How can postevent information influence mem-
ory? Take the example of eyewitnesses who observe a
convenience store robbery. From their observations,
they construct a memory for what transpired during
the robbery. Most of the time, it is this memory that
police officers want to examine. However, virtually all
eyewitnesses to crimes who eventually testify in court
are interviewed by police officers at least once and
typically multiple times. In police interviews, the eye-
witness is questioned about what happened, and if the
investigating officer has specific suspicions about
what occurred, the interview may include some lead-
ing questions (e.g., “Was it a white four-door sedan?”
“Was he or she wearing athletic clothing?” “Was he or
she carrying anything?” “May he or she have had a
gun in his or her hand that was in his or her jacket
pocket?”). Questioning such as this presents one
source of postevent information. Another source of
postevent information is self-generation; that is, the
eyewitness may introduce new information by just
thinking about or talking about the robbery. Either
way, the postevent information affects one’s memory
of the original observed event, and over time, individ-
uals become less able to differentiate between the
information that is in their memory because it was
actually observed and the information that was intro-
duced after the event by postevent information.
Most of the time, the influence of postevent infor-
mation is minimal and inconsequential. However, in
the case of an eyewitness to a crime, when it is impor-
tant to know exactly what transpired, postevent infor-
mation may be an important source of memory error.
For this reason, the distortion in memory that results
from postevent information is often referred to as the
misinformation effect.Research on the Effect of
Postevent Information
There is a great deal of research on the effect of
postevent information, much of it spawned from the
early work of Elizabeth Loftus. In a typical experi-
ment on this topic, participants first view a sequence
of slides, a videotape, or a film of an event. After
viewing this event, they read a narrative or are asked
some questions that intentionally mislead them about
the identity of a small set of target items viewed in the
original event (the misled condition), or they do not
receive the misleading information (the control condi-
tion). The principal result is that the participants are
more accurate recognizing the original target item inthe control condition than in the misled condition; that
is, they are misled by the postevent information pre-
sented in the narrative or questions.
In a related paradigm for studying the effect of
postevent information, Elizabeth Loftus had individu-
als view a video of a traffic accident. They were sub-
sequently asked questions regarding how fast the cars
were traveling prior to the accident. Whereas individ-
uals who were asked, “About how fast were the two
cars going when they hit each other?” provided a
mean response of 34 mph, individuals asked, “About
how fast were the two cars going when they smashed
each other?” responded with a mean speed of 40.8 mph.
Surprisingly, the wording of this question—the
postevent information—also affected their memory of
the car accident more generally. One week later these
individuals were questioned again. When asked
whether they had seen broken glass in the film,
whereas 34% of the individuals who had received the
question, including the word smashed, indicated hav-
ing seen broken glass in the film, only 14% of those
who received the hitquestion reported remembering
broken glass. The impact of postevent information is
thus not limited to immediate questioning but can
have long-term consequences as well.Cognitive Interpretations of the
Effect of Postevent Information
There are several explanations for how postevent
information influences memory, and there is evidence
that the cognitive mechanisms underlying each of
these explanations play some role in the misinforma-
tion effect. Take for an example Elizabeth Loftus’s
now classic study in which participants viewed a car
approaching an intersection with a stop sign.In the
misled condition, the sign was later suggested to be a
yield sign (“Did another car pass the red Datsun while
it was stopped at the yield sign?”). In a subsequent
test, individuals were less likely to recognize the stop
sign if they had been in the misled condition. One
interpretation of this result is that the postevent infor-
mation impairs memory of the observed event. That
is, being presented the yield signliterally degrades
and replaces memory of the observed stop sign. A sec-
ond interpretation of the misinformation effect is that
the original information (stop sign) and the suggested
information (yield sign) are both present in memory,
but individuals make what Marcia Johnson calls a source-
monitoring error and confuse what was seen with what
was subsequently suggested. A third interpretation of608 ———Postevent Information and Eyewitness MemoryP-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 608