241
Legal and Criminological Psychology (2009), 14, 241–252
q 2009 The British Psychological Society
The
British
Psychological
Society
www.bpsjournals.co.uk
Forced confabulation more strongly influences
event memory if suggestions are other-generated
than self-generated
Kathy Pezdek*, Shirley T. Lam and Kathryn Sperry
Claremont Graduate University, Claremont, California, USA
Purpose. Virtually all eyewitnesses to a crime, who eventually testify in court, are
interviewed by police officers at least once. How do these interviews affect what the
eyewitnesses are subsequently likely to report? The purpose of this study is to compare
the relative impact of self- versus other-generated misinformation on confabulated
memory about an event. Self-generated misinformation can occur by encouraging
eyewitnesses to guess or speculate about possible answers to questions about which
they report having no memory. Other-generated misinformation can occur by having an
investigator suggest an answer to an eyewitness.
Methods. After viewing a 5 minutes crime video, participants answered written
questions. One week later these same questions were answered again. We specifically
focused on individuals’ answers to unanswerable questions that probed information not
actually presented in the video. If a participant answered an unanswerable question, we
know that their answer was confabulated because the information was not presented in
the video.
Results. If an answer to an unanswerable question was forced confabulated at time 1,
that answer was more likely to be repeated at time 2 if it had been other-generated
(suggested in the question) rather than self-generated (fabricated by the participant).
Conclusions. Pressuring eyewitnesses to answer questions about an event, when
they indicate that they do not know the answer, can result in false confabulations.
Answers suggested by the investigator are more likely to be repeated later than are
answers that are simply self-generated or speculated by the eyewitness. These results
are consistent with the reality monitoring framework and ‘recollect-to-reject’
metacognitive reasoning strategies.
On the afternoon of September 10, 2003, Anna Lindh, the Swedish Foreign Minister, was
stabbed to death while shopping in the ladies’ department of Nordiska Kompaniet
department store in Stockholm. A large number of people witnessed the attack, many of
whom were subsequently seated together in a room before and while they were
* Correspondence should be addressed to Dr Kathy Pezdek, Department of Psychology, Claremont Graduate University,
Claremont, CA 91711, USA (e-mail: Kathy.Pezdek@cgu.edu).
DOI:10.1348/135532508X344773
242 Kathy Pezdek et al.
interviewed by the police. There were numerous opportunities for cross-contamination
of witness memory. In fact, the investigation was obstructed by the fact that the initial
police bulletins contained information obtained from witnesses that was later dismissed
when a video of the incident was reviewed. It turned out that many of these errors were
the result of witness memory contagion. Further, photographs of the suspected
perpetrator were circulated 3 days after the assassination. Granhag, Ask, and Rebelius
(2005) interviewed 29 witnesses to the assassination and reported that descriptions of
the perpetrator obtained after publication of the pictures were significantly more
accurate (i.e. they better matched the video) than those obtained prior to publication of
the pictures, evidencing another source of witness memory contagion.
Numerous studies have demonstrated that eyewitnesses can be misled by post-event
suggestions following an observed event (Loftus, 1975; Loftus, Miller, & Burns, 1978;
Pezdek, 1977; Pezdek & Blandon-Gitlin, 2005). In most of this research, the post-event
information has been other-generated, for example, the information in an interviewer’s
questions about an event or a narrative that followed viewing an event. Conversations
among co-witnesses is another potential source of forensically relevant other-generated
suggestion (Gabbert, Memon, & Wright, 2006; Wright, Self, & Justice, 2000). A few
studies have demonstrated that self-generated post-event information can also
suggestively influence event memory (Hastie, Landsman, & Loftus, 1978; Schreiber,
Wentura, & Bilsky, 2001; Zaragoza, Payment, Ackil, Drivdahl, & Beck, 2001).
The purpose of this study is to compare the relative impact of self- versus othergenerated misinformation on confabulated memory about an event. This is an important
issue because the research on other-generated post-event information is often generalized
to particular real world situations that are more likely to involve self-generated post-event
information. These situations include, for example, the affect of speculation on the
accuracy of eyewitnesses’ memory, and the role of imagination as a catalyst for false
memories. There may be important constraints on the extent to which the research on
other-generated post-event information can be generalized to self-generated post-event
information, yet there is little research specifically investigating this issue.
