Intelligence Assessment through Cohort and Time

Intelligence: Models of Structure and Theories of Development

Intelligence measurement and theories of intelligence are represented in this encyclopedia by several entries. This corresponds to the importance and relevance that cognition, cognitive abilities, and intelligence have in the Western societies and consequently in psychological research since its beginning some 100 years ago. There exist hundreds of definitions of intelligence and cognitive abilities in philosophy and psychology, and in every day life. Most of them include a core of key concepts such as comprehension, judgement, reasonable thinking, but also successful adaptation to natural, cultural, societal circumstances and challenges in an efficient and practical manner, and finally productive and creative mental energy. As Schaie (1996) argued, in the scientific study of intelligence there is a hierarchy leading from information processing (speed, accuracy, mechanisms, strategies), through products measured in tests of intelligence to practical every day intelligence, and finally to wisdom.

This entry is devoted to the special aspect of development and change of intelligence through time (i.e. through ages), and through cohorts. Development and change are driven by environmental determinants (such as culture, generation, social and educational systems, family conditions and constellations etc.), by genetic determinants (including processes of maturation, growth, and ageing of the organism) and by interactions of influences from both. The entire human age span (or life time) should be included in studying these phenomena. A major task of this type of research is to identify the peaks in intellectual performance as well as to describe and to explain the rate and patterns of change and decline.

Schaie (1996) identified at least four theoretical positions which influenced paradigms of empirical research in intelligence and development of cognitive abilities and functions: unidimensional conceptions (such as those of Spearman, Binet and Simon – g-factor), the multidimensional concepts leading from Thorndike to Wechsler (multiple cognitive abilities), the multiple dimensions approach by Thurstone (primary mental abilities) leading to an expansion by Guilford and to the hierarchization by Cattell (fluid and crystallized intelligence), and finally the stage theoretical Piagetian approach (multiple cognitive abilities). There are some attempts to expand the Piagetian approach beyond childhood and adolescence to adulthood, middle age, and old age. However, the majority of research concerning change, [Page 471]growth, decline and development of intelligence across the lifespan is based on the psychometric assessment of intelligence (i.e. Spearman, Thurstone, Cattell tradition and paradigm).

The Cattellian theory of fluid (gf) and crystallized (gc) intelligence (including the theory of investment from fluid intelligence into crystallized over the lifespan) was important to the lifespan oriented research, since the gf- and gc-components (but various others within this Cattellian system as well) differed in their time/age/cohort trajectories in terms of gains and losses and in types of more or less accelerated decline. Closely related to the Cattellian view Baltes and his co-workers built a slightly different two-component model of lifespan intellectual development: on the one hand fluid mechanics, i.e. intelligence as basic information processing (reasoning, spatial orientation, perceptual speed etc.), which is content-poor, universal, biological and genetically predisposed, and characterized by a declining trajectory (i.e. after 25/30 years of age) similar to gf, and on the other hand crystallized pragmatics (verbal knowledge, semantic memory, some facets of mathematical ability), i.e. intelligence of cultural acquired knowledge, which is content-rich, culture dependent and experience based, and characterized by a trajectory similar to gc (stable, beyond 25/30 years of age even increasing, smoothly declining in very old age) (Baltes, 1997).

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