ABSTRACT
This chapter summarizes several studies which investigated how the relations between individual processes and general intelligence change with phase. It answers questions about a long-standing dispute in developmental and differential psychology: do special processes differentiate from or integrate with g with growth? The chapter discusses Spearman’s law of diminishing returns and Piagetian conceptions about the integration and differentiation of mental processes. New structural equation modelling methods are used to specify changing relations, such as the Tucker-Drob differentiation model and segmented modelling of logistic growth. This approach generated some novel findings, showing that differentiation and intertwining of specific processes from g is a developmental rather than an individual differences phenomenon. The relation between specific processes and g vary with developmental cycle and phase. New acquisitions in each cycle get increasingly integrated into g, at the phase when they infuse g, impregnating it with their properties. Later, when well established, they may differentiate from it. The implications for psychometric and developmental theories are discussed.
