An aspect of adaptation proposed by French psychologist Jean Piaget.
In the cognitive development theory of Jean Piaget, assimilation is one of two complementary activities involved in adaptation, the process of learning from and adjusting to one's environment. Assimilation consists of taking in new information and incorporating it into existing ways of thinking about the world. Conversely, accommodation is the process of changing one's existing ideas to adapt to new information. When an infant first learns to drink milk from a cup, for example, she tries to assimilate the new experience (the cup) into her existing way of ingesting milk (sucking). When she finds that this doesn't work, she then changes her way of drinking milk by accommodating her actions to the cup. The dual process of accommodation and assimilation leads to the formation and alteration of schemas, generalizations about the world which are formed from past experience and used to guide a person through new experiences. According to Piaget, cognitive development involves the constant search for a balance between assimilation and accommodation, which he referred to as equilibration.
In the context of personality, the term "assimilation" has been used by Gordon Allport (1897-1967) to describe the tendency to fit information into one's own attitudes or expectations. In the study of attitudes and attitude change, it means adopting the attitudes of people with whom we identify strongly.
Allport, G. Pattern and Growth in Personality. New York: Holt, Rinehart, and Winston, 1961.
Piaget, Jean, and Bärbel Inhelder. The Psychology of the Child. New York: Basic Books, 1969.