APPLIED COGNITIVE PSYCHOLOGY
Appl. Cognit. Psychol. 24: 673–690 (2010)
Published online 15 May 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/acp.1578
Does Trial Presentation Medium Matter in Jury
Simulation Research? Evaluating the Effectiveness of
Eyewitness Expert Testimony
KATHY PEZDEK*, ELIZABETH AVILA-MORA
and KATHRYN SPERRY
Claremont Graduate University, USA
SUMMARY
This study assesses whether mock jurors’ perceptions of eyewitness expert testimony vary based on
the level of ecological validity—video or transcript trial presentation medium. In Experiment 1,
496 jury-eligible mock jurors were presented a simulated trial. Each served in one condition in a 3 (no
expert or eyewitness expert either with or without prosecution rebuttal witness) 2 (trial presentation
medium: Video or transcript) design. Participants were generally less certain of the defendant’s guilt
after the eyewitness expert testimony, and affective and cognitive ratings of the expert testimony were
higher in the transcript than video condition. However, there were no significant interactions of
modality with expert conditions, thus reducing concerns that jury simulation research must be
conducted with live or video trials to be externally valid. Findings were replicated in Experiment 2
using the testimony of a different eyewitness expert rated to have a more dynamic communication
style. Copyright # 2009 John Wiley & Sons, Ltd.
‘The medium is the message’.
Marshall McLuhan (1964, p. 7)
‘The best current evidence is that media are mere vehicles that deliver instruction but do
not influence student achievement any more than the truck that delivers our groceries
causes changes in our nutrition’.
Richard Clark (1983, p. 445)
Eyewitness evidence is critical for solving crimes, and it is often the sole source of
evidence for determining who the perpetrator is. However, it has been estimated that each
year in the United States, approximately 4500 wrongful convictions occur based on
mistaken eyewitness identifications (Penrod & Cutler, 1999). Studies consistently report
that eyewitness misidentifications are the leading cause of erroneous convictions (Huff,
*Correspondence to: Kathy Pezdek, Department of Psychology, Claremont Graduate University Claremont, CA
91711-3955, USA. E-mail: Kathy.Pezdek@cgu.edu
Copyright # 2009 John Wiley & Sons, Ltd.
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K. Pezdek et al.
1987; Huff, Rattner, & Sagarin, 1996), and eyewitness evidence has been the major source
of evidence used to convict innocent people who were later exonerated based on forensic
DNA (Scheck, Neufeld, & Dwyer, 2000; Wells, Small, Penrod, Malpass, Fulero, &
Brimacombe, 1998). Yet ironically, jurors tend to find eyewitness testimony especially
compelling (Lindsay, Wells, & O’Connor, 1989; O’Toole, Cox, Easterly, & Schmechel,
2005). During a trial, using an expert witness on eyewitness identification and memory is
one way to safeguard against jurors’ over-reliance on eyewitness testimony. But how
effective is an eyewitness expert witness in sensitizing jurors to eyewitness evidence? This
study addresses this question and specifically tests whether the results of research
evaluating the effectiveness of eyewitness expert testimony differ as a function of the trial
presentation medium—trial transcript or trial video.
In the early studies assessing the impact of eyewitness expert testimony (see for example
Blonstein & Geiselman, 1990; Loftus, 1980; Maass, Brigham, & West, 1985), mock jurors
read a brief (only several pages) description of a criminal case, including a summary of the
prosecution’s case and the defence case. They then either read a brief summary of the
testimony of an eyewitness expert or not. It was generally reported that providing a
summary of the eyewitness expert testimony tended to decrease guilty verdicts. In other
studies there were richer assessments of the effectiveness of eyewitness expert testimony.
This work has been thoroughly reviewed by Leippe (1995) and discussed by Pezdek
(2007). For example, Hosch, Beck, and McIntyre (1980) presented a live or video-taped
staged trial to jury-eligible community residents or college students. The trial concerned a
fictitious burglary that involved the testimony of an eyewitness that was either followed by
eyewitness expert testimony or not. Mock juries deliberated after the trial, and all acquitted
the defendant. However, juries that heard the eyewitness expert spent more time
deliberating, and rated the eyewitness testimony as less reliable and less important.
Cutler, Dexter, and Penrod (1989) and Cutler, Penrod, and Dexter (1989) presented over
500 college students and 100 experienced jurors with a video of an armed robbery trial that
included the testimony of an eyewitness to the robbery. The testimony of an eyewitness
expert was either included in the video or not. Although there was not a significant
main effect of expert condition either on verdicts or ratings of eyewitness accuracy, the
eyewitness expert testimony did increase jurors’ sensitivity to the reliability of eyewitness
evidence. That is, the eyewitness expert testimony was more likely to reduce the weight
given by jurors to eyewitness evidence when they were presented weak rather than strong
eyewitness evidence. Similar results were reported by Devenport, Stinson, Cutler, and
Kravitz (2002) using a video of a simulated trial that either included eyewitness expert
testimony or not.
More recently, Devenport and Cutler (2004) assessed whether the inclusion of a
prosecution rebuttal witness affected ratings of mock jurors who watched a video of a
simulated trial. Although overall the expert witness conditions did not affect culpability
ratings or verdicts, participants who heard a prosecution rebuttal witness in addition to the
eyewitness expert perceived the testimony of the eyewitness expert to be significantly less
credible, less influential and less useful.
Although the research evaluating the effectiveness of eyewitness expert testimony is
promising, it is not conclusive; the findings are mixed. One experimental factor that likely
affects the effectiveness of mock trial testimony in general, and eyewitness expert
testimony more specifically, is the ecological validity of the experimental context. One of
the ways this has been varied across mock trial studies is in terms of trial presentation
medium, that is, whether the trial and the expert testimony were presented as a trial
Copyright # 2009 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 24: 673–690 (2010)
DOI: 10.1002/acp
Eyewitness expert testimony
675
transcript or trial video. The ecological validity would be lower in the transcript than the
video presentation condition because relative to the trial video, the trial transcript does not
avail the full audio/visual presentation of the expert. The question of interest in this study is
whether this difference in ecological validity of trial presentation medium affects the
external validity of the findings regarding the effectiveness of eyewitness expert testimony.
