Two years ago, Sarah Shomstein realized she didn’t have a mind’s eye. The vision scientist was sitting in a seminar room, listening to a scientific talk, when the presenter asked the audience to imagine an apple. Shomstein closed her eyes and did so. Then, the presenter asked the crowd to open their eyes and rate how vividly they saw the apple in their mind.

Saw the apple? Shomstein was confused. She didn’t actually see an apple. She could think about an apple: its taste, its shape, its color, the way light might hit it. But she didn’t see it. Behind her eyes, “it was completely black,” Shomstein recalled. And yet, “I imagined an apple.” Most of her colleagues reacted differently. They reported actually seeing an apple, some vividly and some faintly, floating like a hologram in front of them.

In that moment, Shomstein, who’s spent years researching perception at George Washington University, realized she experienced the world differently than others. She is part of a subset of people — thought to be about 1% to 4% of the general population — who lack mental imagery, a phenomenon known as aphantasia. Though it was described more than 140 years ago, the term “aphantasia” was coined only in 2015. It immediately drew the attention of anyone interested in how the imagination works.

That included neuroscientists. So far, they’re finding that aphantasia is not a disorder — it’s a different way of experiencing the world. Early studies have suggested that differences in the connections between brain regions involved in vision, memory and decision-making could explain variations in people’s ability to form mental images. Because many people with aphantasia dream in images and can recognize objects and faces, it seems likely that their minds store visual information — they just can’t access it voluntarily or can’t use it to generate the experience of imagery.

That’s just one explanation for aphantasia. In reality, people’s subjective experiences vary dramatically, and it’s possible that different subsets of aphantasics have their own neural explanations. Aphantasia and hyperphantasia, the opposite phenomenon in which people report mental imagery as vivid as reality, are in fact two ends of a spectrum, sandwiching an infinite range of internal experiences between them.

“We think we know what we mean when we talk about what mental imagery is,” said Nadine Dijkstra, a postdoctoral researcher at University College London who studies perception. “But then when you really dig into it, everybody experiences something wildly different.”

That makes studying aphantasia, hyperphantasia and other internal experiences difficult — but far from unimaginable.

The Mind’s Eye

The brain’s process for creating mental images can be described as perception in reverse.

When we perceive something in front of us, “we try to infer meaning from an image,” Dijkstra said. Electromagnetic waves enter our eyes, are translated into neural signals and then flow to the back of the brain, where they’re processed in the visual cortex. The information then flows forward toward the front of the brain into memory or semantic regions — a pipeline that ends with us knowing we are looking at a cat or a cup of coffee.

“During imagination, we basically do the opposite,” Dijkstra said. You start with knowing what you want to imagine, like a cat, and information flows from the brain’s memory and semantic regions to the visual cortex, where the image is sketched. However, that’s a working model of visual imagination; there’s still much that is not known about the process, such as where mental imagery begins and the exact role of the visual cortex.

These processes were even less defined in 2003, when an articulate and bright 60-year-old man walked into Adam Zeman’s office. Zeman, a neurologist at the universities of Edinburgh and Exeter who studies visual imagery, listened as the patient recounted how, following a cardiac procedure, he could no longer conjure mental images. Before, when he read a novel, he could see the characters and the scenes. When he lost something, he could visualize where it might be. After his procedure, his mental stage was empty.

At the time, evidence was accumulating that the visual cortex activates when people imagine or perceive something. Zeman wondered whether his patient’s visual cortex had become somehow deactivated. He had the patient, Jim Campbell, lie down in a functional magnetic resonance imaging (fMRI) machine, which measures blood flow in the brain as a proxy for neural activity. Zeman showed Campbell pictures of famous people and then asked him to imagine them. In the scans, Campbell’s visual cortex lit up only when he saw the photos. In a 2010 case study, Zeman described him as having “blind imagination.”

After Discover magazine covered the case study, Zeman heard from an additional 20 or so people who said that they, like Campbell, couldn’t visualize images in their minds. Unlike Campbell, however, these people hadn’t lost the ability. They never had it in the first place.

Apparently, this was a somewhat common experience. In 2015, Zeman consulted a classicist friend to come up with a name for it. The classicist suggested adapting Aristotle’s word “phantasia,” for “mind’s eye,” to describe the phenomenon, and the term “aphantasia” was born. Soon after Zeman’s team reported the shiny new term, The New York Times published a story about aphantasia, triggering a fresh flood of interest. Zeman has now received more than 17,000 emails from people wanting to learn more about their vivid mind’s eye, or lack thereof.

“Creating the terms turned out to be an unexpectedly good trick to attract a lot of interest,” Zeman said.

At dinner tables around the world, friends and family discussed whether they could imagine an apple. Philosophers used aphantasia as an excuse to probe explanations for the mind. Art exhibitions displayed works created by people with these extremes in visualization.

And scientists dreamed up new ways to study aphantasia as a window into how imagination works.

Making Connections

Studying aphantasia wasn’t easy. How do you measure someone else’s inner reality? For years, research “focused on showing that the condition exists,” Shomstein said.

Early studies relied on reports from participants — and they still do. The most famous test is called the Vividness of Visual Imagery Questionnaire, created in 1973 to study the strength of mental imagery, long before aphantasia was named. However, such tests rely on introspection and self-reported experience, which made some neuroscientists doubt that aphantasia was real. Could reported differences in visual imagery be a language disconnect, given the ambiguity in how we describe our inner worlds?