Whenever we perceive another person, the first things we notice are very general features like gender and age, according to the feature theory of face perception.
After having identified a person’s gender and age, we then focus on facial expressions in order to make inferences about his or her identity so that we are able to recognize the person.
When we recognize faces that we have seen before, the unique features of that person seems familiar to us. Some features may weight more than others in the recognizing process.
Some suggest that the eyebrows are extremely important (Sadr et al., 2003) since we use the eyebrows to identity the gender of the person. Normally, men have bigger eyebrows than women (click here to see the role of eyebrows in face recognition).
Burton and colleagues (1993) suggest that the eyes are at least as important when we identify gender. This is because men usually have a deeper set of eyes than women.
Gender is believed to be one of the best ways to discriminate individuals, and in fact, it may be quicker to identify gender than familiarity (Bruce et al., 1987). The shape and length of the nose is always gender-specific, and for this reason, the nose is also important in face recognition.
Some people lack the ability to recognize faces (see: prospagnosia), and this is often a consequence of a traumatic brain injury. This ability, however, is very important for our social lives.
We use face recognition to identity people, whether they are friends or family, so people with prospagnosia need to recognize people by the means of other sensory input, such as the voice of another person.