Pezdek, Sperry, and Owens (2007) recently examined whether information is more
likely to be incorporated into memory if it is (a) spontaneously self-generated or (b) forcibly
self-generated, for example by pressing eyewitnesses to answer questions about events that
they are unsure of. Participants viewed a crime video and then answered answerable and
unanswerable questions. Those in the ‘voluntary guess’ condition had an ‘I don’t know’
response option, so if they answered a question, it was considered ‘volunteered’.
Participants in the ‘forced guess’ condition did not have the ‘I don’t know’response option,
so they were forced to provide an answer to each question. One week later the same
questions were answered with an ‘I don’t know’ option available for everyone. Information
self-generated from forced confabulation at time 1 was less likely to be repeated at time 2
than information that had been voluntarily self-generated. Further, when the same
answer was given to an unanswerable question both times, the confidence expressed in the
answer increased over time in both the forced and the voluntary guess conditions.
The results of Pezdek et al. (2007) are forensically relevant because virtually all
eyewitnesses to crimes, who eventually testify in court, are interviewed by police officers
at least once, and more typically, multiple times (Cutler & Penrod, 1995; Poole & White,
1995). Guidelines for forensic interviewing warn police officers about the potential for
suggestively influencing witness memory by the wording of their questions (see Memon
& Bull, 1999; Milne & Bull, 1999, for extensive reviews of this literature). This type of
suggestion – other-generated confabulation – can be induced by having an investigator
Forced confabulation
243
suggest to an eyewitness what the answer to a question might be (‘The other eyewitness
said that the car at the end of the alley was white. What colour do you think the car was?’).
Less is known, however, about the suggestive effect of encouraging witnesses to
speculate answers to questions. If encouraging eyewitnesses to guess answers or
speculate about possible answers to questions about which they report having no
memory leads to false confabulation, forensic interviewers should also be advised
against pressing witnesses to answer questions under these circumstances; these
circumstances could produce self-generated false confabulations. In this study we
compared the relative impact of self- versus other-generated suggestion on memory
confabulations. No data exist documenting how frequently officers in real police
interviews press an eyewitness to answer questions after the eyewitness indicates that
he or she does not know the answer to the question. However, Gudjonsson (1992),
Kassin (1997), and Leo (1996) have reported that this is not an unusual practice. They
reported that eyewitnesses are often pressed to describe events that the interviewer
believed occurred, even when witnesses report that they cannot remember the event or
report that they did not even witness the event. False confessions commonly occur
under similar circumstances.
In this study, the methodology of Pezdek et al. (2007) was replicated, however, the
post-event information was either self-generated by each participant or other-generated
in the questions presented. This study assesses event memory and specifically compares
the relative impact of self-generated versus other-generated misinformation on
subsequent recall. In most suggestibility studies, the focus is on how memory for
information that was actually presented is affected by post-event suggestion. In this
study, we specifically focus on individuals’ answers to unanswerable questions about
information that was not actually presented in the video. If a participant answers an
unanswerable question, we know that the information in his or her answer was
confabulated, because it was not presented in the video.
Methods
Participants and design
One hundred forty-four participants volunteered in eight psychology classes in the Los
Angeles metropolitan area. This was a 2 (forced guess vs. voluntary guess condition) £ 2
(self- vs. other-generated) £ 2 (time 1 vs. time 2) mixed factorial design with the first two
variables manipulated between participants.
Materials and procedure
Individuals participated with their classmates in two 15 minutes sessions, 1 week apart, in
their psychology class. In the first session, participants viewed a 5 minutes video of a carjacking (produced for the study by Clark & Tunnicliff, 2001, and also the same video used
by Pezdek et al., 2007). Participants were told to pay very close attention to the video
because afterward they would be asked some questions. The video was followed
immediately by 22 open-ended questions including 16 answerable and 6 unanswerable
questions. The questions were provided in writing; participants provided answers in
writing as well. The questions used in this study are identical to those used by Pezdek et al.
(2007) and are included in the Appendix. Answerable questions probed information that
was presented in the video; unanswerable questions probed information not presented in
the video. For example, an unanswerable question is, ‘What was the logo on the
244 Kathy Pezdek et al.
perpetrator’s shirt?’ and the perpetrator’s shirt did not have a logo. Questions were
presented in the same order to all participants and followed the chronological order in
which the relevant information appeared in the video. The first three questions were
answerable questions selected from the list presented in the Appendix. The next 19
questions were a mix of answerable and unanswerable questions with no consecutive
unanswerable questions. Although this study focuses only on the answers to
unanswerable questions, answerable questions were included as well so that the
participants would take the task seriously and not be suspicious about nature of the
questions.
