People who fake symptoms of mental illness can convince themselves that they genuinely have those symptoms, a new study suggests. People will also adopt and justify signs of illness that they never reported themselves when presented with manipulated answers, according to the study published online July 9 in the Journal of Clinical and Experimental Neuropsychology. Not only do the findings demonstrate that deliberately feigning illness can evolve into an unconscious embellishment of symptoms, they indicate that self-perception of mental health is susceptible to suggestion. The study has particularly serious implications for cases in which people fake mental illness to take advantage of the legal system.

"This study shows a couple ways people come to believe they have troubles they wouldn't otherwise endorse," says Elizabeth Loftus, a psychologist at the University of California, Irvine, renowned for her research on misinformation and false memories. "One way is to give them misinformation about what they reported before, but this study shows yet another kind of suggestion, which is to induce people to, in essence, lie. And it leaves them with a residual effect to keep doing so. Once you get people to report a particular symptom, like 'I have a little trouble concentrating,' even if they would never say that on their own, you turn them into someone who later on says they do have trouble concentrating."

In the new study psychologist Harald Merckelbach and colleagues at Maastricht University in the Netherlands first asked 31 undergraduates to read a story about a criminal defendant who had trespassed on a medieval building, dislodged some stones that fatally wounded a young girl, and received a charge of manslaughter. The experimenters told all participants to pretend they were the defendant in the story and complete a 75-item true-or-false self-report survey of mental health called the Structured Inventory of Malingered Symptomatology (SIMS). The SIMS includes "very bizarre and extreme symptoms that most real patients would not endorse," Merckelbach says, such as hearing ever-present voices or the sensation of 1,000-kilogram weights attached to one's legs. The researchers asked one subset of the subjects to fill out the survey honestly, instructing the rest to exaggerate their symptoms in hopes of feigning a mental illness and minimizing criminal responsibility.

Once the undergraduates had completed the survey, they were asked to spend an hour on games and tasks like sudoku puzzles before completing the SIMS once again. This time, the researchers instructed both subgroups to fill out the survey honestly (although still playing the role of defendant): participants who had feigned illness were told that they had been detected as fakers and needed to complete the survey with truthful answers; the other group was told that sometimes people change their minds about their symptoms and so they should fill out the SIMS again. The group that initially reported their symptoms honestly hardly changed their answers. But the mental illness pretenders continued to exaggerate their symptoms, despite the request for sincerity.

In a second experiment the researchers asked a group of 28 different undergrads to complete the Symptom Checklist-90 (SCL-90)—a 90-item self-report survey of general psychiatric stress, including difficulty concentrating, social anxiety, depression, sadness and panic attacks as well as somatic symptoms like headaches. Participants rated how frequently they experienced each item using a five-point scale, where 0 meant "not at all," 2 meant "occasionally" and 4 meant "all the time".

Once more, the experimenters had undergrads busy themselves with sudoku puzzles after completing the survey—but this time the researchers secretly changed some of the participants' answers while they were distracted. Specifically, the researchers manipulated two items: one about concentration difficulties and another about social anxiety, increasing low scores by two scale points or decreasing scores by two points if the participant had circled a 3 ("a lot") or 4.

Then the experimenters returned the answer sheets to the undergraduates and asked them to explain their scores on 10 items, including the two tweaked answers. Fifty-seven percent of the subjects failed to notice both manipulated answers, and more than two thirds of the subjects justified scores they had never actually reported. For example, if the researchers had switched a participant's original score on concentration difficulties from 0 to 2, the participant would explain the answer by citing an excess of coffee or anxiety about exams. The experimenters subsequently provided the participants with an abbreviated 30-item version of SCL-90 and found that on the second time around people who had justified their manipulated answers filled out the SCL-90 in the direction of the manipulation. Although this shift was statistically significant, Merckelbach and his colleagues would like to independently confirm it with more research, they noted in their study.

"If you play the role of having a disease, then at some point the symptoms may become very real to you," Merckelbach says, adding that the progression from purposefully faking symptoms to truly believing them could be exacerbated by doctor–patient relationships. "For example, when you talk about whiplash or chronic fatigue disorder, you can imagine a patient who starts out playing these symptoms, but when he is asked by a physician, 'Do you also have this or that?' and the questions are posed over and over again, the patient may lose sight of the fact the they are playing a role."

Loftus thinks the new study also shows how people can delude themselves. "The second experiment is more like the misinformation experiments I have done," Loftus said, referring to studies in which intentionally manipulative questions affected people's memory of footage from a car accident. "They don't know they are being deceived. But this study shows you can deceive yourself, too. In the first experiment, they [the participants] know they are deliberately faking. It's like a lie—a kind of a lie. But later on, they don't stop lying, even though they know they don't need to. They've deceived themselves."

Both Merckelbach and Loftus think the recent study is particularly relevant to malingering in legal procedures—when people feign illness or injury for a specific personal gain, like decreased criminal responsibility or increased financial compensation. Merckelbach drew inspiration for the study from the 20th-century Russian playwright Leonid Andreyev's The Dilemma, in which a character who malingers a disease eventually develops the symptoms that he faked. "Andreyev was the first to describe this phenomenon, and he was a court reporter," Merckelbach says. "He may have seen it with his own eyes."

Faking illness to benefit oneself can actually be a form of self-harm, Loftus says. "In some ways this is suggesting that when people get into litigation and have a motivation to act somewhat more injured than they really are to get a better settlement, they are actually harming themselves by pretending. They're becoming delusional."

Merckelbach agreed, pointing out that malingering could affect how defendants remember events as well. "A lot of perpetrators who are arrested by the police claim amnesia: Their genuine memory for the crime is undermined by faking of memory loss," he says.

"The whole area of malingering research is booming right now," Merckelbach adds, "with new instruments and tests to detect malingerers—almost an epidemic of tools and tests and tactics. I think what this study shows is that people can stick to the role of the malingerer, even when instructed to be honest. If you really want to screen malingerers, you need a test that accounts for both the intentional and unintentional components. It's not enough to have a simple self-report list because you don't know whether the person is really faking or deceiving themselves."

Loftus also sees therapeutic potential in the new study, musing on a hypothetical strategy she calls "feigning good," which could motivate patients by helping them believe in improved cognitive skills and diminished symptoms of illness. "Should clinicians be prescribing a form of feigning? You wouldn't want patients to feign anxiety, but maybe they could feign the opposite. Maybe they could feign crystal clear concentration," Loftus says.

Merckelbach thinks the idea is fascinating. "The whole idea is new to me," he says, "I didn't think of it myself…. But if it could be applied in a more therapeutic way, it might be worth doing some experiments on that."