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RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 1
The Role of Implicit Presentation in Eyewitness Testimony: Investigating Whether
Subliminal Priming Can Modulate Suspect Identification
A Senior Honors Thesis Presented to the Faculty of the Department of Psychology
University of Hawaii at Manoa
In Partial Fulfillment of the Requirements
for Bachelors of Psychology with Honors
By Austin Simpson
May 9, 2013
Committee:
Scott Sinnett, Mentor
Andrew Dewald
Marvin Chandra
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 2
Table of Contents
Table of Contents 2
Abstract 3
Introduction 4
• Influence of Suspect Lineup 4
• Fallibility of Explicit Memory Processes 5
• Implicit Effects on Recognition 7
Methods 9
• Participants 9
• Stimuli and Apparatus 9
• Procedure 11
Results 11
Discussion 12
References 19
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 3
Abstract
The criminal justice system relies heavily on eyewitness testimony for the prosecution
and investigation of criminals. Extensive research has shown that post-event information
can severely alter or reconstruct memory. However, despite empirical evidence
demonstrating that implicitly presented information can influence memory and behavior,
no research has been conducted regarding the ability of information that is presented
below conscious awareness to modulate eyewitness identification. This is precisely what
was investigated in the current manuscript. Participants were instructed to watch a short
video that depicted a man committing a crime, and were then required to identify the
culprit out of a sequential lineup presented on a computer screen. The color of the shirt
that each suspect wore was systematically primed by a subliminally presented color
word. Critically, the color prime either did, or did not match the color of the shirt that the
suspect wore. The findings showed a very high false identification rate, with more than
90% of participants falsely choosing a suspect, despite the actual culprit never being
shown. Contrary to expectations, when compared to chance levels participants did not
choose suspects more frequently if they had been implicitly primed with a matching color
word. Given the powerful determinants of memory bias, the present findings could be of
interest to the criminal justice system.
Keywords: Eyewitness testimony, false memory, misinformation, priming,
recognition
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 4
The Role of Implicit Presentation in Eyewitness Testimony: Investigating Whether
Subliminal Priming Can Modulate Suspect Identification
Eyewitness testimony can be extremely important in the justice system.
However, research from the past 40 years has demonstrated that eyewitness memory can
be flawed, sometimes leading to the unfortunate incarceration of innocents. For instance,
in 1984 Frederick Rene Day was identified from a suspect lineup and served ten years in
prison for rape and kidnapping. Day was released in 1994 after DNA testing revealed his
innocence. The rape victim and another witness both falsely identified Daye as the
kidnapper and rapist, leading to his conviction. While this is just one of many cases,
much research has shown the fragility of human memory when it comes to eyewitness
testimony. For example, laboratory studies where perpetrators are shown on video
(Gronlund & Carlson, 2009), live field experiences (Pryke, Lindsay, Dysart, & Dupuis,
2004), and archival studies with real criminal cases (Behrman & Davey, 2001) have all
consistently demonstrated the fallibility of eyewitness memory. In the real world, the
development of new DNA techniques has revealed many cases of wrongful imprisonment
in which the accused had been found guilty largely based on memory errors by witnesses,
but were subsequently exonerated. Before addressing specific components of memory
and how it can be influenced in the context of eye witnessing an event, it is important to
discuss how different aspects of the process of being an eyewitness can modulate
memory.
Influence of the Suspect Lineup
One way in which memory can be influenced is by systematic variables – factors
controlled by the criminal justice system. For instance, the criminal justice system can
administer lineups in such a way that leads to false recollection of an individual and, at
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 5
times, false accusation. Hence, the content and presentation method of a lineup pose a
significant threat to the reliability of an eyewitness account. Police integrators often
manipulate the structure of the eyewitness lineup, such as deliberately omitting the
perpetrator from the lineup or presenting suspects in a sequential or simultaneous
manner. Lindsay and Wells (1985) were the first to demonstrate the superiority of
presenting a lineup in a sequential manner. Results of their study showed that subjects
made fewer errors in a sequential lineup than a simultaneous lineup (correctly ID
subjects). Others have confirmed similar results concluding that sequential lineups lead to
lower rates of false identifications (Steblay, Dysart, Fulero, & Lindsay, 2001; but see
Carlson, Gronlund, & Clark, 2008 for a counter example). However, the advantage of
sequential lineups is mediated by how much the innocent subject stands out from other
lineup members (Carlson et al., 2008; Gronlund & Carlson, 2009).
A further systematic variable that can influence identification rates is whether or
not the actual culprit (i.e., guilty individual) is present in the lineup. It is important for the
administrator to inform the witness that the perpetrator of the crime may or may not be
present. If not, witnesses often falsely identify a suspect, arguably due to some sort of
expectation to be required to choose someone, leading to the witness choosing the person
in the lineup who most closely resembles the real perpetrator. This was exemplified in a
study by Wells (1992) where 54% of witnesses identified the correct culprit from a
culprit-present lineup while 21% made no identification. However, when researchers
removed the culprit, 68% of subjects falsely identified someone and 32% of people did
not identify anyone (Wells, 1992; see also Ebbesen & Flowe, 2002; Clark, 2009). Seeing
that the absence of a perpetrator leads to high levels of false identifications, the current
study did not include the perpetrator in the lineup.
Fallibility of Explicit Memory Processes
Typically, memory can be fundamentally thought of as a constructive process,
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 6
rather than a replay of life events. The recollection of an explicit memory is often one of
the most powerful, yet inaccurate sources in eyewitness testimony. Questions concerning
the nature of memory systems have been at the forefront of cognitive research. In
eyewitness testimony research, for instance, one of the reasons why error rates are so
high is that incorrect information presented after the event (post event misinformation;
PMI) can impair memory of the original event. For instance Loftus (1974) developed a
landmark theory called the “misinformation effect” to explain how exposure to PMI can
create false memories. In her experiment, participants watched a video clip of a car
accident. Participants were later asked questions that either embellished the event or
provided a more accurate portrayal (i.e., how fast were the cars moving when they
(smashed vs. hit) into each other?). The results showed that participants who received
questions containing the word smashed indicated higher speeds when compared with
participants who had the word hit in the questions. More importantly, when asked to
return to the laboratory a week later, those participants who had received the verb
smashed again recalled the cars to be moving faster, but also more frequently recalled the
presence of broken glass (there was none). In sum, PMI later influenced memory retrieval
and lead to false memories. The robustness of the misinformation effect has been found
in a variety of other studies involving a multitude of materials and techniques (Schreiber
& Serget, 1997).
