Imagination equally influences false memories of high and low plausibility events

APPLIED COGNITIVE PSYCHOLOGYAppl. Cognit. Psychol. 23: 813–827 (2009)Published online 12 September 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/acp.1515
*2

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Imagination Equally Influences False Memories of Highand Low Plausibility Events

STEFANIE J. SHARMAN1* and ALAN SCOBORIA2

1University of New South Wales, Sydney, Australia2University of Windsor, Canada

SUMMARY

To examine the effects of event plausibility on people’s false beliefs and memories for imaginedchildhood events, subjects took part in a three-stage procedure. First, subjects rated how confidentthey were that they had experienced certain childhood events. They also rated their memories of theevents. Second, 1 week later, subjects imagined one high, one moderate and one low plausibilityevent. Third, 1 week later (and 2 weeks after their initial ratings), subjects rated their confidence andmemory a second time. Imagining the events made subjects more confident that they were genuineexperiences and gave subjects clearer and more complete memories. Plausibility did not affectsubjects’ confidence but it did affect their memories. Subjects developed clearer and more completememories for high, followed by moderate, followed by low plausibility events regardless of whetherthose events were imagined. We use a nested model of plausibility, belief and memory to discuss ourfindings. Copyright # 2008 John Wiley & Sons, Ltd.

A number of techniques encourage people to remember childhood events that never

actually happened, such as providing them with false stories attributed to family members

and with false events in doctored photos (Porter, Yuille, & Lehman, 1999; Wade, Garry,

Read, & Lindsay, 2002). Even seemingly harmless techniques can alter people’s memories;

for example, briefly imagining false childhood events can make people believe that those

events were genuine experiences (Garry, Manning, Loftus, & Sherman, 1996; Mazzoni &

Memon, 2003). In the current experiment, we examined the effects of event plausibility on

people’s beliefs and memories for imagined childhood events.

Many experiments investigating event plausibility have focused on the effects of telling

people how frequently certain events occur in childhood (although see Otgaar, Candel,

Merckelbach, & Wade (in press) and Strange, Sutherland, & Garry (2006) for different

manipulations in research with children). In these studies, event plausibility is

operationalised as prevalence information; that is, the probability of an event’s occurrence

for a particular sample. Giving people this prevalence information makes them more

confident that they genuinely experienced those events (Hart & Schooler, 2006; Mazzoni,

Loftus, & Kirsch, 2001; Pezdek, Blandon-Gitlin, Lam, Hart, & Schooler, 2006). For

example, Hart and Schooler’s subjects read articles describing rectal enemas or chicken

pox as common childhood experiences (plausibility information). They also read articles

Correspondence to: Stefanie J. Sharman, School of Psychology University of New South Wales, Sydney, NSW052 Australia. E-mail: [email protected]

opyright # 2008 John Wiley & Sons, Ltd.

814 S. J. Sharman and A. Scoboria

describing the procedure of an enema or a seizure (procedural information). Subjects who

received the plausibility information were more confident that they had had an enema in

childhood than those who did not receive this information. The procedural information had

no effect on subjects’ confidence. This research indicates that telling people about an

event’s prevalence, rather than giving them information about an event’s procedure, can

make them believe that they experienced that event.

Although event plausibility affects people’s beliefs, there is no evidence that it affects

their memories (Hart & Schooler, 2006, Study 2; see also Pezdek, Finger, & Hodge, 1997;

Pezdek & Hodge, 1999).1 Hart and Schooler’s subjects became more confident that they

had experienced an enema in childhood, but they did not remember more about it. This lack

of change in memory ratings is consistent with Scoboria, Mazzoni, Kirsch, and Relyea’s

(2004) model of autobiographical beliefs and memories. According to the model,

plausibility, belief and memory are partially independent constructs. Plausibility can be

further divided into general plausibility (people’s judgments about the possibility of an

event occurring in the general population) and personal plausibility (people’s judgments

about the possibility of an event’s occurrence in their own past). These constructs are

nested such that memory implies belief, belief implies personal plausibility and personal

plausibility implies general plausibility. For example, people who remember experiencing

an event typically believe that the event occurred; people who believe that an event

occurred typically find that event personally and generally plausible.

In addition, Scoboria et al.’s (2004) model proposes that general plausibility does not

imply personal plausibility, personal plausibility does not imply belief and belief does not

imply memory. For example, people who find an event personally plausible neither

necessarily believe that the event happened, nor do they necessarily have a memory of that

event. This nested relationship suggests that manipulations that increase people’s belief

ratings may not affect their memory ratings. Therefore, in Hart and Schooler’s (2006)

experiment, subjects may not have remembered more about receiving an enema in

childhood because the prevalence information they received only affected their judgments

of plausibility and belief about experiencing the event (see Scoboria, Mazzoni, Kirsch, &

Jimenez, 2006), not their memories of the event.

