Download FALSE MEMORIES False Memories

Running head: FALSE MEMORIES
False Memories:
Paradigms for studying the creation and reduction of false memories
Miranda L Trecroce
Algoma University College
False memories 2
Abstract
In recent years, the study of false memory and memory distortion has become an area of
particular interest for psychologists. A false memory can be operationally defined as a
memory for a word that a participant has not been presented, or memories for an event
which has never occurred. There are different types of false memories explored in the
laboratory, with different experimental techniques used to induce them. The present
literature review examines three different paradigms for studying the effect of false
memories: the Deese-Roediger-McDermott (DRM) (1995) paradigm, the Loftus
paradigm, and the ALT paradigm, developed by Kassin and Kiechel. Of the three
paradigms, only research using the DRM framework has examined whether instructional
warnings are effective in reducing or preventing the creation of false memories. Further
research is required using the Loftus paradigm and the ALT paradigm to determine
whether instructional warnings will effectively reduce the occurrence of false memories.
False memories 3
False memories:
Paradigms for studying the creation and reduction of false memories
A wealth of past research indicates that human memory is prone to distortions
(e.g., Deese, 1959; Roediger & McDermott, 1995; Loftus & Pickrell, 1995; Kassin &
Kiechel, 1996). The study of false memory and memory distortion has become an area of
particular interest for psychologists in recent years. A false memory is a memory which is
a distortion of an actual experience, or a confabulation of an imagined one. Many false
memories are created by confusing or mixing fragments or memory events, some of
which may have happened at different times but which are remembered as occurring
together.
This growing interest in false memory has also been accompanied by laboratory
studies (e.g., Loftus & Pickrell, 1995; Roediger & McDermott, 1995; Kassin & Kiechel,
1996) that have provided clear evidence of false memories under controlled conditions.
In experimental research settings a false memory occurs when participants in an
experiment come to remember an event which has never actually occurred (Loftus, 1997;
Kassin & Kiechel, 1996), or remember the presentation of a word which was never
actually presented (Deese, 1959; Roediger & McDermott, 1995).
Research about false memories is important because of its psycho-legal
applications regarding recovered memories, eyewitness testimony, and individual
differences in the formation of false memories. The eyewitness plays a crucial role in a
large number of court cases, particularly robberies and rapes. In these cases,
identification of a suspect by an eyewitness or other personal testimony about an event
False memories 4
often provides important evidence on which a prosecution is based. Faulty eyewitness
testimony is a major source of wrongful convictions (Greene & Loftus, 1984).
Many influences can cause memories to change or even be created anew,
including our imaginations, leading questions, or different recollections of others. The
knowledge that we cannot rely on our memories, however compelling they might be,
leads to questions about the validity of criminal convictions that are based largely on the
testimony of victims or witnesses (Loftus, 2003). Psychological science has informed the
legal system about memory and enabled productive changes in the handling of
eyewitness evidence attempting to reduce or prevent the false memory effect from
occurring.
A number of paradigms have been proposed to study the false memory effect. The
present literature review has two main purposes: (a) to describe and analyze three various
paradigms for studying false memories, and (b) to examine research within each of these
three paradigms.
Paradigms for False Memories
There are different types of false memories explored in the laboratory, with
different experimental techniques used to induce them. Three particularly interesting
paradigms are the Deese-Roediger-McDermott (DRM) (1995) paradigm, the Loftus
paradigm, and the ALT paradigm, developed by Kassin and Kiechel. In research studies,
a false memory is often operationally defined as a memory for a word that a participant
has not been presented, or memories for an event which has never occurred. The DRM
paradigm produces formation of false memory for words, while the Loftus paradigm
False memories 5
produces false memories for perceiving objects or events, and the ALT paradigm
produces false memories for events.
The Deese-Roediger-McDermott (DRM) paradigm
The DRM paradigm is a common and useful technique for studying false
memories in a controlled laboratory setting (Deese, 1959). Roediger and McDermott
(1995) reintroduced a paradigm originally developed by Deese (1959). Because the
paradigm is reliable and easy to use, it has been adopted by a number of researchers
interested in studying the characteristics of false memories. In the original version of this
paradigm, participants are presented with lists of thematically 'related' words (e.g., bed,
rest, awake) that are all associated with a 'critical' non-presented (CNP) item (e.g., sleep)
that is actually not presented. When participants study lists of words, they often falsely
report recognizing a never presented associate word as appearing in the list. In the
recognition version of this paradigm, participants are subsequently given an old/new
recognition test, which includes a subset of the presented related words and the nonpresented critical words. Typically, memory performance is measured by calculating the
hit rate for the words presented on the list (related words) and the false-alarm rate for the
words that had not been presented on the list (critical words). Participants are asked
whether they "know" (i.e., are confident that the word was presented but do not
remember the actual presentation) or "remember" (i.e., are confident the word was
presented and remember something about the actual presentation) seeing the word
presented on the list. In this paradigm, participants have a memory for a certain word
which they think they have heard, although in reality, the word has not been presented
(Gallo et al., 2001).
False memories 6
Prior research has also asked whether different variables can influence the false
memory effect. For example, McDermott (1996) gave subjects multiple study and recall
tests with the same word lists presented in either a blocked or a random manner. Both
forms of presentation yielded false recalls after multiple study-test trials or a final recall
test given 24h later but the random presentation produced less false recall than blocked
presentation.
