Learning and Teaching Unit
Paterson, Helen 2004, Co-witnesses and effects of discussion on eyewitness memory, PhD thesis, University of New South Wales, Psychology department.
Problem/issue: The legal system assumes that the testimony given by eyewitnesses is independent, but this is frequently not the case. Co-witness discussion of a crime could influence memory accuracy introducing the possibility of miscarriages of justice.
Field of literature: Legal psychology
'Gap' in the literature: There is little literature on the prevalence of eye witness discussion and its effects on memory. What has been written utilises varied methodologies and there are inconclusive findings. The concept of memory conformity within social and cognitive theory might explain the effects of co-witness discussion on memory, but this has never been investigated empirically.
Question: What are the effects of co-witness discussion on the accuracy and completeness of eyewitness memory?
Background (chapter 2): Outlines memory conformity theory
Chapter 3: Witnesses talk
Gap in the literature: Although there are numerous anecdotal
instances of co-witness discussion, there have been few studies which measure
the incidence of co-witness discussion related to serious crimes.
Method: A survey of 773 undergraduate psychology students was conducted
to determine the extent to which co-witness discussion of serious crime occurs.
Results: The results showed that the incidence of co-witness discussion
among those who had witnessed a serious crime was as high as 80%.
Discussion: Eyewitness discussion is common.
Chapter 4: The legal perspective
Gap in the literature: Although courts prefer witnesses not to
discuss the events with one another, it is unclear whether this is prevented in
practice.
Method: A survey of 145 police officers was conducted to determine the
extent to which co-witness discussion occurs, and the awareness and perception
of police towards co-witness discussion.
Results: The results show that there is no formal police policy regarding
co-witness discussion. Police officers often attempt to prevent co-witness
discussion
because they believe it could negatively affect accurate recall. However police
also report that they are unable to prevent co-witness discussion before they arrive at a crime scene.
Discussion: Eyewitness discussion is common despite the
preference of the courts and the police to prevent it.
Chapter 5: Co-witness contamination
Gap in the literature: Many studies on the impact of co-witness
contamination of memory compare the memories of persons who did not discuss a
crime event with the memories of persons in groups with
experimental confederates who attempt to induce false information about a crime
event. This is methodologically problematic
because it is not clear whether the comparable memory accuracy of the former
group is due to the lack of discussion, or the lack of misleading information
being induced by confederates. There are no studies which compare discussion
groups without a confederate and discussion groups where a confederate induces
false information.
Method: In order to compare the impact of co-witness contamination upon
memory the study 171 undergraduate students from the
University of New South Wales were shown a crime video and then asked to discuss
the video in groups (some of which received experimentally induced
misinformation from a co-witness and some of which did not). Following the
discussion, participants were asked to give their individual accounts of what
happened.
Results: Witnesses regularly reported misinformation introduced by a confederate when
interviewed later.
Discussion: The results support the hypothesis that witnesses will
incorporate misinformation into their own accounts of a crime.
Chapter 6: Ways of encountering post event information
Gap in the literature: While there is significant evidence that post
event information such as media and leading police questions influence event
recall, it is unclear what effect co-witness discussion has upon event recall.
It would be unwise to generalise from media and police information effects given
that co-witnesses are not accorded the same authority. There are no studies
which compare the relative effects of media, police and co-witness discussion
upon memory accuracy.
Method: In order to compare the relative effects of media, police and
co-witness discussion upon memory, 105 undergraduate psychology students were shown
a crime video and then exposed to one of four different types of post event
information. The four types of post event information included 1) media, 2)
leading questions, 3) indirect co-witness information and 4) co-witness discussion.
A fifth control group received no post event information. Following this, participants were asked to give their individual
accounts of what happened and were asked how confident they felt about the
information.
Results: Tests for memory recall and participant responses on confidence
in the accuracy of memory recall, suggest lower accuracy and higher confidence
for co-witness information, whether directly or indirectly introduced, than for
post event media or police information.
Discussion: Co-witness information and discussion has a more powerful
effect on memory recall than other post event sources such as media and leading
police questions.
Chapter 7: Unintentional hearsay
Gap in the literature: There is some evidence to suggest that
witnesses confuse post event information supplied by an outside source with
their 'memory' of an event. However studies have not tested the impact of
time delay on memory distortion, and are based on photographs and non
naturalistic conversation. The current study tests long term memory distortion
following viewing of a realistic crime video within naturalistic discussion settings.
Method: Three experimental groups were shown two slightly different crime
videos. One group comprised subjects who watched the same video. In the second
group half the subjects had seen either video A or video B. A third
control group were shown either video A or B but asked to record what they had seen without discussion.
Prior to discussion the groups were given either a specific warning, in which
they were told that some group members may have seen a different version of the
crime, or a general warning in which participants were told to disregard what
group members told them and rely on their own memory. Following general recall,
participants were asked to complete a questionnaire that recorded differences
between memories of the two videos as well as similarities. They were also asked
to identify the criminal in a line up. The questionnaire asked respondents to
make a distinction between what they remembered and what they believed to be
true.
Results:
Discussion: Although, co-witness discussion influences what people felt
they 'knew' about a crime, the distinction between memory and known information
or information gleaned from outside source remained clear.
Chapter 8: Source monitoring
Gap in the literature:
Method:
Results:
Discussion:
Chapter 9: Eyewitness interview
Gap in the literature:
Method:
Results:
Discussion:
Co-witness information has a negative effect on the accuracy and completeness of memory.
Last sentence: 'By employing a number of methodological refinements, the research presented in this thesis advances our understanding of the impact of co-witness discussion on individual testimony within a forensically relevant context'.
