It is often said that the eyes are the mirror of the soul, and there is some truth in that. It has long been known that the pupils do not just dilate and contract in reaction to light, but also as a reaction to the mental processes that occur in our brain.

For example, when we see something or someone we are attracted to, they expand more so as not to lose detail of what is in front of us. Similarly, in simple memorization tasks, we have seen that the pupil expands as elements are kept in the memory and contracts each time something previously memorized is remembered.

Thus, our gaze expresses more of our inner world than one would expect. However, recent research takes this idea a step further by providing new evidence about the relationship between pupil behaviour and our psychological side: people with larger pupils tend to be more intelligent, statistically speaking .

The link between pupils and fluid intelligence

The results of this research, published in the journal Cognitive Psychology by a team of American psychologists, show that pupil diameter correlates with higher intelligence scores . In other words, groups of people with larger pupils have a greater chance of being more intelligent than the rest, although this norm does not have to be met in all individuals.

A group of 331 volunteers were used to carry out this research and the size of the pupils in which they adopted their “default” size was measured to ensure that the brightness levels did not affect the results. In addition, the psychologists took into account variables such as age, sex, or the use of certain substances such as nicotine. Once the influence of these variables was subtracted from the equation, the correlation between pupil size and intelligence appeared.

However, the measure of intelligence whose relationship with the diameter of the pupils was recorded by this group of psychologists was not just any intelligence.

Specifically, it was about fluid intelligence, one of the most important components of IQ. Basically, fluid intelligence refers to the mental agility with which we find solutions to unexpected and novel problems . Therefore, it is a type of intelligence that does not depend on our cultural level or on the knowledge acquired over the years.

How do you explain this?

What causes this relationship between pupil size and higher fluid intelligence scores is, for the moment, a mystery. Of course, could be a spurious correlation , be the result of a curious coincidence or reflect that there is a variable between these two that causes them both at the same time. For example, it could be that people with larger than normal pupils come from a line of ancestors with neuroanatomical characteristics that make them more intelligent.

Another brief explanation is proposed by Jason S. Tsukahara, one of the researchers responsible for the study. The answer may lie in a network of neurons sensitive to a substance called noradrenaline that are located in a part of the brain known as the locus coeruleus, located in the brain stem. He notes that other research has shown a relationship between the activity level of this group of nerve cells and the size of the pupils. At the same time, noradrenaline makes neurons more likely to communicate with each other, creating new neural pathways that make it easier to find possible solutions and consider more options.

To clarify this it will be necessary to repeat research of this type in various contexts and see if the correlation is present in each of them. In that way, from there, it will be possible to start developing a theory that explains the phenomenon .