Mental speed hardly changes over a lifespan

"The common assumption is that the older we get, the more slowly we react to external stimuli. If that were so, mental speed would be fastest at the age of about twenty and would then decline with increasing age," says Dr von Krause, a researcher in the Quantitative Research Methods department headed by Prof. Dr Andreas Voß at Heidelberg University's Institute of Psychology. In order to verify this theory, the researchers reevaluated data from a large-scale American study on implicit biases. In the online experiment with over a million participants, subjects had to press a button to sort pictures of people into the categories "white" or "black" and words into the categories "good" or "bad." According to Dr von Krause, the content focus was of minor importance in the Heidelberg study. Instead, the researchers used the large batch of data as an example of a response-time task to measure the duration of cognitive decisions.

When evaluating the data, Dr von Krause and his colleagues noted that, on average, the response times of the test subjects rose with increasing age. However, with the aid of a mathematical model, they were able to show that this phenomenon was not due to changes in mental speed. "Instead, we think that older test subjects are mainly slower because they reply more cautiously and concentrate more on avoiding mistakes," Mischa von Krause explains. At the same time, motor execution speed slows down during the course of adult life: older participants in the experiment needed longer to press the appropriate key after they had found the right answer.

Another finding of the study was that average information processing speed only progressively declined with participants over the age of 60. "It looks as though, in the course of our life, we don't need to fear any substantial losses of mental speed -- particularly not in the course of a typical working life," says Mischa von Krause. "Generally speaking, we should also note that the test subjects in all age groups included individuals with high and low mental speeds. Our results relate to the average trend."

The German Research Foundation (DFG) funded the research work in the context of the research training group for doctoral students "Statistical Modelling in Psychology" (GRK 2277). The results were published in the journal Nature Human Behaviour.