No single test of either ability exists, because each represents a cluster of underlying primary abilities. Of the two, fluid intelligence declines significantly as we grow older. Decline in fluid intelligence is associated with decreasing value in the ability to organize information, ignore irrelevant information, focus or divide attention, and keep information in working memory. There is a belief that there are reasons other than age to explain the changes in intelligence. Piaget's Theory Piaget believes that intellectual development is adaptation through activity.
Adaptation refers to the process of adjusting thinking to the environment.
Piaget had four stages in his theory of intellectual development. It has also been found that the performance on formal operations tasks was correlated with measures of fluid intelligence, linking formal operational abilities to normative decline. However, other research does not show evidence of age-related differences. There is now a fifth stage called postformal thought. This is characterized by a recognition that truth varies from situations to situation, that solutions must be realistic to be reasonable, that ambiguity and contradiction are the rule rather than the exception, and that emotion and subjective factors usually play a role in thinking.