Close your eyes and think about the word "potato." Okay, open them. Now, close your eyes and think about the word "wicket."
Chances are you took a little longer with the second one—it's a small door or gate, in case you were drawing a complete blank.
If you were asked to recall these two words tomorrow, according to new research from Carnegie Mellon University, chances are you'd be quicker to remember the first.
Asking a group of subjects who were experiencing temporary, drug-induced amnesia to perform similar exercises, the Carnegie Mellon team attempted to determine how we form new memories.
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They found that the process comes down to our ability to link new information to prior experiences: In the case of the introductory example, the average person has probably had more practice eating potatoes than climbing through wickets.
"One's ability to associate something to a context depends on it being a 'chunk' or unit," said psychologist Lynne Reder, lead author of the study, which appears in the July issue of Psychological Science.
"Chunking" occurs when otherwise unrelated items are perceived as a unit. For example, the three-letter combination FBI—but not, say, SVQ or TMY—is chunked because it's associated with an entity, and we hear the grouping so often. Items that are chunked take up less of our mental resources to encode since each item doesn't have to be encoded separately.
But when something is not a chunk, it can't be bound to a context, which is important for memory.
To test this concept, the researchers showed a series of words and pictures—the latter ranging from familiar to abstract, including faces, landscapes and nondescript markings—to their subjects after injecting them with either a saline placebo or midazolam, a drug that causes temporary amnesia. (Midazolam is routinely used in surgical procedures to relieve anxiety, and has recently been adopted by researchers for studying memory.)
The researchers found that, under midazolam, subjects were more impaired in their ability to remember words than photos of faces and landscapes. But both subjects who received the drug and the placebo had difficulty remembering the abstract pictures. Reder believes that this is because the abstract pictures cannot be chunked.
"For these abstract pictures, it's hard to encode them," Reder said, "Whereas if it was a picture of [Pablo Picasso's] Guernica or the Eiffel Tower, you could store it away and bind it to the context in which you saw the picture [previously]. You wouldn't have to spend a lot of time staring at it to generate a label for it."
The results of the Carnegie Mellon study are surprising, said George Washington University psychologist Elliot Hirshman, who also studies the effects of midazolam on memory. He points out that other studies have actually shown pictures to be stronger stimuli than words, and therefore more likely to be recalled under the effects of amnesia.
"From a common sense perspective, you might think that if something's unfamiliar, then it should really stand out in your memory, and you might remember it better," he said. "On the other hand, a more sophisticated view is that if the different parts of a stimulus don't cohere in some sense, it'll be harder to recover them."
The findings could lead to a better understanding of patients with anterograde amnesia, those who may have trouble making new memories because they can't record new experiences even though their old memories are still intact. Intriguingly, if the stimuli are sufficiently familiar, these same patients may be able to access old memories in order to make new ones.
"Although people claim that amnesiacs can't remember anything," Reder said, "that's actually not true."