Researchers proposed that just as lists of semantic associates can produce
associative responses to a critical, non-presented item, lists composed of phonological
associates such as bat, beat, bet, bit, etc., can produce false memories to phonologically
related CI's such as but. False memory research in the DRM paradigm using semantically
related words led researchers to question whether word lists composed of phonological,
rather than semantic, associates would also produce significant amounts of false recall
and recognition. One of the principal factors motivating this research was that a number
of the mechanisms that have been proposed to account for false memories with semantic
associates are similar to processes that have been used to explain listeners' ability to
distinguish phonologically similar words (i.e., lexical discrimination). Sommers and
Lewis (1999) conducted a study within the framework of the Neighbourhood Activation
Model (NAM) to examine whether word lists composed of phonological, rather than
semantic, associates would also produced significant levels of false recall and
recognition. The NAM provides a method for quantifying the degree of association
between lists items and critical items and therefore provides a direct comparison to the
studies of false memory with semantic associates. The findings suggest that similar
False memories 7
mechanisms may induce false memories with lists of semantic and phonological
associates.
The DRM paradigm has been widely recognized as an excellent way to produce
false memories in a laboratory setting without creating a stressful situation for the
participant, while excluding some confounds sometimes present in other false memory
tasks, such as social demand and compliance. Roediger and McDermott (1995) argue that
false memories for words may have similar mechanisms as those that underlie the
formation of false memories for perceiving events.
Current theories of memory are derived largely from experiments involving lists
of words or sentence, however many memories occurring in everyday life involve
complex, largely visual, and often fast-moving events. In some instances such recall is
required, as when one has witnessed a crime or an accident.
The Loftus Paradigm
Memory for perceiving events has been considered an important research topic because
of its psycho-legal applications concerning eyewitness testimony. Loftus and Pickerell
(1995) have demonstrated that people can come to believe they were witness to events
which actually never occurred. This happens most frequently through misleading postevent information that alters people's memory.
Often after witnesses have perceived an important event, they are exposed to new
information about it. Examples of the effects of misleading post event information come
from early research (i.e. Lindsay, 1993; Loftus, 1997; Loftus & Pickrell, 1995).
Evidence has accumulated to indicate that post-event experiences such as
exposure to newly released information can dramatically affect the memory of the
False memories 8
original event. Post-event information can enhance existing memories but it can also
change a witness's memory in a powerful way, even leading to the creation of false
memories by incorporating objects and events that never in fact existed into a previously
acquired memory. For example, Loftus and Pickerell (1995) showed that after receiving
misleading information 29% of participants came to believe that they were lost in a
shopping mall at the age of 5. Hyman, Husband, and Billings (1995) showed that 20% of
participants came to believe an event had occurred in their childhood such as a hospital
visit when, in fact, the event had never occurred.
Most of the experimental research on memory distortion has involved deliberate
attempts to change memory for an event that actually was experienced. An important
issue is whether it is possible to implant an entire false memory for something that never
happened.
Loftus's basic procedure consists of three phases: In Phase 1 subjects view an
event; in Phase 2 they receive verbal information about the event (with or without
misleading suggestions about certain "critical" details); in Phase 3 they take a memory
test that includes questions about the critical details (Lindsay, 1993).
A classic experiment by Loftus and her colleagues (1978) demonstrates how
nonexistent objects can be introduced into people's recollections. Nearly two hundred
participants viewed a series of thirty color slides depicting successive stages in an
automobile-pedestrian accident. The automobile was a red Datsun shown travelling along
a side street toward an intersection. The intersection was shown to have a stop sign for
one half of the participants but a yield sign for the other half of participants. The Datsun
became involved in an accident with a pedestrian. Immediately after viewing the slides,
False memories 9
the subjects were asked some questions, one of which was critical. For about half of the
participants the critical question asked was, "Did another car pass the red Datsun while it
was stopped at the stop sign?" The remaining participants were asked the same question
with the words "stop sign" replaced by "yield sign". For some of the participants the sign
mentioned in the question was the sign that had actually been seen; therefore the question
gave them consistent information. For the remaining subjects the question contained
misleading information.
After completing the questionnaire, the participants took part in a twenty-minute
filler activity, which required them to read an unrelated short story and answer some
questions about it. Finally, a recognition test was administered. Pairs of slides were
presented to the participants and they had to indicate which member of each pair they had
seen before. The critical pair was a slide depicting the Datsun stopped at a stop sign and a
nearly identical slide depicting the Datsun at a yield sign.
The results indicated that when the intervening question contained consistent
information, 75 percent of participants responded accurately. When the question
contained misleading information, only 41 percent of the participants responded
accurately. If the participants had been simply guessing, they would have been correct
about half the time, so the misleading question reduced their accuracy below that which
would have been expected from a person who was merely guessing.
In the mid 1990's researchers went beyond changing memory for a detail in a
previously experienced event; they demonstrated that it is possible to plant an entire false
memory into the mind Autobiographical memories represent a particularly useful set of
experiences for exploring the possibility that there are characteristically distinct attributes
False memories 10
for false memories. Simply put, memories for the experiences of one's own life are often
rich and complex representations (Heaps & Nash, 2001).Using fairly strong suggestions,
investigators succeeded in getting people to believe that when they were children they
had been either lost in a shopping mall for an extended time, hospitalized overnight, or
involved in an unfortunate accident at a family wedding (Loftus, 1997). The "strong
suggestion" involved recruiting the help of family members to construct scenarios
describing true and false experiences and feeding these scenarios to the subjects as if they
were all true. This method is most commonly referred to as the "lost in the mall"
procedure and was developed by Loftus and Pickrell (1995).
Loftus and Pickrell asked participants ranging in age from 18 to 53 years to try to
remember childhood events that had been recounted by their parents, older sibling or
other close relative. Each participant received a booklet containing one-paragraph stories
about three events that actually happened to him or her, and one that had not but was
presented as if it had. Researchers constructed the false event about a shopping trip. A
relative also verified that the participant had not actually been lost at about the age of
five. After reading each story in the booklet, the participants wrote what they
remembered about the event. If they did not remember it, they were told to write, "I do
not remember this." In two follow-up interviews, researchers told the participants that
they were interested in examining how much detail they could remember, and how their
memories compared with those of their relative. Portions of the event paragraphs were
provided to participants as retrieval cues. After reading the booklet, 29% of participants
reported they remembered (either partially or fully) the false event; in the two follow-up
interviews, 25% of participants continued to claim that they remembered the fictitious
False memories 11
event. The findings reveal that people can be led to believe that entire events happened to
them after suggestions to that affect.
