Leslie Carrion, Student, School of Psychology; Cinamon Romers, Student, School of Psychology; Henry Soper, Faculty, School of Psychology
The Cattell-Horn-Carroll theory of intelligence is best assessed through the Stanford-Binet. In the fourth edition three intellectual abilities, or second level factors, were evaluated: crystallized abilities (verbal reasoning and quantitative reasoning), fluid/analytic abilities (abstract and visual reasoning), and short-term memory, and all of these were subsumed under general ability, or g. With the newest, 5th, edition the crystalline abilities are now called knowledge, and the four other areas include fluid reasoning, quantitative reasoning, visual-spatial reasoning, and working memory. We decided to see how these five areas change over time, expecting little change in crystalline ability (knowledge), substantial in fluid reasoning and working memory, and little in visual-spatial reasoning. Average performance on each of these areas was computed for each age group for verbal and nonverbal tasks from 20:0-24:11 to 85:0-89:11 and the resultant performances compared to those who are 19 years old. Verbal crystalline held through all the ages observed, whereas verbal fluid abilities dropped in the eighth and ninth decades to the 9th percentile. Nonverbal crystalline also held well through the eighth decade, but nonverbal fluid dropped after the sixth decade to the 5th percentile by the end of the ninth decade. Quantitative and spatial processing and working memory also showed declines. Overall cognitive abilities held pretty well through the 60s, but by retirement age there were slippages in most areas. Several explanations are possible, from a use-it-or-lose-it phenomenon to an organic deterioration. Clinical evidence strongly suggests a non-organic basis for the observed trajectories.