Faces are also important to us because they provide salient cues which help in discerning a persons speech (the perceptible movements in the face of the lips mouth and tongue correlate with the speech sounds a person makes; these visual speech cues are known to be important in us understanding what someone is saying especially in noisy environments).
So given the important social function played by faces, one might imagine that the brain might treat face stimuli differently to other types of everyday visual stimulus (e.g. a house, a tree, a car). Face processing seems to exhibit certain characteristics and attributes which are not found in the perception of other objects. One such attribute is the seeming orientation selectivity of faces. Faces are perceived much better when seen in the upright orientation; when faces are impaired our brains are much poorer at perceiving the information in faces. There are a number of phenomena which attest to this orientation selectivity. You can experience one example of a phenomenon which attests to this, the Thatcher illusion shown in Figure 1 below.
Because face processing seems to exhibit these certain unique characteristics some authors have argued that face processing is qualitatively different to processing of other sorts of object. They suggested that faces should be considered special as a class of stimulus in terms of the way they are dealt with by the visual system. They argue that our brains are essentially hardwired to process face and face-like stimuli in a different way from other classes of object because of their unique important to us.
The face specialness hypothesis has come in for a lot of empirical scrutiny and criticism from a number of directions. Many researchers have argued that this face specialness is incorrect. They argue that faces are not actually special, or at least not inherently special for the brain. They argue that the seeming specialness of faces is actually a consequence of extensive practice. We spend a large portion of our everyday lives looking at and recognising faces, far more than we do for any other category of object. This is unsurprising because faces contain so much useful social and communicative information. Because we spend more time viewing faces we can therefore be said to be more expert at perceiving faces than we are of any other type of stimulus. The expertise hypothesis argues that this seeming specialness of face is no more than a consequence of extensive practice. They would argue that if given sufficient practice, if we were we to spend as much of our lives viewing some other type of object as we did faces then this other type of object would also come to show the same specialness that faces do. So the question is which hypothesis is correct the face specialness hypothesis or the face expertise hypothesis?