Definition of the other-generated and self-generated conditions
In the other-generated condition, all six of the unanswerable questions and six (out of
the 16) answerable questions included suggested answers in the question itself. For
example, an unanswerable question in the other-generated condition asked, ‘The type
of soda the co-worker was drinking looked like a Coke; what do you remember as the
type of soda?’ An answerable question asked, ‘The colour of the backpack the victim
was carrying looked like it was purple; what do you remember the colour to be?’ For
unanswerable questions, the suggested answer to each question was the most
commonly reported answer to that question produced in the study by Pezdek et al.
(2007). We did this to ensure that the suggested answer was not an improbable one. For
answerable questions, the other-generated suggested answer was always the correct
answer. In the self-generated condition, all questions were stated just as they are
indicated in the Appendix.
Definition of forced guess and voluntary guess conditions
Participants in the forced guess condition (N ¼ 78) were provided written instructions
to answer all 22 questions. They were instructed not to leave any questions unanswered,
and that they should make their best guess of each answer even if they were unsure.
Participants in the forced guess condition were not given an ‘I don’t know’ response
option at time 1. On the other hand, participants in the voluntary guess condition
(N ¼ 66) were provided written instructions to answer each question, however they
were instructed that if they did not know an answer they should circle the ‘I don’t
know’ response option. After each of their 22 responses, participants in all conditions
also rated their confidence in the accuracy of their response on a 1 (low) to 7 (high)
scale. Participants did not give confidence ratings for questions to which they
responded, ‘I don’t know.’
One week later at time 2, participants were retested on their memory for the video.
At time 2, participants in all four conditions were provided with the same 22 questions,
but this time all participants were given the ‘I don’t know’ response option and were
instructed to check this option if they did not know the answer to a question. The
‘other-generated’ suggested answers were not included on the questionnaire at time 2.
Again, participants provided confidence ratings for each answer provided.
Results
There was one exclusion criterion. Ten participants in the forced guess condition were
excluded from the analyses because they indicated ‘I don’t know’ at time 1 to at least
Forced confabulation
245
one of the six unanswerable questions.1 Of these participants, five were in the selfgenerated condition and five were in the other-generated condition. Analyses were
performed on the remaining 134 participants (M age ¼ 22:7 years; 51 males; 83
females).
The analyses focus on the responses to unanswerable questions. Responses to these
questions are especially revealing, as these are the questions that probed information
that was not actually presented in the video, and thus any answer provided was
confabulated. In the other-generated condition, the other-generated suggested response
was provided 8.8% of the time 1 responses in the voluntary guess condition and 19.2%
of the time 1 responses in the forced guess condition. Most of the responses to
unanswerable questions in the voluntary guess condition were responses of ‘don’t
know’ at time 1 (75.8% of all responses), and of these, 81.9% received a ‘don’t know’
response at time 2 as well. Despite the high rate of ‘don’t know’ responses in the
voluntary guess and even the forced guess condition, we would argue that the results
that follow have significant forensic relevance. This is first, because in police interviews,
unlike in the present study in which participants simply responded to written questions,
real witnesses are more likely to be pressured to answer questions; they are
consequently less likely to respond that they don’t know the answer to a question.
Second, even if our findings are only applicable to a minority of eyewitness cases, if
these result in erroneous convictions or even the obstruction of police investigations,
these are serious consequences.
The primary analysis addressed the mean proportion of unanswerable questions per
subject that were responded to at time 2 with the self-generated answer in the selfgenerated condition and the other-generated answer in the other-generated condition
given that this same answer had been provided by the subject at time 1. The conditional
probability for each of the four conditions in this study is presented in Table 1. In the
study by Pezdek et al. (2007), the critical results were also analysed in terms of this
conditional probability. Four of the 68 participants in the forced guess condition were
not included in this analysis because they produced different answers at time 1 and time
2 to all six unanswerable questions; this analysis is thus conducted on 64 participants in
the forced guess condition (35 in the self-generated condition and 29 in the othergenerated condition). In the voluntary guess condition only 31 participants (17 in the
self-generated condition and 14 in the other-generated condition) gave an answer to at
least one unanswerable question (i.e. they did not respond, ‘don’t know’). This is
comparable to the proportion of participants in the voluntary guess condition who
responded similarly (56%) in the study by Pezdek et al. (2007).
