<P> In the Wechsler Intelligence Scale for Children - IV (WISC IV), the Perceptual Reasoning Index contains two subtests that assess Gf: Matrix Reasoning, which involves induction and deducation, and Picture Concepts, which involves induction . In the Picture Concepts task, children are presented a series of pictures on two or three rows and asked which pictures (one from each row) belong together based on some common characteristic . This task assesses the child's ability to discover the underlying characteristic (e.g. rule, concept, trend, class membership) that governs a set of materials . Matrix Reasoning also tests this ability as well as the ability to start with stated rules, premises, or conditions and to engage in one or more steps to reach a solution to a novel problem (deducation). In the Matrix Reasoning test, children are presented a series or sequence of pictures with one picture missing . Their task is to choose the picture that fits the series or sequence from an array of five options . Since Matrix Reasoning and Picture Concepts involve the use of visual stimuli and do not require expressive language, they are considered to be non-verbal tests of Gf . </P> <P> Within the corporate environment, fluid intelligence is a predictor of a person's capacity to work well in environments characterised by complexity, uncertainty, and ambiguity . The Cognitive Process Profile (CPP) measures a person's fluid intelligence and cognitive processes . It maps these against suitable work environments according to Elliott Jacques Stratified Systems Theory . </P> <P> Fluid intelligence, like reaction time, typically peaks in young adulthood and then steadily declines . This decline may be related to local atrophy of the brain in the right cerebellum . Other researchers have suggested that a lack of practice, along with age - related changes in the brain may contribute to the decline . Crystallized intelligence typically increases gradually, stays relatively stable across most of adulthood, and then begins to decline after age 65 . The exact peak age of cognitive skills remains elusive, it depends on the skill measurement as well as on the survey design . Cross-sectional data shows typically an earlier onset of cognitive decline in comparison with longitudinal data . The former may be confounded due to cohort effects while the latter may be biased due to prior test experiences . </P> <P> Working memory capacity is closely related to fluid intelligence, and has been proposed to account for individual differences in Gf . </P>

What happens to the crystallized intelligence as one goes from young adulthood to middle adulthood