The major purpose of this study is to assess the effects of varying levels of the trial
presentation medium on jurors’ judgments of culpability and their perceptions of expert
testimony and eyewitness evidence. This study was not designed to assess if showing a
persuasive message in a video versus a written format makes a difference, but rather tests
whether research findings regarding the effectiveness of eyewitness expert testimony, and
likely other matters as well, differ as a function of the trial presentation medium. Concerns
about the ecological validity of jury simulation research was first systematically raised in a
special issue of Law and Human Behaviour published in 1979 (Diamond, 1979) and were
reiterated almost 20 years later by Diamond (1997) and more recently by Penrod and
Bornstein, (2006). Almost a decade ago, Bornstein (1999) reviewed the research on this
topic and reported that of the 11 published studies in which the trial presentation medium
had been varied, in all but three of these studies there was no main effect of medium.
Further, only six of these studies specifically compared a trial video with a trial transcript,
and none of these six studies assessed the impact of expert witness testimony on mock
jurors. The salience of the concern about the effect of trial presentation medium on mock
jury research outcomes is highlighted by the fact that the Social Science Citation Index for
the Bornstein (1999) study is high,1 currently 111.
It is also interesting to note that presenting research participants with written transcripts
has gained ecological validity in that courts can now require parties to submit direct
testimony in writing (Longan, 1995). Written testimony is often employed to shorten trials
(Phonetel v. AT & T, 1989, upholding the use of written testimony), although more
commonly in civil rather than criminal cases. Also, written expert testimony is also
sometimes preferred because it improves mock jurors’ comprehension of complex expert
testimony (ForsterLee, Horowitz, Athaide-Voctor, & Brown, 2000).
In Experiment 1, mock jurors were presented a simulated trial either as a video or a
written transcript. The trial video was that used in the previous studies by Devenport and
Cutler (2004) and Devenport et al. (2002), and most of the questions that were included in
these studies were included in the present study as well. The testimony of the eyewitness
expert was varied to produce three conditions: No expert, eyewitness expert, and
eyewitness expert plus prosecution rebuttal witness. These three conditions were included
to provide a more extensive test of the effect of trial presentation medium on perceptions of
eyewitness expert testimony. The transcripts were verbatim transcripts of each trial video.
We specifically tested whether the impact of the eyewitness expert testimony varied across
these three expert conditions as a function of whether the mock jurors were presented the
trial video or the trial transcript. In this study, we are most interested in determining if there
are statistical interactions with presentation medium; it is the interactions of conditions
with medium that assess the extent to which the pattern of results across conditions is
consistent with a trial video and a trail transcript.
Two predictions can be made regarding the effect of eyewitness expert testimony on
mock jurors as a function of trial presentation modality. First, if verisimilitude trumps all
other variables, then it would be predicted that the eyewitness expert testimony would have
1
Many but not all of the citations to the Bornstein (1999) study concern trial presentation medium.
Copyright # 2009 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 24: 673–690 (2010)
DOI: 10.1002/acp
676
K. Pezdek et al.
more impact if viewed in a trial video than if read in a transcript of that trial. Accordingly,
the impact of the eyewitness expert would be affected by the content of his or her testimony
as well as his or her communication style, and only in the video trial condition are the mock
jurors exposed to both of these dimensions of the expert testimony. Alternatively, if
regardless of verisimilitude, it is the content of the eyewitness expert testimony that is
relatively more important, then there should be less difference between presenting mock
jurors with a video trial or a transcript of that same trial as the content is the same in both of
these trial conditions. If this resulted, it would suggest that mock jury research could be
conducted with trial transcripts rather than live or video trials without sacrificing external
validity. Although there are some studies that have presented mock jurors with trial
transcripts and other studies that have presented mock jurors with trial videos, few studies
have compared the relative impact of trial presentation modality on mock jurors using two
otherwise identical versions of the same simulated trial, and none of these has assessed the
impact of expert witness testimony on mock jurors.
EXPERIMENT 1
Method
Participants and design
The participants were 496 jury-eligible students, all from one of two state universities in
Southern California. In California, the eligibility requirements for serving on a jury are the
following: (a) must be a citizen of the United States, (b) must be at least 18 years of age,
(c) must be able to understand the English language, (d) must be a resident of California
and (e) must not have been convicted of a felony. We included in this experiment, only the
496 respondents who indicated that they satisfied these five requirements. The sample
included 370 females, 113 males and 13 gender unspecified (age: M ¼ 23, SD ¼ 6.65).
The race/ethnicity distribution of the sample was 43% Caucasian (non-Latino), 36% Latino,
8% African-American, 8% Asian, 5% other. Although using community participants is
more ecologically valid than using college participants, this was not practical given the
very large number of participants required. Also, in Bornstein’s (1999) meta-analysis, 21 of
the 26 jury decision-making studies sampling both undergraduates and community
representative mock jurors found no main effect of participant sample; and, of the five
studies that did show an effect, the differences were inconsistent.
Respondents volunteered to participate during a regular class session with their
classmates. Classes were randomly assigned to one of the six conditions in this experiment,
defined by a 3 (expert condition: No expert, eyewitness expert or eyewitness expert
testimony plus prosecution rebuttal witness) 2 (trial presentation medium: Video or
transcript) independent groups design. At least two different classes participated in each
condition, and there were at least 59 participants in each condition (see top of Table 1 for
the N per condition).
The sample size in each of the six conditions exceeded what was required by power
analyses conducted using methods suggested by Faul, Erdfelder, Lang, and Buchner,
(2007). To detect meaningful differences, the power analysis was conducted assuming a
small effect size (h2 ¼ .03, effect size ¼ .17), an a level of .05, and a desired power level of
.90. Accordingly, the required target N was 282 (47 per cell). The size of each sample in
both experiments of this study exceeded this lower limit.
