For most of this century, experimental psychologists have been interested in how and why memory fails. As Greene1 has aptly noted, memories do not exist in a vacuum. Rather, they continually disrupt each other through a mechanism that we call "interference." Virtually thousands of studies have documented how our memories can be disrupted by things that we experienced earlier (proactive interference) or things that we experienced later (retroactive interference).
Relatively modern research on interference theory has focused primarily on retroactive interference effects. After receipt of new information that is misleading in some ways, people make errors when they report what they saw.2,3 The new post-event information often becomes incorporated into the recollection, supplementing or altering it, sometimes in dramatic ways. New information invades us, like a Trojan horse, precisely because we do not detect its influence. Understanding how we become tricked by revised data about a witnessed event is a central goal of this research.
The paradigm for this research is simple. Participants first witness a complex event, such as a simulated violent crime or an automobile accident. Subsequently, half of the participants receive new misleading information about the event. The other half do not get any misinformation. Finally, all participants attempt to recall the original event. In a typical example of a study using this paradigm, participants saw a video depicting a killing in a crowded town square. They then received written information about the killing, but some people were misled about what they saw. A critical blue vehicle, for instance, was referred to as being white. When later asked about their memory for the color of the vehicle, those given the phony information tended to adopt it as their memory; they said the vehicle was white.4 In these and many other experiments, people who had not received the phony information had much more accurate memories. In some experiments, the deficits in memory performance following receipt of misinformation have been dramatic, with performance differences as large as 30% or 40%.5
This degree of distorted reporting has been found in scores of studies involving a wide variety of materials. People have recalled nonexistent broken glass and tape recorders, a cleanshaven man as having a mustache, straight hair as curly, stop signs as yield signs, hammers as screwdrivers, and even something as large and conspicuous as a barn in a bucolic scene that contained no buildings at all. In short, misleading post-event information can alter a person's recollection in powerful ways, even leading to the creation of false memories of objects that never in fact existed.
LOST IH A SHOPPING MALL
Most of the experimental research on memory distortion has involved deliberate attempts to change memory for an event that actually was experienced. An important issue is whether it is possible to implant an entire false memory for something that never happened. Could it be done in an ethically permissible way? Several years ago, a method was conceived for exploring this issue - Why not see whether people could be led to believe that they had been lost in a shopping mall as a child even if they had not been. (See Loftus and Ketcham6 for a description of the evolution of the idea for the study.)
In one of the first cases of successful false memory implantation,7 a 14-year-old boy named Chris was supplied with descriptions of three true events that supposedly happened in Chris' childhood involving Chris' mother and older brother Jim. Jim also helped construct one false event. Chris was instructed to write about all four events every day for 5 days, offering any facts or descriptions he…