Introduction

• Garry et. al found when people imagine events that they initially claim did not happen to them, they will subsequently increase their estimate of how likely it is that the event happened.
• Heaps and Nash wanted to find out how reliable the imagination inflation effect is, and later, who is likely to mistake imagined events for real events (are there cognitive or personality characteristics that might allow for this inflation in some more than others?)
• Possible explanations for imagination inflation discussed: repeated testing, number of imaginings, investigative procedures

• Four characteristics of participants were taken into account to see whether or not they would account for individual differences in imagination inflation (See Hyman & Billings, 1998 for some related findings).

• imagery vividness
• interrogative suggestibility
• hypnotic suggestibility
• dissociation
 
• Prediction: they expected to find a positive association/correlation between imagination inflation and all four of these predictors

• Fifty-five students participated
• All participated in four sessions that they were led to believe were for four different studies/experiments; different tests were administered for each session, and the participants were falsely told about the purpose of these tests and each session had a different experimenter.

Session 1: participants took part in a "group hypnotic induction" and completed the Waterloo-Stanford Scale of Hypnotic Susceptibility, Group C scale (WSGC) to assess hypnotic suggestibility.
Session 2: around 2 weeks later, groups were administered Part 1 of the Gudjonsson Suggestibility Scale (GSS) in which they were read a narrative passage and then given a free recall test.  This scale was given to see how susceptible these participants were to the influence of an authoritative questioning source
Session 3: 2-3 days later individuals completed Part 2 of the GSS in which they had a second free recall and then 20 cued recall questions that they answered twice.  They then participants completed the Life Events Inventory (LEI)(pretest), the Visual Imagery Questionnaire (VVIQ), and the Dissociative Experiences Scale (DES)
Session 4: 14-15 days later, in groups of 1-5, participants were randomly assigned to imagine four critical items (eight critical items that were unlikely to have occurred to the participants and were split into sets two sets of four one set imagined and the other set serving as the control...counterbalanced across subjects).  The LEI (posttest) was then given.

Replication of the Imagination Inflation Effect

• Was there a greater positive change for imagined items over those not imagined? Yes, a significant 8.1%
• Were judged likelihood changes greater for imagined events across subjects or greater for imagined events across events?  Yes, a significant .44 (subjects' average increase for imagined events) to .18 (subjects' average increase for not-imagined events)
• Scores ranged from -7 to 14 for the participants' judged likelihood after imagining the events (44%, positive change; 42%, no change; 15%, negative change)

• Multiple regression was performed
• D.V.: change scores for imagined items
• I.V.: imagery vividness, interrogative suggestibility, hypnotic suggestibility, dissociativity
• Only hypnotic suggestibility and dissociativity contributed significantly to prediction of imagination inflation scores

• Results further suggest that regarding childhood events, imagination plays a role in likelihood judgments
• Results also suggest that imagination inflation is not related to suggestibility in interrogative situations or to the quality of mental images; however, it is related to hypnotic suggestibility and dissociative experiences' frequency
• What results may mean as to what factors are important for the creation of false memories about the past: the creation of false beliefs/memories may not be due to suggestibility, but rather due to the way an individual processes information, their cognitive style (therefore, "imagined events that are later believed to originate with perceptual experience are those that require little effort for creation")



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