Copyright # 2009 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 24: 673–690 (2010)
DOI: 10.1002/acp
1. At the end of the trial, how certain were you
of the defendant’s guilt or innocence? (l ¼ certainly
innocent, 9 ¼ certainly guilty)
2. How convincing was the testimony of the alibi
witness in this case, Diane Reyes? (1 ¼ not at all,
9 ¼ highly)
3. How convincing was the identification by the
eyewitness in this case, Barbara Dunn? (1 ¼ not at
all, 9 ¼ highly)
4. Was the line-up procedure suggestive in this
case? (l ¼ not at all suggestive, 9 ¼ highly
suggestive)
5. What was your impression of the defendant in
this case, Mr Peter Brown? (l ¼ not at all like me,
9 ¼ very similar to me)
6. How easy or difficult was it for you to identify
with the defendant’s situation in this case? (l ¼ very
difficult to identify with, 9 ¼ very easy to identify
with)
7. Prior to the testimony of the eyewitness expert
witness, Dr Foster, how certain were you of the
defendant’s guilt or innocence? (l ¼ certainly
innocent, 9 ¼ certainly guilty)
Questions
Copyright # 2009 John Wiley & Sons, Ltd.
4.29 (2.23)
NA
NA
5.38 (2.12)
5.93 (1.85)
4.61 (1.68)
5.50 (2.20)
5.15 (1.82)
3.50 (2.05)
4.35 (1.95)
4.66 (1.69)
3.66 (2.03)
5.31 (1.86)
Video
N ¼ 106
4.68 (1.78)
Transcript
N ¼ 59
No expert
5.18 (1.61)
4.73 (2.47)
3.23 (1.85)
6.43 (1.98)
5.16 (2.05)
4.16 (1.87)
4.80 (1.89)
Transcript
N ¼ 74
5.13 (1.87)
4.01 (2.17)
3.93 (1.72)
6.53 (2.07)
4.83 (2.05)
4.70 (1.85)
4.70 (2.03)
Video
N ¼ 96
Expert no. 1
Experiment 1
5.25 (1.70)
4.75 (2.09)
3.63 (1.84)
6.19 (2.16)
5.08 (2.13)
4.30 (1.85)
4.96 (1.93)
Transcript
N ¼ 101
5.63 (1.38)
3.75 (2.08)
3.72 (1.80)
5.85 (1.96)
5.53 (1.97)
4.60 (1.80)
5.18 (1.47)
Video
N ¼ 60
Expert no. 1 with rebuttal
(Continues)
5.33 (2.06)
4.57 (2.20)
3.53 (2.08)
5.96 (2.13)
5.43 (2.18)
3.98 (1.87)
5.08 (2.04)
Video
N ¼ 51
Expert no. 2
Experiment 2
Table 1. Post-trial questionnaire used in this study (anchor for each question specified) with the mean (and standard deviation) indicated for each condition for
Experiments 1 and 2
Eyewitness expert testimony
677
Appl. Cognit. Psychol. 24: 673–690 (2010)
DOI: 10.1002/acp
8. What impact did the testimony of the eyewitness
expert witness have on your decision regarding the
defendant’s guilt or innocence? (l ¼ minimal impact,
9 ¼ significant impact)
9. How understandable was the testimony of the
eyewitness expert witness? (l ¼ not at all, 9 ¼ highly)
10. How useful was the testimony of the eyewitness
expert witness? (1 ¼ not at all, 9 ¼ highly)
11. How informative was the testimony of the
eyewitness expert witness? (l ¼ not at all, 9 ¼ highly)
12. How influential was the testimony of the
eyewitness expert witness? (l ¼ not at all, 9 ¼ highly)
13. How confusing was the testimony of the
eyewitness expert witness? (l ¼ highly, 9 ¼ not at all)
14. How did the testimony of the eyewitness
expert witness impact your sense of the credibility
of Psychology as a Science? (l ¼ greatly reduced,
9 ¼ greatly enhanced)
15. How did the testimony of the eyewitness expert
witness impact your sense of the credibility of the
eyewitness identifications in general? (l ¼ greatly
reduced, 9 ¼ greatly enhanced)
Questions
Table 1. (Continued)
Copyright # 2009 John Wiley & Sons, Ltd.
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
Video
N ¼ 106
Transcript
N ¼ 59
No expert
5.41 (1.88)
6.31 (1.30)
7.01 (2.18)
6.14 (2.20)
7.38 (1.76)
6.64 (1.93)
6.95 (2.03)
5.92 (1.98)
Transcript
N ¼ 74
5.16 (1.64)
6.10 (1.34)
6.72 (2.12)
5.74 (2.09)
6.94 (1.61)
6.18 (1.95)
6.79 (1.92)
5.40 (2.21)
Video
N ¼ 96
Expert no. 1
Experiment 1
5.49 (1.74)
6.42 (1.24)
6.73 (2.12)
6.53 (1.49)
7.26 (1.43)
7.04 (1.50)
7.16 (1.64)
6.03 (1.84)
Transcript
N ¼ 101
5.08 (1.29)
5.70 (1.33)
6.12 (2.02)
5.73 (1.56)
6.57 (1.51)
5.78 (1.49)
6.02 (1.81)
5.25 (1.56)
Video
N ¼ 60
Expert no. 1 with rebuttal
5.39 (1.78)
5.84 (1.61)
6.33 (2.49)
5.65 (2.12)
6.82 (1.91)
5.69 (2.16)
6.71 (1.93)
5.47 (1.74)
Video
N ¼ 51
Expert no. 2
Experiment 2
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K. Pezdek et al.
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DOI: 10.1002/acp
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Procedure and materials
Participants were instructed to ‘assume the role of a juror and attend to the case as if you
were actually serving as a juror. Like a real juror, you should pay careful attention as you
will later have to deliver a verdict concerning the guilt or innocence of the defendant’. The
videos ranged in length from 32 minutes (the no expert condition) to 60 minutes
(eyewitness expert with rebuttal witness condition). Within each of the three expert
conditions, participants in the video and transcript conditions were presented the trial for
the same amount of time, that is, the duration of the video. All participants completed
reading the transcript in this period of time. There were no restrictions regarding whether
participants could re-read portions of the transcript.