In the current experiment, we wanted to examine the effects of event plausibility on

people’s beliefs and memories. Given that prevalence information does not affect people’s

memories, what sort of manipulation does? We know that a brief imagination exercise can

make people more confident that they genuinely experienced false events; this effect is

known as imagination inflation (Garry et al., 1996; Sharman, Garry, & Hunt, 2005). This

brief imagination exercise can also make people falsely remember those events (Mazzoni

& Memon, 2003; Sharman & Barnier, in press). For example, Mazzoni and Memon asked

subjects to briefly imagine that a school nurse took a skin sample from a finger. Almost

30% of those who imagined this event developed a false memory, which is nearly four

times as many as those who just read about the event. These false memories occur when

people experience source confusions and misattribute the sensory and perceptual details

generated when imagining the false events to genuine childhood memories.

The Source Monitoring Framework suggests that these source confusions are more

likely to happen when imagined events are richly detailed and feel familiar, and meet some

1Beliefs and memories are separate constructs; for example, people typically believe that they were born withoutremembering it; however, the reverse is highly unlikely to be true (see Mazzoni & Kirsch, 2002; Scoboria,Mazzoni, Kirsch & Relyea, 2004).

Copyright # 2008 John Wiley & Sons, Ltd. Appl. Cognit. Psychol. 23: 813–827 (2009)

DOI: 10.1002/acp

https://www.researchgate.net/publication/227628766_Increasing_belief_in_an_invasive_procedure_that_never_happened_The_role_of_plausibility_and_schematicity?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

https://www.researchgate.net/publication/258430652_Imagination_inflation_Imaging_a_childhood_event_inflates_confidence_that_it_occurred?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

Event plausibility and memory 815

threshold criteria to be judged memories of experienced events (see Johnson, 2006;

Johnson, Hashtroudi, & Lindsay, 1993). These judgments can be based on many factors,

such as the perceptual and sensory details contained in a memory, the level of familiarity

associated with that memory, whether various cognitive operations were used to generate

the memory, and the plausibility of the remembered event (Mitchell & Johnson, 2000).

For example, a woman may have a rich, qualitatively detailed memory of attending an

important meeting. However, when she thinks about this memory strategically and

deliberately, she realises that it is not plausible—and therefore cannot be a memory of

a genuine experience—because she was in another country at the time the meeting

occurred.

In the experiment that we report here, we used the Source Monitoring Framework to

investigate the effects of event plausibility on people’s confidence about and memories for

imagined childhood events. We asked subjects to imagine three different false events: one

high plausibility event (choking on a small object or getting lost in a shopping mall), one

moderate plausibility event (receiving a rectal enema or having a baby tooth pulled out by a

dentist) and one low plausibility event (seeing a ghost or witnessing a demonic possession).

We chose these events for two main reasons. First, these events are consistent with those

used in previous research investigating the effects of plausibility on people’s false beliefs

and memories (e.g. Hart & Schooler, 2006; Mazzoni et al., 2001; Pezdek, Blandon-Gitlin,

Lam, et al., 2006; Scoboria et al., 2006). Second, these events have varying degrees of

plausibility (Scoboria et al., 2004).

This second point is particularly important given that the only experiment addressing

event plausibility and imagination inflation manipulated plausibility using event

prevalence. Pezdek Blandon-Gitlin, and Gabbay (2006) asked subjects to imagine events

after telling them that the events occurred frequently (presumably enhancing plausibility)

or infrequently (presumably decreasing plausibility). Only events manipulated to have

enhanced plausibility showed imagination inflation. However, merely telling people that

events occur frequently can make them more confident that they experienced those events

(Hart & Schooler, 2006; Pezdek, Blandon-Gitlin, Lam, et al., 2006; Scoboria et al., 2006).

Thus, the inflation that Pezdek, Blandon-Gitlin, and Gabbay found for high plausibility

events may have been due to prevalence information, imagination or the combination of

both. In our experiment, we did not operationalise plausibility as prevalence information;

rather, we directly measured plausibility by assessing subjects’ beliefs about how possible

they thought the events were. Thus, we were able to investigate the effects of imagination

alone on people’s beliefs and memories for childhood events that they initially believed

were more or less plausible.

We expected that both imagination and plausibility would play a role in changing

subjects’ beliefs and memories. Consistent with imagination inflation research, we

expected subjects to become more confident that they experienced the imagined than the

not imagined events; we also expected them to remember more about the imagined than not

imagined events. Based on the Source Monitoring Framework, we expected that if the

plausibility of the imagined events caused subjects to make strategic and deliberate source

monitoring decisions, then we should find a difference between the high, moderate and low

plausibility events. Specifically, for more plausible events, subjects should be more

confident and remember more about the imagined than the not imagined events. For less

plausible events, subjects should not be more confident or remember more about the

imagined events than the not imagined events. If, however, the plausibility of the imagined

events does not affect subjects’ source decisions, then subjects should be more confident