Braun, Ellis and Loftus (2002) took the "lost in the mall" study one step further
and developed a procedure for implanting "impossible" memories about experiences.
They investigated whether suggestive referencing in advertisements can cause people to
believe that they had experiences as children that are mentioned in the advertisements.
Participants viewed an advertisement for Disneyland that suggested that they shook
hands with an impossible character (e.g., Bugs Bunny). After evaluating either this
advertisement or a control advertisement subjects were asked about their own childhood
experiences at Disneyland. About 16% of those who had been exposed to the fake Bugs
advertisement later said they had personally met Bugs Bunny at Disneyland. Later studies
showed that with multiple exposures to fake Disney ads that mentioned Bugs Bunny the
percentages rose even higher. Many of those subjects who fell sway to the suggestion
remembered the impossible encounter in quite a bit of detail (e.g., they reported that they
hugged Bugs or touched his ear). Of course, this memory is impossible because Bugs
Bunny is a Warner Bros. character and would not be found at a Disney theme park. The
study shows that suggestive methods are indeed capable of leading to false beliefs or
memories.
Wade, Garry, Read and Lindsay (2002) used the Loftus and Pickerell (1995) "lost
in the mall" method but replaced narratives with photographs. The question was simply
whether showing subjects a doctored photograph (with no supporting narrative) would
lead them to remember a false experience. Each subject viewed four photographs. Three
were real childhood photos and one was fake, showing the subject taking a hot-air-
False memories 12
balloon ride. The doctored photos were created using Photoshop and an assortment of
childhood photos. Wade et al. "cut" the subjects and at least one family member out of
photographs and "pasted" them into a dummy photo of a hot-air-balloon ride. Family
members verified that the balloon ride never happened. After subjects reviewed each
photograph three times over a period of 2 weeks, 50% remembered something about the
ride. Often the reports were rich with detail and at the end of the study subjects tended to
express genuine astonishment when they learned the photographs were fake (Garry &
Genie, 2005).
In the lost-in-the-mall study, implantation of a false memory occurred when
another individual, usually a family member, claimed that the event happened.
Corroboration of an event by another person can be a powerful technique for instilling a
false memory. In fact, merely claiming to have seen a person do something can lead to a
false confession of wrongdoing (Loftus, 1997).
The ALT paradigm
One study that is frequently cited in the false memory literature is Kassin and
Kiechel's experiment (1996) which examined the role of social compliance in the
formation of false memories for a specific event. The researchers showed that
participants were likely to form false memories when accused of experiencing the event
by an associate witness. Participants were asked to type the letters they heard on a
computer, but were asked not to press the ALT key, which they were told was causing
problems. Unknown to the participants the computer was programmed to crash after a
minute of typing. A distraught experimenter accused the participant of ruining all his data
by pressing the ALT key. Half the participants were told by a research associate that they
False memories 13
had witnessed the participant press the ALT key prior to the computer crashing. The
remaining participants were not accused by an associate witness. Participants who were
accused of hitting the ALT key by an associate witness were more likely than those
participants not accused to sign a confession. Moreover they were also more likely to
internalize guilt and to confabulate details consistent with events. Internalization of guilt
and confabulation of details indicate that participants did not just comply with the
experimenter and admit to pressing the ALT key, but that they actually formed a memory
about the event.
Attempts to reduce or avoid the creation of false memories
The ease with which false memories can be generated highlights the need to
understand how they can be reduced or prevented. Previous research has addressed
whether warning participants about the nature of the DRM paradigm can reduce false
memory expression in that paradigm (Gallo, Roberts & Seamon, 1997; Gallo, Roediger
& McDermott, 2001).
Past research (e.g., Gallo, Roberts & Seamon, 1997; Westerberg & Marsolek,
2006) indicates that warning participants of this memory illusion in the DRM paradigm
can reduce false recognition of critical words. Westerberg and Marsolek (2006)
investigated the impact of instructional warnings given prior to reading the word list on
false recognition in the Deese-Roediger-McDermott (DRM) paradigm (Deese, 1959;
Roediger & McDermott, 1995). They used signal detection measures of memory
performance to find whether warnings specifically affect the processing of the critical
words. The results indicate that warnings do not improve the processing of critical words
False memories 14
in particular; rather warnings increase memory performance in general, across all word
types.
Gallo, Roberts and Seamon (1997) conducted a study to determine whether the
false recognition of critical lures in the DRM paradigm could be diminished or eliminated
by the use of forewarning instructions. Subjects were presented with an auditory tape
containing eight lists of 15 words presented in blocked fashion and instructed to
remember the words for a recognition memory test that would follow. The test was
composed of studied words, semantically-related nonstudied words (critical lures), and
unrelated nonstudied words. The independent variable was the foreknowledge of the false
memory effect. Three groups of 16 subjects received different instructions at study or
test. One group was uninformed about the false recognition affect, a second group was
urged to minimize all false alarm (cautions), and a third group was forewarned about
falsely recognizing critical lures (forewarned). Compared with the uninformed and
cautious subjects, the forewarned subjects reduced their false alarm rate for critical lures.
However, forewarning did not eliminate the false recognition effect; these subjects and
those in the other groups made numerous false recognitions in this task. The findings
suggest that inoculation by knowledge may achieve only limited success because
knowledgeable people can only partially control their susceptibility to remembering
events that never occurred. Furthermore, results suggest the DRM effect may possibly be
due to automatic processing.