One of the possible mechanisms driving the misinformation effect could be
retroactive interference, which suggests that new information potentially conflicts or
overrides previously learned information, thus forming a new reconstructed or
reconsolidated memory, often different from objective events. This is especially
dangerous when considering eyewitness memory, as false recognition is often
accompanied by high confidence and detailed, albeit false recollection (Roediger, 1990;
Shaw, 1996). Despite the robustness of studies using explicit memory paradigms, implicit
memory has received little attention in the false memory literature.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 7
Researchers have focused on the distinction between explicit and implicit forms
of memory. Explicit or declarative memory refers to the conscious recollection of events
or experiences. In contrast, implicit or non-declarative memory refers to changes in
behavior or performance elicited by prior experiences for which one has no conscious
awareness. For instance, priming experiments (discussed in more detail below) often
involve the below threshold presentation of stimuli, that despite not leading to conscious
awareness, can nevertheless influence later memory and behavior (Dehaene et al., 1998).
While implicit priming has been robustly demonstrated in the literature (see for example
Kirsner & Smith, 1974; McDermott, 1997), its role in in eyewitness identification has yet
to be explored.
Implicit Priming and Recognition
Priming refers to the phenomenon when the exposure to a prior stimulus effects
the identification of a similar or identical target that is presented later (see for example
Tipper, 1984). The initial stimulus is known as the prime or cue, and has nothing to do
with the actual task of responding to a later stimulus, known as the target. Furthermore,
the prime is often presented subliminally (i.e., below conscious awareness). Critically,
when the cue and target are related, the target is responded to more efficiently,
demonstrating implicit memory. For instance, evidence for the benefits of priming1
have
been observed on tasks such as word completion, lexical decision-making, and semantic
comparisons (Kirsner & Smith, 1974; Warrington & Weiskrantz, 1968; Dehaene et al.,
1998) to name but a few.
Of direct interest to eyewitness memory, the relationship between priming and
face recognition using identical or similar stimuli has been explored, and found to
facilitate identification. That is, robust evidence corroborates the notion that the repeated
1
However, it should be noted that some research has also shown that a prime can slow
down processing of the target (i.e., negative priming, see Tipper, 1985 for example).
Regardless, both facilitation and inhibition demonstrate that the subliminally presented
prime can influence behavior.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 8
exposure to primed faces improves reaction time and accuracy in facial recognition tasks
(Dell’Acqua & Grainger, 1999; Joyce & Kutas, 2005; see also McDermott, 1997 for a
similar example using written words). More importantly, past research has found that
misleading subliminal information can induce false recognition, such as through
repetition priming (Jacoby & Whitehouse, 1989). Jacoby and Whitehouse (1989)
instructed participants to study a wordlist and then presented a recognition test, which
contained words from the original list or new words. Critically, the presentation of a
subliminal word preceded each recognition item that either matched or did not match the
target. Results indicated that participants falsely recognized “new” words as “old” when
primed with words that matched. In the current study, implicit primes (color words) that
were related to (or not) the color of a shirt worn by a suspect were used to assess the
possibility that the implicit prime could influence eyewitness identification. We
deliberately masked the priming stimuli (to eliminate conscious awareness) to explore
whether information presented below threshold can affect recognition of complex stimuli
(i.e., the face of a suspect after viewing a video of a crime). While this type of complexity
is rare in priming paradigms, it is rather applicable to eyewitness testimony, and a
behavioral effect of subliminal stimuli may provide further explanatory power for the
potency of implicit memory. This may open the window for practical applications
examining the nature of misleading questions, eyewitness depictions of an event, and
lineup factors that might be unknowingly perceived.
There are two main objectives that were explored in this honors thesis: First, to
explore whether priming individuals with below threshold (i.e., subliminal) misleading
information can modulate the rate of identification. In other words, can implicit
information lead people to falsely recognize a culprit? The second question explores
whether people will choose someone regardless if the culprit was present in the suspect
lineup. Based on previous research, one could hypothesize that participants will not only
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 9
identify a perpetrator but also choose suspects whose shirt color matches a subliminally
primed and matching color word.
Methods
Participants
Undergraduate students (n=61) from the University of Hawaii at Manoa were
recruited from psychology classes to participate in the study as an opportunity for extra
credit. All participants gave informed consent prior to participating in the experiment.
The experiment was approved by the University of Hawaii at Manoa Committee on
Human Studies.
Stimuli & Apparatus
The experiment was conducted at the Attention and Perception Laboratory at the
University of Hawaii at Manoa. Three MacBook computers were used to perform the
experimental trials using the Psyscope XB7 graphical user interface software program.
The mock video was adopted from a previous experiment done by Gronlund & Carlson
(2009). The video lasted approximately 1 min and 45 seconds and depicted a scene of a
couple walking on a street, hugging, and then walking across the street (see Figure 1).
Intermixed among the scenes was the perpetrator getting out of his car and hiding in the
bushes. As the woman approaches her car, the perpetrator jumps out of the bushes, steals
the purse, and runs off.
Suspect lineup: Pictures were acquired from a selection of Facebook profile pictures from
friends of the author. Five photos were obtained (see Figure 2) and all people approved
the use of their photo for the purposes of the experiment. Using Photoshop, each photo
was changed such that the color of the shirt could be different (either red, black, blue,
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 10
green, or yellow), making a total of 25 pictures total (i.e., the five pictures with five
different colored shirts).
