Memory is fickle. Sometimes, people have great confidence in the accuracy of a particular memory...even if it can be proven that the event they claim to remember never actually happened. For example, a psychologist named Ulric Neisser likes to tell a story about one of his false memories:

Pearl Harbor was bombed on the day before Neisser's 13th birthday. On that day, he was sitting in his living room listening to a baseball game on the radio. Suddenly, in the middle of the game--right in the middle of a play--the broadcast broke off and a reporter came on the air with an announcement: Pearl Harbor has been bombed. The United States is at war with Japan. Then Neisser sprinted upstairs to tell his mother the news.

Neisser vividly remembers the fear and the excitement that he felt then. He remembers the room clearly, he says, even though he only lived in the house for a year. He remembers what the radio looked like. He even remembered which teams were playing that day. The details were so clear and the emotions so strong that he had absolute confidence in this memory for over 40 years.

Then one day he realized the problem. Pearl Harbor was bombed on December 7. There's no baseball in December. The event could not have happened as he remembered it. Nonetheless, he still remembers it that way, even though he knows intellectually that it's wrong.

Of course, anecdotes, even multiple anecdotes, aren't enough. A lot of people have done systematic research on this phenomenon, though. For example, Beth Loftus, a psychologist who does a lot of work in this field, showed a bunch of people a videotape of a car accident. She asked them one of two questions:

  1. Where was the old lady standing when the cars collided?
  2. Where was the old lady standing when the cars smashed?

Then she asked them if there had been any broken glass in the picture. (There hadn't been.) Subjects who received question 1 generally got this question right. Subjects who received question 2 almost always got it wrong--and they had great confidence that there had in fact been broken glass.

All humans can have false memories, but kids are particularly vulnerable. In the McMartin Preschool Trial, for example, kids were induced by an overly aggressive and incompetent psychologist to have false memories of molestation. People then started wondering just how accurately kids could report such experiences. Obviously, it's hard to conduct a systematic study of abused kids, because different kids had different experiences, and it's often difficult to figure out what really went on. So a psychologist named Peter Ornstein came up with a brilliant experiment. He decided to interview three-year-olds, five-year-olds, and seven-year-olds about the Well Child Checkup--the annual physical exam that most kids get. This checkup involves a genital exam, a blood test (which requires a fingerstick), and a urinalysis (which requires the kids to urinate into a cup). Molesters do similar things to their victims, so this is as close as you can ethically get to the situation in which you're really interested.

Ornstein's research asked two questions: first, what would kids tell you about these invasive events; and second, to what extent could they be induced to tell you about something that didn't happen? He found that three-year-olds would volunteer information about the urinalysis and the blood test if you simply asked them to tell you what happened. Seven-year-olds, on the other hand, wouldn't tell you about it unless you asked directly. He also found, though, that you could get three-year-olds to tell you just about anything, especially if you asked a leading question ("He tapped your foot with a hammer, didn't he?"). Five-year-olds were in between. Seven-year-olds usually couldn't be persuaded tell you anything that didn't happen. So he concluded that therapists and police investigators need to ask direct questions, but not leading questions.

It's a tricky subject because the stakes are so high--you don't want to let some scumbag get away with abuse, but you also don't want to ruin an innocent man's life by accusing him falsely. All the research I've seen suggests that we shouldn't convict people on recovered memories alone...unfortunately, sometimes no other evidence is available.