The term identity means the mental image someone has of themself as well as some kind of similarity with others in some particular way. Gender identity, specifically, refers to the experiences someone has that are similar to a person of a particular gender. This gender identity affects how a person views themself as well as how they interact with others. Developmental psychologists have found that the development of an identity begins in early adolescence. Learning about what it means to be a particular gender also starts at an early age. During adolescence, children begin to internalize the gender roles in their surroundings and "gender intensification" occurs. Gender intensification means that the child feels more pressure to conform to socially sanctioned gender norms, resulting in deeper gender role differentiation for boys and girls. Biological, can affect gender identity development as well. Research done with animals has shown that pre-natal sex hormones affect the sexual differentiation of the brain. 