Priming Stimuli. The different colors of the shirts (red, blue, yellow, black, and green)
were presented in written format immediately before the presentation of each photo. The
color words were presented for 13 ms and then masked for 50 ms by random symbols in
order to ensure that the words were presented subliminally. No participants expressed
awareness of the words. The author, advisor, and numerous classmates were unable to
determine the identity of the prime when awareness was informally tested. Each trial
began with a fixation cross (750 ms), immediately followed by the prime word (13 ms),
which was then followed by a mask (50ms). The mask was composed of symbols that
systematically replaced letters (e.g., %#@*). The combination of shirt color, person, and
prime was pseudorandomized. In order to more closely replicate real world lineups, each
participant was given five congruent trials (prime matches shirt color) and 20 incongruent
trials (prime did not match shirt color).
Figure 1: Still frame of a scene shown in the video. This scene depicts the perpetrator just
after stealing the woman’s (standing by the trees) purse and running off.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 11
Figure 2: Presentation of the suspect lineup (in the experiment, suspects were shown
sequentially). Note, each suspect is wearing a different shirt color than the next.
Procedure
Participants first watched a short video clip of a man stealing a woman’s purse.
Immediately following the video, subjects were sequentially shown the twenty-five
pictures and asked to identify the perpetrator with a ‘Y’ or ‘N.’
Results
Overall, 91% of the participants falsely identified someone in the lineup with an
average 22% detection rate (i.e., a suspect was identified on 22% of trials). Of key
importance is the congruency analysis. First, participants chose the suspect with the
congruent matching (prime word to shirt color) only 5% of the time, while they chose the
suspects with incongruent matchings 18% of the time. However, despite the obvious
difference, the initial presentation involved a ratio of 1:4 in favor of incongruent
matchings. Therefore, in order to more accurately analyze this, the number of times a
participant falsely identified a suspect was calculated based on congruency and then
compared to what would have been expected by chance (see Figure 4). For instance, if a
participant had chosen the congruent matching suspect (i.e., prime matched color of shirt)
on 2 of the 5 trials, then the congruency score for that participant would be 40%. When
doing so, a congruent matching was chosen 20.1% of the time and an incongruent
matching was chosen 79.9% of the time (see Figure 3). Note, this is nearly identical to
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 12
the ratio of congruent to incongruent matchings (1:4), and did not differ significantly
when compared to this baseline rate (p >. 05).
Figure 3: Mean performance (ID %) for subjects across all compatibility vs.
incompatibility trials.
Figure 4: Percentage of compatible and incompatible responses compared to the level of
expected chance.
Discussion
There are two main findings that merit discussion. First, our underlying question
was to determine if information presented at the implicit level had the ability to impact
facial recognition in an eyewitness testimony paradigm. The findings suggest that this
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RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 13
was not the case. That is, participants did not more frequently choose the primed suspect
more often than non-primed suspect. Second, nearly all participants (91%) erroneously
identified a perpetrator despite the fact that a culprit-absent lineup was used. This latter
finding is of importance as it shows the propensity of participants to falsely identify an
individual.
The lack of any influence of the implicitly presented prime is intriguing, as
research typically finds a facilitation in performance when identifying previously primed
stimuli. For instance, Dehaene et al. (1998) used a number priming paradigm and asked
participants to classify target digits as either greater than or less than five. Importantly,
preceding the target a masked digit was presented that was also either above or below
five. Dehaene et al. (1998) observed faster and more accurate responses for congruent
prime-target matchings (i.e., when both prime and target were either above or below five)
when compared to incongruent matchings (i.e., when prime was above five and target
below five, or vice versa), despite the lack of conscious awareness of the prime.
These priming effects are not related to only low-level stimuli. Indeed,
Dell’Acqua and Grainger (1999) examined the effects of unconsciously presenting
picture primes on semantic identification and naming responses on both word and picture
targets. They found that when targets belonged to the same semantic category as the
prime, responses were faster compared to different category primes. Thus, it is interesting
that the present research did not observe any priming effect. It should be noted however,
that the stimuli used here were much more complex than previously used. That is, this is
the first experiment to use an eyewitness paradigm, requiring participants to view a video
of a crime and then identify suspects from a lineup, with the inclusion of primes. It could
be the fact that an identification decision might not be susceptible to implicit priming,
although further research is needed to support such a claim.
While the research described above supports the notion that a prime will facilitate
performance, there are instances when the reverse occurs, that is an inhibition for primed
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 14
stimuli. When this occurs the majority of research posits that stimuli must be presented
supraliminally or above conscious awareness (see for example Allport et al., 1985; also
see Eimer & Schlaghecken, 2003). Evidence for this has been found in a number of
studies investigating negative priming (Allport et al., 1985) and voluntary or involuntary
shifts in spatial attention (McCormick, 1997). These studies have employed stop signal or
go/no-go tasks, which require participants have to refrain from responding when
presented with a specific signal. Findings such as these have lead to the prediction that
implicitly presented material can affect behavior, however, the subliminal presentation of
our stimuli did not lead to the predicted facilitation.
A related experiment conducted by Eimer and Schlaghecken (2003) displayed
primed stimuli for 16ms, immediately followed by a mask (100ms), and then by a target
(100ms) requiring a left or right hand response. The data revealed a striking pattern of
results. Error rates were lower and a faster RT was observed in the incompatible
condition, whereas slower RTs and higher error rates were found in the compatible
condition. This phenomenon is known as the negative compatibility effect and has been
robustly demonstrated in the literature (see also Eimer, 1998, 1999; Eimer &
Schlaghecken, 2001). It should be noted, that the negative compatibility effect is the
opposite of what we would have hypothesized. However, it is important to point out that
the implicit prime did lead to an effect in Eimer and Schlaghecken’s (2003) experiment.
