Normal development varies widely. The variation is partly accounted for by factors associated with IQ, sex, personality, intrafamilial/genetic characteristics and social influences, but much of the variance is poorly understood. This chapter does not aim to be a comprehensive survey of all aspects of normal development. It is intended as a background for a better understanding of the degree to which symptoms seen in abnormal states deviate qualitatively or quantitatively from the so-called norm. The reader wanting a more detailed description and fuller theoretical background of normal development is referred to specific textbooks on this topic (e.g. Illingworth, 1979; Lewis, 1982) or to comprehensive appraisals of the state-of-the-art as regards research findings (Rutter, 1980, 1984).

However, recent developments in social/cognitive psychology (e.g. Astington, Harris & Olson, 1988; Frith, 1989; Baron-Cohen, 1990; Duncan, 1986; Ozonoff, Pennington & Rogers, 1991), and in particular in the fields of ‘shared attention’, ‘theory of mind’, and ‘executive function’ have changed some of the conceptual framework for understanding normal social, communicative and cognitive development, and there are, as yet, no good comprehensive texts on normal development that adequately take these changes into account. Because of this dearth of good reviews, the current section will focus mostly on the recent expansion of knowledge in the fields of social interaction and communication.

Developmental milestones

Before discussing the important new insights gained with reference to the child's ‘inner world’, Table 4.1, outlining some of the outwardly obvious developmental milestones can serve as a crude point of reference.