Research has found that larger pupil sizes are associated with greater levels of fluid intelligence, attention control, and higher short-term memory capacity, suggesting a remarkable link between the eyes and the brain.
It is often said that the eyes are “the windows to the soul”, but new research indicates that they may also be “windows to the brain.”
A study from the Georgia Tech laboratory shows that baseline pupil size is closely related to intelligence differences among individuals. Researchers utilized results from logic, attention, and memory tests to measure intelligence, finding that the larger a participant’s pupil, the higher their intelligence score.
In fact, the difference in pupil size between the highest and lowest scorers on cognitive ability tests was observed in three experiments.
By examining the effort participants exerted to complete memory tasks, researchers found a strong correlation between pupil size and intelligence.
Pupil size refers to the diameter of the black circle in the center of the eye. (Illustrative image).
Researchers selected over 500 participants aged 18 to 35 from the Atlanta area. Each participant’s pupil size was measured using high-powered cameras and computers to capture the light reflected from the pupil and cornea.
Participants were instructed to look at a computer screen for four minutes, during which the tool recorded changes in pupil size throughout the process, allowing for the calculation of each individual’s average pupil size during this period.
Pupil size specifically refers to the diameter of the black circle in the center of the eye, ranging from 2 to 8 mm. The colored part surrounding the pupil is known as the iris, which functions to control pupil size. We instinctively squint in bright light, so in this experiment, all participants performed the tasks under relatively dim lighting conditions.
In the next phase of the experiment, participants completed a series of cognitive ability tests designed to assess their “fluid intelligence,” which is the ability to retain information for a period and avoid distractions.
During the attention control test, participants were asked to avoid glancing at a bold, blinking asterisk on one side of the computer screen and instead quickly look in the opposite direction to identify a letter. This letter would only appear for a short time, meaning that even if you inadvertently glanced at the asterisk beside it for a second, you would miss the letter on that side.
Instinctively, humans pay attention to what appears in their peripheral vision, but this task required participants to redirect their attention from the asterisk to the letter.
The study found that larger pupil sizes are associated with higher levels of fluid intelligence, better attention control, and greater short-term memory capacity, suggesting a remarkable connection between the eyes and the brain. Interestingly, pupil size and age have an inverse relationship: older participants tend to have smaller and more constricted pupils. However, when age was standardized, the relationship between pupil size and intelligence remained consistent.
But why is pupil size correlated with intelligence?
To answer this question, we need to understand what is actually happening in the brain. Pupil size is related to the activity of the locus coeruleus. The locus coeruleus is located at the top of the brainstem and contains many long neural connections that reach the rest of the brain. The locus coeruleus releases norepinephrine, a neurotransmitter and hormone in the brain and body that helps regulate activities such as cognition, attention, learning, and memory.
Pupil size is closely related to differences in intelligence. (Illustrative image).
It is also responsible for maintaining order in brain activity so that different regions can coordinate to complete complex tasks. Dysfunction of the locus coeruleus can lead to a breakdown in the cooperation of brain parts, resulting in conditions such as Alzheimer’s disease and attention disorders.
The cooperative system of brain activity is so important for humans that we expend the most energy to keep it functioning normally. Even when we are doing nothing, such as staring at a blank computer screen for a few minutes, the brain’s cooperative system continues to operate.
The research hypothesizes that individuals with larger resting pupils in the locus coeruleus may manage brain activity more effectively, enhancing cognitive performance and brain functioning at rest. However, further research is needed to explore the validity of this hypothesis.