It is difficult to speculate as to why a null result was observed here. In similar
research, one possibility pertains to the idea that previous research used mostly simple
stimuli devoid of real world complexity. It is possible that the use of faces here, or the
video prior to the presentation of the experiment, somehow negated any priming effect on
memory. Despite some research claiming facilitatory effects in complex semantic
associations (Dell’Acqua & Grainer, 1999), the majority of research relies on recognizing
simple target stimuli that hold a strong association with the prime. Our experiment relied
on higher-level decision-making (i.e., attaching guilt to a suspect), which may not have
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 15
adequately transferred from our priming mechanism. Furthermore, adequate attention
may not have been captured by the shirt color of the suspect, and therefore was not fully
processed or even perceived. Consequently, our subliminal information may not have
been sufficiently relevant to the task, weakening the efficacy of the prime, and therefore
restricting any facilitating effect. This suggests that only activation caused by strong and
simple implicit presentation will cross the threshold and trigger a response.
One potential complication in the present experiment would be whether or not the
prime was truly subliminal in nature. It is possible that some participants might have
observed it while others did not, perhaps leading to opposing trends in the data canceling
each other out. This is unlikely as two procedures were undertaken to ensure that our
prime stimuli were presented outside of conscious awareness. First, although we chose a
prime of a different visual property (words) than the target stimulus, a post-presentation
mask was used. And second, prior to our formal experimental trials, we repeatedly pre-
tested (duration and font size) our masking and priming stimuli during a pilot session to
ensure there was no detection of the priming color or masking stimulus. Also,
immediately following the pilot trials, participants stated that they were unable to
consciously detect or discriminate the masked primes. Although, it should be noted that a
complete pilot test was not conducted, and therefore this remains a small, albeit potential
possibility.
Only a small subset of participants (9%) failed to exhibit any false identification.
That is, more than 90% of participants incorrectly chose someone who was not the
culprit. This dovetails with prior research (e.g., Wells, 1993) showing a high false
identification rate. Interesting, a sequential lineup was used here, and we nevertheless
observed a high rate of false identification. Traditionally, the false identification rate
increases when using simultaneous lineups, likely due to the use of relative-judgment
when identifying suspects. The relative-judgment notion states that an eyewitness often
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 16
selects a suspect from the lineup who closely resembles the eyewitness’s memory of the
culprit relative to the other lineup members (Olson & Wells, 2003). The problem
becomes readily apparent when we observe the process under a culprit absent lineup.
Therefore, the relative judgment process may yield a positive identification when
someone possesses more resemblance to the culprit, compared to the other lineup
members. A sequential lineup was specifically employed here in an attempt to avoid any
subjective comparisons, utilizing past research demonstrating the robustness of the
sequential lineup advantage (Steblay et al., 2001). Theoretically, eyewitnesses use an
absolute judgment process in a sequential lineup, in which lineup members are compared
directly to the witness’ memory of the culprit, instead of other lineup members in a
simultaneous lineup. Thus, it is noteworthy that such a high false identification rate was
still observed.
In addition to the use of the sequential lineup, the culprit was not included in the
lineup to further explore the possibility of false identification in culprit-absent lineups.
Our instructions were simply to identify the perpetrator, with no indication if the culprit
was actually in the lineup. Other studies have demonstrated the improvement of
eyewitness reports (i.e., lower false identification rates) when participants are warned that
the suspect might not be in the lineup (Malpass & Devine, 1981). Despite the slightly
misleading nature of our design, our procedure was neither coercive nor suggestive; with
all participants having the opportunity to not select anyone. Regardless, it should be
noted that the principle aim of our study was not to examine systematic variables and
manipulate lineup properties, but rather determine the influence of information presented
below conscious awareness.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 17
It is necessary to point out that the current study has some important implications
when evaluating eyewitness testimony. At the forefront, the viewing pool of potential
suspects was substantially narrow. That is, our suspect lineup was relatively small and
limited, thus raising the possibility for biases due to prior exposure of frequently
presented photographs. Furthermore, it is possible that repeated exposure to the same
photos caused participants to identify the same photo regardless if another suspect
resembled the perpetrator. Dysart, Lindsay, Hammond, and Dupuis (2001) coined the
term “the commitment effect” which essentially states that if a witness chooses a face
from a set of photographs and this face reappears in the suspect lineup, the witness will
choose that face again, exhibiting a feeling of commitment to the prior choice. Although,
it should be noted that this argument holds little weight here given that there was no
preference was for any single picture, as demonstrated by the almost exact chance results.
Memory research is especially important for the investigation of the judicial
process, since many trials revolve around eyewitness accounts. Priming may have
practical value for eyewitness testimony given that it is often more impressionable and
persistent than other forms of explicit memory (Joyce & Kutas, 2005) and can be
extremely durable and resilient (Shacter, 1992). Moreover, in order to more directly
investigate the potential of implicit memory, other studies are encouraged to examine
external properties of the event such as organization of information, causal and spatial
temporal relationships, and previous knowledge, which could possibly have rendered
actions of the event resistant to facilitatory and inhibitory processes (Eimer, 1999). The
current system exclusively relies on long term, declarative retention of faces after
exposure to a suspect lineup, even though it has been shown that this type of memory is
often very malleable and susceptible to misidentification.
In sum, the present research affirms the ability for human memory to be
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 18
reconstructed based on post-event information, as more than 90% of participants falsely
identified a suspect. At the same time, it appears that subliminal priming did not have any
influence on suspect identification. Despite these results, it is still vitally important to
examine the role of implicit information in the context of eyewitness testimony due to the
vast amount of information eyewitnesses unconsciously perceive and the ability for that
information to influence memory and decision making.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 19
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McDermott, K. (1997). Priming on perceptual implicit memory tests can be achieved
through presentation of associates. Psychonomic Bulletin and Review, 4, 582-586.
Migueles, M., & Garcia-Bajos, E. (2007). Selective retrieval and induced forgetting in
eyewitness memory. Applied Cognitive Psychology, 21, 1157-1172.
Pryke, S., Lindsay, R. C., Dysart, J. E., & Dupuis, P. (2004). Multiple independent identification
decisions: a method of calibrating eyewitness identifications. Journal of Applied
Psychology, 89, 73-84.
Roediger, H. L. (1990). Implicit memory: retention without remembering. American
Psychologist, 45, 1043-1056.
Schreiber, T., & Sergent, S. (1998). The role of commitment in producing misinformation
effects in eyewitness memory. Psychonomic Bulletin and Review, 5, 443-448.