A 2 (voluntary vs. forced guess condition) £ 2 (self- vs. other-generated condition)
analysis of variance (ANOVA) was conducted on the data in Table 1. Only the interaction
1
In this study, we examine in each condition, the pattern of responses at time 2 given that participants provided an answer to
each question at time 1. There are two ways to achieve this conditional probability. In some previous studies (Ackil &
Zaragoza, 1998; Zaragoza et al., 2001) the experimenters made sure that everyone in the forced confabulation condition
provided an answer to each question at time 1. Zaragoza et al. (2001), for example, reported that, ‘When participants
resisted answering these questions, the experimenter prompted them to provide their best guess (repeatedly, if necessary) until
they eventually acquiesced’ (p. 474). They could do this because each participant was interviewed separately. However, in our
study individuals participated with other volunteers from their class. So although participants were instructed to provide a
response to every question, and the experimenters walked around the room and reminded participants of this, nonetheless,
some participants turned in their protocol without answering all questions. Thus, to examine the pattern of responses at time 2
given that participants provided an answer to each question at time 1, we had to exclude from the analysis participants in the
forced guess condition who indicated, ‘I don’t know’ to any question at time 1.
246 Kathy Pezdek et al.
Table 1. Mean proportion of unanswerable questions (and standard deviation) that were responded to
at time 2 with the self-generated answer in the self-generated condition or the other-generated answer
in the other-generated condition given that this same answer had been provided at time 1, in the
voluntary versus forced guess conditions
Voluntary guess condition (N ¼ 31)
Self-generated condition
Other-generated condition
Forced guess condition (N ¼ 64)
Self-generated answer
0.59 (0.41)
Other-generated answer
0.54 (0.46)
0.33 (0.24)
0.57 (0.39)
was marginally significant, Fð1; 95Þ ¼ 3:63, p ¼ :06, h2 ¼ :04. If an answer was
volunteered at time 1, there was no significant difference between the probability that
that answer would be repeated at time 2 as a function of whether the time 1 response
had been self-generated (M ¼ 0:59) or other-generated (M ¼ 0:54), tð29Þ ¼ 0:34,
p . :05, d ¼ :12. On the other hand, if the time 1 answer had been forced, that response
was more likely to be repeated at time 2 if it had been an other-generated response
(M ¼ 0:57) rather than a self-generated response (M ¼ 0:33), tð62Þ ¼ 3:12, p , :01,
d ¼ :79. The means in the two self-generated conditions reveal the same pattern of
results reported by Pezdek et al. (2007) (M ¼ 0:54 vs. 0.40, respectively).
This result suggests that in responding to unanswerable questions, self-generated
responses that were spontaneously volunteered at time 1 were equally likely to be
repeated at time 2 as other-generated responses that were volunteered at time 1. On the
other hand, when forced to guess answers to unanswerable questions, self-generated
answers were less likely to be repeated at time 2 than other-generated answers. If an
unanswerable question was responded to with an answer at time 1, even though the ‘I
don’t know’ response option was available at time 2, that question was equally likely to
be responded to with the same answer if the participant’s time 1 response was (a) othergenerated forced (M ¼ 0:57), (b) other-generated volunteered (M ¼ 0:54), or (c) selfgenerated volunteered (M ¼ 0:59). In these three conditions, if a question was
answered at time 1, the modal response at time 2 was the same response given at time 1.
However, for self-generated responses in the forced guess condition, if a question was
answered at time 1, the modal response at time 2 was ‘I don’t know’ (M ¼ 0:48) rather
than the answer that had been self-generated at time 1 (M ¼ 0:33).
Analyses of confidence ratings
We next assessed the change in confidence from time 1 to time 2 in the forced guess
versus the voluntary guess conditions for self- versus other-generated answers to
unanswerable questions. A 2 (forced guess vs. voluntary guess condition) £ 2 (self- vs.
other-generated) £ 2 (time 1 vs. time 2) mixed factorial ANOVA was conducted on the
confidence data (range in confidence ratings ¼ 1–7). For this analysis we specifically
looked at the responses to questions for which the same self-generated answer was
provided at time 1 and time 2 in the self-generated condition, and the same othergenerated answer was provided at time 1 and time 2 in the other-generated condition to
see if the confidence expressed in these responses differed across conditions. These
data are presented in Table 2. Note that the sample sizes across the four conditions vary
considerably.
