You start counting without even listening to the task - scientists have explained why

In the experiment, participants were given simple addition problems - the numbers were read out one at a time through headphones. While people were counting in their minds, the researchers monitored the size of their pupils.

It turned out that the pupils began to dilate after the first number - even before the second number was read out.

Details

This means that the brain is switched on in advance.

In other words, a person does not wait for complete information, but begins to "estimate" a possible answer at once.

The more information the first number gave, the stronger the response. For example, a two-digit number narrowed the range of possible answers - and the brain was more actively involved in calculations.

Interestingly, participants whose brains responded more strongly in the first step ended up giving the correct answer faster.

Why it matters

The results show that the brain doesn't work like a calculator that waits for all the data, but like a system that is constantly making assumptions.

This helps:

• make decisions faster
• reduce the time it takes to calculate
• process information more efficiently

Essentially, the brain "guesses" the answer and refines it as new data becomes available.

Background

Scientists believe that this approach is used not only in maths, but also in other tasks - for example, in the perception of speech, movement and the world around us.

The brain is constantly predicting what is happening and adjusting its expectations.

Source

The study is published in the journal Proceedings of the Royal Society B (2026). Scientists from France and Belgium studied how people solve simple maths problems by tracking changes in pupil size.