Researchers have informed subjects about the nature of the false memory
phenomenon, even giving subjects a sample trial. In a study by McDermott and Roediger
(1998) subjects were informed about the false memory effect and then tested on
False memories 15
recognition when the critical items were sometimes present in the list and sometimes not.
Subjects who were informed about the nature of the false memory phenomenon and
instructed to attempt to avoid it become more cautious, reducing both their hit rates and
their false alarm rates.
Informing subjects about the nature of the effect and asking them to avoid false
recognition does not come close to eliminating the effect.
In summary, there is now ample evidence from multiple paradigms that people
can be led to believe that they experienced things that never happened. However, only
research within the framework of the DR1VI paradigm has tested whether warning
instructions have an effect on the avoidance or reduction of false memories. It is
imperative that further research is conducted within the framework of both the Loftus
paradigm and the ALT paradigm, as results of these studies are more likely to be
generalized to real life situations, for example eyewitness testimonies.
Research using the Loftus paradigm demonstrates that false memories can be
implanted deliberately, but does not indicate whether or not these memories have a long
lasting influence on behaviour, or, whether warning participants of the false memory
effect would reduce or avoid present distortions in memory. Similarly, Kassin and
Kiechel (1996) developed the ALT paradigm to demonstrate that corroboration of an
event by another person can be an influential technique for instilling a false memory.
Furthermore, false incriminating evidence can induce people to accept guilt for a crime
they did not commit and even to develop memories to support their guilty feelings.
Further research within this paradigm should focus on whether warning instructions will
effect the reduction or prevention of false memories.
False memories 16
Mental health professionals and others should be aware of how much they can
influence the recall of events and of the great need for maintaining restraint in situations
in which imagination is used as an aid in recovering presumably lost memories (Loftus,
1997). Finding which paradigm is most effective in studying the false memory
phenomenon and which is best for generalizing results to real life situations will help
researchers to further investigate the underlying processes of the creation of false
memories, as well as effective ways to reduce or avoid the creation of such memories.
False memories 17
References
Deese, J. (1959). On the prediction of occurrence of particular verbal intrusions in
immediate recall. Journal of Experimental Psychology, 58, 17-22.
Gallo, D.A., Roberts, M.J., & Seamon, J.G. (1997). Remembering words not presented in
lists: Can we avoid creating false memories? Psychonomic Bulletin and Review, 4,
271-276.
Gallo, D.A., Roediger, H.L. III, & McDermott, K.B. (2001). Associative false
recognition occurs without strategic criterion shifts. Psychonomic Bulletin and
Review, 8, 579-586.
Greene, E., & Loftus, E. (1984). Solving the eyewitness problem. Behavioral Sciences &
the Law, 2, 395-405.
Hyman, I.E., Jr., Husband, T.H., & Billings, J.F. (1995). False memories of childhood
experiences. Applied Cognitive Psychology, 9, 181-197.
Loftus, E. (1997). Creating false memories. Scientific American, 277, 1-7.
Loftus, E., & Pickerell, J. (1995). The formation of false memories. Psychiatric Annals,
25, 720-725.
Loftus, E. F., Miller, D. G. & Burns, H. J. (1978). Semantic integration of verbal
information into a visual memory. Human Learning and Memory, 4, 19-31
Neuschatz, J.S., Benoit, G.E., & Payne, D.G. (2003). Effective warnings in the DeeseRoediger-McDermott false-memory paradigm: The role of identifiability. Journal of
Experimental Psychology: Learning, Memory, and Cognition, 29, 35-41.
McDermott, K.B. (1997). Priming on perceptual implicit memory tests can be achieved
through presentation of associates. Psychonomic Bulletin and Review, 4, 582-586.
False memories 18
McDermott, K.B., & Roediger, H.L. III (1998). Attempting to avoid illusory memories:
Robust false recognition of associates persists under conditions of explicit warnings
and immediate testing. Journal of Memory and Language, 39, 508-520.
Roediger, H.L. III, & McDermott, K.B. (1995). Creating false memories: remembering
words not presented in lists. Journal of Experimental Psychology: Learning, Memory
and Cognition, 21, 803-814.
Roediger, H.L. III, & McDermott, K.B. (2000). Tricks of Memory. Current Directions in
Psychological Science, Department of Psychology, Washington University
Seamon, J., Luo, C., & Gallo, D. (1998). Creating false memories for words with or
without recognition of list items: Evidence for nonconscious proceses. Psychological
Science, 9, 20-26.
Tulving, E. (1985). How many memory systems are there? American Psychologist, 40,
385-398.
Westerberg, C.E., & Marsolek, C.J. (2006). Do instructional warnings reduce false
recognition? Applied Cognitive Psychology, 20, 97-114.
1
Running head: EYEWITNESS TESTIOMONY AND FALSE MEMORY
Eyewitness Testimony and False Memory:
Attempting to reduce false memories for events using the Loftus paradigm
Miranda L Trecroce
Algoma University College
Eyewitness testimony and false memory 2
Abstract
The purpose of this experiment was to investigate how warning instructions informing
participants about the false memory phenomena could reduce the recall of false memories
of an event. A total of 60 undergraduate students saw a 40 second video clip depicting an
auto-motorcycle accident. Participants received either neutral instructions or warning
instructions prior to watching the video clip. Later, participants were exposed to either
correct or misleading post-event infounation embedded in questions. Participants who
received misleading post-event information and warning instructions correctly recalled
more events than those who did not receive a warning. Results suggest that warning
instructions given prior to the encoding of an event to participants who received
misleading post-event information can help reduce the occurrence of false memories.
Further, warnings given to participants who received correct post-event information
resulted in an increase in false recall.
