The purpose of this chapter is to review and synthesize available data regarding the sensorimotor development of infants with Down syndrome. The term sensorimotor development refers to qualitative changes in the psychological functioning of infants occurring during the period from birth to the beginnings of symbolic and representational thought. Qualitative changes in psychological functioning reflect the infant's capacity to acquire, store, and use information about the social and nonsocial world. The study of the sensorimotor capabilities of infants has its roots in Baldwin's (1895, 1897) psychobiological model of child development; reached the forefront of psychology with Piaget's (1936/1952, 1937/1954, 1945/1951) publication of his trilogy on infant intelligence; and has more recently been the focus of attention, most notably reflected in the work of McCall (1979) and Uzgiris (1983).

The notions of sequence, stage, and structure are central to the study of psychological (cognitive) functioning in general (Flavell, 1982a, 1982b) and sensorimotor development in particular (Uzgiris, 1987). The term sequence refers to the constant and invariant order of acquisition of progressively more complex cognitive competencies. The term stage refers to the distinct forms of behavior that are manifested at different ages or periods of development. The term structure refers to the manner in which different manifestations of behavior bear some developmental (stagelike) relationship to one another, and share some sort of common mediator or denominator.

The sensorimotor period is generally considered to consist of six progressively more complex types of psychological sets of competencies (Piaget, 1952). Each level in this sequence is defined by classes of behavior that exemplify distinct stages of development. Piaget (1952) describes these stages in terms of the various types of adaptations the infant is capable of making in response to different environmental demands.