Forced confabulation
247
Table 2. Mean confidence ratings (and standard deviations) for responses to unanswerable questions
that were responded to at time 1 and time 2 with the self-generated answer in the self-generated
condition or the other-generated answer in the other-generated condition, in the voluntary versus
forced guess conditions
Self-generated
Voluntary guess
(N ¼ 12)
Time 1
Time 2
2.83 (1.99)
2.42 (1.68)
Other-generated
Forced guess
(N ¼ 29)
2.50 (1.44)
3.07 (1.49)
Voluntary guess
(N ¼ 9)
4.44 (1.67)
4.11 (1.27)
Forced guess
(N ¼ 22)
3.03 (1.93)
3.77 (1.84)
In this analysis, the other-generated responses that were consistently provided at
time 1 and time 2 were more confidently held (M ¼ 3:65) than the self-generated
responses (M ¼ 2:74), Fð1; 68Þ ¼ 9:27, p , :01, h2 ¼ :12. There was also a significant
interaction of time by the forced versus voluntary guess condition, Fð1; 68Þ ¼ 5:09,
p , :05, h2 ¼ :07. Whereas in the voluntary guess condition, confidence did not
significantly change from time 1 (M ¼ 3:52) to time 2 (M ¼ 3:14), tð20Þ ¼ 0:98,
p . :05, d ¼ :21, in the forced guess condition, the confidence ratings actually
significantly increased from time 1 (M ¼ 2:72) to time 2 (M ¼ 3:37), tð50Þ ¼ 2:71,
p ¼ :01, d ¼ :39.
These results suggest that when participants repeat an answer at time 2 that had
been confabulated at time 1, their confidence in this answer was higher if it had been
other-generated than self-generated. In addition, when participants were forced to
confabulate answers to unanswerable questions, although their confidence in the
accuracy of their forced answers was initially low, after 1 week, their confidence in the
answers that were repeated was significantly higher – within the confidence range
expressed for voluntarily generated answers. The increase over time in the confidence
expressed in repeated forced guess answers occurred for both self-generated and othergenerated responses.
The analyses of responses to answerable questions, questions for which the relevant
information was provided in the video, replicated the comparable effects reported by
Pezdek et al. (2007). No effects involving the self-generated versus other-generated
condition were predicted for responses to answerable questions, nor were any of the
results involving this variable significant.
Discussion
The purpose of this study was to assess the relative impact of self-generated versus
other-generated misinformation on event memory, specifically under the conditions in
which individuals are forced to confabulate answers to unanswerable questions. The
results replicate the findings reported by Pezdek et al. (2007) with self-generated postevent information and extend these findings to other-generated post-event information.
The results suggest that under the conditions of the present study, other-generated
forced confabulated information is more likely to be incorporated into memory than
self-generated forced confabulated information. As can be seen in the right column of
Table 1, if an answer to an unanswerable question was forcibly confabulated at time 1,
that answer was more likely to be repeated at time 2 if it had been other-generated than
248 Kathy Pezdek et al.
self-generated. Further, the other-generated answers that were repeated were more
confidently held than those that were self-generated, although this was true for both the
voluntary and forced guess conditions. This finding is important in light of the fact that
jurors (Brigham & Bothwell, 1983; Noon & Hollins, 1987) and the courts (Manson v.
Braithwaite, 1977; Neil v. Biggers, 1972/1979) often assume that confident eyewitnesses
are accurate eyewitnesses.
According to the primary interpretation of how post-event information affects
memory, when individuals answer unanswerable questions about a target event, the
answers that they provide become incorporated into their memory for the target event.
On a subsequent test then, individuals are likely to make a source monitoring error and
confuse the information in their previous answers with information actually observed.
Source monitoring errors occur when individuals integrate new information about an
event into their memory for the target event, but then do not remember that the new
information did not come from the originally experienced target event ( Johnson,
Hashtroudi, & Lindsay, 1993; Lindsay, 1990).
Distinguishing between externally and internally generated information represents a
specific type of source monitoring known as reality monitoring ( Johnson & Raye, 1981).
In studies of reality monitoring, it has been reported that individuals are more accurate
differentiating between one external information source and one internal information
source than between two external information sources (Raye & Johnson, 1980).
According to Johnson and Raye (1981), this is because externally generated memories
typically include more sensory information than do internally generated memories.
