A common defense in murder cases is “focal retrograde amnesia”: the defendant claims to have simply forgotten what occurred around the time of the crime (perhaps due having consumed too much alcohol or other drugs). In fact, “amnesia” is claimed in as many as 45 percent of murders. Psychologists know that this sort of amnesia is actually quite rare, so it’s very likely that most, if not all of these defendants are faking amnesia.
We can confirm that many of these cases are faked: when defendants are given multiple-choice questions about the crime, they get the answers wrong too often. Think about it this way: if you are given a ten-item true/false test and you know none of the answers, you should get five of the answers right just by guessing. But if you actually know the answers and are just pretending not to know, you might get every single answer wrong. Unfortunately, this sort of test can’t tell us who’s faking and who’s not, because some honest respondents might legitimately have an especially “bad” performance, purely based on chance. On a large scale, we know there’s a lot of cheating going on, but there’s no way to reliably pick out the cheaters.
But in testing for faking amnesia, a secondary phenomenon seemed to be appearing. Several studies found that people who were asked to pretend to have amnesia were later unable to recall as much as people who told the truth from the start.
The studies worked like this: Volunteers were told a story — or actually acted out a story — where they were the primary character: “you” robbed someone, or beat a man to death with a pool cue, or killed a girl in a car accident. Then half these participants were told to pretend not to remember the key details of the crime in an effort to avoid punishment, while the other half was told to remember as many as possible of the details. They were tested on their memory (or their false reconstruction) immediately after the story, and then returned to the laboratory a week later, and this time everyone was asked to try to recall the details of the crime accurately. The volunteers who told the truth the first time around did better on the second test. Does this mean that faking amnesia impairs your memory later on? Not necessarily.
There were a couple problems with these studies. First, it could be that the memory difference was due to the fact that the truth-tellers had “practiced” giving the correct responses, not the faking of amnesia. Indeed, one study included a third group, which was not tested immediately after the “crime.” This untested group performed just as badly the fake amnesics one week later. Second, these scenarios weren’t very realistic for the college students acting them out. It could be that the students remembered (or forgot) details because of the unusual nature of the stories they were listening to or acting out.
So a team led by Xue Sun designed a study to address these problems. They divided their student volunteers into three groups: fake amnesics, truth-tellers, and untested. Students heard one of two stories while they read along with a script. Here’s an excerpt from one of the stories, describing a party where the student has been drinking and meets a dog named Ollie:
When you walk into the kitchen, you find it empty except for Ollie, who is curled up and sleeping in a little ball on his blue shag rug in the corner. Hearing you, he wakes up and leaps toward you, trying to play. You pick him up and he licks your face. When you put him down, he keeps jumping up trying to reach the counter. You realize he’s trying to get at the pile of chicken bones that have been left on an aluminum platter next to the sink. Thinking, “dogs like bones, ” you pick the biggest one an give it to him, saying, “Here you go, Ollie. You’d better not tell Sam I gave this to you!” ….
[later] You turn around and realize that Ollie is choking… You realize that it could be that he’s choking on the bone you just fed him, which is now nowhere in sight.
Eventually the dog dies, and the students (in the fake amnesic and truth-telling groups) were asked to imagine confronting the owner the next day and explaining what happened. They wrote out a description of the key events and also answer a multiple-choice test. Then, a week later, everyone returned to write out the story again and retake the test. This time, everyone was instructed to try to answer accurately. Here are the results:
While the truth-tellers did respond more accurately than the fake amnesics, the fake amnesics didn’t do any worse than the students who weren’t tested at all. The results were the same for a second story, which involved giving nuts to a person with allergies, resulting in their death. Sun’s team says the difference between the fake amnesics and the truth-tellers is probably completely due to the fact that the truth-tellers had a chance to practice the accurate story.
In other words, pretending to have amnesia doesn’t hurt your memory, but rehearsing the correct answers improves it. There’s still a separate question about how all this applies to the real world. A criminal probably does rehearse his or her alibi. How does this rehearsal affect memory for the actual crime? It’s hard to say, and also difficult to envision a study that would address this question. Perhaps our readers have some ideas.
Sun, X., Punjabi, P., Greenberg, L., & Seamon, J. (2009). Does feigning amnesia impair subsequent recall? Memory & Cognition, 37 (1), 81-89 DOI: 10.3758/mc.37.1.81