Different ERP peaks associated with different aspects fo face processing. n170 is relatively specialised for faces. p250 is for famous and familiar faces. ERP categorised by N and P which is positive and negative. a markedly reduced p300 is seen within dementia'alzheimer's patients. An ERP is an electrical signature of all different cognitive components that contribute to processing of that stimulus. Systematically varying aspects of a stimulus (e.g. any face vs. famous face) may lead to variations in aspects of ERP waveform. This can tell us about the timing and independence of cognitive processes