It turns out that the human brain processes numbers 4 and 5 differently

It is said that humans can count up to four at a glance, but for larger numbers they need to count and guess. A research team from Eberhard Karl-University Tübingen and Bonn University Hospital has announced that humans have two different systems for processing numbers.

Distinct neural representation of small and large numbers in the human medial temporal lobe | Nature Human Behavior

However, in the case of the photo below, you can't figure out the number just by looking at it, and you need to count the apples in your head.

It has long been known that humans can grasp numbers of four or less in an instant, but need to count numbers of five or more, but it is not completely clear why this phenomenon occurs. did not.

The hypothesis that ``multiple number processing systems exist in the human brain'' had been proposed, but it had not been proven. However, a paper published in 2018 showed that there are neurons that correspond to numbers in the human brain, and that specific neurons selectively respond to specific numbers. .

To examine this phenomenon, the research team recruited 17 patients who were preparing for brain surgery to treat epilepsy. As part of the treatment, patients have tiny electrodes implanted in the temporal lobe of their brains, allowing their brain activity to be measured.

The research team showed patients a computer monitor, displayed various numbers of dots for 0.5 seconds, and then asked them, ``Did you see an odd number of dots or an even number of dots on the screen?'' Ta.

As a result, patients answered quickly and accurately when there were four or fewer dots, and they did not make any mistakes. However, when five or more dots were displayed, there was an increase in cases where the answer was delayed or incorrect.

When we investigated the responses of the patient's neurons, we found that neurons that respond to certain numbers also respond slightly to smaller or larger numbers.

For example, a neuron that responds to the number 7 also responds to 6 and 8, but the response seems to be weaker than when it responds to 7. Also, the reaction to 5 and 9 will be weaker.

On the other hand, when neurons that respond to the number 3 respond, the responses of neurons that respond to 2 and 4 are simultaneously suppressed. This phenomenon makes it less likely that you will mistakenly recognize the number 3. However, this mechanism does not exist in neurons that respond to numbers greater than 5. Therefore, the research team claims that numbers over 5 cannot be recognized at a glance.

The research team says they will continue to conduct further research into how humans process numbers, and in the future they may be able to explain why some people are born with a hard time understanding numbers. .