Eyewitness testimony and false memory 3
Eyewitness Testimony and False Memory:
Attempting to reduce false memories in the Loftus paradigm
The eyewitness plays a crucial role in a large number of court cases, particularly
robberies and rapes. In these cases, identification of a suspect by an eyewitness, or other
personal testimony about an event, often provides an important piece of evidence on
which a prosecution is based. Faulty eyewitness testimony is a major source of wrongful
convictions (Greene & Loftus, 1984). Jurors have been known to accept eyewitness
testimony pointing to guilt even when it is far outweighed by evidence of innocence
(Loftus, 1979).Wells and his colleagues (1978) concluded that eyewitness testimony is
likely to be believed by jurors, especially when it is offered with a high level of
confidence, even though the accuracy of an eyewitness and the confidence of that witness
may not be related to one another at all. The evidence points rather noticeably to the
conclusion that there is almost nothing more convincing than a live human being who
takes the witness stand, points the finger at the defendant, and says "That's the one!"
(Loftus,1979).
There are questions about the validity of criminal convictions that are based
largely on the testimony of victims or witnesses (Loftus, 2003). When a witness
perceives a complex event, a number of factors, such as the exposure time, or the
witness's prior expectations, will affect the accuracy of what is perceived and stored in
memory. To further complicate the problem, once the material has already been encoded,
further changes can take place. Many influences can cause memories to change or even
be created anew, including our imaginations and the leading questions or different
Eyewitness testimony and false memory 4
recollections of others. The time between a complex experience and a witness's
recollection of that experience is a crucial period.
False Memories
A wealth of past research indicates that human memory is prone to distortions
(e.g., Deese, 1959; Roediger & McDermott, 1995; Loftus & Palmer, 1974). The ability to
create a false memory has been demonstrated in various experiments with participants
who come to remember an event which has never actually occurred (Loftus, 1997).
Evidence from the false memory literature indicates that questioning techniques used on
participants can influence their memories. Similar experiences might occur to
eyewitnesses based on police questioning techniques (Greene & Loftus, 1984).
Paradigms for False Memories
A false memory can be operationally defined as a memory or memories for an
event which has never occurred. There are different types of false memories explored in
the laboratory, with different experimental techniques used to induce them. Two
particularly interesting paradigms are the Deese-Roediger-McDermott (DRM) (1995)
paradigm and the Loftus paradigm (1974). The DRM paradigm produces the formation of
false memory for words, while the Loftus paradigm produces false memories of objects
or events.
The Deese-Roediger-McDermott (DRM) paradigm
The DRM paradigm is a common and useful technique for studying false
memories in a controlled laboratory setting (Deese, 1959). This paradigm shows that
when participants study lists of words, they often falsely report recognizing a never
presented associate word as appearing in the list. In the original version of this paradigm,
Eyewitness testimony and false memory 5
participants are presented with lists of thematically 'related' words (e.g., bed, rest, awake)
that are all associated with a 'critical' nonpresented (CNP) item (e.g., sleep) that is
actually not presented. In the recognition version of this paradigm, participants are
subsequently given an old/new recognition test, which includes a subset of the presented
related words and the nonpresented critical words. Typically, memory performance is
measured by calculating the hit rate for the related words and the false-alarm rate for the
critical words. Participants are asked whether they "know" (are confident that the word
was presented but do not remember the actual presentation) or "remember" (are confident
the word was presented and remember something about the actual presentation) that the
never presented word was on the list. In this particular paradigm, participants have a
memory for a certain word which they think they have heard, although in reality, the
word has not been presented (Gallo, Roediger & McDermott, 2001). The ease with which
false memories can be generated highlights the need to understand how they can be
prevented.
Warning participants about the nature of the DRM paradigm can reduce false
recognition of critical words in that paradigm (Gallo, Roberts & Seamon, 1997; Gallo,
Roediger, & McDermott, 2001).Gallo, Roberts and Seamon (1997) conducted a study to
detemtine whether the false recognition of critical lures in the DRM paradigm could be
diminished or eliminated by the use of forewarning instructions. They presented
participants with an auditory tape containing eight lists of 15 words presented in blocked
fashion and instructed the participants to remember the words for a recognition memory
test that would follow. The test was composed of studied words, semantically-related
nonstudied words (critical lures), and unrelated nonstudied words. The independent
Eyewitness testimony and false memory 6
variable was foreknowledge of the false memory effect. Three groups of 16 subjects
received different instructions at the study or test phase. One group was uninformed
about the false recognition effect, a second group (cautions) was urged to minimize all
false alarms, and a third group was forewarned about falsely recognizing critical lures.
Compared with the uninformed and cautious subjects, the forewarned subjects reduced
their false alarm rate for critical lures; however forewarning did not eliminate the false
recognition effect; these subjects and those in the other groups made numerous false
recognitions in this task. The findings suggest that inoculation by knowledge may
achieve only limited success because knowledgeable people can only partially control
their susceptibility to remembering events that never occurred.
The DRM paradigm has been widely recognized as an excellent way to produce
false memories in a laboratory setting without creating a stressful situation for the
participant, as well as excluding other confounds present in other false memory tasks
such as social demand and compliance. Roediger and McDermott (1995) argue that false
memories for words may have similar mechanisms as those that underlie the formation of
false memories for perceiving actual events.
Memory for perceiving events has been considered an important research topic
because of its forensic applications concerning eyewitness testimony. Loftus and
Pickerell (1995) have demonstrated that people can come to believe they were witness to
entire events which actually never occurred. This happens most frequently through
misleading post-event information which alters people's memory.
Often after witnesses have perceived an important event, they are exposed to new
information about it. Evidence has accumulated to indicate that post-event experiences
Eyewitness testimony and false memory 7
such as exposure to newly released information can dramatically affect the memory of
the original event. Post-event information can enhance existing memories but it can also
change a witness's memory in a powerful way. Misleading post-event information can
alter a person's recollection, even leading to the creation of false memories by
incorporating objects and events that never in fact existed into a previously acquired
memory.