DOI: 10.1002/acp

https://www.researchgate.net/publication/11770157_Changing_beliefs_about_implausible_autobiographical_events_A_little_plausibility_goes_a_long_way?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

https://www.researchgate.net/publication/227986507_The_effects_of_prevalence_and_script_information_on_plausibility_belief_and_memory_of_autobiographical_events?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

https://www.researchgate.net/publication/227986507_The_effects_of_prevalence_and_script_information_on_plausibility_belief_and_memory_of_autobiographical_events?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

https://www.researchgate.net/publication/227628766_Increasing_belief_in_an_invasive_procedure_that_never_happened_The_role_of_plausibility_and_schematicity?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3

https://www.researchgate.net/publication/227522120_Plausibility_and_belief_in_autobiographical_memory?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3


and remember more about the imagined than the not imagined events regardless of event

plausibility.

We also made predictions based on the nested structure of Scoboria et al.’s (2004) model.

Because each construct (e.g. memory) is nested in its superordinate (e.g. belief), we

predicted that a change in a particular construct should cause a corresponding change in its

superordinate. Specifically, we expected that as subjects’ memories became clearer and

more complete, they should be more confident that the remembered events were real

experiences. Furthermore, as subjects become more confident that the events were real,

they should find those events more personally plausible. Finally, as subjects find the events

more personally plausible, they should also find them more generally plausible.

METHOD

Subjects

Subjects were 60 students (49 females) from the University of New South Wales, Australia.

Forty undergraduate psychology students received course credit for their participation.

Twenty students from other disciplines received $40 for their participation. Subjects ranged

in age from 18 to 40 years (M¼ 22.62, SD¼ 4.97).

Materials and procedure

Subjects took part in three sessions individually (see Figure 1).

Session 1

Following Garry et al. (1996), subjects were told that we were investigating how clearly

and completely people could visualise childhood events. In Session 1, they completed two

questionnaires to ‘gather background information about events that they may have

experienced in childhood’. All subjects completed the Life Events Inventory (LEI) and

Autobiographical Belief and Memory Questionnaire (ABMQ) in the same order (LEI first).

Pilot testing of 197 subjects at the University of New South Wales (N¼ 100) and the

University of Windsor (N¼ 97) revealed that the order in which subjects completed the

questionnaires had no effect on their total LEI or ABMQ belief ratings, F(1, 195)¼ 1.65, ns

and F(1, 195)¼ 1.62, ns, respectively. Furthermore, pilot subjects’ LEI and ABMQ belief

ratings were very similar, as shown by a high positive correlation, r¼ .72, p< .01.

Subjects’ LEI and ABMQ belief ratings also had moderate positive correlations of similar

magnitude with ABMQ memory ratings (LEI: r¼ .51, p< .01; ABMQ belief: r¼ .53,

p< .01).2

The LEI (Garry et al., 1996) is a 20-item measure that assesses subjects’ confidence that

they experienced certain childhood events on an 8-point Likert scale (1¼ definitely did not

happen, 8¼ definitely happened). The version used in this experiment contained 20 events,

10 of which were also included in the ABMQ and are described below. The other ten events

2Because of this similarity between LEI confidence and ABMQ belief ratings we only report changes in subjects’LEI confidence ratings below. We chose to focus on these ratings to be consistent with previous plausibilityresearch (e.g., Hart & Schooler, 2006; Mazzoni et al., 2001; Pezdek, Blandon-Gitlin, & Gabbay, 2006; Pezdek,Blandon-Gitlin, Lam et al., 2006) and because the pattern of results for ABMQ belief ratings was similar to that ofLEI ratings.


DOI: 10.1002/acp

https://www.researchgate.net/publication/11770157_Changing_beliefs_about_implausible_autobiographical_events_A_little_plausibility_goes_a_long_way?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3




Session 1 Session 2 Session 3

Pretest Imagination exercise Posttest

LEI

ABMQ

LEI

ABMQ

(MCQ)

Group 1 eventsn = 30

High: Choke

Moderate: Enema

Low: Ghost

Group 2 eventsn = 30

High: Lost

Moderate: Tooth

Low: Demon

1 week 1 week

Figure 1. Diagram of the procedure


were those typically used in imagination inflation research (e.g. Broke a window with your

hand; Garry et al., 1996; Sharman, Garry, et al., 2005); these events were filler events.

Subjects rated how confident they were that each of the events happened to them before the

age of 10.

The ABMQ (Scoboria et al., 2004) is a five-item measure that assesses subjects’

judgments about autobiographical events. Specifically, the items assess general

plausibility, personal plausibility, autobiographical belief, and autobiographical memory

on eight-point Likert scales (general plausibility and personal plausibility: 1¼ not at all

plausible, 8¼ extremely plausible; belief: 1¼ definitely did not happen, 8¼ definitely

happened; memory: 1¼ no memory of event at all, 8¼ clear and complete memory of

event). The fifth item asks subjects to estimate how frequently (out of 100) people

experience each event. We did not include this item in the current experiment because

subjects’ prevalence judgments are not integral to the nested model. We used the ABMQ to

assess the ten events described below. Subjects rated each event with respect to children

under the age of 10.

