New findings on the development of intelligence in adulthood
Do cognitive abilities change in adulthood often together or independently? An international research team from the USA, Sweden and Germany, in which the Max Planck Institute for Human Development was also involved, presented new results in this regard. The study was published in the journal science progress Released.
It is usually easier for people to learn new things when they are in their twenties than it was when they are in their seventies. On the other hand, people in their 70s usually know more about the world than they do in their 20s. In age psychology, this is referred to as the difference between “liquid” and “crystalline” brain abilities. Fluid abilities primarily record individual differences in brain performance at the time of measurement, and crystal abilities primarily record individual differences in knowledge bases.
Accordingly, the capacities of liquids and crystals differ in their mean lifetime curves. While fluid abilities, such as memory, begin to decline in mid-adulthood, crystal abilities, such as vocabulary, continue to increase into adulthood and only begin to deteriorate as we age.
This difference in average fluid and crystal capacity pathways led to the assumption that humans could compensate for their fluid loss with crystal gains. If a person’s memory has deteriorated, for example, he can, and therefore presumably, compensate for it with more knowledge.
The study by a research team from Germany, Sweden and the USA now shows that this compensation hypothesis is subject to narrower limits than is often claimed. The researchers analyzed data from two follow-up studies, the Virginia Cognitive Aging Project (VCAP) study from the USA and the Betula study from Sweden. The VCAP study examined more than 3,600 females and 1,900 males aged 18 to 99 years at the time of the first survey and were examined up to eight times over a period of up to 18 years. About 1,800 women and 1,500 men participated in the Bitola study. Subjects were between 25 and 95 years old at the time of the first measurement and were examined up to four times over a maximum period of 18 years.
The research team used multivariate methods of change measurement to determine how individual differences in crystal capacity changes correlate with individual differences in fluid changes. The result is clear: in both studies, very high correlations were observed between changes. It follows that individual differences in cognitive development are transversal and do not follow the distinction between liquid and crystalline abilities. In other words, people who show greater losses in fluid skills also show lower gains in crystal skills. Individuals who show a slight decrease in their fluid abilities also show significant gains in crystalline abilities.
These findings are consistent with the observation in everyday life that some people are mentally fit in many areas in old age, while in others cognitive performance in general declines sharply.
Eliot Tucker Drop, lead author of the study and professor in the Department of Psychology and Population Research Center at the University of Texas at Austin, US, explains. “In previous work, we have already shown that not only differences at a particular point in time, but also changes in cognitive abilities are a general factor. These results show this again. They confirm that changes in crystal abilities can also be attributed to this general change factor.”
“Our findings make it necessary to review biblical knowledge,” adds Ulman Lindenberger, Director of Research in Developmental Psychology at the Max Planck Institute for Human Development in Berlin. “If those with the greatest fluid losses show the fewest crystalline increases, this places narrower limits on increasing the compensatory capacity of knowledge than previously assumed.” Conversely, people with small fluid losses and strong crystal gains are less dependent on reparative processes from the outset.
The findings underscore the importance of identifying and enhancing modifiable effects that contribute to the overall maintenance of cognitive abilities in adulthood. This includes, for example, physical exercise that prevents cardiovascular disease and thus can also contribute to maintaining cognitive abilities.