Examples of the effects of misleading post event information come from early
research (Loftus & Palmer, 1974; Loftus, Miller & Bums, 1978). Researchers have
developed innovative paradigms to examine the malleability of human memory. For
example, Loftus and Pickerell (1995) showed that after receiving misleading information
29% of participants came to believe that they were lost in a shopping mall at the age of 5.
Hyman, Husband, and Billings (1995) showed that 20% of participants in their study
came to believe an event (such as a hospital visit) had occurred in their childhood when,
in fact, the event had never occurred.
The Loftus paradigm
Elizabeth Loftus' basic procedure consists of three phases: In Phase 1, subjects
view an event; in Phase 2, they receive verbal infaurration about the event (with or
without misleading suggestions about certain "critical" details); in Phase 3, they take a
memory test that includes questions about the critical details (Loftus & Greene, 1984).
A classic experiment by Loftus and her colleagues (1978) demonstrates how
nonexistent objects can be introduced into people's recollections. Nearly two hundred
participants viewed a series of thirty color slides depicting successive stages in an
automobile-pedestrian accident. The automobile was a red Datsun shown travelling along
Eyewitness testimony and false memory 8
a side street toward an intersection. The intersection was shown to have a stop sign for
half of the participants and a yield sign for the remaining participants. The Datsun
became involved in an accident with a pedestrian. Immediately after viewing the slides,
the subjects were asked some questions, one of which was critical. For about half of the
participants the critical question asked was, "Did another car pass the red Datsun while it
was stopped at the stop sign?" The remaining participants were asked the same question
with the words "stop sign" replaced by "yield sign". For half of the participants, the sign
mentioned in the question was the sign that had actually been seen; therefore the question
gave them consistent information. For the remaining subjects, the question contained the
sign that had not been seen (misleading information).
After completing a twenty-minute filler activity a recognition test was
administered. Pairs of slides were presented to the participants and they had to indicate
which member of each pair they had seen before. The critical pair was a slide depicting
the Datsun stopped at a stop sign and a nearly identical slide depicting the Datsun at a
yield sign.
The results indicated that when the intervening question contained consistent
information, 75 percent of participants accurately responded. When the question
contained misleading information, only 41 percent of the participants accurately
responded. If the participants had been simply guessing, they would have been correct
about half the time, so the misleading question reduced their accuracy below that which
would have been expected if they had been merely guessing.
After a witness experiences a complex event, he or she may be exposed to new
information about that event. The new information may come in the powerful form of
Eyewitness testimony and false memory 9
questions or in the form of a conversation, a newspaper story, etc. The implication of
these results for courtroom examinations, police interrogations and accident
investigations is fairly obvious: interrogators should do whatever possible to avoid the
introduction of any external information into the witness's memory (Loftus, 1997).
Present Study
Previous experiments have demonstrated that when participants are warned about
the false memory effect before the encoding phase in the DRM paradigm, the ability to
differentiate old and new critical words improves (Gallo et al., 1997, 2001; McDermott &
Roediger, 1998; Neuschatz et al., 2003). Though these results are useful in demonstrating
the effect of warnings on reducing false memories, the DRM paradigm creates an
artificial lab setting that can't be generalized to real-life eyewitness situations.
To my knowledge, no experimental studies have been done with instructional
warnings to reduce the effect of false memories for events, for example, by implementing
warnings in the Loftus paradigm. If warnings can improve the recall of accurate
memories in a word list, can they also improve the recall of memories for an actual event?
More specifically, will warning witnesses about the power of suggestive questioning and
the effect of such misinformation on memory help them to reduce or avoid making false
memories of an event?
The goal of the present investigation was to deteinfine whether warning
instructions are effective measures to reduce false memories for events by using the
Loftus paradigm. The main prediction is that warning instructions given to participants in
the misleading information condition will increase the accurate recall of that event. A
second outcome to consider is whether warning instructions will have the opposite effect
Eyewitness testimony and false memory 10
for the condition receiving correct post-event information and a warning, that is, whether
warning instructions in the correct post-event information condition will decrease
participants' correct recall. It is expected that the participants in the misleading
information condition receiving the warning instruction would have a higher number of
hits and a lower number of false alarms for the critical items (those items containing
misleading information).
Method
Participants
Sixty undergraduate students who were enrolled in a degree program at Algoma
University College, ranging from ages 18-24, volunteered to participate in this
experiment. Participants were randomly assigned to the warning condition or to the no
warning condition and to one of two post-event information conditions, either receiving
consistent or inconsistent post-event information in the form of suggestive questioning
(15 in the misleading information and warning condition, 15 in the misleading
information and no warning condition, 15 in the correct information and warning
condition, and 15 in the correct information and no warning condition).
Design
A 2 (instruction condition: warning, no warning) X 2 (post-event information: correct,
misleading) factorial design was used.
Materials and Procedure
Upon arrival the participants were told that they were taking part in an honours thesis
study, but were not informed of the goal of the study. All participants signed a consent
form and were assured of complete confidentiality and the right to withdrawal from the
Eyewitness testimony and false memory 11
study at any time. Participants were randomly assigned to one of four groups. The
experiment consisted of an encoding phase (presentation of the video with instructions)
immediately followed by a test phase. Prior to the encoding phase, one-half of
participants (no warning condition) were simply told to pay close attention to the events
in the video segment that was going to be presented because their memory and
confidence in these memories would be tested later. The other half of participants in the
warning condition were given similar instructions regarding the procedure but were also
told the following:
When one witnesses an important event, such as a crime or accident, one may be exposed
to subsequent information that can influence the memory of that event. For example, in a
previous study, participants saw films of complex fast-moving events such as automobile
accidents. Immediately afterward, the subjects were asked a series of questions, some
presenting misleading information by suggesting the existence of an object that did not
exist in the original scene. For example, the participant might have been asked, "How fast
was the car going when it ran the stop sign?" when a stop sign did not actually exist in
the scene. It was found that such questions increased the likelihood that subjects would
later report having seen these objects. The information from these misleading questions
became integrated into one's memory of the event, thereby causing an alteration of the
actual information stored in memory.
