Pupil Size found to Vary based on Number of Objects You’re Looking at

A compelling study has found pupils respond in the same way to the number of objects in one’s field of vision as they do to light. Experiments revealed pupils dilate in response to images with larger quantities of dots, indicating sensing numbers is an intrinsic perceptual mechanism.

Everyone is familiar with their pupil size varying in response to different light conditions. It is one our most basic automatic sensory responses. And while luminance is the main factor determining pupil size, there are plenty of other stimuli that can influence pupillary responses, from drugs and hormones to arousal and attention.

“When we look around, we spontaneously perceive the form, size, movement and color of a scene,” explains David Burr, co-author on the new study. “Equally spontaneously, we perceive the number of items before us. This ability, shared with most other animals, is an evolutionary fundamental: it reveals immediately important quantities, such as how many apples there are on the tree, or how many enemies are attacking.”

This new study focused on the relationship between pupillary response and our seemingly hardwired ability to sense numbers. A number of participants were tasked with passively looking at several images containing varying numbers of dots.

“Participants passively observed arrays of black or white dots of matched physical luminance but different physical or illusory numerosity,” the researchers explain in the study. “In half the patterns, pairs of dots were connected by lines to create dumbbell-like shapes, inducing an illusory underestimation of perceived numerosity; in the other half, connectors were either displaced or removed.”

A graphic depiction of the study’s results Castaldi et al.

The results revealed pupils widened, or dilated, in response to a greater number of individual dots. When images were shown with fewer single dots, participants’ pupils rapidly constricted. Elisa Castaldi, an author on the new study from Florence University, says the findings demonstrate how deeply connected primary visual perception is to numerical information. And this discovery could also lead to practical clinical applications diagnosing problems in numerical cognition.

“For example, this ability is compromised in dyscalculia which is a dysfunction in mathematical learning, so our experiment may be useful in early identification of this condition in very young children,” says Castaldi. “It is very simple: subjects simply look at a screen without making any active response, and their pupillary response is measured remotely.” The new study was published in the journal Nature Communications.

Source: University of Sydney

This article was originally published in New Atlas.