Cambridge, Mass. ? Susan Clancy is sick of space aliens.

The Harvard psychologist figures she has read every book and seen every movie ever made about extraterrestrials, and she has interviewed roughly 50 people who claim to have been abducted by aliens.

And it’s all in the name of scientific truth, not science fiction.

“I have become a reluctant scholar of alienography,” Clancy said.

Clancy is bracing for a fresh round of hate mail with her new book, “Abducted: How People Come to Believe They Were Kidnapped by Aliens,” published by Harvard University Press.

Those who believe aliens are among us haven’t taken kindly to her theory that abductees have created “false memories” out of, she writes, a “blend of fantasy-proneness, memory distortion, culturally available scripts, sleep hallucinations and scientific illiteracy.”

That doesn’t mean Clancy thinks her subjects are crazy. In fact, she was surprised how many of them seemed quite normal, intelligent and articulate.

“Arguing weird beliefs is a very normal thing,” she said in an interview from Nicaragua, where she is a visiting professor at INCAE, the Central American Institute for Business Administration. “It’s very human for us to believe in things for which there is no scientific evidence.”

Susan Clancy, a Harvard psychologist, is the author of Abducted:

Common threads

When she arrived at Harvard in 1996, Clancy didn’t set out to debunk the stories of little green men kidnapping people from their bedrooms and using them for painful experiments. Instead, she started her research on false memories by studying victims of sexual abuse.

She quickly found herself the target of angry “outsiders” who accused her of trying to discredit victims. One irate letter-writer called her a “friend of pedophiles everywhere.”

Around the same time, Harvard Medical School started investigating the research methods employed by Pulitzer Prize-winning psychologist John Mack, who used hypnosis to retrieve memories from people who claimed to be alien abductees. (The school decided not to censure Mack, who was struck and killed by a drunken driver in London last year.)

Mack’s work gave Clancy an idea: Wouldn’t it be easier to test her theories if she could be certain that her subjects’ memories were not real? She and her adviser, Harvard psychologist Richard McNally, placed a newspaper ad that asked, “Have you been abducted by aliens?” It took less than a day for callers to fill her voice mail.

As Clancy and McNally interviewed the abductees, they started to find some common threads. Many of them, for example, described the terrifying experience of waking up and being unable to move, certain that an intruder was lurking in their room.

To the Harvard psychologists, it was obvious that their subjects had suffered an episode of sleep paralysis – a state of limbo between sleep and being awake, sometimes punctuated by hallucinations.

“It’s a little bit like a hiccup in the brain. It’s harmless,” said McNally, adding that 20 percent of the population will experience sleep paralysis at least once.

False memories

Many of the abductees also could be described as “spiritual people” who have abandoned conventional religious beliefs, McNally added. “The people convinced of this are getting genuine spiritual payoff,” he said. “To encounter a naturalistic account of it is deeply offensive.”

In her book, Clancy describes her subjects’ stories of abduction in detail, changing only their names.

One man, “an articulate, handsome” chiropractor with a “strikingly attractive wife” and twin sons, claimed to have fathered hybrid babies with an alien, a “streamlined, sylphlike creature.”

Another subject, a 34-year-old artist with a college education, couldn’t identify “disturbing sleep-related experiences” until he was hypnotized by an abduction researcher he found on the Internet. During his second hypnosis session, the artist said he recovered memories of being abducted by aliens who strapped him down on a black marble table and subjected him to a painful sexual experiment.

Clancy said a wealth of research shows that hypnosis makes it easier for people to create false memories.

“This is in large part because it both stimulates the imagination and relaxes reality constraints,” she writes in her book.

However, Clancy learned it was impossible to categorically disprove alien abductions.

“All you can do is argue that they’re improbable and that the evidence adduced by the believer is insufficient to justify the belief,” she wrote. “Ultimately, then, the existence of ETs is a matter of opinion, and the believers have their own opinions, based on firsthand experience.”

Clancy said the volume and nasty tone of the hate mail she gets these days is far worse than what her research on sexual-abuse victims generated.

“I’m done with aliens,” she said.