In most densely-packed urban cities, one will be able to observe a disturbing phenomenon: wealthy people marching past the homeless, day in and day out. Often, the residents of the street and the residents of the apartments recognize each other and even know each other's routines. And, yet, familiarity doesn't breed concern.
Psychologists Lasana Harris and Susan Fiske were able to detect a neurological process behind the ability to get used to seeing others suffer. Using functional MRIs, they exposed individuals to images of the homeless. These images tended to activate parts of the brain associated with disgust. This, they argue, supports the idea that "extreme out-groups may be perceived as less than human..." It is easy to overlook the suffering of the homeless, then, because we dehumanize them.
Originally posted at Sociological Images.