We drew the ten events from Scoboria et al. (2004) and Scoboria et al. (2006) to

represent a range of plausibility. The events were: losing a toy (Toy), choking on a small

object (Choke), getting lost in a shopping mall (Lost), having a tooth extracted (Tooth),

seeing parents naked together (Naked), having a skin sample taken by a school nurse

(Skin), receiving a rectal enema (Enema), having a bone density screening (Density),

witnessing a demonic possession (Demon) and seeing or hearing a real ghost (Ghost). Six

events were our target events (Choke, Lost, Tooth, Enema, Demon, Ghost); the other four

events were filler events (Toy, Naked, Skin, Density).

Session 2

Subjects returned 1 week later to visualise three childhood events. Half of the subjects

imagined Group 1 events (Choke, Enema, Ghost), the other half imagined Group 2 events


DOI: 10.1002/acp

https://www.researchgate.net/publication/7776811_Using_source_cues_and_familiarity_cues_to_resist_imagination_inflation?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3




(Lost, Tooth, Demon). The group of events that subjects did not imagine served as control

events. For both groups of events, subjects imagined the events in the same order, from

most plausible to least plausible (High: Choke, Lost; Moderate: Enema, Tooth; Low:

Ghost, Demon); these rankings were based on plausibility ratings from pilot subjects and

from Scoboria et al. (2004). We chose this order to encourage subjects to create believable

and realistic images for each of the events. If subjects had imagined the low plausibility

event first, it might have encouraged them to create unrealistic, unbelievable images of all

three events.

Subjects were told that the experimenter was interested in how completely and clearly

they could visualise a range of childhood events. They were told to picture each event as

clearly and completely as they could, and to include familiar people and places from their

childhood in the imagined events. For each event, the experimenter read out two to three

sentences describing the event location and background (e.g. Choke: Imagine that you are

at home eating a snack after school. You eat quickly, because you are excited about going

outside to play afterwards). Subjects were given 30 seconds to picture the event before

answering questions about their images (What are you going to go and play with? What is

likely to happen next?). Once subjects answered the questions, the experimenter read out

two to three more sentences describing the main part of the event (While you are eating, a

piece of food gets caught in your throat. You start to choke, but the food does not come out

and you are having trouble breathing. You look around for help). Subjects were given

another 30 seconds to imagine this part of the event, then they answered two more

questions (What are you choking on? What happens next?). Subjects went through this

guided imagination sequence once for all three events.

Session 3

One week later, in the third session, subjects completed the LEI and ABMQ; they were not

told why they needed to complete the questionnaires a second time. Subjects also

completed the Memory Characteristics Questionnaire (MCQ; Johnson, Foley, Suengas, &

Raye, 1988) for events they imagined and subsequently increased their ABMQ memory

ratings by 2 or more points on the scale. Finally, subjects were debriefed.

RESULTS

All subjects believed our cover story about investigating people’s abilities to visualise

childhood events; they expressed surprise at the true purpose of the experiment.

Manipulation checks

Plausibility categorisations

To determine whether subjects’ pretest plausibility ratings were consistent with our event

plausibility categorisations, we examined subjects’ general and personal plausibility

pretest ABMQ ratings for high, moderate and low plausibility events. Subjects gave the

highest pretest plausibility ratings to high plausibility events, followed by moderate

plausibility events, followed by low plausibility events; there were no pretest differences

between imagined and not imagined events (see Table 1). A 3 (event plausibility)� 2

(plausibility rating)� 2 (imagined) repeated measures ANOVA revealed that the main

effect for event plausibility was significant, F(2, 116)¼ 182.3, p< .01, h2p ¼ 0.76; posthoc


DOI: 10.1002/acp


Table 1. Pretest and posttest means for imagined and not imagined events

Pretest Posttest

Imagined Not imagined Imagined Not imagined

ABMQ general plausibilityHigh 7.73 (0.64) 7.64 (0.71) 7.63 (1.18) 7.60 (1.09)Moderate 6.18 (2.02) 5.80 (2.19) 6.78 (1.68) 6.03 (2.15)Low 4.05 (2.47) 3.90 (2.14) 3.97 (2.44) 4.20 (2.25)

ABMQ personal plausibilityHigh 6.71 (1.85) 6.61 (2.06) 6.98 (1.76) 7.03 (1.60)Moderate 4.28 (2.48) 4.57 (2.78) 5.10 (2.28) 4.47 (2.64)Low 2.83 (2.04) 2.53 (1.91) 3.03 (2.11) 3.07 (2.28)

