Our pupils, the deep black dots at the center of our eye, respond to much more than just light. They can express our arousal, reveal our tiredness, and perhaps even show whether we are lying. According to a new study, our pupils may also have a link to our cognitive abilities: the bigger the pupil, it seems, the sharper the brain.
A string of recent studies have found some relationship between pupil size and certain cognitive skills. However, the link had become shrouded in uncertainty and controversy after a number of studies failed to replicate the same results – some found that larger baseline pupil size was associated with higher cognitive ability, but others found the opposite. Many of these studies also suffer from a small sample size.
In a new study, reported in the journal Cognition, two psychologists from the Georgia Institute of Technology argue that the conflicting results seen in previous research were the product of inconsistent lighting. Once the lighting was controlled, they discovered that a larger baseline pupil size had a strong link to fluid intelligence, working memory capacity, and attention control.
Two joint experiments saw over 500 people aged 18 to 35 have their pupils measured by a high-powered camera and computer. Since pupil dilation is clearly related to the strength of surrounding light, the researchers ensured the lighting in the lab was kept steadily dim.
The eye tracker device was then used while some participants undertook a series of cognitive tasks designed to test their “fluid intelligence,” – the ability to think speedily and reason flexibly in order to solve new problems – “working memory capacity,” – the ability to retain information over a period of time – and “attention control,” – the capacity to control attention.
Across the board, a larger baseline pupil size was tightly linked to a greater ability to perform these tasks.
But what’s the nature of this link? Is it mere correlation? The research did not specifically look to identify a causal relationship, but they suspect it might have something to do with the locus coeruleus, a small site found in the upper brain stem that has deep neural connections to the rest of the central nervous system. Not only does activity in this little-known crevice on the brain closely related to changes in pupil size, but also plays a role in the wider organization of brain activity needed to perform complex tasks.
The researchers argue there is some kind of relationship between a “well-oiled” locus coeruleus, an ability to perform well in tasks, and a larger pupil size.
“One possibility is that high ability individuals, even during a passive baseline state, are in a more task-ready state and at optimal levels of phasic locus coeruleus activity,” the study authors conclude in their paper.
“Another possibility, is that high ability individuals more optimally regulate activity in the locus coeruleus and this allows them greater ability to switch from one mental state to another; specifically, for switching between a high tonic exploration mode to a phasic exploitation mode of locus coeruleus activity. This function of switching from one mental state to another would also be consistent with the network-reset theory of locus coeruleus function and various interpretations of the pupil size – cognitive ability relationship,” they added.
Edited 10/06/2021: Due to an error, the 7th paragraph of this article originally said "The research did specifically look to identify a causal relationship." It has since been amended to say "did not."