In the aging mind, memory falters not just in terms of what people forget, but also in terms of what they remember, according to recent research. And even among the younger set, studies indicate that false memories--recollections of stimuli that were never presented--can be quite robust, said Washington University psychologist Henry (Roddy) Roediger, PhD, speaking at APA's 2000 Annual Convention in Washington, D.C., Aug. 4­8.

In 1995, Roediger and colleague Kathleen McDermott, PhD, described research on what they termed an associative memory illusion. In Roediger and McDermott's paradigm, participants study lists of 15 associated words. For example, one such list includes the words bed, rest, awake, tired, dream, wake and snooze, among others--all words that are associated with the word sleep, which the researchers call a "critical item." The critical item is never presented in the list.

Next, participants are asked to recall the words that were on the list, without guessing. In their first published account of such an experiment, Roediger and McDermott reported that participants are about as likely to mistakenly remember the word sleep as they were to correctly remember words that were presented in the middle of the study list. That finding has now been replicated numerous times.

At the APA convention, Roediger described efforts to reveal why such a false memory effect arises and the circumstances necessary to strengthen or weaken it.

"We believe that the concept of 'sleep' is aroused through activation spreading through a semantic network while people listen to the list words," Roediger said. "During the test, subjects must monitor their memories to distinguish events that actually occurred from those that were only activated internally. While we're perceiving things from the outside world, we automatically make inferences that form a coherent knowledge structure."

Roediger's group has learned that false memories are least likely to occur when study words are only weakly associated with the critical item, when critical items are distinctive and when participants have greater opportunity to encode detailed information about the items on the list. Likewise, allowing participants to study word lists multiple times and warning them about the false memory effect in advance each boost accuracy.

"The bottom line is that we can diminish the effect, but we've had a terrible time making it go away," Roediger said.

False recall is further heightened, the researchers have found, when critical items rhyme with or look similar to list items. For example, the word sleep is more likely to be falsely recalled when a study list includes not only semantically related words such as bed and rest, but also rhyming words such as weep and keep.

"The more sources of activation you can get to converge, the greater is false recall," Roediger explained.

Recently, Roediger and a team of colleagues led by psychologist David Balota, PhD, have examined how false memory is associated with normal aging and Alzheimer's disease. They have found that older participants and Alzheimer's patients remember fewer list words than do younger participants and wrongly recall critical items more often.

"Aging and Alzheimer's disease are a kind of double-edged sword," said Roediger. "You are less likely to remember things that really did happen to you but you're more likely to remember things that never happened to you."

Roediger pointed out that these recent results agree with the observations of another Missourian 100 years ago, who was "an acute student of the human condition." Late in life, Mark Twain remarked that, "When I was younger, I could remember anything, whether it had happened or not; but my faculties are decaying now, and soon it shall be so I cannot remember any but the things that never happened. It is sad to go to pieces like this, but we all have to do it."