Your brain works at the same speed until you are sixty. Still, it takes longer to make a decision as you get older.

Do older people think more slowly than younger people? That is the picture that emerges from a few decades of psychological research. Show people a test in which they have to use their brains and a person in their twenties will come up with answers much more quickly than someone in their sixties.

But what’s in it for him? Not in how fast the brain does its job, set Mischa von Krause, Stefan Radev and Andreas Voss from Ruprecht-Karls University in Heidelberg.

Mental speed

Von Krause and colleagues draw this conclusion from a large amount of data: that of 1.2 million people who use a so-called implicit association test (IAT) filled in. This is a well-known psychological test in which you have to classify words or pictures with your left and right hands. Most often, the IAT is used to expose unconscious biases – but that was not the aim of the German scientists. They looked purely at the average time it took the participants to make a choice.

Now all kinds of things actually happen in the one or two seconds between seeing a word and pressing a key. First of all, of course, your brain has to actually come up with the answer. This is where the so-called mental speed plays a crucial role. Then follows a short moment in which you ask yourself ‘am I right?’ Finally, there is the time you need to actually enter the answer; to translate your choice into the push of a button. The reaction time is then the sum of those three processes.

Neural Networks

To ‘chop up’ the reaction times in those three parts, von Krause and his team used the so-called diffusion model for decision making† This works for choices that meet a number of conditions: you must have a choice of exactly two options, only one step of thinking is needed to make your decision (so no whole reasoning), and the entire process must not exceed 1 to 1 on average. .5 seconds to complete. The IAT satisfies all those conditions perfectly.

The only problem is that it is quite a job for a computer to apply that diffusion model to reaction times. Especially if you have more than a million of them. “In order to get results from our huge amount of data, we had to use a new method based on artificial neural networks,” says von Krause. “We first trained them using simulations. Then we let them loose on our real data.”

The older, the more doubtful

From the charts the scientific publication about the study shows first of all that, as expected, the reaction time increases with age between twenty and sixty years old. But: the mental speed remains more or less the same during the same period. As far as a peak can be seen, it is not among the twenty-year-olds, but around the thirty. It is only towards the age of sixty, and especially at an even higher age, that the brain clearly takes longer to arrive at an answer.

What’s with the longer reaction time? First, from your twentieth birthday, the older you are, the longer you doubt the answer your brain has coughed up. (Teenagers, by the way, also hesitate longer than someone in their 20s.) Second, from about age 15, people take longer and longer to enter the chosen answer as they get older.

Other ages too

These results do not come completely out of the blue, by the way. Previous research yielded similar results, but involved an average of about sixty subjects per study. A larger number would soon have required too much computing power—or at least, without the neural networks that Von Krause and his team could deploy.

Moreover, previous studies usually compared only two groups: students in their early twenties and sixties. The new study looked at data from people between the ages of 10 and 80. So it also gives a picture of what happens in our brains at other ages when we have to make a choice.

And what next? “It would certainly be interesting to replicate our research questions by looking at other tasks,” says von Krause. “But as far as I know, there are no other datasets large enough for that.”