Stage theories are commonly used to represent the structure of cognitive processes in the domains of cognitive processing and cognitive development. Hierarchical unidimensional theories consisting of a single sequence of stages through which development proceeds in one direction only have predominated. However, a review of stage theories revealed that a two-dimensional, interactive (multidimensional) structure is warranted. Particularly in the area of cognitive development, results of research have supported subdivision of the stages of prominent unidimensional theories. Following this trend a small number of theorists have developed multidimensional theories, most of which consist of a sequence of stages in which each stage contains a number of subsidiary stages or levels. The emergence of a similar trend in other domains is examined, and the prospects of using an existing multidimensional framework to enable future comparisons and integration of different stage theories is explored.
THE DIMENSIONS OF STAGE THEORIESStage theories based on discrete, quantifiable degrees of ability or modes of functioning can be found in most areas of psychology. The main areas which have been influenced by the frequency of such contributions are the fields of neuropsychology, social development, information processing, language, learning and cognitive development. On one hand the literature appears to lack integration and consensus regarding stage divisions, stage order, and stage content. On the other hand a comparison of some of the stages of different theories may be possible, based on similarities in the underlying structure of the theories and on links that a few researchers have made across these fields of psychology. In the literature there is a network of connections by which physiological stages and stages of social and cognitive development are linked with the learning processes, levels of learning and perception are linked with language, and language is linked in turn with stages of cognitive development. The following overview is confined to selected theories which may illustrate these links or underlying structure.The majority of stage theories are unidimensional whereas a multidimensional structure may be warranted. Jensen (1970) described a diverse range of hierarchical theories and stated that as established fact mental ability is multidimensional, not unidimensional. Unidimensionality refers here to a single sequence or hierarchy of steps in the processing or ontogenetic systems. For example in the processing system information enters at the input end and is processed at each step either serially or in parallel, resulting in output at the other end of the system. Multidimensionality refers here to an