Shacter, D. (1992). Priming and multiple memory systems: perceptual mechanisms of
implicit memory. Journal of Cognitive Neuroscience, 4, 244-256.
Shaw, J.S. III. (1996). Increases in eyewitness confidence resulting from postevent
questioning. Journal of Experimental Psychology, 2, 126–146.
Steblay, N., Dysart, J., Fulero, S., & Lindsay, R. C. (2001). Eyewitness accuracy rates in
sequential and simultaneous lineup presentations: a meta-analytic comparison. Law and
Human Behavior, 25, 459-473.
Tipper, S. (1985). Negative priming effect: inhibitory priming by ignored objects.
RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 22
Journal of Experimental Psychology, 37, 571-590.
Warrington, E., & Weiskrantz, L. (1968). The study of retention and learning in amnesic
patients. Neuropsychologia, 6, 283-291.
Wells, G. L. (1993). What do we know about eyewitness identification? American
Psychologist, 48, 553-571.
Wells, G. L., & Olson, E. A. (2003). Eyewitness testimony. Annual Review of Psychology, 54,
277-295.
.

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Simpson_Austin_Thesis Paper

  • 1. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 1 The Role of Implicit Presentation in Eyewitness Testimony: Investigating Whether Subliminal Priming Can Modulate Suspect Identification A Senior Honors Thesis Presented to the Faculty of the Department of Psychology University of Hawaii at Manoa In Partial Fulfillment of the Requirements for Bachelors of Psychology with Honors By Austin Simpson May 9, 2013 Committee: Scott Sinnett, Mentor Andrew Dewald Marvin Chandra
  • 2. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 2 Table of Contents Table of Contents 2 Abstract 3 Introduction 4 • Influence of Suspect Lineup 4 • Fallibility of Explicit Memory Processes 5 • Implicit Effects on Recognition 7 Methods 9 • Participants 9 • Stimuli and Apparatus 9 • Procedure 11 Results 11 Discussion 12 References 19
  • 3. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 3 Abstract The criminal justice system relies heavily on eyewitness testimony for the prosecution and investigation of criminals. Extensive research has shown that post-event information can severely alter or reconstruct memory. However, despite empirical evidence demonstrating that implicitly presented information can influence memory and behavior, no research has been conducted regarding the ability of information that is presented below conscious awareness to modulate eyewitness identification. This is precisely what was investigated in the current manuscript. Participants were instructed to watch a short video that depicted a man committing a crime, and were then required to identify the culprit out of a sequential lineup presented on a computer screen. The color of the shirt that each suspect wore was systematically primed by a subliminally presented color word. Critically, the color prime either did, or did not match the color of the shirt that the suspect wore. The findings showed a very high false identification rate, with more than 90% of participants falsely choosing a suspect, despite the actual culprit never being shown. Contrary to expectations, when compared to chance levels participants did not choose suspects more frequently if they had been implicitly primed with a matching color word. Given the powerful determinants of memory bias, the present findings could be of interest to the criminal justice system. Keywords: Eyewitness testimony, false memory, misinformation, priming, recognition
  • 4. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 4 The Role of Implicit Presentation in Eyewitness Testimony: Investigating Whether Subliminal Priming Can Modulate Suspect Identification Eyewitness testimony can be extremely important in the justice system. However, research from the past 40 years has demonstrated that eyewitness memory can be flawed, sometimes leading to the unfortunate incarceration of innocents. For instance, in 1984 Frederick Rene Day was identified from a suspect lineup and served ten years in prison for rape and kidnapping. Day was released in 1994 after DNA testing revealed his innocence. The rape victim and another witness both falsely identified Daye as the kidnapper and rapist, leading to his conviction. While this is just one of many cases, much research has shown the fragility of human memory when it comes to eyewitness testimony. For example, laboratory studies where perpetrators are shown on video (Gronlund & Carlson, 2009), live field experiences (Pryke, Lindsay, Dysart, & Dupuis, 2004), and archival studies with real criminal cases (Behrman & Davey, 2001) have all consistently demonstrated the fallibility of eyewitness memory. In the real world, the development of new DNA techniques has revealed many cases of wrongful imprisonment in which the accused had been found guilty largely based on memory errors by witnesses, but were subsequently exonerated. Before addressing specific components of memory and how it can be influenced in the context of eye witnessing an event, it is important to discuss how different aspects of the process of being an eyewitness can modulate memory. Influence of the Suspect Lineup One way in which memory can be influenced is by systematic variables – factors controlled by the criminal justice system. For instance, the criminal justice system can administer lineups in such a way that leads to false recollection of an individual and, at
  • 5. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 5 times, false accusation. Hence, the content and presentation method of a lineup pose a significant threat to the reliability of an eyewitness account. Police integrators often manipulate the structure of the eyewitness lineup, such as deliberately omitting the perpetrator from the lineup or presenting suspects in a sequential or simultaneous manner. Lindsay and Wells (1985) were the first to demonstrate the superiority of presenting a lineup in a sequential manner. Results of their study showed that subjects made fewer errors in a sequential lineup than a simultaneous lineup (correctly ID subjects). Others have confirmed similar results concluding that sequential lineups lead to lower rates of false identifications (Steblay, Dysart, Fulero, & Lindsay, 2001; but see Carlson, Gronlund, & Clark, 2008 for a counter example). However, the advantage of sequential lineups is mediated by how much the innocent subject stands out from other lineup members (Carlson et al., 2008; Gronlund & Carlson, 2009). A further systematic variable that can influence identification rates is whether or not the actual culprit (i.e., guilty individual) is present in the lineup. It is important for the administrator to inform the witness that the perpetrator of the crime may or may not be present. If not, witnesses often falsely identify a suspect, arguably due to some sort of expectation to be required to choose someone, leading to the witness choosing the person in the lineup who most closely resembles the real perpetrator. This was exemplified in a study by Wells (1992) where 54% of witnesses identified the correct culprit from a culprit-present lineup while 21% made no identification. However, when researchers removed the culprit, 68% of subjects falsely identified someone and 32% of people did not identify anyone (Wells, 1992; see also Ebbesen & Flowe, 2002; Clark, 2009). Seeing that the absence of a perpetrator leads to high levels of false identifications, the current study did not include the perpetrator in the lineup. Fallibility of Explicit Memory Processes Typically, memory can be fundamentally thought of as a constructive process,
