It is well-known that pupils size changes depending on how bright the environment is. However, scientists have discovered that pupil size also changes depending on how many objects are being observed.
As if to accommodate all the objects it sees, the pupil will grow larger if there are more objects in a scene. The new research has shown that this "perceived numerosity” is an automatic reflex.
Researchers measured 16 participants' pupil sizes while they viewed pictures of dots. Some of the photos featured dots linked in dumbbell shapes, creating an illusion that there were fewer objects. The pupil size then decreased.
What the pupil does with different patterns and objects. (Castaldi et al., Nature Communications, 2021)
Elisa Castaldi, a neuroscientist and psychologist from the University of Florence, Italy says that this result proves that numerical information is intrinsically linked to perception.
"This could have important and practical implications. This ability can be impaired in dyscalculia, which is a disorder in math learning. Our experiment could help in the early detection of this condition in very young children.
The number of black and white dots in the images was not affected by the joining lines. However, it did affect the perception of the objects present. Participants were asked to simply look at the images without paying attention to any particular task or to pay special attention to the number of items.
It's possible that this reaction is related to survival. Most species have a dedicated number sense, which allows them to spot threats in the wild, find food and get home safely.
Humans are born with the ability to calculate numbers. Even if you don't know much about math, this ability is evident. It appears that our pupils dilate in response to this.
David Burr, a psychologist from Australia's University of Sydney, says that "when we look around, it spontaneously perceives the form, size and movement of a scene." He is also affiliated with University of Florence.
"We perceive the number of items in front of us equally spontaneously. This ability is shared by most animals: It reveals important quantities immediately, such as the number of apples on the tree or the number of enemies attacking.
Research has shown that light doesn't affect pupil size. Previous studies have also indicated that visual illusions such as brightness, size, context, and size can also influence the size of the pupils. This supports the theory that the brain controls the dilation.
Researchers are eager to find out more about why this is occurring and how it could impact pupil size, such as the movement required for the eye to absorb all that is in a scene.
There are many other things to learn here. Future studies will be able to analyze this reaction. It seems that our eyes are more sensitive to the number and arrangement of items.
Paola Binda, a physiologist at the University of Pisa in Italy, says that recent research has shown that pupil size can also be controlled by cognitive and perceptual factors.
Nature Communications published the research.