Do you have a mind’s eye, the ability to not just remember, but visualize the past? Do you have an interior monologue? Rich childhood memories, full of sights, sounds, and smells? For science writer Sadie Dingfelder — speaking to an audience of about a dozen Monday night at the Edgewood Avenue bookstore Possible Futures — the answer to all these questions and a few more like it were a clear no.And until just a few years ago, she thought the same was true for everyone else. Until a fateful trip to the grocery store led her to become the subject of a few lab studies, and to the work of New Haven-area science journalist Carl Zimmer, and on and on — heading toward the edges of neurologists’ understanding of how varied the human experience can be.Dingfelder and Zimmer were present to celebrate the release of Dingfelder’s first book, Do I Know You?, a book that Dingfelder states in the book’s trailer she has no recollection of having written. That’s just a taste of the off-kilter and often self-deprecating humor that filled the evening, in the service of a much deeper point about how everyone’s brains might just be wired much more differently from one another than any of us think.Do I Know You? came about, Dingfelder said, because of a ​“mid-life crisis” she had at the age of 40, triggered by an encounter at the grocery store, in which she accosted a stranger that she thought for far too long was her partner. As she extricated herself from the situation, she had an unsettling thought: ​“This is not actually the kind of mistake anyone makes.”Sadie Dingfelder and Carl Zimmer. “Some people would have consulted a doctor,” she said. But being a science reporter, she instead signed up for a few neurological studies. Through them, she discovered she has four unusual neurological conditions. First, she is faceblind: she can’t recognize faces she has seen before. Second, she is stereoblind, meaning that her brain doesn’t construct vision equally from her right and left eyes, which means in turn that she doesn’t see in three dimensions. Third, she has aphantasia, which is the inability to visualize things in her mind, or as Zimmer put it, she doesn’t have a ​“mind’s eye.” Finally, she has severely deficient autobiographical memory (SDAM).“I have no childhood memories,” she said.Regarding faceblindness, she said, most humans ​“have a near-photographic memory for faces.” It’s not foolproof, but we do tend to remember people we have met. Police rely on victims of crimes to be able to remember the faces of criminals, and many people can do it. By contrast, ​“if a squirrel mugged you,” Dingfelder said, you wouldn’t be able to pick it out of a lineup of squirrels. That’s how it is for Dingfelder regarding other humans. ​“I learned that I’m in the bottom 2 percent for face recognition,” she said.Faceblindness is often associated with traumatic brain injuries, but in Dingfelder’s case it’s purely developmental. Her brain ​“did not get the neural tuning it needed when I was a kid.” It turned out she wasn’t the only one. Starting in the 1990s, she said, ​“people with rare diseases were the power users of the internet,” finding each other and forming online communities. They had much in common with one another, and not as much in common with, well, everyone else.“Learning this about myself was a shock,” Dingfelder said. Up until she was 40, she assumed she was normal; she now knows ​“my consciousness and inner life are really different from the norm.” But as she read about the latest developments in neurology about these topics, she found a broader lesson in that — that there’s ​“way more variety in the human experience than we might have thought.”She also found, in hindsight, that it explained a lot about her past. She wrote an article in the Washington Post about her faceblindness, and one result of that was to reconnect with friends and acquaintances from high school and earlier. She recalled often feeling lonely then. ​“I thought I was weird and that kids were mean.” She allowed that might still be true, but also, ​“people were trying to be friends with me” and she couldn’t sustain many of those relationships because she didn’t recognize them from day to day, leading others to believe she was blowing them off. Her brother then sent her an article by Zimmer about aphantasia — people who don’t have a mind’s eye. A neurological scan of her brain confirmed she had it. Most people’s brains, she said, light up when they recognize faces and places. ​“My brain is not doing anything.” At the other end of the spectrum is hyperphantasia: people who can remember and imagine in great detail; neurologically, it turns out, ​“remembering is actually a lot like seeing,” Dingfelder said. She happens to have a friend with hyperphantasia. One of the products of it, Dingfelder said, is that her friend has difficulty moving on from romantic relationships, as ​“the guys are living in her mind,” Dingfelder said, whereas Dingfelder has been able to move on in a matter of weeks. Her friend also has a rich interior monologue, and sometimes dialogue, whereas Dingfelder doesn’t know what she’s thinking until she talks or writes, and assumed for years that the internal monologue she saw in movies was also a metaphor.Zimmer explained that the article Dingfelder read was part of a regular series of articles he writes, now for the New York Times, about neurology and the brain. It was about a case of a man ​“who had lost his mind’s eye,” Zimmer said, possibly because he’d had a small stroke. ​“He couldn’t picture things anymore.” In response to that article and articles like it since, he said, he has gotten a flood of correspondence from readers who don’t have a mind’s eye either, and until they read the article, had always assumed that it was a metaphor. Zimmer has been forwarding their information to British neurologist Adam Zeman, who has been able to do more research thanks to that — research that suggests that worldwide there are probably hundreds of millions of people with aphantasia.“It was cool to be there, watching something begin,” he said of Zeman’s expanding studies.Those studies have yielded other results. A person with aphantasia doesn’t get as worked up by reading an account of a stressful situation — say, a shark attack, Dingfelder said. Most people, she said, ​“shvitz a little bit,” whereas aphants ​“stay cool.” “I don’t think I can be hypnotized,” she added.There are also wrinkles in her ability to visualize. She hallucinates under the effects of psychedelics. And ​“I have beautiful, vivid, interesting dreams that I forget as soon as I wake up,” she said.For both Dingfelder and Zimmer, the differences in cognition had no value judgment attached to them; they simply reflected different ways of thinking. For some people, ​“language is for thinking.” For others, it’s ​“for communication.” Not everyone thinks with words; it doesn’t mean they’re not thinking. Having met a community of people with similar wiring, she identifies a spectrum even within that group. Some, she thinks, are doing some ​“unconscious visualizing” when they think. ​“And then there’s people like me,” Dingfelder said.“The mind’s eye and the mind’s voice — these are all on a spectrum,” Zimmer said.Meanwhile, Dingfelder’s stereoblindness means that she can neither catch a ball nor thread a needle, and she often stubs her toe or trips on things. Her conditions are ​“an invisible force” that has shaped her life, but it’s also ​“a way in which my brain is measurably different.” And ​“the joy of writing is finding out what I think.”There are downsides to Dingfelder’s state. One is that it runs diagonal to a lot of therapeutic approaches, which associate few memories with a state of trauma. But ​“I wasn’t traumatized,” Dingfelder said. ​“It’s just the way my brain works.” Dingfelder saw advantages, too — including being free of what she perceived sometimes as inner turmoil in others. A certain clarity can also come with having fewer memories. ​“I can’t remember any details, but I always get the big picture,” she said. She struggled early in school, when memorization was important. But once schooling was testing for abilities to grasp larger concepts and general ideas, she excelled.“I would not trade my brain for these visualizing, talkative brains,” she said. In mindfulness exercises she’s done, in which she’s told to clear her head, she’s already there, and the danger is mostly that she will fall asleep. ​“My mind is quiet,” she said.For information about other events at Possible Futures, visit the bookstore’s website.