differentiation /dif′əren′shē·ā″shən/ [L, differentia, difference] , 1. (in embryology) a process in development in which unspecialized cells or tissues are systemically modified and altered to achieve specific and characteristic physical forms, physiological functions, and chemical properties. Kinds include correlative differentiation, functional differentiation, invisible differentiation, self-differentiation. 2. progressive diversification leading to complexity. 3. acquisition of functions and forms different from those of the original. 4. distinguishing of one thing or disease from another, as in differential diagnosis. 5. (in psychology) mental autonomy or separation of intellect and emotions so that one is not dominated by reactive anxiety of a family or group emotional system. 6. the first subphase of the separation-individuation phase in Mahler’s system of preoedipal development. It generally occurs between 5 and 9 months of age, coinciding with the maturation of partial locomotor functioning and the beginning of the child’s viewing the mother as a separate being. −differentiate, v.
