Facial responses
HEAT
The face of the participants was videotaped throughout the phasic heat stimulation procedures. The camera was located approximately 1.5 m from the participant. To mark the plateau phase of the stimuli, a LED visible to the camera, but not to the participant, was lit concurrently with the 5 s-thermal stimulation, starting when the target temperature was reached. During stimulation, participants were instructed not to talk and to look at a cross on the wall behind the camera to ensure that the face would always be recorded in an upright and frontal view. Facial expressions were coded from the video recordings using the Facial Action Coding System (FACS; Ekman and Friesen For the purpose of necessary data reduction, we fused AU-frequency and AU-intensity values of each Action Unit by computing the product term (frequency × intensity) and also combined similar facial responses as has been done in preceding studies (Kunz et al. 