  • 6. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 6 rather than a replay of life events. The recollection of an explicit memory is often one of the most powerful, yet inaccurate sources in eyewitness testimony. Questions concerning the nature of memory systems have been at the forefront of cognitive research. In eyewitness testimony research, for instance, one of the reasons why error rates are so high is that incorrect information presented after the event (post event misinformation; PMI) can impair memory of the original event. For instance Loftus (1974) developed a landmark theory called the “misinformation effect” to explain how exposure to PMI can create false memories. In her experiment, participants watched a video clip of a car accident. Participants were later asked questions that either embellished the event or provided a more accurate portrayal (i.e., how fast were the cars moving when they (smashed vs. hit) into each other?). The results showed that participants who received questions containing the word smashed indicated higher speeds when compared with participants who had the word hit in the questions. More importantly, when asked to return to the laboratory a week later, those participants who had received the verb smashed again recalled the cars to be moving faster, but also more frequently recalled the presence of broken glass (there was none). In sum, PMI later influenced memory retrieval and lead to false memories. The robustness of the misinformation effect has been found in a variety of other studies involving a multitude of materials and techniques (Schreiber & Serget, 1997). One of the possible mechanisms driving the misinformation effect could be retroactive interference, which suggests that new information potentially conflicts or overrides previously learned information, thus forming a new reconstructed or reconsolidated memory, often different from objective events. This is especially dangerous when considering eyewitness memory, as false recognition is often accompanied by high confidence and detailed, albeit false recollection (Roediger, 1990; Shaw, 1996). Despite the robustness of studies using explicit memory paradigms, implicit memory has received little attention in the false memory literature.
  • 7. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 7 Researchers have focused on the distinction between explicit and implicit forms of memory. Explicit or declarative memory refers to the conscious recollection of events or experiences. In contrast, implicit or non-declarative memory refers to changes in behavior or performance elicited by prior experiences for which one has no conscious awareness. For instance, priming experiments (discussed in more detail below) often involve the below threshold presentation of stimuli, that despite not leading to conscious awareness, can nevertheless influence later memory and behavior (Dehaene et al., 1998). While implicit priming has been robustly demonstrated in the literature (see for example Kirsner & Smith, 1974; McDermott, 1997), its role in in eyewitness identification has yet to be explored. Implicit Priming and Recognition Priming refers to the phenomenon when the exposure to a prior stimulus effects the identification of a similar or identical target that is presented later (see for example Tipper, 1984). The initial stimulus is known as the prime or cue, and has nothing to do with the actual task of responding to a later stimulus, known as the target. Furthermore, the prime is often presented subliminally (i.e., below conscious awareness). Critically, when the cue and target are related, the target is responded to more efficiently, demonstrating implicit memory. For instance, evidence for the benefits of priming1 have been observed on tasks such as word completion, lexical decision-making, and semantic comparisons (Kirsner & Smith, 1974; Warrington & Weiskrantz, 1968; Dehaene et al., 1998) to name but a few. Of direct interest to eyewitness memory, the relationship between priming and face recognition using identical or similar stimuli has been explored, and found to facilitate identification. That is, robust evidence corroborates the notion that the repeated 1 However, it should be noted that some research has also shown that a prime can slow down processing of the target (i.e., negative priming, see Tipper, 1985 for example). Regardless, both facilitation and inhibition demonstrate that the subliminally presented prime can influence behavior.
  • 8. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 8 exposure to primed faces improves reaction time and accuracy in facial recognition tasks (Dell’Acqua & Grainger, 1999; Joyce & Kutas, 2005; see also McDermott, 1997 for a similar example using written words). More importantly, past research has found that misleading subliminal information can induce false recognition, such as through repetition priming (Jacoby & Whitehouse, 1989). Jacoby and Whitehouse (1989) instructed participants to study a wordlist and then presented a recognition test, which contained words from the original list or new words. Critically, the presentation of a subliminal word preceded each recognition item that either matched or did not match the target. Results indicated that participants falsely recognized “new” words as “old” when primed with words that matched. In the current study, implicit primes (color words) that were related to (or not) the color of a shirt worn by a suspect were used to assess the possibility that the implicit prime could influence eyewitness identification. We deliberately masked the priming stimuli (to eliminate conscious awareness) to explore whether information presented below threshold can affect recognition of complex stimuli (i.e., the face of a suspect after viewing a video of a crime). While this type of complexity is rare in priming paradigms, it is rather applicable to eyewitness testimony, and a behavioral effect of subliminal stimuli may provide further explanatory power for the potency of implicit memory. This may open the window for practical applications examining the nature of misleading questions, eyewitness depictions of an event, and lineup factors that might be unknowingly perceived. There are two main objectives that were explored in this honors thesis: First, to explore whether priming individuals with below threshold (i.e., subliminal) misleading information can modulate the rate of identification. In other words, can implicit information lead people to falsely recognize a culprit? The second question explores whether people will choose someone regardless if the culprit was present in the suspect lineup. Based on previous research, one could hypothesize that participants will not only
  • 9. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 9 identify a perpetrator but also choose suspects whose shirt color matches a subliminally primed and matching color word. Methods Participants Undergraduate students (n=61) from the University of Hawaii at Manoa were recruited from psychology classes to participate in the study as an opportunity for extra credit. All participants gave informed consent prior to participating in the experiment. The experiment was approved by the University of Hawaii at Manoa Committee on Human Studies. Stimuli & Apparatus The experiment was conducted at the Attention and Perception Laboratory at the University of Hawaii at Manoa. Three MacBook computers were used to perform the experimental trials using the Psyscope XB7 graphical user interface software program. The mock video was adopted from a previous experiment done by Gronlund & Carlson (2009). The video lasted approximately 1 min and 45 seconds and depicted a scene of a couple walking on a street, hugging, and then walking across the street (see Figure 1). Intermixed among the scenes was the perpetrator getting out of his car and hiding in the bushes. As the woman approaches her car, the perpetrator jumps out of the bushes, steals the purse, and runs off. Suspect lineup: Pictures were acquired from a selection of Facebook profile pictures from friends of the author. Five photos were obtained (see Figure 2) and all people approved the use of their photo for the purposes of the experiment. Using Photoshop, each photo was changed such that the color of the shirt could be different (either red, black, blue,
  • 10. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 10 green, or yellow), making a total of 25 pictures total (i.e., the five pictures with five different colored shirts). Priming Stimuli. The different colors of the shirts (red, blue, yellow, black, and green) were presented in written format immediately before the presentation of each photo. The color words were presented for 13 ms and then masked for 50 ms by random symbols in order to ensure that the words were presented subliminally. No participants expressed awareness of the words. The author, advisor, and numerous classmates were unable to determine the identity of the prime when awareness was informally tested. Each trial began with a fixation cross (750 ms), immediately followed by the prime word (13 ms), which was then followed by a mask (50ms). The mask was composed of symbols that systematically replaced letters (e.g., %#@*). The combination of shirt color, person, and prime was pseudorandomized. In order to more closely replicate real world lineups, each participant was given five congruent trials (prime matches shirt color) and 20 incongruent trials (prime did not match shirt color). Figure 1: Still frame of a scene shown in the video. This scene depicts the perpetrator just after stealing the woman’s (standing by the trees) purse and running off.
