Concepts of intellect in relation to learning and adult development

Abstract

This article is a summary and integration of results from studies of the organization and development of human abilities. Several kinds of results are interpreted as converging toward support of theories stipulating a hierarchy of intellectual functions. Near the top of this hierarchy, most related to intelligence as this is usually conceived, are the two broad sets of abilities known as fluid intelligence (Gf) and crystallized intelligence (Gc). The major focus of the review is on the decline of Gf through the “vital years of adulthood,” from 20 to 60 years of age. Major conclusions are: 1. Sensory detector functions, near the bottom of the hierarchy of intellectual capacities, decline with development through the vital years, but this kind of decline is not responsible for aging decline of the major features of fluid intelligence: keenness of sensory function is not of the sine qua non of mature expressions of human intelligence. 2. Memory abilities are somewhat higher in the hierarchy of intellectual functions, and thus are more strongly related to intelligence, than are sensory detectors. With increase in time interval over which retention is required, there is increase in the relationship of memory to Gf and to decline of Gf over the vital years. Accompanying this increase is an increase in the extent to which memory is dependent upon adequacy of organization at the stage of encoding. This, in turn, reflects the adequacy of eduction of relations and correlates, which is an essential feature of Gf. 3. To the extent that very short-term memory is implicated in fluid intelligence, and the decline of this, it is intimately related to either a capacity or inclination to maintain close attention under conditions of high demand for attention. 4. The speed with which one obtains correct answers to difficult problems is not closely related to the number of correct answers obtained when all subjects attempt all items in fluid intelligence tests, but clerical/perpetual speed, as indicated in tasks of quickly finding a particular symbol among others or tasks of making same/different judgments, is related to aging decline of Gf. As with short-term memory, this form of intellectual speediness appears to be closely related to capacities (or inclinations) for maintaining attention, dividing attention, and holding things in mind while doing other things. 5. Crystallized intelligence probably increases over the vital years. This reflects dynamic restructuring of knowledge systems. It appears that there is not only an aging increase in knowledge but also an increase in the accessibility of information, a result being that humans become more creative (in one sense) as age increases through the vital years. 6. Results from multivariate cross-sectional studies of intelligence are seen to be consistent with comparable results obtained with other kinds of research strategies.