When I was in elementary school, I occasionally had trouble falling asleep, and people would tell me to count sheep. I had seen the activity graphically depicted in cartoons, but when I tried it, I never saw anything — just black. I’ve been counting silently into the darkness for years.

There were other puzzling comments about visualizing things. My dad would poke fun at my bad sense of direction and reference a “mental map” of the city that he used for navigation. I thought he had superhuman powers.

But then, in my freshman year of college, I was struggling through Chinese, while my friend Shayley found it easy. I asked her how she did it, and she told me she was just “visualizing the characters.”

That’s when I discovered I had aphantasia, the inability to conjure mental images. Little is known about the condition, but its impact on my education led me to wonder about how it might be impacting others.

Aphantasia was first described by Sir Francis Galton in 1880 but remained largely neglected until Dr. Adam Zeman, a cognitive neurologist at the University of Exeter in England, began his work in the early 2000s and coined the name from the Greek word “phantasia,” which means “imagination.”

“My interest in it was sparked by a patient who had lost the ability to visualize following a cardiac procedure,” Dr. Zeman said. “He gave a very compelling account. His dreams became avisual; he ceased to enter a visual world when he read a novel.”

Dr. Zeman wrote about the case, calling the patient MX, and in 2010, the science journalist Carl Zimmer wrote about it in Discover magazine, and later, in The Times. Hundreds of people started contacting Dr. Zeman, saying they were just like MX, except that they had never had the ability to visualize.

Many educators believe visualization is key to reading comprehension since it allows readers to organize information in their minds, make inferences, and remember content more effectively. Research done by Marisa Cohen, an educational psychologist at St. Francis College in Brooklyn, has shown that students who were asked to create mental images of vocabulary words learned two to three times more words than those who simply read them aloud.

If visualization were essential to learning, the inability to do so might constitute a learning disability, but the reality is not that simple. Aphantasia is not a monolithic condition. People who believe they have aphantasia, known as aphants, debate in online groups about whether it should be deemed a disability. Some who are just finding out about their condition in their 50s or 60s say they never felt hindered, while others believe they failed courses in school because of it.

But aphantasia not only impacts people’s learning experiences; it also extends into their personal lives. Not being able to visualize means never picturing the faces of family or close friends and remembering images as abstract information. According to Dr. Zeman, it is correlated with having trouble recognizing faces (prosopagnosia), a bad sense of direction and poor autobiographical memory.

Dr. Zeman considers it merely a difference in perception and said many aphants who have contacted him are working successfully in creative fields such as art or architecture.

Many don’t discover that their experience is any different from that of others until their late teens or early 20s. It might be while reminiscing about the past and realizing they’re having a different experience with memory than their friends or family. It’s not that they don’t notice that they don’t visualize. They just don’t know that other people do.

Ashley Xu, a rising junior at Williams College, had this experience. A friend had come across an article about the condition and mentioned it to her in passing. “Did you know that there are some people who can’t picture things with their mind’s eye?” her friend asked.

Ms. Xu was confused. What did it mean to picture things in one’s mind? To try to explain, her friend asked her to visualize an apple.

“I couldn’t see it, but I didn’t know that was abnormal,” she explained. “In my mind, it was black, but I knew that there was a little leaf, there was a brown stem, it was a red apple, but I just couldn’t see it.”

It is possible that people who have identified their aphantasia still don’t know the full extent of what they’re missing. I learned only recently that metaphors are meant to evoke images. For instance, when some people hear “My job interview was a slam dunk,” they envision someone playing basketball. Who knew?

Robin Reymond, a third-grade teacher in New Haven, Conn., said that during her teacher training she was instructed to encourage students to create “mind movies” as they read. She was taught that visualization was “a key skill” and “if a child can’t do this, that’s detrimental to their learning.”

But Ms. Reymond herself had never been able to visualize, and was shocked to learn that other people did. Eventually she discovered that with concentration, she can see faint black and white outlines. Some see vivid, colorful images automatically, and they rely on these images to process information. Some can’t see anything at all, and many fall somewhere in between.

Ms. Reymond said she initially taught her students visualization as a strategy, but she has recently moved away from it, believing that as with other learning strategies, visualization is not the only way to succeed in school.

Aphants use an array of strategies to compensate for their lack of mental imagery, but since aphantasia varies from person to person, what works for some may not work for others.

Some draw on other mental senses, such as what might be called the mind’s ear. For example, I often read my notes aloud to myself and rely on auditory recall on tests. But that won’t work for everyone: Approximately half the people who have contacted Dr. Zeman about their aphantasia also describe an inability to conjure sounds, feelings or smells in their minds.

Others take a kinesthetic approach. When studying for her pre-med classes, Ms. Xu acts out scientific concepts with a friend, gesturing with her hands to make a lesson on ligand-receptor interactions stick.

I find patterns and make up elaborate mnemonics. To remember the Canadian provinces that border the United States for a quiz in high school, I came up with “British Airways! Sasquatch made it over the queue to New Brunswick” (British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, and New Brunswick). My teacher saw me doing this once and asked, “Isn’t it easier to just look at the map and memorize it?”

It’s not.

Teachers who are aware of aphantasia can help with tweaks to their lessons that may benefit the rest of the class, just as accommodations for students with learning disabilities can help reinforce lessons for other students.

For example, my Chinese professor adapted by drawing characters that look similar side by side on the board and discusses the distinctions between them, helping me and perhaps others as well.

Ultimately, aphantasia is just one of the many ways that people’s brains and learning styles are different. One of my friends says she visualizes every word that is spoken in class, while another friend who has attention deficit hyperactivity disorder has trouble filtering important noise from background noise to process lectures. Perhaps our difficulty in accepting and adjusting to these differences points to a limited understanding of the neurodiversity that surrounds us.

When I close my eyes, all I see is faint blue dots and darkness, and for 19 years, I assumed that’s what everyone else saw too. I wonder what else we take for granted.

Serena Puang, from Rogers, Ark., is a rising junior at Yale majoring in linguistics.