It is widely accepted as one of life’s bleak but unavoidable facts: as we get older, our brains get slower. But now a study, based on data from more than 1 million people, suggests that mental processing speed remains almost constant until the age of 60.
The analysis puts perceived reductions in speed down to people becoming more cautious as they get older. This could account for the large body of research that has concluded that mental processing speed peaks at about the age of 20 and undergoes a steady decline from that point onwards.
“Our finding is encouraging, as our results show that average levels in mental speed in contexts demanding fast and forced decisions do not decline until relatively late in the lifespan,” said Dr Mischa von Krause, of Heidelberg University and first author of the work.
The study, published in the journal Nature Human Behaviour, used data from 1,185,882 participants, aged 10 to 80 years, in Harvard’s Project Implicit, an online tool that has been used to collect data and educate people about biases they hold on gender, race and other characteristics.
Participants are required to sort words into positive and negative categories, while also assigning image to racial categories. The test is primarily designed to measure the strength of a person’s associations between race (in this case black or white people) and evaluations (represented by positive or negative words), but the latest analysis simply used the age of the participants, their response times and accuracy.
The data showed, as previous studies have done, that average time to give a correct response peaked at about 20 years. However, the researchers argue that this metric also captures how cautious a person is in delivering their answer and also their basic motor reaction speeds.
By using machine learning, the researchers aimed to extract more information about these two hidden factors from patterns in the data. For instance, if someone consistently responded more slowly, regardless of the difficulty of a given question, the model might be more likely to attribute this to slow motor responses.
The analysis suggested that 20-year-olds were quickest because they were the most willing to trade accuracy for speed. The researchers concluded that the purely mechanical part of the response (how fast a person sees the question and taps the keyboard) was quickest in those aged 14-16. Mental processing speed appeared to peak about age 30, and declined only very slightly between 30 and 60. Participants also made fewer mistakes as they became older, at least until the age of about 60.
Dr Joshua Hartshorne, a psychologist at Boston College who was not involved in the latest work, said the machine learning method used was impressive and would prompt psychologists to reconsider some earlier findings based simply on response times. “This joins a body of work suggesting that the way mental abilities change throughout life is complicated and we don’t really know what’s going on,” he said. “But whatever’s going on, it’s definitely not that we peak at 20 and go downhill from there.”
Von Krause said the work raised the suggestion that people may excel at different tasks depending on their age. “Obviously, there are real-life tasks where it is crucial to avoid mistakes, such as in a medical diagnosis, while in other tasks, such as avoiding an obstacle on the road, speed is more important,” he said. However, he added that, within certain limits, people were likely to be able to adapt their decision-making style to suit the demands of a situation.
