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The human brain processes the numbers 4 and 5 in a very different way

Answer quickly: How many apples are there in the picture above? It’s easy to spot three apples, but thanks to your brain’s distinct processing mechanism, it might be even easier than you think.

According to a new studythe human brain has two distinct ways of processing numbers: a system for values ​​of four or less and another system for values ​​of five and above.

Scientists have long known that people respond differently when asked to quickly detect values ​​above or below this threshold, but it has not been clear whether this is actually evidence of two distinct neural mechanisms.

Certain neurons in the brain fire in response to certain values

Humans can usually recognize numbers of four or less at first glance without counting, and they are almost always right. This ability is known as subitizing. Psychologists invented this term last century and it is different from counting and estimating. This term refers to the fact that when looking at several objects, you can immediately tell their number without having to count or guess.

While we can easily recognize values ​​up to four, this ability disappears when we reach five or more. For example, if we are asked to immediately determine the number of a set of seven apples, we usually hesitate and estimate and take a little longer to answer. However, our answers are less accurate.

Because our immediate recognition skills suddenly fade for values ​​higher than four, some researchers have wondered whether the brain might use two separate processing methods for lower and higher values. It may be that our brain always uses the estimation method, but the error rate for smaller numbers is so low that we don’t notice it.

Previous studies have shown that the human brain has neurons that are responsible for each number, and certain neurons fire in response to specific values.

Some neurons fire primarily when a person sees two numbers of the same thing (say, two apples), while others fire when they see a different number. However, many of these neurons also fire slightly more or slightly less in response; However, their response becomes weaker for values ​​further away from their original number.

Researchers have shown in their past studies that the “numerical distance effect” also occurs in monkeys. However, in humans it usually only happens when we see five or more numbers, which points to unknown differences in how our brains recognize smaller numbers.

The authors of the article say that there seems to be an additional mechanism for numbers less than 5, which makes these neurons work more accurately.

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Neurons responsible for smaller numbers may inhibit neurons responsible for nearby numbers and thus limit any mixed signals about the desired quantity. For example, when a neuron fires for the number 3, it also inhibits neurons that normally fire in response to 2 or 4. Neurons responsible for the number of 5 and more apparently lack this mechanism.

The researchers selected 17 patients at Bonn University Hospital who were being prepared for brain surgery to treat epilepsy. As part of the treatment procedure, microelectrodes were placed in the patients’ temporal lobes. The researchers used electrodes to measure the response of individual nerve cells to visual stimuli.

Our skill at instantly recognizing the number of things suddenly fades for values ​​higher than four

Subjects looked at a computer screen that displayed a different number of dots for half a second. After that, the researchers asked the subjects whether the number of dots they saw was even or odd.

When the number of dots was up to four numbers, the subjects answered quickly and accurately and practically there was no error. But when the number of points reached 5 and more, both the error and the response time increased.

According to the scientists, their research provides new clues about the mechanics of the human brain and reveals important details about how the brain processes numbers. Such research can increase our understanding of disorders such as math learning disorder (dyscalculia).

Study findings in the journal Nature Human Behavior It has been published.

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