General intelligence does not appear to influence specific mental skills uniformly across a person’s life or across different levels of mental ability. A large study published in the journal Psychology and Aging reveals that the connections between different cognitive skills fluctuate considerably as people age and are notably weaker in people with higher overall intelligence. These changing patterns suggest that a single overall IQ score may be a less reliable measure of brainpower for certain people, depending on their age and baseline abilities.
In the field of psychology, researchers have observed that cognitive abilities tend to be linked. A person who performs well on a test of memory will likely also perform well on a test of spatial reasoning. This widespread pattern is known as the positive manifold.
Statisticians represent this phenomenon using a single variable called the general intelligence factor, or the g-factor. This metric acts as a kind of umbrella, capturing the shared variance across a wide variety of mental tasks.
Despite its widespread use in clinical and educational settings, experts still disagree on the underlying mechanisms of the g-factor. Some scientists argue that general intelligence represents a biologically inherent mental capacity. Others propose that it merely emerges as a statistical byproduct of different areas of the brain developing at the same time.
To better understand general intelligence, scientists look at how the strength of the g-factor might vary among different types of people. This area of questioning is known as differentiation research. Specifically, researchers explore whether the biological and environmental links between different mental skills change as a person grows older or as their overall ability level changes.
Psychologist Moritz Breit of the University of Trier led a team of researchers from institutions across Germany to investigate these differentiation effects across the human lifespan. The researchers point out that previous studies often looked at narrow age groups, making it difficult to spot lifelong trends. By analyzing data from a single population over a vast age range, the team aimed to map exactly how the structure of human intelligence changes from early childhood into late adulthood.
For this large study, Breit and his colleagues examined data from 4,129 participants. These individuals ranged in age from two to nearly ninety years old. The participants were drawn from the German standardization samples for the Wechsler tests.
The Wechsler tests are the most frequently used intelligence diagnostic tools worldwide. Test takers complete a battery of specific exams designed to measure different kinds of mental output. These areas include fluid reasoning, visual processing, working memory, processing speed, and acquired knowledge.
The researchers applied advanced statistical models to the scores from these distinct tests to see how strongly each specific mental skill connected back to the overarching g-factor. They tracked these relationships across different age brackets and across the spectrum of overall intelligence.
The team observed a pronounced phenomenon called ability differentiation across all age groups. Mathematical modeling revealed an inverse relationship between a person’s overall intelligence level and the strength of their g-factor. As a person’s general cognitive ability increased, the statistical connections among their specific mental skills became weaker.
This means that for individuals with very high assessment scores, a single measurement of general intelligence becomes less representative of their actual, varied mental capabilities. The researchers note that this ability differentiation effect is relatively stable during childhood. It then increases sharply from middle adolescence through the late twenties, before moderating again in later adulthood.
The study also mapped out a highly varied pattern of age differentiation. Rather than a steady decline or increase in the strength of general intelligence over a lifespan, the researchers documented alternating phases.
From early childhood to early elementary school, the g-factor weakens, meaning specific intellectual skills grow more distinct from one another. Then, from about age eight into early adulthood, a process of dedifferentiation takes over. During this span, the connections among different cognitive abilities strengthen, making mental skills more unified.
As people enter their thirties, the trend reverses once again. General intelligence begins to weaken, continuing a process of differentiation until about age sixty. Finally, in late adulthood, the data show hints of another reversal where cognitive abilities begin to merge together once more.
The study relies on data solely from the German population. These specific Wechsler tests are adapted from a widely used European standardization kit, but the regional focus may limit how well these exact trends apply to populations in other cultural contexts. Future investigations could examine intelligence test data from different countries to see if these patterns hold up globally.
Because the researchers focused entirely on the mental skills measured by the Wechsler assessments, some cognitive areas were left out of the analysis. Human intellect includes distinct mental domains such as auditory processing and retrieval fluency, which these specific diagnostic tools do not evaluate. Examining a wider variety of test batteries could offer a larger window into how specific brain skills develop and diverge.
These changing patterns in the structure of intelligence carry practical meaning for educators and clinicians. Many schools and diagnostic centers rely heavily on a single composite score, often called a Full Scale IQ, to make decisions about academic placement or clinical interventions.
The finding that general intelligence is dramatically weaker in highly capable individuals means that a single score has a much higher margin of error for that demographic. To account for this shifting accuracy, the researchers suggest that psychologists should apply specific error margins based on a person’s age and cognitive level rather than using a blanket standard for everyone.
The study, “The contribution of general intelligence to cognitive performance across the life span: A differentiation analysis of the Wechsler tests,” was authored by Moritz Breit, Martin Brunner, Julian Preuß, Monika Daseking, Franz Pauls, Franziska Walter, and Franzis Preckel.