Thus, discriminating between an externally generated memory and an internally
generated memory should be relatively easy because the former will typically be
accompanied by more sensory information than the latter. However, because two
externally generated memories typically cannot be differentiated on this general
dimension, individuals would have to assess the content of the information and not just
the sensory qualities to assess source. Because this is a more difficult task, more reality
monitoring error would likely result.
This would suggest in the present study that the self-generated forced confabulated
information would be easier to discriminate from the information in the originally
viewed target event. Thus, at time 2, the self-generated answer forced at time 1 would
less likely be repeated and the ‘I don’t know’ response option would more likely be
indicated. Consequently, event memory was less likely to be suggestively influenced by
the self-generated information. On the other hand, the other-generated forced
confabulated information would be more similar to and thus harder to discriminate
from the information in the target event. The source of presented information and othergenerated information would more likely be confused and thus memory for the
presented event would more likely be suggestively influenced by the other-generated
information. This prediction fits the obtained pattern of results in the forced
confabulation condition with unanswerable questions in the present study.
Another factor that would come into play and explain why self-generated items are
more memorable and less likely to be confused with presented items is the ‘recollect-toreject’ process (Brainerd, Reyna, Wright, & Mojardin, 2003; Rotello, Macmillan, & Van
Tassel, 2000). According to the recollect-to-reject process, individuals use metaknowledge to reason, ‘I remember that I generated the words “Coke” when I was forced to
guess, so I know that it was not something that I saw’. The generated items in the selfgenerated, forced guess condition are those to which individuals are likely to have
devoted more cognitive effort. Accordingly, these are the items more likely to be
Forced confabulation
249
remembered and thus more likely to lead to accurate recollect-to-reject reasoning. As a
consequence, the self-generated items in the forced guess condition were less likely to
be repeated at time 2.
This study examined the extent to which the research on other-generated postevent information can be generalized to real world situations that involve selfgenerated post-event information. Self-generated forced confabulation might occur (a)
when individuals are encouraged to imagine a traumatic event of which they appear to
have no memory or (b) when eyewitnesses are pressed to describe events that the
interviewer believed occurred, even when witnesses report that they cannot
remember the event or report that they did not even witness the event. The results of
this study suggest that although self-generated forced confabulation does occur, forced
confabulations are more likely to be produced by other-generated than self-generated
information. Numerous methodologies have been used to experimentally induce selfgenerated misinformation (cf. Mazzonni & Memon, 2003; Pezdek, Blandon-Gitlin, &
Gabbay, 2006). Certainly there may be conditions under which it is possible to
produce self-generated forced confabulations that affect memory more than some
other conditions that produce other-generated forced confabulations. However, when
comparable conditions were included in the present study, self-generated forced
confabulations were less likely to suggestively influence event memory than othergenerated confabulations.
Are generalizations from this study to forensic interviews likely to be constrained by
the fact that most of the questions that we asked participants were not actually about
the car-jacking itself, but rather about the victim and details from the video that
preceded the crime? We would argue, no. First, from a cognitive point of view, there is
no reason to suggest that forced confabulation of information would differentially affect
memory for crime-relevant versus crime-neutral information. In fact, in the study by
Yuille and Cutshall (1986), A Case Study of Eyewitness Memory of a Crime, real
witnesses to a shooting were questioned about three types of memory that differed in
forensic relevance: what occurred; person descriptions; and object descriptions. Similar
patterns of results were reported across these three types of memory, some of which
were crime-relevant and some crime-neutral. Similar findings were reported by Fahsing,
Ask, and Granhag (2004) concerning offender descriptions by 250 witnesses to actual
bank robberies.
Second, it is often difficult to tell in advance what the forensically relevant details will
be in any particular case. For example, in the bombing of the Murrah Federal Building in
Oklahoma City in 1995, thousands of people were questioned by the FBI about whether
they had seen a yellow Ryder truck on the streets of Oklahoma City. It is likely that these
people had seen hundreds of cars and trucks in the days preceding the bombing. And, in
the case of People of the State of California v. Sara Jane Olson, the eyewitness was linked
to the case because he claimed to have remembered a female, who had accompanied a
male who had purchased a particular pipe fitting seven weeks prior in his plumbing
supply store. This fitting was the type that had been used in the 1975 attempted
bombing of a Los Angeles police car by the Symbionese Liberation Army that claimed
Patty Hearst as a member. The forensic relevance of memory for a yellow Ryder truck
and memory for a specific pipe fitting would have been difficult to predict in advance.