LEI confidenceHigh 5.23 (2.66) 5.15 (2.62) 5.78 (2.38) 5.73 (2.25)Moderate 2.38 (2.35) 2.97 (2.92) 3.05 (2.57) 3.13 (2.84)Low 1.55 (1.13) 1.72 (1.49) 1.95 (1.41) 1.90 (1.43)

ABMQ memoryHigh 3.81 (2.73) 4.07 (2.66) 4.95 (2.55) 4.68 (2.68)Moderate 1.98 (2.13) 2.75 (2.82) 2.48 (2.45) 2.68 (2.72)Low 1.50 (1.31) 1.62 (1.55) 1.58 (1.42) 1.58 (1.42)

Note: For all tables standard deviations are in parentheses. ABMQ¼Autobiographical Belief and MemoryQuestionnaire; LEI¼Life Events Inventory.


contrasts showed the effect was linear, F(1, 58)¼ 338.9, p< .01, h2p ¼ 0.85. There was also

a main effect for plausibility ratings: general plausibility ratings were higher than personal

plausibility ratings, F(1, 58)¼ 109.4, p< .01, h2p ¼ 0.65. There was no effect for

imagination, F(1, 58)¼ 0.63, ns, and no significant interactions, all ps> .05. Overall,

subjects’ plausibility ratings were consistent with our event categorisations.

Imagination inflation

Table 1 shows subjects’ pretest and posttest LEI confidence ratings. There were no pretest

differences between imagined and not imagined events; however, subjects were more

confident that they had experienced the high, followed by the moderate, followed by the

low plausibility events. That is, a 2 (imagination)� 3 (plausibility) repeated measures

ANOVA on subjects’ pretest confidence ratings revealed a significant main effect for

plausibility, F(2, 118)¼ 85.42, p< .01, h2p ¼ 0.59, but no significant effect for imagination,

F(1, 59)¼ 1.21, ns, nor a significant interaction, F(2, 118)¼ 0.60, ns. Bonferroni-corrected

pairwise comparisons revealed that subjects were more confident that they had experienced

high than moderate, high than low and moderate than low plausibility events. These

differences in confidence are consistent with those found by Scoboria et al. (2004): as

events become less plausible, subjects give lower belief and memory ratings. The most

important point to note is that there were no pretest differences between the imagined and

not imagined events.

To determine whether our subjects showed imagination inflation, we focused on events

initially rated between 1 and 4 on the LEI (Garry et al., 1996; see Garry, Sharman, Wade,

Hunt, & Smith, 2001, for a discussion of the best way to analyse imagination inflation

data); that is, we focused on moderate and low plausibility events. The left side of Figure 2

shows the mean change in subjects’ confidence ratings from pretest to posttest for imagined


DOI: 10.1002/acp



Figure 2. Mean confidence and memory change scores for imagined and not imagined events


and not imagined events. Subjects showed imagination inflation regardless of event

plausibility: their confidence increased more for the imagined events than not imagined

events. Put another way, a 2 (imagination)� 2 (plausibility) repeated measures ANOVA on

confidence change scores showed a main effect for imagination, F(1, 59)¼ 4.04, p< .05,

h2p ¼ 0.06. There was no effect for plausibility, F(1, 59)¼ 0.49, ns and no interaction, F(1,

59)¼ 0.77, ns. These results are evidence of imagination inflation regardless of event

plausibility.

Memory ratings

Table 1 shows subjects’ pretest and posttest memory ratings. There were no pretest

differences between imagined and not imagined events; however, subjects had clearer and

more complete memories of the high, followed by the moderate, followed by the low

plausibility events. That is, a 2 (imagination)� 3 (plausibility) repeated measures ANOVA

on subjects’ pretest memory ratings revealed a significant main effect for plausibility, F(2,

116)¼ 34.29, p< .01, h2p ¼ 0.37, but no significant effect for imagination, F(1, 58)¼ 3.90,

ns, nor a significant interaction, F(2, 116)¼ 0.83, ns. Bonferroni-corrected pairwise

comparisons revealed that subjects had clearer and more complete memories of high than

moderate, high than low and moderate than low plausibility events. These differences in

memory ratings show the same pattern as our differences in confidence ratings. Again, the

most important point to note is that there were no pretest differences between the imagined

and not imagined events.


DOI: 10.1002/acp


To determine whether imagining false events with different initial levels of plausibility

changed subjects’ memories, we looked at the change scores for all three types of events

because they were all initially rated between 1 and 4 (see Table 1). The right side of

Figure 2 shows that subjects had clearer and more complete memories of imagined events

than not imagined events; they also had clearer and more complete memories of high

plausibility events, followed by moderate plausibility events, followed by low plausibility

events. In other words, a 2 (imagination)� 3 (plausibility) repeated measures ANOVA

showed a main effect for imagination, F(1, 58)¼ 6.80, p¼ .01, h2p ¼ 0.11, and a main effect

for event plausibility, F(1, 59)¼ 5.77, p¼ .02, h2p ¼ 0.09. Follow-up tests indicated that this

plausibility main effect was linear, F(1, 58)¼ 13.68, p< .01, h2p ¼ 0.19. There was no

interaction between event plausibility and imagination, F(2, 116)¼ 1.25, ns. These results

indicate that regardless of event plausibility, imagining false childhood events gave

subjects clearer and more complete memories. Overall, however, event plausibility

affected subjects’ memories: they developed clearer and more complete memories of high,

followed by moderate, followed by low plausibility events.

