When you remember a past event,
you are not just playing back a video or audio file of a previous
encounter. Instead, memories are
reconstructed. That means that many
sources of information can be combined to influence what you remember about the
past.
Most of the time, of course, that
is a good thing. When you are having a
discussion about World War II, for example, it does not matter if the
information about the war that you talk about came from a single lecture you
attended or from years of classes and books you read. What is important is just that the
information is organized around the topic of discussion.
Of course, the specific events and
the order of those events do matter a lot in eyewitness situations. However, quite a bit of research demonstrates
that eyewitness accounts are also reconstructed, and the means that information
encountered after the initial event can influence later memory.
Does the amount of sleep you get
affect how likely it is that you will mix together different sources of
information when thinking about an eyewitness event? This question was explored in a paper by
Steven Frenda, Lawrence Patihis, Elizabeth Loftus, Holly Lewis, and Kimberly
Fenn in the September, 2014 issue of Psychological Science.
They used a typical misinformation
procedure in this study. First,
participants saw a sequence of photographs of two crimes (a car break-in and a
thief stealing a woman’s wallet). At some point after seeing the photo
sequences, participants read text stories that described the events in the
photographs. However, three of the facts
in the story differed from what was shown in the photos. For example, a photo might show the thief
putting the stolen wallet in a jacket pocket, while the story might describe
him putting it in his pants pocket. About
20 minutes after reading the text, participants then got a test about the
event. The critical questions on this
test focused on the misinformation parts of the event. The key measure is whether participants
recall what happened in the photograph or whether they use the information from
the text of the story to answer the question.
For each question on the test, participants were also asked the reason
for their response. The strictest
measure of a false memory is when participants choose the information they read
in the story, but tell state that they saw it in the picture.
To explore the influence of sleep
deprivation, some participants were kept awake for a full night, while others
were allowed to sleep as much as they wanted. Half the participants saw the pictures in the
morning followed by the stories with the misinformation about 40 minutes
later. The other half the participants
saw the pictures followed by the misinformation in the morning.
When participants see the pictures
in the morning and then the misinformation soon after, sleep deprivation
influences their tendency to have false memories. The sleep deprived participants remember more
of the misinformation than the rested participants.
When participants see the pictures
the evening before seeing the misinformation, though, sleep deprivation has no
reliable impact on false memories. The
likelihood of incorporating information from the stories in their recall is low
for all participants who saw the photos the night before.
What is going on here?
Think about how people could
respond accurately on this test. When
they encounter the initial event, they have to remember both what they saw as
well as when they saw it. That is, they
have to keep track of the source of
the memory. That way, when they read
about the event later, they can separate what they saw from what they read.
People who are sleep deprived seem
to have more trouble than those who are rested keeping track of the source of
the information they get. They are able
to remember facts about the events, but they are more likely to combine
together different sources of information.
This result suggests that we might
want to be careful about how much we trust the details of memories of events
that happened when we were sleep deprived.
The lack of sleep may make it difficult for us to remember the source of
the information we have encountered.