Wright et al. (2000) have made this same argument and called for research using a
broader range of stimuli in eyewitness memory research. Even so, the findings in this
study were based on peripheral details; additional research is necessary to assess if more
central details can be changed in a similar fashion.
250 Kathy Pezdek et al.
There are caveats to consider. First, there may be limits in generalizing the findings
from any research setting to the real world context of forensic interviewing due to
procedural and contextual differences. This includes the fact that the recalled event in
this study was less emotional and less personally relevant than are the typical events
recalled in police interviews. Second, because the suggestions made in this study were
conveyed in written text rather than face-to-face interviews, the results of this study
probably present a conservative estimate of the degree of forced confabulation that is
likely to occur in real police interviews.
Nonetheless, the results of this study and those of Pezdek et al. (2007) suggest that
when interviewing eyewitnesses, investigators should be especially careful not to
suggest information to the eyewitnesses. Pressuring eyewitnesses to answer questions
when they indicate that they do not know the answer can result in false confabulation,
especially if the investigator suggests a specific answer to the eyewitness. Answers
suggested by the investigator are more likely to be repeated later than are answers that
were simply self-generated or speculated by the eyewitness, and these other-generated
answers are likely to be more confidently held.
Acknowledgements
We are very grateful to Steve Clark for providing us with the car-jacking video that we used in this
study. This project was supported in part by a grant from the Fletcher Jones Foundation to the first
author.
References
Ackil, J. K., & Zaragoza, M. S. (1998). Memorial consequences of forced confabulation: Age
differences in susceptibility to false memories. Developmental Psychology, 34, 1358–1372.
Brainerd, C. J., Reyna, V. F., Wright, R., & Mojardin, A. H. (2003). Recollection rejection: False
memory editing in children and adults. Psychological Review, 110, 762–784.
Brigham, J. C., & Bothwell, R. K. (1983). The ability of prospective jurors to estimate the accuracy
of eyewitness identifications. Law and Human Behavior, 7, 19–30.
Clark, S. E., & Tunnicliff, J. L. (2001). Selecting lineup foils in eyewitness identifications:
Experimental control and real-world simulation. Law and Human Behavior, 25, 199–216.
Cutler, B. L., & Penrod, S. D. (1995). Mistaken identification: The eyewitness, psychology, and the
law. Cambridge: Cambridge University Press.
Fahsing, I., Ask, K., & Granhag, P. A. (2004). The man behind the mask: Accuracy and predictors of
eyewitness offender descriptions. Journal of Applied Psychology, 89, 722–729.
Gabbert, F., Memon, A., & Wright, D. B. (2006). Memory conformity: Disentangling the steps
towards influence during a discussion. Psychonomic Bulletin and Review, 13, 480–485.
Granhag, P. A., Ask, K., & Rebelius, A. (2005). ‘I saw the man who killed Anna Lindh’. A case study
of witnesses’ offender descriptions. Paper presented at the 2nd Meeting of the Nordic
Network for Research on Psychology and Law. Kristianstad, Sweden.
Gudjonsson, G. (1992). The psychology of interrogations, confessions and testimony. New York:
Wiley.
Hastie, R., Landsman, R., & Loftus, E. F. (1978). Eyewitness testimony: The dangers of guessing.
Jurimetrics Journal, 19, 1–8.
Johnson, M. K., Hashtroudi, S., & Lindsay, D. S. (1993). Source monitoring. Psychological Bulletin,
114, 3–28.
Johnson, M. K., & Raye, C. L. (1981). Reality monitoring. Psychological Bulletin, 88, 67–85.
Forced confabulation
251
Kassin, S. M. (1997). The psychology of confession evidence. American Psychologist, 52,
221–233.
Leo, R. A. (1996). Inside the interrogation room. Journal of Criminal Law and Criminology, 86,
266–303.
Lindsay, D. S. (1990). Misleading suggestions can impair eyewitnesses’ ability to remember event
details. Journal of Experimental Psychology: Learning, Memory, and Cognition, 16,
1077–1083.
Loftus, E. F. (1975). Leading questions and the eyewitness report. Cognitive Psychology, 7,
560–572.
Loftus, E. F., Miller, D. G., & Burns, H. J. (1978). Semantic integration of verbal information into
visual memory. Journal of Experimental Psychology: Human Learning and Memory, 4,
19–31.
