DENVER, Feb. 17 (UPI) -- Memories can be vivid, emotionally powerful, realistic -- and completely false, researchers reported late Sunday.
The findings could have important implications for evidence presented in court that is based on the testimony of witnesses.
Elizabeth Loftus, professor of psychology at the University of California, Irvine, described studies in which more than one-third of the subjects could be persuaded they had experiences that turned out to be demonstrably false.
At a news briefing at the annual meeting of the American Association for the Advancement of Science, Loftus detailed one study in which college students reviewed several "ads" for Disneyland that featuring Bugs Bunny -- a Warner Brothers cartoon character with no connection to the amusement park.
Afterward, when the students were asked questions about childhood visits they made to Disneyland, 36 percent responded they had met Bugs Bunny there, Loftus reported.
"Many of them described detailed experiences with Bugs, a memory that has to be impossible," she told reporters.
Loftus also found subjects' memories surrounding traumatic events could be manipulated. She and colleagues in Russia documented how approximately 12 percent of study subjects there could be manipulated by interviewers. The subjects later described specific false details -- planted by the interviewers -- about news events, such as a 1999 terrorist bombing in Moscow that killed more than 200 people, and the World Trade Center attack.
The vividness of false memories also can produce intense physiological symptoms similar to Post Traumatic Stress Disorder when relived, said Richard McNally, a psychology professor at Harvard University in Cambridge, Mass.
McNally said he had 10 individuals, all of whom had claimed to be abducted by aliens, listen to tape recordings of their previous descriptions of the experience. He found their heart rates, levels of sweating and other measures of emotional response paralleled those of individuals who actually had experienced traumatic events in their lives and who listened to their own tape recordings of those experiences.
"If you genuinely believe you've been traumatized, you'll show the same physiological reactions as people who have PTSD," McNally said, adding the individuals who claimed to be abducted showed no signs of mental illness.
He said such persons tended to be interested in so-called New Age beliefs, such as tarot cards and channeling. They also tended to fantasize and experience hypnopompic hallucinations, in which subjects think they have been awakened while dreaming.
Although his research did not deal directly with memory, Joel Weinberger, professor of psychology at Adelphi University in New York, said the controversial practice of flashing subliminal messages on a television screen could influence subjects' attitudes, for example, about political candidates. Subjects who viewed screens where the word "rats" was flashed over political ads later rated the candidates negatively.
"They regarded them as less trustworthy, more fishy, more disgusting," Weinberger said, adding subjects who viewed screens that flashed positive messages did not rate the candidates positively.
Loftus said although fewer than half the subjects in her studies displayed false memories, she argued the effect can be quite persuasive -- even if it is to the subject's detriment. She cited instances in which police interrogators will lie to suspects and cause them to confess to crimes they did not commit.
The false-memory effect can be widespread -- to the point of mass hysteria -- Loftus noted, as in last fall's sniper incidents in Washington, D.C., in which "there was the case of the white van that everyone was searching for that did not exist."