Through direct observation of infants and mothers in an "experimental" nursery, Mahler and her associates have accumulated data which when analyzed point to distinct phases (stages) during the long process of the development of the concepts of self and object. These phases, autism, symbiosis, and separation-individuation (itself subdivided into four subphases, differentiation, practicing, rapprochement, and consolidation of individuation) correspond well with the stages described by Piaget as constituting the period of cognitive growth described as sensorimotor intelligence. The intercorrelation of the phasic development along these two separate lines (objectal-affective and cognitive), expectable as it may be, is of considerable interest as it underlines the intrinsic strength of the psychoanalytic concept of the object. Furthermore, this intercorrelation enhances and enlarges our understanding of the process of consolidation of self and object during the first years of life.