Manson v. Braithwaite, 432 U.S. 98, 112, 97 S.Ct. 2243, 53 L.Ed.2d 140 (1977).
Mazzonni, G., & Memon, A. (2003). Imagination can create false autobiographical memories.
Psychological Science, 14, 186–188.
Memon, A., & Bull, R. (Eds.), (1999). Handbook of the psychology of interviewing. Chichester:
Wiley, (Published in paperback 2001).
Milne, R., & Bull, R. (1999). Investigative interviewing: Psychology and practice. Chichester, UK:
Wiley.
Neil v. Biggers, 409 U.S. 188, 34 L.Ed.2d 401 (1972), cert. denied, 444 U.S. 909, 100 S.Ct. 221, 62
L.Ed.2d 144 (1979).
Noon, E., & Hollins, C. R. (1987). Lay knowledge of eyewitness behaviour: A British survey.
Applied Cognitive Psychology, 1, 143–153.
Pezdek, K. (1977). Cross-modality semantic integration of sentence and picture memory. Journal
of Experimental Psychology: Human Learning and Memory, 3, 515–524.
Pezdek, K., & Blandon-Gitlin, I. (2005). When is an intervening lineup most likely to affect
eyewitness identification accuracy? Legal and Criminological Psychology, 10, 247–263.
Pezdek, K., Blandon-Gitlin, I., & Gabbay, P. (2006). Imagination and memory: Does imagining
implausible events lead to false autobiographical memories? Psychonomic Bulletin and
Review, 13, 764–769.
Pezdek, K., Sperry, K., & Owens, S. (2007). Interviewing witnesses: The effect of forced
confabulation on event memory. Law and Human Behavior, 31, 463–478.
Poole, D. A., & White, L. A. (1995). Two years later: Effects on the eyewitness testimony of
children and adults. Developmental Psychology, 29, 844–853.
Raye, D. L., & Johnson, M. K. (1980). Reality monitoring vs. discrimination between external
sources. Bulletin of the Psychonomic Society, 15, 405–408.
Rotello, C. M., Macmillan, N. A., & Van Tassel, G. (2000). Recall-to-reject in recognition: Evidence
from ROC curves. Journal of Memory and Language, 43, 67–88.
Schreiber, N., Wentura, D., & Bilsky, W. (2001). ‘What else could he have done?’ Creating false
answers in child witnesses by inviting speculation. Journal of Applied Psychology., 86,
525–532.
Wright, D. B., Self, G., & Justice, C. (2000). Memory conformity: Exploring misinformation effects
when presented by another person. British Journal of Psychology, 91, 189–202.
Yuille, J. C., & Cutshall, J. L. (1986). A case study of eyewitness memory of a crime. Journal of
Applied Psychology, 71, 291–301.
Zaragoza, M. S., Payment, K. E., Ackil, J. K., Drivdahl, S. B., & Beck, M. (2001). Interviewing
witnesses: Forced confabulation and confirmatory feedback increase false memories.
Psychological Science, 12, 473–477.
Received 21 May 2007; revised version received 25 May 2008
252 Kathy Pezdek et al.
Appendix
List of the answerable and unanswerable questions used
Answerable questions:
(1) Describe the victim’s shirt.
(2) Describe the victim’s tattoo.
(3) What building material were the walls in the computer laboratory made of?
(4) What colour was the mouse pad in the computer lab?
(5) What time was indicated on the clock in the hallway outside the computer lab?
(6) In the lab, what colour was the shirt worn by the victim’s co-worker?
(7) Describe the handrail in the interior stairway.
(8) What colour backpack was the victim carrying?
(9) Inside the building, how many flights of stairs did the victim walk down?
(10) How many floor mats were in front of the exit to the building?
(11) Just outside the building was an archway. What material was this archway made of?
(12) What shape were the planters in the courtyard just outside the building?
(13) What traffic sign was posted at the entrance to the parking lot?
(14) What type of car was stolen?
(15) Describe the shorts the perpetrator was wearing.
(16) Which direction did the perpetrator drive as he exited the parking lot?
Unanswerable questions:
(1)
(2)
(3)
(4)
(5)
(6)
What type of soda was the victim’s co-worker drinking in the computer lab?
What was depicted in the framed picture on the wall in the computer lab?
Describe the victim’s watch.
How many panels did the window in the stairway have?
What was in the bed of the white pick-up truck parked in the parking lot?
What was the logo on the perpetrator’s shirt?