Trial video. The trial video was that used in the previous studies by Devenport and Cutler
(2004) and Devenport et al. (2002) (see this latter reference for details of the trial). The trial
involved an armed robbery that resulted in a murder. The trial video included opening
statements by the prosecution and the defence followed by testimony of an eyewitness, the
police officer in charge of the identification procedure, and an alibi witness who testified
for the defence. The trial ended with closing statements by both attorneys and jury
instructions presented by the Judge. The eyewitness evidence presented in this case was
dubious because of the eyewitness’s opportunity to see the perpetrator and the line-up
procedures used by the police. The video was edited such that when the eyewitness expert
testified, his testimony was inserted at the beginning of the defence case, right after the
police officer. In the condition specified as eyewitness expert with prosecution rebuttal
witness, the testimony of a rebuttal witness was added after the alibi witness, during the
prosecution’s redirect. In the no expert condition, participants saw or read all other aspects
of the trial except there was no eyewitness expert testimony on rebuttal witness.
Trial transcript. Each of the three versions of the trial, defined by the three expert
conditions, was transcribed word-for-word to produce the three trial transcripts used in the
transcript conditions. The formatting of the trial transcripts followed that used for
transcriptions of real trials including a cover page with the case details indicated.
Eyewitness expert testimony. The eyewitness expert was a Ph.D. psychologist who is a
faculty member and occasionally testifies in this capacity in court cases. The direct
testimony of this eyewitness expert included a description of the encoding, storage and
retrieval stages of memory and discussed various factors that influence eyewitness
accuracy (e.g. viewing time, weapon focus, eyewitness confidence). The eyewitness expert
also talked about the potential role of systems variables such as line-up construction and
line-up instructions. The duration of the expert testimony in the video condition was
21 minutes, including direct testimony and cross-examination. Although the duration of the
testimony of the eyewitness expert represented a significant proportion of the whole trial,
this is consistent with the treatment in previous relevant studies by Devenport and Cutler
(2004) and Devenport et al. (2002).
In the condition specified as eyewitness expert with prosecution rebuttal witness, the
rebuttal witness was also a Ph.D. psychologist. He criticized the research presented by the
eyewitness expert for its reliance on crime simulations rather than actual crimes, for using
college students as participants, and for the lack of real-world implications of the decisions
made by typical research participants. The rebuttal witness also opined that the line-up
procedures used in this case were not unduly suggestive. The duration of his testimony in
the video condition was 7.6 minutes including direct testimony and cross-examination.
Copyright # 2009 John Wiley & Sons, Ltd.
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K. Pezdek et al.
Post-trial questionnaire. Immediately after reading or watching the trial, each participant
completed the post-trial questionnaire. Prior to conducting the post-trial questionnaire, the
trial transcripts were collected; thus the transcripts were not available to participants while
they completed their responses. The post-trial questionnaire included the 15 questions
presented in Table 1 with a 1–9 rating response for each. The anchors for each question are
provided in Table 1. These questions probed jurors’ judgments regarding trial testimony
and defendant culpability (questions 1–7),2 affective and cognitive perceptions of the
eyewitness expert (questions 8–13), and two general credibility questions (questions 14
and 15). Participants in the no expert condition only received the first six questions;
questions 7–15 specifically asked about the testimony of the eyewitness expert and these
individuals did not read or hear this testimony. The questions regarding the trial were
followed by nine demographic questions including a question regarding the jury eligibility
of each participant.
Results and discussion
Analyses were first conducted to assess if there were differences across conditions in age or
gender. None of these affects approached significance, thus minimizing concern that
differences among conditions resulted from differences in the demographics of the
participants.
Jurors’ judgments
To assess the effects of conditions on juror judgments, first, separate 3 (expert testimony
condition) 2 (modality) Analyses of Variance (ANOVAs) were conducted on responses
to each of the first six questions (see results in Table 1). It is important to note that there
were no significant main effects or interactions in the analyses of the responses to questions
about the eyewitness (question 3), the defendant (question 5) or the alibi witness (question 2).
It is possible that any differences in results obtained between the video and the transcript
conditions could simply result from the opportunity to see the appearance of the witnesses
and the defendant in the video but not the transcript condition. In other words, does the
defendant look like most people’s stereotype of a bad guy or not? Does the eyewitness look
like most people’s stereotype of a good citizen or not? The absence of significant effects on
these three questions suggests that this interpretation is not likely to account for any effects
of modality in this experiment. In the analysis of question 6 about the defendant’s situation,
there was a significant main effect of modality; the defendant’s situation was rated as easier
to identify with in the transcript (M ¼ 4.71, SD ¼ 2.12) than the video (M ¼ 4.06,
SD ¼ 2.19) condition, F(1, 490) ¼ 11.63, p < .01, h2 ¼ .02. Perhaps being convicted of a
crime seems more real, and thus less easy to identify with when participants actually see
the situation than just read about it.
The major question concerns whether the conditions in this experiment affected jurors’
responses regarding the defendant’s guilt. The 3 2 ANOVA conducted on responses to
question 1 (‘At the end of the trial, how certain were you of the defendant’s guilt or
innocence?’) yielded no significant effects. To examine further, jurors’ judgments of guilt,
a 2 (expert testimony condition) 2 (modality) ANOVA was conducted on responses to
question 7 (‘Prior to the testimony of the eyewitness expert witness, Dr Foster, how certain
2
It is true that a dichotomous measure of culpability is more ecological valid, however it is less sensitive to change
than a 1–9 rating scale. We decided to use a 1–9 rating scale to assess culpability in this study to reduce the risk of
Type II error.
