Commentary: development of perception-action systems and general principles of pattern formation.

Our commentary on this special issue devoted to Developmental Biodynamics: Brain, Body, and Behavior Connections is divided into 3 main sections. The first section is an overview of the individual contributions. 5 major themes are identified: (1) inappropriateness of computational treatments of development and the need for more biologically and physically relevant treatments; (2) significance of tailoring muscular to nonmuscular forces in developing movement coordination; (3) importance of spontaneous movements as exploratory and formative mechanisms; (4) influences of action capabilities on the development of perception capabilities, and vice versa; (5) applications of methods and techniques of nonlinear dynamics to developmental processes. In the second section, we provide a synopsis of current ways of thinking about prototypical developmental processes, namely, pattern formation and pattern differentiation, in various classes of physical and biological systems. It is suggested that efforts to understand the progressive formation and differentiation of patterns in terms of very general principles provide a valuable resource of concepts and methods for students of child development. In the third section, hypotheses about the development of perception-action systems are generated from juxtaposing the themes and conjectures of this special issue with general principles of pattern formation. The hypotheses suggest the possibility of a pattern formation or dynamics approach to child development as an alternative to the conventional approaches emphasizing maturation (nativist), specific learning experiences (empiricist), cognitive stages (Piagetian), and strategies of encoding and retrieval (information processing).