An article about Zeman’s second paper appeared in the New York Times, and, after that, e-mails poured in. Around seventeen thousand people contacted him. Most were congenital aphantasics, and most not only lacked visual imagery; they could not mentally call up sounds, either, or touch, or the sensation of movement. Many had difficulty recognizing faces. Many said that they had a family member who was aphantasic, too. Most said that they saw images in dreams. Zeman recruited colleagues to work with him, and together they tried to reply to every correspondent.

Some people who wrote had once had imagery but lost it. About half of these had lost it as a consequence of physical injury—stroke, meningitis, head trauma, suffocation. The other half attributed their loss to a psychiatric cause—depersonalization syndrome, depression. A few told him that they thought they’d suppressed their capacity to visualize because traumatic memories had made imagery intolerable. [...]

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Zeman also received messages from people who appeared to have the opposite of aphantasia: they told him that their mental pictures were graphic and inescapable. There was evidently a spectrum of mental imagery, with aphantasia on one end and extraordinarily vivid imagery on the other and most people’s experience somewhere in between. Zeman figured that the vivid extreme needed a name as well; he dubbed it hyperphantasia. It seemed that two or three per cent of people were aphantasic and somewhat more were hyperphantasic.

Many of his correspondents, he learned, had discovered their condition very recently, after reading about it or hearing it described on the radio. Their whole lives, they had heard people talk about picturing, and imagining, and counting sheep, and visualizing beaches, and seeing in the mind’s eye, and assumed that all those idioms were only metaphors or colorful hyperbole. It was amazing how profoundly people could misunderstand one another, and assume that others didn’t mean what they were saying—how minds could wrest sense out of things that made no sense.

Some said that they had a tantalizing feeling that images were somewhere in their minds, only just out of reach, like a word on the tip of their tongue. This sounded right to Zeman—the images must be stored in some way, since aphantasics were able to recognize things. In fact, it seemed that most aphantasics weren’t hampered in their everyday functioning. They had good memories for facts and tasks. But many of them said that they remembered very little about their own lives.

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Isabel, like Parfit, remembered very little about her life. She kept boxes of souvenirs—ticket stubs, programs—but unless she looked at these things, or a friend reminded her, she didn’t recall most of the places she’d visited or things she’d done. She imagined that this could be a problem in a relationship, if you didn’t remember what you’d done together and the other person got upset and accused you of not caring, though fortunately she’d never been with someone like that. When she went out with friends who were full of stories, she’d worry that she wasn’t entertaining enough [...]

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In talking to a friend of hers, an aphantasic painter who was one of Zeman’s research subjects, Clare had realized that she was the opposite—hyperphantasic. Her imagery was extraordinarily vivid. There was always so much going on inside her head, her mind skittering and careening about, that it was difficult to focus on what or who was actually in front of her. There were so many pictures and flashes of memory, and glimpses of things she thought were memory but wasn’t sure, and scenarios real and imaginary, and schemes and speculations and notions and plans, a relentless flood of images and ideas continuously coursing through her mind. It was hard to get to sleep.

At one point, in an effort to slow the flood, she tried meditation. She went on a ten-day silent retreat, but she disliked it so much—too many rules, getting up far too early—that she rebelled. While sitting in a room with no pictures or stimulation of any kind, supposedly meditating, she decided to watch the first Harry Potter movie in her head. She wasn’t able to recall all two hours of it, but watching what she remembered lasted for forty-five minutes. Then she did the same with the other seven films.

She tried not to expose herself to ugly or violent images because she knew they would stick in her mind for years. But even without a picture, if she even heard about violence her mind would produce one. Once, reading about someone undergoing surgery without anesthetic, she imagined it so graphically that she fainted. [...]