Stereotypes
Stereotypes are schemas for classes or subtypes of people. The stereotype of an extrovert, the fan of a rival soccer team, or a young black man is a mini-theory about what particular traits or behaviors go with certain other traits or behaviors. Study of stereotype deserves focus because they are a kind of person schema that has far reaching consequences for impression formation.
Several decades of research on stereotypes tell us that, whether we like it or not, our initial impressions of others can be biased by our preexisting expectations. Everytime we perceive any object or event, we implicitly categorize it, comparing the incoming information with our memories of previous encounters with similar objects and events.
Stereotypes, like schemas usually, helps us to process information. This is because the instruction to form an impression induces them to search for relevant stereotypes that help them organize and recall material better.