Copyright # 2009 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 24: 673–690 (2010)
DOI: 10.1002/acp
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681
were you of the defendant’s guilt or innocence?’). Participants in the no expert condition
were not presented this question. Neither the main effects nor the interaction approached
significance in this analysis either.
The next analysis was conducted to assess jurors’ judgments of guilt between the two
conditions that included the eyewitness expert testimony.3 In this analysis, we compared
the mean ratings for questions 1 and 7 for each participant to assess whether their
judgments of guilt changed from the point in time just before the eyewitness expert testified
to the end of the trial, and if the magnitude of this change was consistent in the video and
transcript condition. A 2 (question 1 versus question 7) 2 (expert testimony condition) 2
(modality) ANOVA was conducted on respondents’ ratings. Overall, participants were less
certain of the defendant’s guilt after the testimony of the eyewitness expert (question 7:
M ¼ 4.89, SD ¼ 1.88) than before (question 1: M ¼ 5.27, SD ¼ 1.68), F(1, 326) ¼ 14.09,
p < .001, h2 ¼ .04. However, no other main effects or interactions were significant. Thus,
overall the testimony of the eyewitness expert significantly reduced respondents’ certainty
of the defendant’s guilt (which is a good thing, given that the eyewitness testimony in this
trial was dubious), but the degree to which this occurred did not vary as a function of the
expert condition or trial presentation modality.
Further, we tested the correlation between (a) the difference in each respondent’s
response to questions 1 and 7 and (b) their response to question 8 (‘What impact did the
testimony of the eyewitness expert witness have on your decision regarding the defendant’s
guilt or innocence?’). This correlation was modest (r ¼ .14) but significant ( p < .01),
suggesting that jurors who reported larger changes in their certainty of the defendant’s guilt
from just prior to the eyewitness expert testimony to the end of the trial were slightly more
likely to report a greater impact of the eyewitness expert’s testimony. These analyses
should be considered with caution, however, because it is unclear how accurately
individuals can introspect about their past judgments at different points in time (cf. Nisbett
& Wilson, 1977). However, in many research contexts, analyses of difference scores within
individuals reveal findings that are not apparent when analysing mean pre-test scores or
mean post-test scores alone. In the present study, analysing jurors’ judgments at two points
in time allowed for this comparison, and the fact that findings with difference scores were
significant suggests that subjects can differentially assess their past judgments at two
different points in time. Nonetheless, the accuracy of such assessments cannot be verified.
Question 4 (‘Was the line-up procedure suggestive in this case?’) was included to assess
the extent to which the expert condition affected jurors’ perceptions regarding the fairness
of the lineup that was described in the investigating officer’s testimony (the lineup
described was suggestive). A 3 (expert condition) 2 (modality) ANOVA was performed
on responses to question 4. The only significant effect was the main effect of expert
condition, F(2, 488) ¼ 6.50, p < .01, h2 ¼ .03. Post hoc analyses confirmed that respondents rated the line-up procedure as more suggestive when the expert testified (M ¼ 6.49,
SD ¼ 2.03) then there was no expert testimony (M ¼ 5.58, SD ¼ 2.04). Ratings in the expert
with rebuttal testimony condition (M ¼ 6.06, SD ¼ 2.09) did not differ from the other two
conditions. Thus, presenting the eyewitness expert testimony effectively influenced jurors’
perceptions regarding the fairness of the lineup, and this effect was consistent in the video
and transcript conditions.
3
Note that participants in the no expert condition are not included in this analysis because clearly they could not
have been questioned about the testimony of the eyewitness expert witness.
Copyright # 2009 John Wiley & Sons, Ltd.
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Question 15 (‘How did the testimony of the eyewitness expert witness impact your sense
of the credibility of eyewitness identification in general?’) assessed whether the eyewitness
expert testimony affected general scepticism regarding the credibility of eyewitness
identifications or whether the influence of the testimony was more case-specific. In the
2 (expert condition) 2 (modality) ANOVA on the mean responses to question 15, neither
the main effects nor the interaction were significant. Also, across all four conditions in
which this question was posed, the mean response was M ¼ 5.30 (SD ¼ 1.67), which is
slightly above the middle of the 1–9 credibility scale. These results suggest that the
eyewitness expert testimony did not affect respondents’ scepticism regarding the
credibility of eyewitness evidence in general.
Perceptions of the eyewitness expert testimony
Several analyses were conducted on questions 8–13 pertaining to the participants’
perceptions of the eyewitness expert testimony. The mean response for each of these
questions is presented in Table 1. These questions were categorized as assessing cognitive
dimensions (question 9: ‘Understandable’; question 11: ‘Informative’; and question 13:
‘Confusing’; Cronbach’s a ¼ .70) or global/affective dimensions (question 8: ‘Impact’;
question 10: ‘Useful’; and question 12: ‘Influential’; Cronbach’s a ¼ .83) of the eyewitness
expert testimony. We analysed these responses in categories to minimize the extent to
which we were capitalizing on chance when analysing the results of each question
separately. Within each of these two categories, the responses to the relevant questions
were averaged and a 2 (expert testimony condition) 2 (modality) ANOVA was conducted
on these means. For the cognitive questions, there was a significant main effect of modality,
F(1, 325) ¼ 11.35, p < .001, h2 ¼ .03. Participants found the testimony of the eyewitness
expert to be more understandable, informative and less confusing in the transcript
(M ¼ 7.08, SD ¼ 1.48) than the video (M ¼ 6.60, SD ¼ 1.45) condition. There was also a
significant main effect of expert condition, F(1, 325) ¼ 4.18, p < .05, h2 ¼ .01; the mean
response was higher in the expert after eyewitness condition (M ¼ 6.96, SD ¼ 1.54) than in
the expert with rebuttal testimony condition (M ¼ 6.75, SD ¼ 1.43). The interaction was
not significant.