  • 11. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 11 Figure 2: Presentation of the suspect lineup (in the experiment, suspects were shown sequentially). Note, each suspect is wearing a different shirt color than the next. Procedure Participants first watched a short video clip of a man stealing a woman’s purse. Immediately following the video, subjects were sequentially shown the twenty-five pictures and asked to identify the perpetrator with a ‘Y’ or ‘N.’ Results Overall, 91% of the participants falsely identified someone in the lineup with an average 22% detection rate (i.e., a suspect was identified on 22% of trials). Of key importance is the congruency analysis. First, participants chose the suspect with the congruent matching (prime word to shirt color) only 5% of the time, while they chose the suspects with incongruent matchings 18% of the time. However, despite the obvious difference, the initial presentation involved a ratio of 1:4 in favor of incongruent matchings. Therefore, in order to more accurately analyze this, the number of times a participant falsely identified a suspect was calculated based on congruency and then compared to what would have been expected by chance (see Figure 4). For instance, if a participant had chosen the congruent matching suspect (i.e., prime matched color of shirt) on 2 of the 5 trials, then the congruency score for that participant would be 40%. When doing so, a congruent matching was chosen 20.1% of the time and an incongruent matching was chosen 79.9% of the time (see Figure 3). Note, this is nearly identical to
  • 12. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 12 the ratio of congruent to incongruent matchings (1:4), and did not differ significantly when compared to this baseline rate (p >. 05). Figure 3: Mean performance (ID %) for subjects across all compatibility vs. incompatibility trials. Figure 4: Percentage of compatible and incompatible responses compared to the level of expected chance. Discussion There are two main findings that merit discussion. First, our underlying question was to determine if information presented at the implicit level had the ability to impact facial recognition in an eyewitness testimony paradigm. The findings suggest that this 0   10   20   30   40   50   60   70   80   90   100   %  Identi)ied  on  Recognition  Test   Compatible   Incompatible   0   10   20   30   40   50   60   70   80   90   100   Incompatible   Compatible   %  Identi)ied  on  Recognition  Test   Chance  Level  
  • 13. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 13 was not the case. That is, participants did not more frequently choose the primed suspect more often than non-primed suspect. Second, nearly all participants (91%) erroneously identified a perpetrator despite the fact that a culprit-absent lineup was used. This latter finding is of importance as it shows the propensity of participants to falsely identify an individual. The lack of any influence of the implicitly presented prime is intriguing, as research typically finds a facilitation in performance when identifying previously primed stimuli. For instance, Dehaene et al. (1998) used a number priming paradigm and asked participants to classify target digits as either greater than or less than five. Importantly, preceding the target a masked digit was presented that was also either above or below five. Dehaene et al. (1998) observed faster and more accurate responses for congruent prime-target matchings (i.e., when both prime and target were either above or below five) when compared to incongruent matchings (i.e., when prime was above five and target below five, or vice versa), despite the lack of conscious awareness of the prime. These priming effects are not related to only low-level stimuli. Indeed, Dell’Acqua and Grainger (1999) examined the effects of unconsciously presenting picture primes on semantic identification and naming responses on both word and picture targets. They found that when targets belonged to the same semantic category as the prime, responses were faster compared to different category primes. Thus, it is interesting that the present research did not observe any priming effect. It should be noted however, that the stimuli used here were much more complex than previously used. That is, this is the first experiment to use an eyewitness paradigm, requiring participants to view a video of a crime and then identify suspects from a lineup, with the inclusion of primes. It could be the fact that an identification decision might not be susceptible to implicit priming, although further research is needed to support such a claim. While the research described above supports the notion that a prime will facilitate performance, there are instances when the reverse occurs, that is an inhibition for primed
  • 14. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 14 stimuli. When this occurs the majority of research posits that stimuli must be presented supraliminally or above conscious awareness (see for example Allport et al., 1985; also see Eimer & Schlaghecken, 2003). Evidence for this has been found in a number of studies investigating negative priming (Allport et al., 1985) and voluntary or involuntary shifts in spatial attention (McCormick, 1997). These studies have employed stop signal or go/no-go tasks, which require participants have to refrain from responding when presented with a specific signal. Findings such as these have lead to the prediction that implicitly presented material can affect behavior, however, the subliminal presentation of our stimuli did not lead to the predicted facilitation. A related experiment conducted by Eimer and Schlaghecken (2003) displayed primed stimuli for 16ms, immediately followed by a mask (100ms), and then by a target (100ms) requiring a left or right hand response. The data revealed a striking pattern of results. Error rates were lower and a faster RT was observed in the incompatible condition, whereas slower RTs and higher error rates were found in the compatible condition. This phenomenon is known as the negative compatibility effect and has been robustly demonstrated in the literature (see also Eimer, 1998, 1999; Eimer & Schlaghecken, 2001). It should be noted, that the negative compatibility effect is the opposite of what we would have hypothesized. However, it is important to point out that the implicit prime did lead to an effect in Eimer and Schlaghecken’s (2003) experiment. It is difficult to speculate as to why a null result was observed here. In similar research, one possibility pertains to the idea that previous research used mostly simple stimuli devoid of real world complexity. It is possible that the use of faces here, or the video prior to the presentation of the experiment, somehow negated any priming effect on memory. Despite some research claiming facilitatory effects in complex semantic associations (Dell’Acqua & Grainer, 1999), the majority of research relies on recognizing simple target stimuli that hold a strong association with the prime. Our experiment relied on higher-level decision-making (i.e., attaching guilt to a suspect), which may not have
