Pupils Perceive Numerosity

A New Study Demonstrates That Pupils Perceive Numerosity

You may be aware of the fact that the size of the pupils in human’s eyes alters based on the light of the environment, however, there is much more to be understood. Researchers have recently found that the changes in pupil size are additionally determined by the number of objects people are observing.

The more objects we see, the bigger the pupil becomes so as to get a better picture of what we are looking at. This observed numerosity is an automatic and simple reflex, according to the new study.

In this research, scientists examined 16 participants’ pupil sizes as they observed the images of dots. In a few images, the dots were connected together in the form of a dumbbell- producing a fewer object illusion- and the size of the pupil then contracted.

Elisa Castaldi, Neuroscientist & Psychologist from the Italy’s University of Florence stated that this finding (i.e. Pupil dilates based on the number of objects) indicated that numerical information is intrinsically associated with perception.

This can have practical and important implications. For instance, this potential is compromised in dyscalculia, a math learning disability, hence their study might be beneficial for the early diagnosis of this condition in toddlers.

Although the numbers of white or black dots in the images observed did not alter, the number of objects perceived changed, due to the connection of lines. The participants were requested to passively view these images, without a particular task to finish and without paying close attention to the total number of objects.

The reaction of pupils to different patterns and objects. Image Credits: Castaldi et al., Nature Communications, 2021

As for the reason behind this response, it is probably going to be associated with the need for survival- the majority of the species are considered to have a specific number sense that allows them to return home, find food, identify predators or enemies in the wild, and many others.

For humans, perceiving numbers is something that is acquired as soon as a couple of hours after birth- despite your poor mathematical skills, you have a built-in potential for perceiving numerosity, and it seems the pupil dilation is part of a reaction to this.

David Burr, who is affiliated with Italy’s University of Florence and a Psychologist at the Australia’s University of Sydney mentioned that when randomly observing the surrounding, humans immediately perceive the color, movement, size, and the form of a scene.

Humans perceive the number of objects in front of them equally spontaneously. This aptitude, which is present in many other animals, is an evolutionary basic: it shows immediately crucial quantities like the number of attacking enemies or the number of apples present on the tree.

The former study had demonstrated that the size of the pupil was not simply affected by the light: visual illusion comprising context, size, and brightness have an influence as well, supporting the notion that this dilation of the pupils is at least partially regulated by signals present within the brain.

The scientists are curious to explore more to find the reason behind this response and find other factors that can affect the size of the pupil- like the movement need by the eye to perceive everything as seen.

Also, there is much more to be understood. Human eyes are quite sensitive to the number of objects observed rather than their arrangement or spacing, which is another response that can be further examined in the future.

Paola Binda, a Physiologist from Italy’s University of Pisa claimed that new studies from their lab demonstrated that the size of the pupil is additionally controlled by perceptual and cognitive factors.

The findings have been published in the journal, Nature Communications.


Pupils Perceive Numerosity, Pupil Dilates Based On Number Of Objects

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