In the 2 (expert condition) 2 (modality) ANOVA conducted on the global/affective
questions, only the effect of modality was significant, F(1, 327) ¼ 15.67, p < .001,
h2 ¼ .05. Consistent with the results with the cognitive measures reported above, participants found the testimony of the eyewitness expert to have greater impact and be more
useful and influential in the transcript (M ¼ 6.41, SD ¼ 1.53) than the video (M ¼ 5.70,
SD ¼ 1.63) condition. This is consistent with the results of question 14, (‘How did the
testimony of the eyewitness expert witness impact your sense of the credibility of
Psychology as a Science?’). Respondents were more likely to indicate that the eyewitness
expert testimony enhanced the credibility of Psychology as a Science if they had read the
trial transcript (M ¼ 6.37, SD ¼ 1.27) than watched the trial video (M ¼ 5.90, SD ¼ 1.35),
F(1, 326) ¼ 10.03, p < .01, h2 ¼ .03. No other results involving question 14 were significant.
Conclusions
In this experiment, we were most interested in determining if there are statistical interactions with modality; the interactions assess the extent to which the pattern of results is
consistent in the trial video versus transcript conditions. The major finding in Experiment 1
was that few main effects of modality and no interactions involving modality resulted. The
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pattern of results was consistent across the trial video and transcript conditions. The
conclusions from Experiment 1 may be restricted to the testimony of the specific
eyewitness expert used in that trial. Simply put, it is possible that the communication style
of this eyewitness expert may not have enhanced the effectiveness of his testimony above
and beyond what was available to those who read the transcript. After all, the presentation
style of this eyewitness expert was serious and not very animated. It is important to note,
however, that this simulated trial with the same testimony of this eyewitness expert was
used in previous studies where it was effective in elevating participants’ sensitivity to
eyewitness evidence (Devenport & Cutler, 2004; Devenport et al., 2002). Each of these
previous studies was conducted using only one simulated trial, and it was the same one
used in Experiment 1.
Nonetheless, Experiment 2 was conducted to test the generalizability of the results of
Experiment 1. In Experiment 2 the testimony of a different eyewitness expert was recorded
and edited into the trial video from the eyewitness expert (no rebuttal witness) condition in
Experiment 1. The eyewitness expert used in Experiment 2 was also a Ph.D. psychologist
who is a faculty member and frequently testifies in this capacity in court cases. This eyewitness expert was selected because the testimony of this expert was considered to reflect a
more dynamic communication style than that used in Experiment 1, and this was verified in
a pilot study, the results of which are reported below. The eyewitness expert in Experiment
2 presented the same verbatim testimony presented by the expert in Experiment 1. This was
done specifically to hold content constant while varying communication style. Participants’
responses to this new video were then compared to responses of participants in Experiment
1 who read the transcript of the trial in the eyewitness expert condition with no rebuttal
witness. Experiment 2 thus includes one condition from Experiment 1 as the control
condition. This comparison tests if the testimony of an eyewitness expert with a more
dynamic communication style yields differences between the trial video versus transcript
conditions, differences that did not result in Experiment 1 when the trial video included a
less dynamic expert testimony.
EXPERIMENT 2
Method
Participants and design
Experiment 2 consists of two conditions—a new experimental condition and a control
condition from Experiment 1. There were 51 participants in the new experimental
condition in Experiment 2. These were 51 jury-eligible students from two psychology
classes at one of the state universities used in Experiment 1. This sample included
33 females,12 males, and 6 gender unspecified (age: M ¼ 26, SD ¼ 8.08). The race/ethnicity
distribution of the sample was 31% Caucasian (non-Latino), 37% Latino, 16% AfricanAmerican, 10% Asian, and 6% other. The performance of participants in this condition was
compared to that of the 59 participants from Experiment 1 who read the transcript of the
trial in the eyewitness expert condition with no rebuttal witness. All respondents
volunteered to participate during a regular class session with their classmates.
Procedure and materials
All participants in the new experimental condition in Experiment 2 viewed the same trial
video. This trial video was the same video presented in Experiment 1 in the eyewitness
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expert (no rebuttal witness) condition, with the exception that a different eyewitness expert
testified in the video condition in Experiment 2. The eyewitness expert used in the video
condition in Experiment 2 was a female Ph.D. psychologist, who is a faculty member and
frequently testifies in this capacity in court cases. The testimony of this expert was selected
because it was considered to reflect a more dynamic communication style than that used in
Experiment 1. However, to hold content constant while varying communication style, the
expert in the video condition in Experiment 2 presented the same verbatim testimony as
was presented by the expert in Experiment 1. The testimony of the new eyewitness expert
was edited into the video from Experiment 1 by a professional video editor. Participants in
the pilot study indicated no significant difference in the quality of these two videos.
Participants in Experiment 2 received the same instructions and post-trial questionnaire
that was used in Experiment 1.
Pilot test comparing the eyewitness expert testimony
in Experiments 1 and 2
Two different psychology classes at one of the state universities used in Experiment 1 were
each randomly assigned to view the video of either the eyewitness expert testimony from
Experiment 1 (N ¼ 54) or that from Experiment 2 (N ¼ 92). Immediately after viewing the
video of the expert testimony, participants rated the presentation using a 1 (not at all)–7
(highly) scale for each of eight dimensions associated with a more dynamic communication style: Engaging, assertive, credible, persuasive, confident, attractive, competent and
convincing. A factor analysis of the ratings identified two components, and seven of the
eight dimensions loaded more heavily on one component than the other. Only the dimension, attractive, did not load more heavily on this component. This dimension was then
dropped from the analyses. The association among the other seven dimensions was strong,
Chronbach’s a ¼ .84. Pooling across these seven dimensions, the mean rating was
significantly higher for the eyewitness expert in Experiment 2 (M ¼ 5.47, SD ¼ .92) than in
Experiment 1 (M ¼ 4.84, SD ¼ 1.03), t(144) ¼ 3.85, p < .01, d ¼ .64.4 These pilot data
verified that the communication style of the eyewitness expert testimony in Experiment 2
was more dynamic than that used in Experiment 1. Experiment 2 thus presents a stronger
test of whether differences are likely to result from mock jury research conducted with a
trial video versus transcript.
