What's in a face? The late positive potential reflects the level of facial affect expression

Morphed faces depicting varying degrees of affect expression can be used to investigate the processing of ambiguous and thus more ecologically valid facial stimuli. Event-related brain potentials (ERPs) were measured while participants viewed a series of faces ranging in 10% increments from prototypically happy to prototypically neutral to prototypically angry. Results revealed that the late positive potential (LPP) - an ERP reflecting later stages of stimulus processing - followed the degree of expression of facial affect such that faces depicting a greater amount of affect elicited larger LPPs as compared to faces depicting less affect. The enhanced LPP to faces depicting greater amounts of affect was also more sustained for angry compared to happy faces - in general, angry faces elicited larger LPPs. Overall, these results demonstrate the sensitivity of the LPP to more ecologically valid facial expressions and thus the visual system's finely tuned discriminability of important social signals.