Memory qualities

One explanation for our finding that subjects developed clearer and more complete

memories of high, then moderate, then low plausibility events is that the high plausibility

events were easier to imagine than the moderate plausibility events, which in turn were

easier to imagine than the low plausibility events. In other words, event plausibility might

have been confounded with event imageability. If this hypothesis were true, increased ease

of imagining should result in memories with more qualitative characteristics. To examine

this possibility, we focused on the MCQ ratings of the 32 subjects whose memory ratings

increased by 2 or more points for at least one event. We calculated subjects’ mean scores

for each of the five MCQ scales as described by Suengas and Johnson (1988): Clarity,

Sensory details, Contextual details, Thoughts and feelings and Intensity of thoughts and

feelings. We found a difference for plausibility on one of these memory characteristics:

subjects’ memories of high plausibility events contained more intense thoughts and

feelings than their memories of low plausibility events.

In other words, a 5 (scale)� 3 (event plausibility) repeated measures ANOVA revealed

that there was a main effect for scale, F(4, 116)¼ 6.74, p< .01, h2p ¼ 0.19, but no main

effect for plausibility, F(2, 29)¼ 2.23, ns, and no interaction between scale and plausibility,

F(8, 116)¼ 0.62, ns. Follow-up univariate ANOVAs conducted on each of the five scales

revealed that there was a main effect of plausibility on the Intensity of thoughts and feelings

scale, F(2, 29)¼ 7.81, p< .01, h2p ¼ 0.35. Bonferroni-corrected posthoc tests revealed that

high plausibility events contained more intense thoughts and feelings (M¼ 3.63,

SD¼ 0.91) than low plausibility events (M¼ 1.88, SD¼ 0.63). Overall, these results

indicate that event plausibility had an effect on only one of the five types of memory

characteristics. Subjects found it easier to generate more compelling thoughts and feelings

when imagining high plausibility events; however, plausibility did not appear to influence

subjects’ imagining of other memory features.

Testing predictions based on the nested model

We examined the nested structure of Scoboria et al.’s (2004) model by investigating

whether memory was nested in belief, belief was nested in personal plausibility and


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personal plausibility was nested in general plausibility. Prior studies have examined the

proportion of instances in which the organisation of variables have fit the predicted

arrangement (General plausibility� Personal plausibility�Belief�Memory; Scoboria

et al., 2004, 2006). If the model holds, a majority of ratings are expected to fit this equation.

In the present experiment, 94% of ratings were consistent when collapsed across event and

time of test (range¼ 87–98% consistency across cells).

To examine the model’s more specific predictions about nesting, we investigated

whether increases in one construct caused increases in the superordinate constructs.

We compared the confidence ratings of subjects whose memory ratings increased with the

confidence ratings of subjects whose memory ratings stayed the same or decreased (see the

top third of Table 2 for all means, standard deviations and one-sided independent t-test

results). Subjects whose memory ratings increased should have a greater tendency to

increase their confidence ratings because change in memory will result in change in belief

for some. Consistent with this prediction, subjects whose memories became clearer and

more complete became more confident that they had experienced the events than those

whose memories stayed the same or became less clear. This pattern held across high,

moderate and low plausibility events.

To determine whether changes in belief influenced changes in personal plausibility, and

if changes in personal plausibility influenced changes in general plausibility, we conducted

similar analyses (see the middle and bottom of Table 2). Consistent with predictions,

subjects who became more confident that they had experienced the childhood events also

found those events more personally plausible than subjects whose confidence stayed the

same or decreased. Subjects who found the events more personally plausible also found

the events more generally plausible than subjects whose personal plausibility ratings stayed

the same or decreased. Again, these patterns occurred for high, moderate and low

plausibility events. Overall, these findings are consistent with the nested model of

autobiographical beliefs and memories.

DISCUSSION

Our subjects showed imagination inflation regardless of event plausibility; that is, they

became more confident that they had experienced both moderate and low plausibility false

childhood events after imagining those events. This finding contrasts with that of Pezdek,

Blandon-Gitlin, and Gabbay (2006), who only found imagination inflation for events

manipulated to have high plausibility; that is, events that subjects were told occurred

frequently. In our experiment, subjects were not given prevalence information to indicate

the plausibility of the events; rather, they relied on their own beliefs about the possibility of

the events’ occurrence. Thus, imagination was not confounded with prevalence

information. Our results suggest that event plausibility—as opposed to event

prevalence—does not affect imagination inflation.

