Does it go downhill from 20? This has been suggested by many studies over the years, which have used the speed in reaction tests to infer the mental fitness of their participants. However, a new analysis with data from almost 1.2 million test persons now shows: The longer reaction times are due to greater caution in decision-making and the fact that older test persons need more time for processes that are not relevant to the decision – such as pressing the answer button. Cognitive speed, on the other hand, hardly changes between the ages of 20 and 60 and only slowly decreases as we get older.
Older people think more slowly than younger people. This assumption is widespread and seems to be supported by numerous studies. Most of these are based on measuring the response speed of subjects of different ages in simple decision-making tasks. Such studies have shown that people respond fastest in their early 20s, and from that age onward, response time gradually decreases.
The response time is too imprecise
“However, the average reaction time is not a direct measurement of mental speed, but represents the sum of different cognitive processes,” explains a team led by Mischa von Krause from Heidelberg University. “Different trade-offs between speed and accuracy, known as reaction caution, and the time it takes to encode the motor processes also contribute to the mean reaction time. Both factors influence reaction time, although they are not related to mental speed.”
Smaller studies have examined these different processes separately and have suggested that there is less of a difference in mental speed between young and old people than is commonly thought. However, most of these studies only had a small number of subjects, so that their validity is limited. One of the reasons for this is that the computational effort involved in the corresponding statistical models is so high that classic computers are overwhelmed with large groups of test subjects.
Association test as a data basis
In order to solve this problem, von Krause’s team developed a deep learning approach that can statistically model the respective proportions of the reaction time for each individual, even with millions of test subjects. The researchers obtained a correspondingly large data set by evaluating publicly available data from a test that is actually intended to record implicit racist associations. In this test, subjects have to take turns assigning words such as “happiness”, “joy”, “hate” and “failure” to the categories good or bad, or faces to the categories black or white. Sometimes the answer key for “good” is the same as for “white” and “bad” the same as for “black”, sometimes the other way around.
However, von Krause and his team were not interested in possible unconscious prejudices of the subjects, but only in their reaction time. The dataset includes tests from millions of subjects who completed them online. Overall, the researchers evaluated data from almost 1.2 million participants between the ages of ten and 80 years. How cautious the subjects were in their decision was measured by the reaction time in relation to right and wrong answers. They were able to read off the time it took just to press the button, since test subjects in the test are asked to press the other button after an incorrect answer – a process that does not require a decision, but only the motor reaction.
Decline in mental speed later than expected
The result: In fact, reaction times were fastest in 20-year-olds and slowed with age – “But this slowdown was more due to increasing caution in decision-making and slower non-decision-making processes than to differences in mental speed,” the researchers report . “A slowdown in mental speed was only observed from the age of about 60 years.” The speed at which cognitive processes take place in humans therefore decreases much later and more slowly than earlier studies suggested.
In fact, according to the data, mental speed actually increased up to around age 30 and remained stable for much of adult life. This applied equally to women and men and was independent of the level of education. On the other hand, caution in decision-making increased from the age of 20, and the non-decision time even from around 15 years of age. “Thus, for large parts of the human lifespan and typical careers, our results challenge the widely held notion of an age-related slowdown in mental speed,” the researchers write. “Our analysis suggests that the decline begins much later in life than previously thought.”
Source: Mischa von Krause (University of Heidelberg) et al., Nature Human Behaviour, doi: 10.1038/s41562-021-01282-7