(NEXSTAR) – How vivid is your mind’s eye? If you were to try to picture an apple right now, can you see it? The shape, the color, the skin, the stem?

Or is there no picture at all?

Aphantasia, a phenomenon experienced by an estimated tens of millions of people across the globe, is characterized by the inability to actually conjure up a mental image — or “picture” something — in one’s mind.

“This symptom, although it’s rare, had been recognized for more than 100 years,” Adam Zeman, the neurologist who coined the term “aphantasia” and whose research on the topic raised awareness for the phenomenon, told Nexstar.

Zeman, also a Fellow of the Royal College of Physicians (FRCP) and professor of neurology at the University of Exeter in England, said there’s literature on the subject dating as far back as the 1880s — citing British psychologist Sir Francis Galton as one of the first to record the phenomenon — “but no one really paid that any attention.”

In a comprehensive review published recently in the Trends in Cognitive Sciences medical journal, Zeman drew from early writings on the absence of mental imagery, as well as his own extensive research with people who have experienced both lifelong and acquired aphantasia.

Many of the people Zeman studied were not even aware they were affected by aphantasia until they learned such a thing existed.

“Quite often in school, you’re asked to ‘picture’ something,” Zeman said. “Many of the [students] thought that was just a figure of speech.”

John Green, the best-selling author of “The Fault in Our Stars,” had nearly this exact experience upon realizing he had aphantasia in 2023.

“It’s baffling to me that some of y’all see stuff in your mind. You SEE it? The way your eyes see? I always thought ‘visualize’ meant thinking of the words/ideas/feelings associated with a thing, not actual visuals,” Green revealed, tweeting in real time that he was “freaking out” upon learning that he didn’t form mental images like the majority of his readers.

“Very occasionally — I can count the number of times it’s happened on one hand — I will suddenly feel as if I can glimpse something visually that’s in a story, but 99.99% of the time, it’s just text,” he said.

Zeman said this type of discovery later in life (John Green was in his mid-40s) is not uncommon in the aphantasia community. After publishing his initial paper on the phenomenon (and another in 2015 in which he coined the term “aphantasia”), said he’s been contacted by some people “in their 90s” who just learned they have this characteristic.

“I’m sure there are people who never know,” he told Nexstar.

Those with aphantasia frequently find out they have it via school (as mentioned above) or social situations like “reminiscing with family and friends,” Zeman has observed.

“You realize that other people seem to be reliving [the experience] in a way that you can’t,” he said. “That’s one common trigger.”

Or, like John Green, those with aphantasia may realize they have this characteristic via social media. A number of popular posts on the subject utilize a chart (like one Greene referenced in his tweet) which depicts a scale of visual imagination, usually based off of the work of psychologist David Marks, who developed the Vivid Visual Imagery Questionnaire (VVIQ) in the 1970s.

The makers of these charts often ask participants to picture an apple (or a bird, or a horse) and to match what they “see” in their minds with one of several pictures on the chart. These pictures are presented in a spectrum, with a realistic apple on one end and a blank space on the other. The former usually represents hyperphantasia — a condition characterized by extreme vivid mental imagery — and the latter indicates aphantasia.

Zeman, in researching aphantasia for decades, estimates that 3–4% of the population would score significantly low on evaluations of their own visual imagination, but only about 1% score the “lowest of the low” on such tests, meaning they don’t “visualize” anything at all, at least not while awake.

That doesn’t mean people without aphantasia can’t develop it later in life, though. Zeman’s first experience with an aphantasia case was a male patient who had just undergone heart surgery, and lost the ability to see with his mind’s eye.

“He previously entered a visual world in his mind, he dreamt visually, but not after a heart procedure,” Zeman said. “It was a symptom I’ve never come across before.”

Aphantasia can also develop after a stroke, head trauma, a brain injury or infection, or along with conditions including “depersonalization, depression, occasionally psychosis,” Zeman said.

It can also be genetic (though it doesn’t necessarily run in families), and research has shown an association between those with autistic traits and aphantasia.

In any case, aphantasia is not generally thought to be an obstacle in day-to-day life. One of the only abilities that affects many people with aphantasia, Zeman said, is face recognition and autobiographical memory, or memories of one’s own past.

“It may be a bit of a hindrance in social interactions, if you can’t reminisce,” Zeman said, “though there would be ways in which it’s actually an advantage.”

People with aphantasia, Zeman told Nexstar, have conveyed their belief that they “move on more easily” from potentially traumatic situations (they may not be “haunted” by the mental image of an ex-girlfriend or boyfriend, for instance), and live more in the “here and now” than others.

There’s also anecdotal evidence to suggest that those with aphantasia are less prone to PTSD, and they don’t tend to have the same neurological reactions when asked to recall disturbing imagery or film clips they had previously viewed.

And although aphantasia seems to “bias people a little toward the sciences,” Zeman said, it doesn’t mean it hampers creativity. Magician Penn Jillette (the vocal half of Penn & Teller) and former head of Pixar animation Ed Catmull are just a few prominent people who have spoken of their experiences with aphantasia. Oscar-winning animator Glen Keane, who worked with Disney’s animation studio for decades and is credited with designing Ariel from “The Little Mermaid,” is also frequently cited as an example of an artist with aphantasia.

“When he first did ‘The Little Mermaid,’ it’s a bunch of scribbles,” Catmull once told the BBC of Keane’s process. “And then it converges, after he works on it for a while, into this gorgeous piece of art.

“And as far as he’s concerned, that’s the right way to work because it means he’s looking deep down inside, for his emotions, and that’s what drives his drawing,” Catmull said.

Still, the concept of aphantasia can be shocking, confusing or even disheartening for those learning they have it, especially after being unaware that the majority of the population “visualizes” an apple in a much different way than they previously imagined possible.

“People tend to need a little time to reflect on it, and let the discovery bed down,” Zeman said. “But I would say I don’t think it’s a disorder. I think it’s an intriguing discovery in the human experience … Just one small piece in the big jigsaw of cognition.”