PUPIL SIZE IS AN INDICATOR OF INTELLIGENCE

 

They describe a striking correlation between the resting diameter of the pupils and various measures of cognitive ability.

 

   They say that the eyes are the window to the soul, but according to new research, they could also be a window to the brain.

 

   The pupils not only respond to light, but also reflect a state of excitement, interest, or mental exhaustion. Even the US Federal Bureau of Investigation (FBI) uses pupil dilation to detect when a person is lying. Now a study, conducted in our laboratory at the Georgia Institute of Technology, suggests that pupil size is closely related to individual differences in intelligence . Specifically, the larger the pupils, the greater the intelligence, assessed by tests of reasoning, attention, and memory. In fact, in three studies, we found that the difference in initial pupil size between the people who scored the highest on cognitive tests and those who scored the lowest was large enough to be detected with the naked eye.

 

   We found this surprising relationship for the first time while investigating the mental effort required to complete memory tasks. The dilation of the pupils constitutes a marker of effort, since the psychologist Daniel Kahneman popularized this parameter between the 60s and 70s of the 20th century. At first, when we discovered the association between pupil size and intelligence, we doubted the veracity of this relationship, as well as its meaning.

 

   Intrigued by this, we conducted a series of large-scale investigations and recruited more than 500 volunteers ages 18-35 from Atlanta. To measure the size of the participants' pupils, we used an eye tracker, a device that captures the reflection of light from the pupil and cornea using a high-powered camera and a computer. The measurement was performed while the subjects stared at a blank computer screen for four minutes. The data collected with the tracker allowed us to calculate the average size of the pupils of each person.

   When we talk about the size of the pupil, we refer to the diameter of the circular black opening in the center of the eye, which can range from two to eight millimeters. The area of ​​color, known as the iris, that surrounds the pupil is responsible for controlling its size. Since the intense light causes constriction of the pupils, we controlled the illumination of the laboratory, which we kept in the dark.

 

   In the next stage of the experiment, participants completed a series of cognitive tests designed to measure 'fluid intelligence' or ability to reason through new problems, 'working memory' or ability to recall information over a period of time. of time, and "attention control" or ability to focus attention amid distractions and interference.

As an example of the attention control test, volunteers had to avoid the temptation to look at a blinking asterisk located on one side of the screen and instead focus their eyes in the opposite direction to identify a letter. It disappeared quickly, so even looking away from the asterisk for an instant was enough to lose it. Human beings are programmed to react to any object that passes through our peripheral vision, as this allowed our ancestors to detect both predators and prey. However, the cognitive task required participants to perform the opposite action, that is, redirect their attention from the asterisk to the letter.

 

   According to the results, a larger basal size of the pupils correlated with greater fluid intelligence and attention control and, to a lesser extent, with greater working memory. This suggests a fascinating relationship between the eye and the brain. Interestingly, the size of the pupils was negatively associated with the age of the participants, as older people had smaller and more constricted pupils. However, after adjusting for this factor, the relationship between pupil diameter and cognitive ability remained.

 

   But what is the origin of this association? To answer this question, it is necessary to understand what happens in the brain. The size of the pupil is related to the activity of the locus ceruleus, a nucleus located in the upper part of the brain stem, whose powerful neural projections connect with the rest of the brain. The cerulean locus releases norepinephrine, which acts as a neurotransmitter and hormone, and regulates processes such as perception, attention, learning, and memory. It also contributes to the maintenance of the correct organization of brain activity, so that distant areas can work together, in order to complete demanding tasks and objectives. The dysfunction of the cerulean locus, and the consequent alteration of brain architecture, is related to different disorders, such as Alzheimer's disease or hyperactivity deficit. In fact, the organization of brain activity is so important that our brain invests much of its energy in maintaining it, even when we do not perform any type of action or activity.

 

   One possible explanation is that people with larger pupils at rest have greater regulation of brain activity, mediated by the locus cerulean, a fact that benefits cognitive performance and brain function in an inactive state. Further research will be necessary to confirm this hypothesis and to determine why a larger pupil diameter is associated with greater fluid intelligence and control of attention. However, it is clear that something is happening, beyond what we perceive with the naked eye.