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Imagination inflation refers to the finding that imagining an event which never happened can increase confidence that it actually occurred.
This effect is relevant to the study of memory and cognition, particularly false memory. Imagination inflation is one way that techniques intended to retrieve repressed memories (i.e. via recovered memory therapy) may lead to the development of false or distorted memories.
Imagination inflation may occur via increased familiarity: imagining a false event makes it feel more familiar, and people mistake this feeling of familiarity for evidence that they have experienced the event. Alternatively, imagination inflation could be the result of source confusion. When imagining a false past event, people generate information about it, and some is stored in their memory. Later they might remember the content but not its source, mistakenly attributing the information they can recall to a real experience instead of to their imagination.
Research on imagination inflation can be applied to other fields, such as criminal justice. The police interrogation practices of asking suspects to repeatedly imagine committing a crime, or explaining how they could have done it, are claimed to be causes of false confessions.
In 1996 Elizabeth Loftus, along with Maryanne Garry, Charles Manning, and Steven Sherman, conducted the original imagination inflation study. This was the first study to examine what imagining false events would do to memory in the absence of other factors present in previous studies, such as social pressure to attempt to recall an incident or to report one’s past consistently with information provided by a parent. 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 on their own report. This leaves open the possibility that imagination does not actually have any effect on beliefs about false past events, but simply helps people to retrieve actual memories of true experiences. Another early study by Lyn Goff and Henry Roediger used a different method to study imagination inflation effect for events which can be confirmed not to have taken place. It also extended this body of research by looking at the effect of imagination on recognition reports rather than confidence ratings. People performed some actions (such as breaking a toothpick) but not others, then imagined doing some actions out of 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. They were more likely to mistakenly say that they had performed imagined than unimagined actions.
Some 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.
Imagination inflation has implications for the criminal justice system, in particular interrogation and interviewing procedures, as it supports the claim that interrogators who ask suspects to repeatedly imagine committing a crime may risk making them more confident that they are the perpetrators, ultimately producing false confessions from innocent suspects. In one case in the United States in 1990s, a man who initially denied accusations of raping his daughters was given an intense police interrogation. He confessed to abusing his children and leading a satanic cult which sacrificed babies, even admitting to crimes that were denied by his accusers. The psychologist Richard Ofshe argued that the confessions were recovered memories created by repeated suggestion.
In another interrogation technique, suspects explain how a crime might have been committed or how they themselves could have done it. This practice has been suggested as another cause of self-generated false confessions, by forcing an innocent suspect to create a believable narrative of their own guilt. This is supported by research in which people explained how a false childhood event could have occurred, and became more confident that it had really happened.
Regression to the mean
A 2001 critique argued that the original findings of the 1996 imagination inflation study did not in fact reflect changed beliefs about the past via imagination, but were instead a product of regression to the mean. That is, events with confidence ratings at the extreme (low or high) ends of the scale at the first time of measurement happened to have such scores due only to observational error, so they became more moderate at post-test. The authors of the '96 paper disagreed with this interpretation, pointing out several issues that they found in Pezdek’s reasoning. In particular, they agreed that regression to the mean was present in their own data and contributed to the overall changes in confidence at the second test. But this could not explain the finding that imagining events that were low in confidence led to a greater increase in ratings than for unimagined low-confidence events, as regression to the mean should affect all events equally.
- Garry, Maryanne; Manning, Charles G., Loftus, Elizabeth F., Sherman, Steven J (1996). "Imagination inflation: imagining a childhood event inflates confidence that it occurred". Psychonomic Bulletin & Review 3 (2): 208–214. doi:10.3758/bf03212420.
- Garry, Maryanne; Polaschek, Devon L.L. (2000). "Imagination and memory". Current Directions in Psychological Science 9 (1): 6–10. doi:10.1111/1467-8721.00048.
- Loftus, Elizabeth F. (2001). "Imagining the past". The Psychologist 14 (11): 584–587.
- Davis, D.; Donohue, J. (2004). O'Donohue, W.T.; Laws, P.R.; Hollin, C., eds. "The road to perdition: Extreme influence tactics in the interrogation room". Handbook of Forensic Psychology (NY: Elsevier, Academic Press): 897–996. ISBN 0471177717.
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- Ofshe, Richard (1992). "Inadvertent hypnosis during interrogation: False confession due to dissociative state: Mis-identified multiple personality and the satanic cult hypothesis.". International Journal of Clinical and Experimental Hypnosis 40 (3): 125–156. doi:10.1080/00207149208409653. PMID 1399152.
- McNally, Richard (2003). Remembering Trauma. Cambridge, M.A: Belknap Press/Harvard University Press. ISBN 9780674018020. Retrieved February 14, 2014.
- Sharman, Stefanie J.; Manning, Charles G., Garry, Maryanne (2005). "Explain this: Explaining childhood events inflates confidence for those events". Applied Cognitive Psychology 19: 67–74. doi:10.1002/acp/1041.
- Pezdek, Kathy; Eddy, Rebecca M. (2001). "Imagination inflation: A statistical artifact of regression toward the mean". Memory & Cognition 29 (5): 707–718. doi:10.3758/BF03200473. Retrieved February 14, 2014.
- Garry, Maryanne; Sharman, Stefanie J., Wade, Kimberly A., Hunt, Maree J., Smith, Peter J. (2001). "Imagination inflation is a fact, not an artifact: A reply to Pezdek and Eddy". Memory & Cognition 29 (5): 719–729. doi:10.3758/BF03200474. Retrieved February 14, 2014.