Inability to See Pictures in the Mind Can Be Seen in a Person's Pupils

Your pupils may give away a telltale sign of whether or not you have a mental characteristic known as aphantasia—the inability to create visual imagery in your mind—a study suggests.

A couple of years ago, aphantasia took social media by storm. In February 2020, a viral Twitter post challenged users to close their eyes and conjure up an image of an apple in their heads. They were then asked to rate their apple from one to five depending on how clear and vivid it appeared in their heads, with one being a very clear apple and five being no apple at all.

The user who created the post stated that they themselves could not imagine an apple at all and so scored a five.

The post went viral and today has more than 56,000 likes and 33,000 quote tweets. The comments are full of people claiming different results. Some users were shocked that others could not visualize an apple. Others seemed surprised that other people possessed the ability to do so.

Clearly, people who cannot mentally visualize objects are not alone—though apparently the phenomenon only crops up in a small percentage of people. The name for it is aphantasia, and until recently it has been relatively unstudied.

Earlier this year, a team of researchers set out to investigate whether the pupils in peoples' eyes react to purely imaginary stimulation—that is, would someone's pupil contract if they simply imagined seeing a bright light?

To find out, the researchers formed a group of 42 people who self-reported as having a visual imagination and fitted them with glasses that tracked their pupil sizes. They were then shown bright or dark shapes to see how their pupils responded. Then, they were asked to simply imagine those same shapes of varying darkness and brightness.

The researchers found that the pupils of people who were able to visualize objects in their minds did indeed react when they were asked to simply visualize dark and light objects, and the effect was more pronounced in people who reported greater vividness in their imaginations.

The researchers then gathered a group of 18 people who self-reported as having aphantasia. Their pupils reacted similarly in the first part of the test involving real light. However, in the second part of the test where they were asked to simply visualize the light and dark objects, their pupils did not significantly change.

Joel Pearson is a professor at the University of New South Wales School of Psychology in Australia and senior author of a paper describing the findings. He said in a university press release: "Our results show an exciting new objective method to measure visual imagery, and the first physiological evidence of aphantasia. With over 1.3 million Australians thought to have aphantasia, and 400 million more internationally, we are now close to an objective physiological test, like a blood test, to see if someone truly has it."

The research, titled "The pupillary light response as a physiological index of aphantasia, sensory and phenomenological imagery strength," was published in the journal eLife on March 31, 2022.