Consistent with our imagination inflation results, we found that subjects developed

clearer and more complete memories of imagined events than not imagined events

regardless of event plausibility. We also found that, for both imagined and not imagined

events, subjects developed clearer and more complete memories of high, followed by

moderate, followed by low plausibility events. This finding suggests that even thinking

about the events while completing the pretest and posttest questionnaires is enough to boost

subjects’ memories of high plausibility events. Overall, their memory ratings for these high


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Table 2. Changes in nested model constructs as a function of change in subordinate constructs

Confidence ratingsa

Memory increasedMemory same/

decreased

t pN Mean (SD) N Mean (SD)

High 30 1.23 (2.06) 29 �0.10 (0.87) 3.27 .00Moderate 17 0.79 (1.21) 43 0.27 (0.89) 1.86 .03Low 12 1.00 (1.09) 48 0.11 (0.87) 3.00 .00

Personal plausibility ratingsb

Confidence increasedConfidence same/

decreased


High 27 0.74 (1.29) 32 0.02 (1.52) 1.95 .03Moderate 25 0.66 (1.14) 35 0.14 (1.56) 1.41 .08Low 26 0.87 (1.47) 34 �0.01 (1.41) 2.36 .01

General plausibility ratingsc

Personal plausibilityincreased

Personal plausibilitysame/decreased


High 23 0.33 (0.70) 36 �0.29 (1.24) 2.18 .02Moderate 30 0.73 (1.19) 30 0.10 (1.23) 2.03 .02Low 24 1.10 (1.32) 36 �0.56 (1.05) 5.42 .00aChange in confidence as a function of increase or lack of increase in memory.bChange in personal plausibility as a function of increase or lack of increase in confidence.cChange in general plausibility as a function of increase or lack of increase in personal plausibility.


plausibility events went from ‘not much of a memory’ (just under 4 on the scale at pretest)

to ‘a slightly clearer memory’ (about 5 on the scale at posttest). Subjects’ memories of

moderate plausibility events increased about half a point on the scale, although their ratings

remained nearer the ‘no memory’ end of the scale. Subjects’ memories of low plausibility

events showed a small increase from pretest to posttest. These results indicate that merely

questioning people about whether highly plausible events occurred can help them to

remember those events. Thinking about the events might have led subjects to generate

sensory and perceptual details, which they later mistook for memory fragments of genuine

experiences. Additionally, encountering the events at least twice—once at pretest and once

at posttest—may have made the events feel familiar, which increased subjects’ memory

ratings. This feeling of familiarity may have been greater for high plausibility events.

Imagination had a similar effect on subjects’ confidence and memory ratings: subjects’

ratings increased more for imagined than not imagined false events. Event plausibility,

however, had a different effect on subjects’ confidence and memory ratings: event


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plausibility affected memory, but not confidence, ratings. This difference may be due to the

criteria subjects adopted when judging whether they remembered the imagined events as

genuine experiences or whether they believed that the imagined events occurred without

remembering them. According to Mazzoni and Kirsch’s (2002) model, false memories

develop from false beliefs when: (1) the criteria people use to judge whether an event

happened change, and (2) the qualitative details of the ‘remembered’ event are enhanced.

In our experiment, imagining the childhood events enhanced their qualitative details such

that subjects became more confident that the imagined events really happened and had

clearer and more complete memories of the imagined events compared to the not imagined

events. In other words, imagination enhanced their beliefs and memories. Only some of

these beliefs—those associated with high and, to a lesser extent, moderate plausibility

events—developed into memories. Mazzoni and Kirsch’s model proposes that event

plausibility is one of the criteria subjects use to determine whether events are remembered

or just believed to have happened (see also Johnson, 2006; Mitchell & Johnson, 2000).

Because high and moderate plausibility events are more likely to have happened, subjects

should have been more likely to develop clearer and complete memories of these events.

The imagination exercise may have directly or indirectly affected subjects’ memories. It is

possible that imagining the events changed their memories, which in turn changed their

beliefs. It is equally possible that imagining the events changed subjects’ beliefs, which in

turn changed their memories. Furthermore, imagining the events might have changed

subjects’ memories and beliefs simultaneously. Our experiment does not shed light the

order in which imagination affects beliefs and memories, although future research might

do so.

Our results are consistent with Scoboria et al.’s (2004) nested model of autobiographical

beliefs and memories. The predicted ordering of ratings was consistent with the model both

pre- and postmanipulation. Subjects whose memory ratings increased had higher

confidence ratings than those whose memory ratings stayed the same or decreased.

Similarly, subjects whose confidence ratings increased had higher personal plausibility

ratings than those whose confidence ratings stayed the same or decreased. Finally, subjects

whose personal plausibility ratings increased had higher general plausibility ratings than

those whose personal plausibility ratings stayed the same or decreased. Our results provide

further support that plausibility, belief and memory are partially independent constructs

that people use to judge whether autobiographical events were genuinely experienced.

