Looking for the Roots of 'False Memories'

VOLUME 30 , NUMBER 9 October 1999

Looking for the roots of 'false memories'

By Beth Azar
Monitor staff

Get together with friends and you'll most likely hear countless stories of sincere childhood memories that on close analysis by family members turn out to be false. It wasn't you but your sister who was with Aunt Barbara when she wrecked her car. And that favorite ride-on toy belonged to your neighbors, not you.

Somehow reality merges with fantasy to create these kinds of false, yet seemingly real, memories. Over the past decade, experimental psychologists have begun to methodically piece together how such memories might form.

Several researchers discussed what they've learned at a symposium called "Memory illusions"--part of the Divs. 3 (Experimental) and 6 (Behavioral Neuroscience and Comparative Psychology) "Mind, Brain and Behavior" series at APA's 1999 Annual Convention, Aug. 20 - 24 in Boston.

In work they've done using basic memory tasks, such as word-list recall, psychologists can easily get people to falsely recall words they've never seen, explained speaker Roddy Roediger, PhD, chair of the Washington University psychology department. And he and his colleagues have used that phenomenon to discover that falsely remembered words occur most typically when they have been strongly activated by some other experience.

In addition, according to Dan Schacter, PhD, chair of Harvard University's psychology department, researchers can suppress people's tendency to have a false memory by making the memory task distinctive--showing people pictures of the objects that words stand for rather than just the words themselves.

Promoting false recall

A primary experiment researchers use to study false memory was devised by Roediger and his colleague Kathleen McDermott, PhD. They use a type of word list designed by James Deese, PhD, in 1959 to nudge participants to recall a nonrepresented word suggested by the list. Each list contains words related to the critical word, but not the critical word itself. For example, the sleep list contains words such as bed, rest, awake and tired, but not sleep.

Researchers use various methods to test people's memory for these word lists, checking whether they recall seeing the critical word along with the other words in the list. In a much-cited 1995 Journal of Experimental Psychology: Learning, Memory and Cognition article (Vol. 21, No. 4, p. 803 - 814), Roediger and McDermott reported that the probability of recalling the critical word was about the same as or even higher than the probability of recalling words that appeared in the middle of the lists.

The experiment worked for the lists the researchers used. But there are many lists produced by Deese and other researchers that seem strong but that don't work. For example, people never recall the word butterfly when shown the butterfly list, which includes words such as moth, insect, wing and bird, Roediger said.

To find out what makes a list likely to generate a false memory, he and his colleagues used multiple regression analysis to compare 55 lists, some of which they found elicited high rates of false memories and others they found elicited low rates of false memories. The analysis identified three factors that determine whether people are likely to falsely recall a list's critical word:

The strength of the association between the list items and the critical word: The stronger the link between the list items and the critical word--for example, between bed and sleep--the more likely the people will falsely recall the target word.

The visual distinctiveness of the target word: People are less likely to falsely recall critical words that are more visually distinct with several letters that go above and below the line; for example, sleep would be better remembered than butterfly, partly for this reason.

Memory for the actual list items: People are less likely to recall the critical missing word on lists that are well recalled.

The study has implications for when false memories are more or less likely to occur, said Roediger. First, lists that people remember well are less likely to arouse a false memory than lists that are poorly recalled, said Roediger.

In addition, false memories--the word sleep in our example--appear to be activated by true experiences that are strongly associated with the false memory-as the words in the sleep list are associated with the word sleep. The critical word is "associated," said Roediger. People will not falsely remember words that are semantically related, but not easily associated with the critical word--as with the words in the butterfly list.

"It's not the theme or the gist of the list that is causing this effect," he said.

Preventing false recognition

Schacter and his colleagues have built on these findings to study how to minimize false recognition. They propose that people are more likely to remember words accurately if they are told to focus on details that differentiate words on the list from associated words that aren't on the list.

In their first study, published in the Journal of Memory and Language (Vol. 40, p. 1 - 24), one group of participants heard a word list and saw the words. Another group heard the words and saw pictures of the objects the words represented. The researchers reasoned that people who saw pictures would demand more information from their memories during the recognition test than would people who just saw words--they'd think, "I don't remember seeing a picture of that item, so it must not have been on the list," said Schacter.

The results were clear-cut, said Schacter. People who saw pictures falsely recognize the critical word less often than people who didn't see pictures.

"We get a nice reduction in susceptibility to false recognition when people have previously studied pictures," he said.

But the pictures lost their effect in another study when researchers showed people pictures for some words and not for others on the same memory trial. In the study, people heard and saw half of the words and heard and saw pictures of the other half. Their false recognition of the words was not reduced, said Schacter. This finding implies that pictures don't help people discriminate between individual words on the list; rather, they make words seen as pictures distinctive from words not seen as pictures.

"When you study some lists as words and others as pictures, looking for pictorial information is no longer diagnostic," said Schacter.

To test that it is distinctiveness and not just pictures that works to reduce the false-memory effect, Schacter and postdoctoral fellow Chad Dodson, PhD, extended these findings to another kind of distinctive information: saying words out loud. Participants who said all the words on a list aloud were able to reduce their false recognition of words by half, as compared with participants who heard and saw the words. This protection disappeared if participants said only half the words aloud.

Another group of studies still unpublished confirms that distinctive information can suppress false recognition of words, said Schacter. He and Dodson used a different memory paradigm: People see a list of words, then, after a time they see another list with half new and half old words. They're then tested with another list that includes "old" and "new" words and they have to determine if a word is old or new.

People who see pictures of the first list of words have lower rates of false recognition than do people who just see the words. In fact, if people see pictures for only half or even a quarter of the time they saw the original words, they continue to have low rates of false recognition, said Schacter.

"Pictures are not diagnostic," said Schacter. Instead, they encourage people to weigh their answers based on the presence or absence of distinctive information, which in this case is a picture.

"The study conditions allowed encoding of some distinctive information--a quarter of the list being pictures or half of the list being pictures," said Schacter. "And subjects seem to weigh this information very heavily" in their decision of whether a word is old or new.

These studies imply that production of false memories is quite common, particularly when information in the real world strongly activates words and, possibly, concepts in the brain associated with that information. They also imply that the more distinctive and well remembered an event, the less likely false memories will occur, said the researchers.

That events we remember may or may not have happened is an unnerving thought. But studies such as those by Roediger, Schacter and their colleagues may some day help us begin to distinguish accurate memories from truly felt but simply wrong ideas about the past.Y

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