Refers to any information
that arrives after an event
that may affect or distort
an eye-witness' memory
of what happened.
As memory is suggested to be
reconstructive, the recall of events
such as crime may be based more on
schemas, rather than what actually
happened. Post-event information may
influence and change these schemas,
distorting the accuracy of the recall of
the event.
Gabbert et al found that when post-event discussion was
encouraged after everyone was shown a different video of
the same crime, a large majority of participants referred to
details that they must have picked up as part of discussion.
People in the non-discussion control group did not report
any information that they would not have seen in their
video. This supports the idea that post-event information,
such as through discussion, can lead to more inaccurate
EWT.
Leading questions
Leading questions are a form
of post-event information and
trigger schemas through the
way in which questions are
phrased when the witness is
asked to recall the event.
Leading questions are phrased in
a way to lead the witness to
answer the question in a specific
way. This may lead to the witness
recalling the event inaccurately as
they access the information
provided in the leading question,
rather than what they remember.
The effect of leading questions on EWT has been demonstrated in
lab conditions. Loftus and Palmer found that using more violent
verbs like "smashed" in questions relating to a video of a car crash
participants saw, resulted in higher estimated speeds than when
gentler verbs like "contacted" were used. Furthermore, when
"smashed" was used, more participants reported seeing glass in the
video than when "hit" was used, despite there being no glass in the
original clip. This supports the idea that leading questions has a
significant effect on the recall of events, and therefor may lead to
EWT being unreliable.
The influence of anxiety
Experiencing a dramatic or
traumatic event is likely
going to be stressful for the
witness, and this may affect
their ability to recall the
events witnessed.
Deffenbacher concluded that
moderate levels of stress are
actually beneficial to memory.
However, if an eye witness'
anxiety continues to rise and
becomes too extreme, there
may be a decline in recall.
Real-life evidence from real crimes, however, does not support
the idea that leading questions or anxiety/weapon focus has
an effect on recall. Yuille and Cutshall interviewed witnesses
of a real-life shooting. They produces accurate recall of the
events despite the researchers using two leading questions
and extremely high levels of self-reported anxiety at the time
of the event. This suggests that the effect of leading questions
and anxiety levels may be less pronounced when applied to
real-life events.
Weapon focus
Anxiety may be 'pushed over the
edge' due to weapon focus. In violent
crimes, such as when the perpetrator
is carrying a weapon, it is suggested
that our natural response is to zoom
in on the weapon as the main source
of stress.
Weapon focus may mean that
the eye witness' recall of other
important details of the event,
such as the perpetrator's
appearance and clothing, may
have been forgotten or
misremembered.
Weapon focus is explained by
'tunnel theory', which
suggests that noticing a
weapon produces a form of
selective attention which
ignores any other competing
bits of information.
The influence of weapon focus on recall is supported
by experimental evidence. Johnson and Scott found
that the group who witnessed a man emerging with
a bloodied knife did not correctly recall the man
holding the knife as much as the other group who
saw the man emerging with greasy hands and a pen.
This supports the idea that our attention is drawn to
weapons and away from other peripheral details.
However, Pickel found a similar effect to
weapon focus when a man pulled out a raw
chicken rather than his wallet to pay a
cashier in the shop. This suggests that
'weapon focus' is more about the
unusualness of the situation and surprise
rather than the anxiety levels.
Application to court cases
Research into EWT caused changes in the legal system. For
example, leading questions are no longer allowed to be used
in court in order to try and avoid inaccurate EWT and potential
miscarriages of justice. This suggests that research into the
fallibility of human memory is useful in reducing the risk of
miscarriages of justice in the legal system.