(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........

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