Ratings
During the experiment, we obtained participants’ valence and arousal ratings of the stimuli, using the Self-Assessment Manikin scale (SAM; Bradley and Lang, 1994). Both valence and arousal scales range from 1 “very pleasant” (valence) or “very calm” (arousal) to 9 “very unpleasant” (valence) or “very arousing” (arousal). Furthermore, we measured US-expectancy, and after the generalization test, we employed a visual discrimination task of the stimuli. Participants used the arrow keys in the keyboard to indicate their affective responses and then pressed “enter”. US-expectancy was measured with the question “How likely is this face to be followed by a scream?” presented along with each face. Participants could give an answer ranging from 0 - 100 by dragging a red bar to the most appropriate point in the scale with their cursor. Finally, we measured participants’ ability to discriminate the different stimuli to further explore whether the responses in the generalization phase were due to inability to perceptually differentiate between the different stimuli (Resnik et al., 2011; Struyf et al., 2017). Discrimination was assessed in five trials, by comparing each face with the CS+. In each trial two stimuli (CS+ and one of the other pictures) were presented one by one (no interstimulus interval) for 1 s each in a random order. After each presentation participants answered whether the two pictures showed the same face by pressing either “y” for yes or “n” for no using the keyboard. All ratings’ questions were presented for an indefinite amount of time until a response was given.