  • 15. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 15 adequately transferred from our priming mechanism. Furthermore, adequate attention may not have been captured by the shirt color of the suspect, and therefore was not fully processed or even perceived. Consequently, our subliminal information may not have been sufficiently relevant to the task, weakening the efficacy of the prime, and therefore restricting any facilitating effect. This suggests that only activation caused by strong and simple implicit presentation will cross the threshold and trigger a response. One potential complication in the present experiment would be whether or not the prime was truly subliminal in nature. It is possible that some participants might have observed it while others did not, perhaps leading to opposing trends in the data canceling each other out. This is unlikely as two procedures were undertaken to ensure that our prime stimuli were presented outside of conscious awareness. First, although we chose a prime of a different visual property (words) than the target stimulus, a post-presentation mask was used. And second, prior to our formal experimental trials, we repeatedly pre- tested (duration and font size) our masking and priming stimuli during a pilot session to ensure there was no detection of the priming color or masking stimulus. Also, immediately following the pilot trials, participants stated that they were unable to consciously detect or discriminate the masked primes. Although, it should be noted that a complete pilot test was not conducted, and therefore this remains a small, albeit potential possibility. Only a small subset of participants (9%) failed to exhibit any false identification. That is, more than 90% of participants incorrectly chose someone who was not the culprit. This dovetails with prior research (e.g., Wells, 1993) showing a high false identification rate. Interesting, a sequential lineup was used here, and we nevertheless observed a high rate of false identification. Traditionally, the false identification rate increases when using simultaneous lineups, likely due to the use of relative-judgment when identifying suspects. The relative-judgment notion states that an eyewitness often
  • 16. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 16 selects a suspect from the lineup who closely resembles the eyewitness’s memory of the culprit relative to the other lineup members (Olson & Wells, 2003). The problem becomes readily apparent when we observe the process under a culprit absent lineup. Therefore, the relative judgment process may yield a positive identification when someone possesses more resemblance to the culprit, compared to the other lineup members. A sequential lineup was specifically employed here in an attempt to avoid any subjective comparisons, utilizing past research demonstrating the robustness of the sequential lineup advantage (Steblay et al., 2001). Theoretically, eyewitnesses use an absolute judgment process in a sequential lineup, in which lineup members are compared directly to the witness’ memory of the culprit, instead of other lineup members in a simultaneous lineup. Thus, it is noteworthy that such a high false identification rate was still observed. In addition to the use of the sequential lineup, the culprit was not included in the lineup to further explore the possibility of false identification in culprit-absent lineups. Our instructions were simply to identify the perpetrator, with no indication if the culprit was actually in the lineup. Other studies have demonstrated the improvement of eyewitness reports (i.e., lower false identification rates) when participants are warned that the suspect might not be in the lineup (Malpass & Devine, 1981). Despite the slightly misleading nature of our design, our procedure was neither coercive nor suggestive; with all participants having the opportunity to not select anyone. Regardless, it should be noted that the principle aim of our study was not to examine systematic variables and manipulate lineup properties, but rather determine the influence of information presented below conscious awareness.
  • 17. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 17 It is necessary to point out that the current study has some important implications when evaluating eyewitness testimony. At the forefront, the viewing pool of potential suspects was substantially narrow. That is, our suspect lineup was relatively small and limited, thus raising the possibility for biases due to prior exposure of frequently presented photographs. Furthermore, it is possible that repeated exposure to the same photos caused participants to identify the same photo regardless if another suspect resembled the perpetrator. Dysart, Lindsay, Hammond, and Dupuis (2001) coined the term “the commitment effect” which essentially states that if a witness chooses a face from a set of photographs and this face reappears in the suspect lineup, the witness will choose that face again, exhibiting a feeling of commitment to the prior choice. Although, it should be noted that this argument holds little weight here given that there was no preference was for any single picture, as demonstrated by the almost exact chance results. Memory research is especially important for the investigation of the judicial process, since many trials revolve around eyewitness accounts. Priming may have practical value for eyewitness testimony given that it is often more impressionable and persistent than other forms of explicit memory (Joyce & Kutas, 2005) and can be extremely durable and resilient (Shacter, 1992). Moreover, in order to more directly investigate the potential of implicit memory, other studies are encouraged to examine external properties of the event such as organization of information, causal and spatial temporal relationships, and previous knowledge, which could possibly have rendered actions of the event resistant to facilitatory and inhibitory processes (Eimer, 1999). The current system exclusively relies on long term, declarative retention of faces after exposure to a suspect lineup, even though it has been shown that this type of memory is often very malleable and susceptible to misidentification. In sum, the present research affirms the ability for human memory to be
  • 18. RESPONSE RECOGNITION IN EYEWITNESS TESTIMONY 18 reconstructed based on post-event information, as more than 90% of participants falsely identified a suspect. At the same time, it appears that subliminal priming did not have any influence on suspect identification. Despite these results, it is still vitally important to examine the role of implicit information in the context of eyewitness testimony due to the vast amount of information eyewitnesses unconsciously perceive and the ability for that information to influence memory and decision making.
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