After participants read all instructions, the experimenter played the video clip.
The video clip was approximately forty seconds in length and depicted an automotorcycle accident in which a white car, while turning into a gas station, is struck by an
oncoming motorcycle. The clip was found on the website www.cbaumsworld.com .
Following the presentation of the video segment, the participants filled out a 12item questionnaire containing questions about details from the video clip. For the
Eyewitness testimony and false memory 12
participants in the correct post-event information condition, all questions contained
infon iation consistent with what occurred in the video. For the remaining half of
participants in the misleading post-event information condition, 2 out of the 12 questions
contained inconsistent or misleading information about the scene in the video segment.
The first misleading question, Question 6 was "Did you see the third witness run over to
the accident?" when in fact there were only two witnesses present in the video. The
second misleading question, Question 11 asked "Was there an empty trashcan beside the
man pumping gas?" There was no man in the video clip and no one pumping gas. Each
question was accompanied by a confidence rating scale with the numbers one through 3
(1 for certain, 2 for intermediate levels of confidence and 3 for guess). The participants
were instructed to make a certain or guess judgment for each recognized scene by
circling a number from 1 to 3 on their answer sheets. The participants were told to circle
1 if they were certain of the memory; they had a conscious recollection of the scene from
the video, such as the way the scene was presented or what they were thinking about at
the time, or 3 if they were not confident in remembering the scene, but they could not
recollect its actual occurrence or any related details. The participant was told to circle 2 if
they were unsure of the memory.
After completing the questionnaire, the participants participated in a 15-min filler
activity that required them to read an unrelated passage and answer questions about it.
The passage was approximately one page in length and was followed by six multiple
choice questions. Finally, a forced-choice recognition test consisting of 10 statements
was administered. Each statement included 2 scenarios: one scenario that was included in
Eyewitness testimony and false memory 13
the video (old) and one that was not (new). The critical pair of statements was the same
scenario depicted in the misleading questions. Item #3 presented the choice between:
There were two witnesses at the gas station when the accident occurred.
There were three witnesses at the gas station when the accident occurred.
The second pair of statements was related to the misleading post-event information from
Question 11 of the first questionnaire. Item #5 presented participants with the choice
between:
There was a man pumping gas at the time the accident occurred.
There was no one pumping gas at the time the accident occurred.
Participants were to choose the statement that corresponded with what they had seen
earlier in the video and also to rate their confidence on the same scale used in the first
questionnaire.
Analysis
For each participant, the correct responses of the critical items (those items
containing misleading information) were measured as a hit. The incorrect responses were
measured as a false alarm, or false memory. The participants' correct recall on the critical
items, #3 and #5 on the forced-choice recognition test, were examined both separately
and together and compared among the four different conditions. The mean confidence
rating for both critical items was also calculated for each participant.
The criterion for statistical significance was set at p <.05 for all analyses.
Results
Correct Recall on Forced-choice Recognition Test
Item #3. Of the 60 participants who completed the forced-choice recognition test,
53 chose the correct statement; 7 chose the incorrect statement. Accuracy depended on
Eyewitness testimony and false memory 14
whether the participant had been given correct or misleading post-event information on
the initial questionnaire This relationship can be seen in Table 1. Participants who
received misleading post-event information and a warning were less confident in their
response (M = 1.60) than participants who received misleading post-event information
and no warning (M= 1.13). Participants who received correct post-event information and
a warning were slightly less confident (M= 1.40) in their response than participants who
received correct post-event information and no warning (M= 1.53).
Table 1. Number of Hits and Mean Confidence Rating for Item #3
Post-event information
Warning
Instruction
No Warning
Hits
Confidence (M)
Hits Confidence (M)
Correct
14
1.40
14
1.53
Misleading
14
1.60
11
1.13
Note: n = 15 in each cell
Item #5. For Item #5 on the forced-choice recognition test, 32 out of the 60
participants chose the correct statement; 28 chose the incorrect statement. As with Item
#3, accuracy depended on whether the participant had been given correct or misleading
post-event infolination. Results for Item #5 are shown in Table 2. Participants who
received correct post-event information and a warning (M = 2.07) were slightly less
confident than those participants who did not receive a warning (M =2.13). Those
participants who received misleading post-event information were more confident than
those who received correct post-event information. Participants who received misleading
Eyewitness testimony and false memory 15
post-event information and a warning (M= 1.67) were slightly more confident than those
who did not receive a warning (A 1 = 1.87).
Table 2. Number of Hits and Mean Confidence Rating for Item #5
Instruction
Warning
No Warning
Post-event information
Hits
Confidence (M)
Correct
7
2.07
9
2.13
Misleading
10
1.67
6
1.87
Hits
Confidence (M)
Note: n = 15 in each cell
Both critical items, #3 and #5, were examined together to measure the mean hit
rate. A 2 (instruction: no warning, warning) X 2 (information: correct, misleading)
univariate analysis of variance (ANOVA) was performed. A statistically significant
interaction was found, F (1, 56) = 4.050,p =.049, for type of post-event information and
instruction (warning, no warning)
The mean hit rate for participants who received misleading information and a
warning (M=1.60) was greater than the mean hit rate for participants who received
misleading information and no warning (M=1.13). For those participants in the correct
post-event information condition, those who received a warning had a lower mean hit rate
(M= 1.40) than those who did not receive a warning (M= 1.53). These results are shown
in Table 3.
