Resting pupil size could be a predictor of cognitive ability in humans, according to a study recently published in Cognitive Psychology.
It is established that pupil size reflects more than simply the amount of light entering the eye. However, it was previously thought that pupil size was too crude a measure of brain activity. More recently though, the discovery that activity in an area of the brain known as the locus coeruleus results in changes to pupil size has opened the possibility that pupil size could be a useful indicator of neural processing.
The locus coeruleus is a part of the brainstem with connections across the rest of the brain, including the prefrontal cortex, which plays a crucial role in cognitive abilities such as memory and intelligence. The locus coeruleus is the main source of neurotransmitter, norepinephrine in the central nervous system, which amongst other things regulates cognitive activity in areas such as the prefrontal cortex. Therefore, it is possible that pupil size may actually be a valuable reflection of neural activity which can be used to determine differences in cognitive ability in humans.
512 people took part in a series of studies conducted by Jason Tsukahara, Tyler Harrison & Randall Engle (Gerogia Institute of Technology), that investigated the relationship between resting pupil size and working memory (part of short term memory associated with immediate processing) capacity and fluid intelligence (the ability to think abstractly and problem solve). Pupils were measured by eye tracking units whilst participants carried out tasks relating to memory and fluid intelligence.
The results of the studies revealed that there are huge differences in resting pupil size in individuals with high cognitive ability compared to those with low cognitive ability. In some cases these differences were even visible to the naked eye. Additionally, differences in pupil size are maintained even when people are doing a task that requires mental exertion. Even factors like age and drug abuse (which are related to pupil size) did not account for the relationship between fluid intelligence and resting pupil size, meaning that determining resting pupil size could be an effective measure of an individual’s intelligence and cognitive capacity.
Although the findings of this study show that resting pupil size has the potential to help us understand mental processing, the authors state that ‘baseline pupil size is only reasonably formed speculation’. This means that further research is needed to fully understand the individual differences in resting pupil size.