Results and discussion
Analyses were first conducted to assess if there were differences across conditions in age or
gender. As in Experiment 2, none of these affects approached significance, thus minimizing
concern that differences among conditions resulted from differences in the demographics
of the participants.
Jurors’ judgments
Experiment 2 tests the generalizability of the results of Experiment 1. The primary purpose
of Experiment 2 was to see if the minimal effects of modality in Experiment 1 replicated
with a different video that included an eyewitness expert with a more dynamic
communication style. The critical comparisons are between the video condition in
4
The mean ratings for these two eyewitness experts also significantly differed when ratings were pooled across all
eight dimensions, t(144) ¼ 3.22, p < .01.
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Experiment 2 (these data are presented in the right column of Table 1) and the transcript of
this testimony from the eyewitness expert (no rebuttal witness) condition in Experiment 1.
Independent groups t-tests were conducted to compare these two groups on the mean
response to each of the first seven questions in Table 1. None of these mean differences
approached significance.
An additional analysis was conducted to assess if jurors’ judgments of culpability
changed from the point in time just before the eyewitness expert testified to the end of the
trial, and if the magnitude of this change was consistent in the video and transcript
condition. A 2 (question 1 versus question 7) 2 (video versus transcript) ANOVA was
conducted. Only the main effect of question was significant. Participants were less certain
of the defendant’s guilt after the testimony of the eyewitness expert (question 7: M ¼ 4.74,
SD ¼ 1.97), than before (question 1: M ¼ 5.15, SD ¼ 1.76), F(1, 168) ¼ 8.68, p ¼ .01,
h2 ¼ .05). However, this main effect did not interact with the modality condition. This
finding is consistent with the comparable results of Experiment 1 from a 2 (question 1
versus question 7) 2 (video versus transcript) ANOVA conducted on the mean responses
in the two expert after the eyewitness (no rebuttal testimony) conditions.
Perceptions of the eyewitness expert testimony
Several analyses were conducted on questions 8–13 pertaining to the participants’
perceptions of the eyewitness expert testimony. The mean response for each of these
questions is presented in Table 1. These questions were categorized as assessing cognitive
dimensions (question 9: ‘Understandable’; question 11: ‘Informative’; and question 13:
‘Confusing’; Cronbach’s a for responses in Experiment 2 ¼ .75) or global/affective
dimensions (question 8: ‘Impact’; question 10: ‘Useful’; and question 12: ‘Influential’;
Cronbach’s a for responses in Experiment 2 ¼ .77) of the eyewitness expert testimony. As
in Experiment 1, we analysed these responses in categories to minimize the extent to which
we were capitalizing on chance when analysing the results of each question separately.
Within each of these two categories, the responses to the relevant questions were averaged
and a t-test was conducted to compare mean ratings in the video versus transcript
conditions. The between groups differences were not significant on ratings of the cognitive
dimensions. However, participants who read the transcript (M ¼ 6.23, SD ¼ 1.73) rated it
higher on global/affective dimensions than did those who viewed the video (M ¼ 5.60,
SD ¼ 1.66), t(123) ¼ 2.03, p < .05, d ¼ .37. In comparable comparisons in Experiment 1,
of the mean ratings of the expert in the video versus transcript conditions in the expert after
the eyewitness (no rebuttal testimony) conditions, the differences were not significant for
either the cognitive or the global/affective dimensions. Further, in Experiment 2 there was
no significant difference in the mean ratings for question 14 (‘How did the testimony of the
eyewitness expert witness impact your sense of the credibility of Psychology as a
Science?’) between the trial video and transcript conditions.
Question 15 (‘How did the testimony of the eyewitness expert witness impact your sense
of the credibility of eyewitness identification in general?’) assessed whether the eyewitness
expert testimony affected general scepticism regarding the credibility of eyewitness
identifications or whether the influence of the testimony was more case-specific. Mean
response to this question did not significantly differ between the video and transcript
conditions. As can be seen in Table 1, in both of these conditions, the mean response was
slightly above the middle of the 1–9 credibility scale, suggesting that the eyewitness expert
testimony did not affect respondents’ scepticism regarding the credibility of eyewitness
evidence in general.
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Conclusions
The major results of Experiment 1 were replicated in Experiment 2, using a trial video that
included an eyewitness expert rated to have a more dynamic communication style. In terms
of jurors’ judgments, none of the main effects of modality were significant, and although
judgments of guilt significantly decreased from the point in time just before the eyewitness
expert testified to the end of the trial, the magnitude of this change was consistent in the
video and transcript condition. In terms of jurors’ perceptions of the eyewitness expert,
the only difference as a function of the modality condition was that jurors actually found
the testimony of the eyewitness expert to have more impact, and to be more useful and
influential in the transcript than the video. Interestingly, however, this finding was not
corroborated by the finding reported above that the magnitude of the decrease in culpability
judgments from just before the eyewitness expert testified (question 7) to the end of the trial
(question 1) was similar in the video and transcript condition. Further, we tested the
correlation between (a) the difference in each respondent’s response to questions 1 and 7
and (b) their response to question 8 (‘What impact did the testimony of the eyewitness
expert witness have on your decision regarding the defendant’s guilt or innocence?’). This
correlation, computed for the video and transcript conditions together, was not significant.
This suggests that jurors who reported larger changes in their certainty of the defendant’s
guilt from just prior to the eyewitness expert testimony to the end of the trial were not more
likely to have reported a greater impact of the eyewitness expert’s testimony in their
response to question 8.
GENERAL DISCUSSION
Was there a consistent effect of eyewitness expert condition?
Several findings suggest that providing eyewitness expert testimony generally affected
mock jurors’ perceptions of the reliability of the dubious eyewitness testimony that was
included in this simulated trial. First, in both experiments, participants were less certain of
the defendant’s guilt after the trail (question 7) than before the testimony of the eyewitness
expert (question 1). However, these difference scores did not vary as a function of the
expert condition or trial presentation modality. Second, the pattern of responses to question
4 regarding whether the line-up procedure was suggestive in this case is also revealing. In
Experiment 1, presenting the eyewitness expert testimony effectively influenced jurors’
perceptions regarding the fairness of the lineup relative to both the no expert condition and
the expert with rebuttal witness condition.