Eyewitness testimony and false memory 16
Table 3. Mean Hit Rates for Critical Items
Post-event information
Warning
Instruction
No warning
Correct
M= 1.40
M= 1.53
Misleading
M= 1.60
M= 1.13
SD = .507
SD = .507
SD = .516
SD = .743
Note: n = 15 in each cell
Discussion
The goal of this experiment was to determine whether warning participants of the
false memory phenomenon would result in a reduction in the rate of false recognitions.
To examine this issue, the mean percentage of hits (correct recall) was examined between
participants who received either correct or misleading post-event information and either a
warning instruction or neutral instruction. As predicted, the act of warning participants in
the misleading information condition reduced the false-memory effect, compared with
participants in the misleading information condition who did not receive a warning.
Overall, the mean hit rate for the half of the participants in the warning condition
(M=1.50) was greater than the mean hit rate for the half of the participants in the no
warning condition (M=1.33). There were no main effects found in the data that were
statistically significant however there was an interaction for the independent variables:
instruction (warning, no warning) and post-event information (consistent, misleading)
information.
The predicted hypothesis was shown to be correct; warning instructions in the
misleading condition did increase accuracy by reducing false memories. The accuracy
Eyewitness testimony and false memory 17
mean was higher for the participants in the misleading information condition who
received the warning instruction than for those in the misleading information condition
who did not receive a warning
The second part of the hypothesis, which predicted that warning instructions in
the correct information condition will decrease accuracy by increasing false memories
also proved to be true. The group of participants who received correct information and a
warning (M = 1.40) had a lower accuracy mean on the recognition test than the group
receiving misleading information and a warning (M = 1.60). Therefore these findings
present somewhat of a cost and benefit dilemma. Obviously, the benefit of warning
participants in the presence of misleading information is the higher accuracy of correct
recall. The cost, however, is the reduced accuracy as a result of a warning when postevent information is correct, or consistent.
Results from the present experiment confirmed that misleading post-event
information can produce false recall of an event and demonstrated that providing a
witness with a warning about false recall can: (a) reduce false recall when post-event
information is misleading, and (b) reduce correct recall when post-event information is
correct. A possible explanation for the reduction of false recall when post-event
information is misleading is that the warning made the participants aware of suggestive
questions and their ability to discriminate such questions and ignore the false information.
Thus, those participants who received a warning were able to retain their original
memory of the event, without incorporating false post-event information into the memory,
resulting in more accurate recall of the event. As for the participants in the correct postevent information condition that received a warning, the warning may have made the
Eyewitness testimony and false memory 18
participants overly cautious when choosing a response on the forced-choice recognition
test. The warning may have had the opposite effect than was intended because it may
have primed participants to believe that the post-event information they received was
false, thus causing the participants to second guess themselves or doubt the infoimation
that was embedded in the questions.
Future Research
There are several improvements that could be made for future research in the
investigation of reducing false memories. The present experiment examined the effect of
warning instructions on recall only when the warning instructions were given to
participants prior to the encoding of an event. Future research should investigate the
effects of similar warning instructions when given to participants following the encoding
of a witnessed event. These findings may be better generalized to real-life situations, as
witnesses can not always be warned of the dangers of misleading post-event information
and false memories prior to observing a crime or accident. It would be both interesting
and of much benefit to the criminal justice system to examine whether warnings given to
witnesses immediately after observing an event would have the same effect as when
given prior to observing an event.
In order to create more of a real-life situation in an experimental setting, it would
be useful to stage an actual event instead of using a video clip to show an event. This
would make the situation more realistic and may have more of an impact on those who
are witness to the event. Also, in future research, it may be beneficial to include more
than one measure of memory.
Eyewitness testimony and false memory 19
Results from the present experiment indicate a strong trend in the right direction.
A similar study conducted with a larger sample of participants may yield results of
statistical significance.
General Discussion
Previous experiments have demonstrated that when participants are warned about
the false memory effect before the encoding phase in the DRM paradigm, the ability to
differentiate old and new critical words improves (Gallo et al., 1997; McDermott &
Roediger, 1998; Neuschatz, Benoit & Payne, 2003). However, no previous studies have
investigated the use of warning instructions in the Loftus paradigm. The goal of the
present investigation was to determine whether warnings given to participants prior to
witnessing an event would increase memory performance by reducing false recall of the
event. To conclude, there were two main findings in this experiment. First, the results
indicate that warnings do reduce the false recall of an event when participants are given
misleading information. Second, providing a witness with a warning about false
memories can reduce correct recall when the post-event information is correct.
The present findings have implications concerning the accuracy of memory in
everyday life, specifically to eyewitness testimony. First, they suggest that warning
people of the dangers of false recognition and the false memory phenomenon can be
effective at reducing false alarms. For example, consider a witness to a robbery who is
asked to identify the thief in a line-up, or recall important details from the event. The
witness will most likely have encountered some sort of post-event information from the
event, whether it is correct or misleading, and therefore may have an altered memory of
the actual witnessed event. Without being warned about false post-event infoimation,
Eyewitness testimony and false memory 20
there is a high likelihood that the witness may incorrectly identify an innocent individual
from the line up, or falsely recall details from the event. However, in a situation in which
the post-event information is correct, a witness may doubt the information or become
overly cautious to such information, thus creating an inaccurate account of the event.
This can be a major problem in our justice system which operates on the principle that it
is better to let 10 guilty persons go free than to convict one innocent person. Therefore, in
following this important principle, in actual eyewitness situations in the real-world,
warning witnesses may have more of a negative effect than a positive effect on the
accuracy of recall.
Eyewitness testimony and false memory 21
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