Threatening Measures, at Face Value : Electrophysiology Indicating Confounds of the Facial Width-to-Height Ratio

Abstract: Previous studies support that the relative width of the upper face (facial width-to-height ratio; fWHR) has evolved to signal threat, but these studies rely greatly on subjective facial ratings and measurements prone to confounds. The present study objectively quantifies threat perception to the magnitude of the observers’ electrophysiological reaction, specifically the event-related potential (ERP) called the late positive potential (LPP), and investigate if brow height and jaw width could have confounded previous fWHR studies. Swedish and international students (N = 30, females = 11, Mage = 24 years, SDage = 2.9) were shown computer-generated neutral faces created with the underlying skeletal morphology varying in brow ridge height, cheekbone width and jaw width. Participants first rated how threatening each face was and then viewed 12 blocks of 64 faces while their electroencephalography (EEG) was recorded. The results supported that the LPP could be used to index threat perception and showed that only brow height significantly affected both facial ratings (p < .001, ɳp2 = .698) and magnitude of the LPP within the 400 to 800 ms latency (p = .02, d = .542). Hence, brow height, not facial width, could explain previous findings. The results contradict the hypothesis that fWHR is an evolved cue of threat and instead support the overgeneralisation hypothesis in that faces with similar features to anger will be perceived as more threatening.