Maarten Peters and his colleagues, of the Department of Experimental Psychology at Maastricht University in the Netherlands, investigated the propensity for memory errors in people who make implausible claims. In many cases of false memories, it is very difficult to determine whether or not the perceived events actually occurred - that is, the “ground truth” can not be established. The experimental group was therefore chosen on the basis of a highly implausible claim - the group consisted of 11 women and 2 men, all of whom claimed to have recollections of a previous life. The performance of this group on a memory task was compared to that of a control group. It was found that people who claim to have lived past lives were more prone than the control group to memory errors. The findings were published recently in the journal Consciousness and Cognition.

The researchers used a modified version of a well established laboratory procedure for eliciting false recall of words. Participants were first asked to read aloud a list of 40 names of non-famous people. Two hours later, they were presented with another list, containing the old non-famous names (those that had been included in the previous list), new non-famous names, and the names of well-known actors, writers and politicians. They were then asked to make “fame judgements” on the names in the second list; that is, they were asked to determine whether or not each of the people on the list was famous or not. Those in the experimental group were found to be more susceptible than the control group to the “false fame illusion” - they were about twice as likely to identify the old non-famous names as famous names more than those in the control group.

How might such false memories form? In the study by Peters et al, the misidentification of names occurs because the previous encounter with the non-famous names is mistakenly taken as an indication that those people must be famous. This is an example of what is called a source monitoring error. Recollection of an event involves using information from various sources - one’s own memory, for example, and other peoples’ accounts of the event. When source monitoring is impaired, one has difficulty attributing where and how information was acquired, but the origins of unreliable pieces of information are unquestioned nevertheless; the unreliable information is therefore easily incorporated into a memory.

Clearly, people can, to a greater or lesser extent, be influenced by the suggestions of others. If one becomes convinced that a suggested event is plausible, one may start to believe that the event has actually taken place. Reiteration of the false memory leads to what is known as the “illusion of truth”. Furthermore, such claims can seem even more realistic when corroborated by other people. Hence, a group of people who share in common claims of an implausible event - such as being abducted by aliens, for example - will be convinced that their claims are real, because they will corroborate each other. The use of leading questions can also result in the inadvertent planting of false memories in people undergoing interrogation or cross-examination. Psychopathology is another cause of false memories; it is well documented that schizophrenics are prone to source monitoring errors in memory and other cognitive processes; thus, schizophrenics believe that the auditory or visual hallucinations they experience are real.

It is now also acknowledged that false memories can be deliberately planted. Psychiatrists have been known to implant completely false memories in their patients during therapy. Most commonly, these false memories are of events such as childhood sexual abuse or participation in Satanic rituals. In some cases, psychiatrists have been sued for malpractice, and defendants have been awarded millions of dollars in damages for the traumas they have experienced as a result.

Peters and his colleagues did not deliberately implant false memories in their participants, but other researchers have shown how easy it is to distort peoples' recollections of real events, or to coax people into "remembering" entire events that did not happen. In one experiment, led by Elizabeth Loftus, a professor of psychology at the University of California, Irvine, a false memory of a plausible and mildly traumatic event - getting lost in a shopping mall or a large department store as a child - was falsely implanted in experimental subjects. The subjects were asked to recall childhood events that had been recounted to them by their parents, older siblings or other close relatives. A booklet containing a paragraph about each of the recalled events, and one false memory (of being lost in a shopping mall) was then prepared for each of the participants. The participants were then asked to read each story in their booklet, and to write down what they remembered about each event. It was found that 5 out of the 24 subjects thought that they had experienced the false event; some claimed to remember it only partially, while others reported that they remembered it fully. Work by other research groups shows that memories of highly implausible events, and even impossible events, such as alien abduction and reincarnation, can be planted just as easily.