Stress can encourage false memories, possibly explaining why crime victims pick the wrong man in a line up Stress makes people much more likely to create false memories, say American researchers. It also appears to make them more certain that these false memories are correct.
The results could help explain why crime witnesses give conflicting evidence or pick the wrong man in a line up, the researchers say. But they do not account for "reconstructed memories" of childhood abuse.
Psychology student Jessica Payne of the University of Arizona, Tucson and colleagues read to 66 college students a list of 20 words. All related to sleep, such as "bed", "rest", "tired" and so on.
When asked a few minutes later if they heard the word "hat", they nearly always say no. But when asked if "sleep" was on the list, 60 per cent say yes, even though it wasn't.
Such false memories have been demonstrated before. "We wanted to know if stress would increase the rate of false memories," says Payne.
So the researchers then repeated the experiment. But before taking the test, half the students had to give an impromptu presentation under glaring light with a video camera rolling. "It was very stressful," says Payne.
The stressed group thought "sleep" was on the list nearly 80 per cent of the time. They did not pick unrelated words like "chair" as being on the list any more often then the relaxed controls.
Even more surprising was how fast the stressed students clicked the "yes" button, says Payne. Unstressed subjects usually took a tenth of a second longer before saying yes to "sleep". "It's as if they weren't quite sure," she says.
But stressed students clicked yes equally fast for all their answers, as if they were just as sure of the false memory as of the real ones. Stress hormone
The hippocampus, a brain structure needed to form new memories, is riddled with receptors for the stress hormone cortisol. Payne believes cortisol may cause the effect by suppressing the hippocampus.
The thematic nature of the false memories suggests people might tend to let stored associations influence their recall of a stressful event. It might be possible for memories of a crime scene to be influenced by beliefs about the sorts of people who commit crimes, Payne says. But a more direct experiment is necessary to be sure.
However, the results do not deal with recovered memory syndrome, in which adults become convinced they were abused as children, Payne says. This type of false memory only involves adding related details to real events.
"I'm worried that people will interpret this as meaning recovered memories are false," she says, "It doesn't."