Future research may investigate other parts of the model, such as situations in which these

constructs are atypical of their nesting structure; for example, when people might

remember events without believing that they happened or when people judge events to be

personally plausible but not generally plausible (see Scoboria et al., 2004, for a further

discussion of exceptions).

Our results have both theoretical and practical implications. Theoretically, they suggest

that event plausibility does not affect imagination inflation: people’s confidence that

imagined events occurred increased equally for low and moderate plausibility events.

People also had clearer and more complete memories for imagined than not imagined

events; these memories were clearer and more complete for high, followed by moderate,

followed by low plausibility events. These results are consistent with major models of

autobiographical beliefs and memories. Practically, our results suggest that whenever

people are in situations in which they imagine false childhood events, they may become

more confident that those events occurred and may also develop clearer and more complete

memories of those events, regardless of how plausible those events seem. This finding may


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shed light on how people can come to believe and remember that they experienced very

implausible events for which there is no physical evidence such as alien abductions,

previous life experiences and satanic ritual abuse. It is possible that once people suspect

that they have had such an experience, they create images of these events while thinking

about how and when they might have occurred. These images may be misattributed to

genuine experience, which can make people more confident and give them clearer and

more complete memories about very implausible events. For example, people who

experience paralysis and hallucinations on awakening—which often occur during

episodes of sleep paralysis—may search for explanations about these strange sensations

(Clancy, 2005; McNally & Clancy, 2005). We know that asking people to explain how

events might have happened has a similar effect on their beliefs as imagining those events

(Sharman, Manning, & Garry, 2005). Therefore, people who explain their sleep paralysis in

terms of an alien abduction may become more confident that they were actually abducted,

and—through repeated imaginings—ultimately come to ‘remember’ their abduction

experiences.

Our research also raises an important theoretical and applied question: at what point do

people call their mental representations ‘memories’ and does event plausibility affect this

point? Is there a threshold at which people judge their mental representations to be genuine

representations of events experienced during childhood (see Johnson et al., 1993), and can

crossing this threshold cause a change in people’s behaviour (Bernstein, Laney, Morris, &

Loftus, 2005; Geraerts, Bernstein, Merckelbach, Linders, Raymaekers, & Loftus, in press;

Scoboria, Mazzoni & Jarry, 2008; also see Smeets, Merckelbach, Horselenberg, & Jelicic,

2005)? In our experiment, imagination had the same effect on people’s memories of events

with different levels of plausibility. Therefore, it is important to consider where such a

threshold may lie, and under what circumstances events of different plausibilities may

cross this point. Our subjects’ memories for high plausibility events may have been near or

at the threshold, as they were slightly closer to the ‘no memory’ end of the scale prior to

imagination and moved towards ‘some sort of memory’ (i.e. at the scale midpoint)

following imagination. However, our subjects’ memories for low and moderately plausible

events may have been well below the threshold as they were rated down towards the ‘no

memory’ end of the scale both before and after the imagination exercise. Thus for low and

moderate plausibility events, multiple exposures to the events may be necessary to increase

people’s mental representations over and above the threshold such that they call these

representations ‘memories’.

How many times might a lower plausibility event be imagined before changes in

confidence and memory are sufficient for people to judge that the events really occurred or

that they ‘remember’ those events? Laboratory work suggests that increasing the number of

imaginings for simple actions results in greater source confusion and higher false memory

rates, even for bizarre actions (Goff & Roediger, 1998; Seamon, Philbin & Harrison, 2006;

Thomas & Loftus, 2002). Indeed, other false memory paradigms suggests that repeatedly

imagining unusual false events on separate occasions (e.g. 48 hours apart) in the context of

trying to recall those events increases false memory formation (Hyman & Billings, 1998;

Hyman, Husband, & Billings, 1995). Thus, future research might investigate the effects of

repeatedly imagining false events with different levels of plausibility. The number of

imaginings, the interval between imaginings, manipulations that influence plausibility and

confidence ratings, and the temporal sequencing of imagination and such manipulations,

will likely prove fruitful in understanding how false memories for initially implausible

events are developed.


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https://www.researchgate.net/publication/7860377_Sleep_Paralysis_Sexual_Abuse_and_Space_Alien_Abduction?el=1_x_8&enrichId=rgreq-84d9fde0-c78e-44bb-944e-2693d69e75b0&enrichSource=Y292ZXJQYWdlOzIyNzcyMTMyNTtBUzo5OTU3MDg1NTk3Mjg3M0AxNDAwNzUwOTUwODI3


ACKNOWLEDGEMENTS

Stefanie Sharman was supported by a Vice Chancellor’s Postdoctoral Fellowship at the

University of New South Wales. Alan Scoboria was supported by a Natural Science and

Engineering Research Council of Canada Discovery Grant.

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Imagination equally influences false memories of high and low plausibility events

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