Kaavya Viswanathan has an excuse. In this morning’s New York Times, the author of How Opal Mehta Got Kissed, Got Wild, and Got a Life explained how she “unintentionally and unconsciously” plagiarized upward of 29 passages from the books of another young-adult novelist, Megan McCafferty. Viswanathan said she has a photographic memory. “I never take notes.”

This seems like as good an opportunity as any to clear up the greatest enduring myth about human memory. Lots of people claim to have a photographic memory, but nobody actually does. Nobody.

Well, maybe one person.

In 1970, a Harvard vision scientist named Charles Stromeyer III published a landmark paper in Nature about a Harvard student named Elizabeth, who could perform an astonishing feat. Stromeyer showed Elizabeth’s right eye a pattern of 10,000 random dots, and a day later, he showed her left eye another dot pattern. She mentally fused the two images to form a random-dot stereogram and then saw a three-dimensional image floating above the surface. Elizabeth seemed to offer the first conclusive proof that photographic memory is possible. But then in a soap-opera twist, Stromeyer married her, and she was never tested again.

In 1979, a researcher named John Merritt published the results of a photographic memory test he had placed in magazines and newspapers around the country. Merritt hoped someone might come forward with abilities similar to Elizabeth’s, and he figures that roughly 1 million people tried their hand at the test. Of that number, 30 wrote in with the right answer, and he visited 15 of them at their homes. However, with the scientist looking over their shoulders, not one of them could pull off Elizabeth’s trick. *

There are so many unlikely circumstances surrounding the Elizabeth case—the marriage between subject and scientist, the lack of further testing, the inability to find anyone else with her abilities—that some psychologists have concluded that there’s something fishy about Stromeyer’s findings. He denies it. “We don’t have any doubt about our data,” he told me recently. Still, his one-woman study, he says, “is not strong evidence for other people having photographic memory.”

That’s not to say there aren’t people with extraordinarily good memories—there are. They just can’t take mental snapshots and recall them with perfect fidelity. Kim Peek *, the 53-year-old savant who was the basis for Dustin Hoffman’s character in Rain Man, is said to have memorized every page of the 9,000-plus books he has read at 8 to 12 seconds per page (each eye reads its own page independently), though that claim has never been rigorously tested. Another savant, Stephen Wiltshire, has been called the “human camera” for his ability to create sketches of a scene after looking at it for just a few seconds. But even he doesn’t have a truly photographic memory. His mind doesn’t work like a Xerox. He takes liberties.

Photographic memory is often confused with another bizarre—but real—perceptual phenomenon called eidetic memory, which occurs in between 2 and 15 percent of children and very rarely in adults. An eidetic image is essentially a vivid afterimage that lingers in the mind’s eye for up to a few minutes before fading away. Children with eidetic memory never have anything close to perfect recall, and they typically aren’t able to visualize anything as detailed as a body of text.

In every case except Elizabeth’s where someone has claimed to possess a photographic memory, there has always been another explanation. A group of Talmudic scholars known as the Shass Pollakssupposedly stored mental snapshots of all 5,422 pages of the Babylonian Talmud. According to a paper published in 1917 in the journal Psychological Review, psychologist George Stratton tested the Shass Pollaks by sticking a pin through various tractates of the Talmud. They responded by telling him exactly which words the pin passed through on every page. In fact, the Shass Pollaks probably didn’t possess photographic memory so much as heroic perseverance. If the average person decided he was going to dedicate his entire life to memorizing 5,422 pages of text, he’d probably also be pretty good at it. It’s an impressive feat of single-mindedness, not of memory.

Truman Capote famously claimed to have nearly absolute recall of dialogue and used his prodigious memory as an excuse never to take notes or use a tape recorder, but I suspect his memory claims were just a useful cover to invent dialogue whole cloth. Not even S, the Russian journalist and professional mnemonist who was studied for three decades by psychologist A.R. Luria, had a photographic memory. Rather, he seemed to have implicitly mastered a set of mnemonic techniques that allowed him to memorize certain kinds of information.

Viswanathan is hardly the first plagiarist to claim unconscious influence from memory’s depths. George Harrison said he never intended to rip off the melody of the Chiffons’ “He’s So Fine” when he wrote “My Sweet Lord.” He had just forgotten he’d ever heard it. And when a young Helen Keller cribbed from Margaret Canby’s “The Frost Fairies” in her story “The Frost King,” Canby herself said, “Under the circumstances, I do not see how any one can be so unkind as to call it a plagiarism; it is a wonderful feat of memory.” Keller claimed she was forever after terrified. “I have ever since been tortured by the fear that what I write is not my own. For a long time, when I wrote a letter, even to my mother, I was seized with a sudden feeling, and I would spell the sentences over and over, to make sure that I had not read them in a book,” she wrote. “It is certain that I cannot always distinguish my own thoughts from those I read, because what I read become the very substance and texture of my mind.”

Psychologists label this kind of inadvertent appropriation cryptomnesia, and have captured the phenomenon in the laboratory. In one study, researchers had subjects play Boggle against a computer and then afterward try to recreate a list of the words they themselves found. Far more often then expected, the researchers found that their subjects would claim words found by the computer opponent as their own. Even if cryptomnesia is a real memory glitch that happens to all of us from time to time, however, it’s hard to figure how it could lead to the involuntary swiping of 29 different passages.

Then again, who knows, maybe Viswanathan really does have a photographic memory. She could be the first (or second). Earlier this year, a group of memory researchers at the University of California-Irvine published an astonishing article about a woman called AJ who can apparently remember every day of her life since childhood. Such people weren’t supposed to exist. Her case totally upends everything we thought we knew about the limits of human memory. The scientists even had to coin a new name for her disorder, hyperthymestic syndrome. If Viswanathan really wants to stick to her story, I know a few scientists who’d probably like to meet her. She might even be able to get a syndrome named after her.

Correction, April 28, 2005: Kim Peek’s name was originally misspelled. ( Return to the corrected sentence.) May 8, 2006: The original paragraph stated incorrectly that John Merritt was skeptical of Charles Stromeyer III’s claims. It also stated that 15 people who took Merritt’s test came into his lab. In fact, he visited them at their homes. Return to the corrected paragraph.