (Unconditional Stimulus; US), participants rated to what extent they expected the noise to follow by using a 0 ( certain no noise ) to 100 ( certain noise ) visual analogue scale (VAS) shown on the computer screen.