Visual Perception of the Facial Width-to-Height Ratio : Possible Influences of Angry Facial Expressions as Revealed by Event-Related Brain Potentials

The facial width-to-height ratio (fWHR) is a measure of the cheekbone width divided by the height of the face from the upper lip to the brows. The metric is hypothesised to have evolved as an intra-sexual competition mechanism in males, where large fWHRs are thought to signal both threat and aggression. The fWHR is suggested to subtly resemble angry facial expressions, which, in turn, also signal threat. The late positive potential (LPP) and the vertex positive potential (VPP) are two event-related potentials (ERPs) especially sensitive to emotional content. Studies have also found that viewing angry compared to neutral facial expressions elicit a stronger response on the LPP. However, no study has tested how responses to the fWHR and angry facial expressions elicit changes in the LPP or VPP. In this study, participants firstly rated how threatening faces were with either low or high fWHRs with neutral or angry facial expressions. Secondly, EEG-activity was recorded during a picture-viewing task of the same faces. In the first task, participants rated the faces with angry facial expressions as more threatening compared to all other faces, regardless of fWHR, although the high fWHRs were rated as more threatening than the low fWHRs. In the second task, LPP and VPP mean amplitudes were significantly higher for the angry, high fWHR face compared to all other faces tested. This suggests that an additive effect of both angry facial expressions and high fWHRs together creates the highest threat level in both subjective ratings as well as in ERP mean amplitudes. Further ERP research is needed on the relationship between fWHRs and anger to establish how the two features work both separately and together