A new study shows that people with larger pupils in their eyes are more intelligent than those with smaller pupils.
Volunteers took tests of thinking, attention and memory so the Georgia Institute of Technology team could investigate the link between pupil size and intelligence.
They found that in addition to being associated with arousal and fatigue, pupil dilation can be used to understand individual differences in intelligence, discovering that the larger the pupil, the higher the intelligence.
Differences in baseline pupil size between those with the highest scores and those with the lowest scores on IQ tests can be seen with the naked eye.
The team says this may be because people who have larger pupils have better results for regulating brain activity in an area associated with intelligence and memory.
About 500 people between the ages of 18 and 35 from Atlanta took part in a battery of tests while researchers monitored their pupil size with an eye tracker.
This device captures the reflection of light from the pupil and cornea through a high-powered camera. It was measured at rest while the volunteer stared at a blank screen for four minutes to establish a baseline.
This allowed them to create an average pupil size for each of the volunteers that could be used to track changes through different types of tests and activities.
The average human pupil, the black circular opening in the center of the eye, can range from 2 to 8 mm and is surrounded by the iris that controls pupil size.
Once a baseline was established for each volunteer, they were asked to complete a series of tests that measured a range of intelligence areas.
This included the ability to think about a range of problems, the ability to remember information over time, and the ability to stay focused even when distracted.
They found that those with a “larger baseline pupil size” performed better on tests of attention, memory, and reasoning.
This suggests a strong link between the brain and the eye that researchers hope to study in more detail in the future.
Pupil size was negatively correlated with age, and the researchers found that older volunteers tended to have smaller and more narrow pupils.
However, even with removing the age factor, and they created a uniform number, the relationship between intelligence and pupil size remained, regardless of age.
It is noteworthy that knowing exactly why pupil size is associated with intelligence requires a more detailed study of the brain, to look for areas that are activated.
The researchers found that pupil size is linked to a region known as the locus blue at the top of the brainstem, which extends to the rest of the brain through synapses.
It releases a chemical that acts as a hormone in the brain and body and a neurotransmitter for regular processes such as cognition, attention, and memory.
This area also plays a broader role in helping distant regions of the brain work together to complete complex tasks.