Imagination inflation

Imagination inflation is a type of memory distortion that occurs when imagining an event that never happened increases confidence in the memory of the event.

Several factors have been demonstrated to increase the imagination inflation effect. Imagining a false event increases familiarity, which may cause people to mistake this as evidence that they have experienced the event. Imagination inflation could also be the result of source confusion or source monitoring errors. When imagining a false event, people generate information about the event that is often stored in their memory. Later, they might remember the content of the memory but not its source and mistakenly attribute the recalled information to a real experience.

This effect is relevant to the study of memory and cognition, particularly false memory. Imagination inflation often occurs during attempts to retrieve repressed memories (i.e. via recovered memory therapy) and may lead to the development of false or distorted memories. In criminal justice, imagination inflation is tied to false confessions because police interrogation practices involving suspects to imagine committing or planning the crime in question.

In 1996, Elizabeth Loftus, Maryanne Garry, Charles Manning, and Steven Sherman, conducted the original imagination inflation study. The study examined the effect of imagining a childhood event on childhood memories. It was the first study to examine the effects of imagining false events on memory in the absence of other factors present in previous studies, such as social pressure. In the study, the act of imagining unexperienced childhood events, such as being rescued by a lifeguard or breaking a window with one's hand, increased confidence that the events had occurred. After people imagined events with low initial confidence ratings (i.e. ones which they originally said they had not experienced) they became more confident that the events took place compared with unimagined ones.

Due to the unreliability of memory, it is not possible to be certain whether or not someone has had a given experience based solely self-reports. This leaves open the possibility that imagination does not actually have any effect on beliefs about false past events, but instead helps people retrieve actual memories of true experiences. In 1998, Lyn Goff and Henry Roediger used a different method to study imagination inflation effect for events that could be confirmed. It also looked at the effect of imagination on recognition reports rather than confidence ratings. Participants performed certain actions (such as breaking a toothpick) but not others, then imagined doing other actions in the overall set, and finally were given a list of old actions encountered in the first two parts of the study and brand new actions. Participants were more likely to mistakenly say that they had performed imagined actions compared to unimagined actions.

Later studies have used similar methods with a pre-test rating of a series of events, an intervening cognitive task using the events, and a post-test confidence rating. These have shown that a similar imagination inflation effect occurs when instead of imagining, people simply explain how events could have happened or paraphrase them. These findings suggest that vivid imagining is not always necessary for "imagination inflation" to occur; explanation or paraphrasing may function to make the false event seem more fluent and thus more familiar without producing a detailed image of it.

Other research has investigated what types of events can show an imagination inflation effect, often using a method similar to Goff and Roediger's, in which participants perform some actions but not others, then imagine some of them, and later mistakenly believe they have performed imagined actions but not control unimagined ones. One comparison found a similar imagination inflation effect for actions identical to those in Goff and Roediger's study (i.e. "break the toothpick") and altered, bizarre versions of such actions (i.e. "kiss the magnifying glass"). Another found an effect when people imagined a highly unusual action such as kissing a vending machine or lying on a couch and talking to Sigmund Freud. Some people have developed false beliefs of having performed bizarre actions or experienced more ordinary events even after imagining somebody else, rather than themselves, performing them.

The cause of the imagination inflation effect is debated. There is evidence that source-monitoring framework, the familiarity misattribution theory, and the effects of sensory elaboration contribute to the formation of false memories through imagination inflation. It has been theorized that these effects, and other unknown effects, all contribute to the imagination inflation effect.