Generally, however, on few measures was the main effect of expert condition significant,
and on no measures was the interaction of this variable with trial presentation modality
significant. These findings essentially replicated the results involving similar eyewitness
expert conditions reported by Devenport and Cutler (2004).
Was the effect of eyewitness expert condition affected
by trial presentation modality?
The major purpose of this study was to assess the effects of varying levels of ecological
validity of the trial presentation medium on jurors’ perceptions of trial evidence and expert
testimony. It is the interactions that are most important in any test of external validity. That
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is, we want to know if the results of any study are consistent across levels of the
independent variable that is assessing the external validity condition, in this case, trial
presentation modality. Together, the results of both experiments suggest that although there
are some advantages to the transcript over the video trial presentation modality,
presentation modality did not affect judgments of culpability and did not vary the effects of
expert conditions on either judgments of culpability or perceptions of the eyewitness expert
testimony. The effects of expert condition were consistent in the trial video and trial
transcript conditions; in other words, there were no significant interactions of modality
with the expert condition.
The primary effects of presentation modality were on perceptions of the eyewitness
expert testimony and not judgments of culpability. Respondents in the transcript compared
to the video condition rated the eyewitness expert testimony higher on global/affective
dimensions in both experiments, and higher on cognitive dimensions in Experiment 1. One
interpretation of this effect is that participants do more systematic processing of
information in a transcript than a video. The heuristic-systematic model of persuasion is a
message-based model of persuasion that maps onto cognitive processes that are applicable
to information processing of mock trials (Chaiken, Wood & Eagly, 1996). Systematic
processing occurs when an individual focuses on message- and issue-relevant thinking in
forming their opinions. Heuristic processing involves little detailed processing of the
message content. Although both systematic and heuristic processing typically co-occur,
judgments that result from systematic processing are more likely to persist than those that
result from heuristic processing alone (Chaiken & Eagly, 1983). Chaiken and Eagly (1976)
reported that with difficult to understand material, material similar to the mock trial
presented in the current study, greater changes in opinion resulted in a text than a video
condition. More systematic processing of information in the transcript than the video
condition is one explanation for why perceptions of the eyewitness expert testimony were
generally higher in the transcript than video condition in the current study.
CONCLUSIONS
In any test of external validity, it is the interactions that are most important. The absence of
any significant interactions between trial presentation modality and expert condition in this
study suggests it is likely that mock jury research—at least mock jury research on the role
of an eyewitness expert testimony—can be conducted with trial transcripts rather than live
or video trials without sacrificing external validity.
One interpretation of these findings is that it is the content of the expert testimony that is
relatively more important than the communication style of the presenter in determining
culpability. By communication style in this case, we refer to how dynamic the presentation
style is, communicated, for example by mannerisms, use of gestures, eye contact, vocal
quality, etc. These are dimensions that are apparent in the video but not the transcript
version of the trial. The content was the same in each pair of trial video and transcript
conditions. The results of this study suggest that the extra information pertaining to the
communication style of the presenter that was available in the trial video but not the
transcript, did not have an advantageous effect on respondents’ ratings of culpability, nor
did it produce an interaction with the effect of expert condition on any measure. Thus, it
appears that regardless of verisimilitude, it is the content of the expert testimony that is
relatively more important than the communication style of the presenter.
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Ultimately, the research on trial presentation modality should dovetail with two other
lines of psychology research—research on instructional technology (cf. Mayer, 2001) and
media processing (cf. Pezdek, Lehrer, & Simon, 1984). In this other research, outcomes
typically are better in the visual plus narration condition (video) than in the text alone
condition (reading). In the current study, when there were presentation modality
differences, the trial transcript produced more favourable results than the trial video.
Although this finding does not appear consistent with these other lines of research, this
might be a result of the different dependent measures used. Whereas most research on
instructional technology or media processing uses memory and comprehension assessment
measures, the measures used in the current study focused on assessments of person
perception and decision making. It is nonetheless interesting that presentation modality
may have different effects on different dependent measures.
There are caveats to consider. First, the overall ecological validity of this study is limited
by the fact that this was a simulated trial that was viewed by college students, and rather
than utilizing a dichotomous verdict measure, in this study, culpability was assessed using a
1–9 scale 2. It remains a topic for future research, the extent to which jurors’ perceptions of
trial evidence and expert testimony are affected by variations in the ecological validity of
these other variables. Second, in this study, participants in the trial transcript and video
conditions were exposed to the material for the same duration, that is, the duration of the
video. It is possible that differences between conditions of medium could have resulted
from the fact that some mock jurors may have had time to re-read portions of the trial in the
transcript condition. This remains a question for future research. Third, we note that the
conditions in this study did not assess whether eyewitness expert testimony affected mock
jurors’ sensitivity versus their scepticism regarding eyewitness evidence. Nonetheless, the
results of this study, with eyewitness expert testimony reflecting two quite different
communication styles, suggest that mock jury research—at least mock jury research on the
role of an eyewitness expert testimony—can be conducted with trial transcripts rather than
live or video trials without sacrificing external validity. And, although this study focused
the effects of trial presentation medium on processing eyewitness expert testimony, these
results are likely to generalize as well to processing other types of trial evidence.
ACKNOWLEDGEMENTS
This project was supported in part by a grant from the Fletcher Jones Foundation to the first
author. We are especially grateful to Jennifer L. Devenport for the generous use of her trial
video. We also thank Michael Thomas for so competently performing the video editing,
and Marilyn Ambrosini for her prompt and careful transcription of these materials. Kathy
Pezdek, in the Department of Psychology at Claremont Graduate University, can be
contacted by e-mail at Kathy.Pezdek@cgu.edu.
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