People are woefully bad at recalling details of their own traumatic experiences. When military personnel were subjected to threatening behaviour during mock interrogations, most failed to identify the questioner a day or so later, and many even got the gender wrong.
The finding casts serious doubt on the reliability of victim testimonies in cases involving psychological trauma.
Numerous studies have questioned the accuracy of recall of traumatic events, but the research is often dismissed as artificial and not intense enough to simulate real-life trauma. Other studies have suggested that intense, personal experiences might produce near photographic recollection, something that prosecutors and juries in legal cases often assume.
But some researchers think this is an illusion. "People come away from these experiences feeling they will never forget what happened," says Gary Wells, an expert on eyewitness testimony at Iowa State University in Ames, "but they confuse that with thinking they remember the details."
Now Andy Morgan at Yale University and his colleagues have evidence from truly stressful situations. They studied over 500 soldiers, sailors and pilots at "survival schools" - three mock POW camps run by the US military, who partly funded the study. The subjects, whose mean age was 25, were being trained to withstand the mental and physical stresses of capture.
After 48 hours without food or sleep, they were subjected to intense interrogation. Half of the subjects were physically threatened, and this caused them to show all the signs of intense physiological stress - very high heart rate and levels of adrenalin and cortisol, combined with plummeting sex hormones.
Twenty-four hours after release from the camp, the subjects were asked to identify their interrogators. Some of them were shown a live line-up of 15 people, others were shown a photo-spread, and a third group was shown single photos sequentially.
Using a scale of 1 to 10, participants were asked to say how confident they were that they had chosen the right person. Most of the mock interrogators appeared or were pictured dressed in standard military garb, but some were shown dressed exactly as they had been during the questioning.
The performance of all groups was abysmal. Only 30 per cent could find the right person in a line-up, 34 per cent from a photo-spread and 49 per cent from sequential photos - though the clothing cue boosted correct identification to 66 per cent. Thirty people got the gender wrong, and those subjected to physical threats were the worst at recognising their interrogator.
Elizabeth Loftus, a psychologist at the University of California at Irvine, says the study is unique because the stresses were intense and real. "I think people will pay attention to this," she adds. Wells agrees: "What it illustrates is that stress does not help memory."
Journal reference: International Journal of Law and Psychiatry (vol 27, p 265)