Picture a sandy beach, waves lapping at the shore, and the Sun setting on the horizon. For most people this is an easy task, but for a small proportion, it’s impossible. Known as “aphantasia,” doctors have described for the first time a condition where people can’t form mental images in their “mind’s eye.”

It’s thought that as many as one in fifty people might have aphantasia. Some report that it makes them feel “alone” or “isolated,” knowing that they can’t see things that most people can, and that they feel distressed they can’t picture friends or deceased relatives. But others have learnt to live with it, and simply think that they experience life in a different way. One such person is Niel Kenmuir from Lancaster, England.

“I can remember not understanding what 'counting sheep' entailed when I couldn't sleep,” said Kenmuir in a statement. “I assumed they meant it in a figurative sense. When I tried it myself, I found myself turning my head to watch invisible sheep fly by. I've spent years looking online for information about my condition, and finding nothing. I'm very happy that it is now being researched and defined.”

This is where cognitive neurologist Professor Adam Zeman from the University of Exeter comes in, who named the condition in a new study published in Cortex. It was first identified in the 1880s and has occasionally been described as a result of major brain damage, but the phenomenon has, until now, attracted little attention. Then an article published in Discover magazine citing a previous paper by Zeman prompted 21 people to get in contact with him. Zeman then decided to describe their experiences in the new paper.

One of the patients with the condition, Tom Ebeyer from Ontario, Canada, didn’t realize he had it until he was 21. All of his senses are impacted, and he cannot recall sound, texture, or even smell. “It had a serious emotional impact,” he explained. “I began to feel isolated – unable to do something so central to the average human experience. The ability to recall memories and experiences, the smell of flowers or the sound of a loved one's voice; before I discovered that recalling these things was humanly possible, I wasn't even aware of what I was missing out on.”

Visualization is thought to be the result of a network of regions found throughout the brain all working together to generate images based on memories. The best guess so far is that in those who have aphantasia, somehow the links between these areas in the brain are disrupted. This would also help to explain how the condition can also be caused by major brain damage.

To confuse the situation even more, while those with aphantasia can’t voluntarily imagine pictures, the do still dream. Zeman is certain that the condition is real, but stresses that it is “not a disorder,” and plans on delving deeper and conducting more research.