Williams, J. M. G.,
Barnhofer, T., Crane, C., Hermans, D., Raes, F., Watkins, E., & Dalgleish,
T. (2007). Autobiographical Memory
Specificity and Emotional Disorder. Psychological Bulletin, 133(1), 122-148. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.721.1249&rep=rep1&type=pdf
What is OGM –
overgeneral autobiographical memory?
When certain people are asked to retrieve specific
autobiographical memories (memories of specific events that happened at a
specific time and place) related to key words, they tend to retrieve
categorical, overgeneral memories – memories that group similar events together
(for example, "I used to walk the dog every morning") instead of
specific memories.
This phenomenon was first found by researchers
Willians and Broadbent (1986) in suicidal patients. Later it was found as a consistent
characteristic of patients with a diagnosis of depression, postnatal depression and people with sub clinical levels of
depression. The phenomenon is also found
in people
with a tendency for rumination (passive and repetitive thinking about the
depressive symptoms, and the possible causes and consequences of these
symptoms. For example, "What did I
do wrong?" "Why am I not getting over this?"). Memory
remains overgeneral in those with a history of emotional disorder, even if not
currently in an episode.
The phenomenon of overgeneral autobiographical
memory is also found in
people with a history of trauma, like sexual abuse, physical abuse, traffic
accidents, war trauma, cancer diagnosis etc.
OGM is found in these people even
when they are not asked to retrieve memories related to their trauma, but
rather memories that are related to certain
key words. OGM doesn't occur in every
person who has gone through trauma. It tends
to occur more in people who reacted with post traumatic stress disorder and in people who experienced trauma in childhood.
The OGM phenomenon was assessed mainly by various versions
of the AMT –
autobiographical memory test. This
test usually uses emotional key words, for instance "excited",
"happy", "relaxed ", "bored",
"helpless", "lonely" and so on. The person is asked to retrieve a specific
event (that occurred at a specific time and place, lasting no more than one
day) that is related to this key word.
People with depression or post trauma tend to have OGM in
response to both positive and negative key words. People with depression or post trauma tend to
respond with OGM even when the stimuli are not key words but situations (for
example, " Recall a time when a neighbour helped
you with a practical problem"), a
general instruction ("Recall as many episodes from your life as you can in
ten minutes") or actions ("Try to recall going to a concert").
How do researchers explain
OGM?
There are three kinds
of explanations: Functional
Avoidance,
"capture" and executive dysfunction.
Functional
Avoidance
The explanation is related to the structure of
autobiographical memory. According to Conway – Pleydell-
Pearce model (2000),
autobiographical memory has three hierarchical levels:
The highest level is the level of representations of life
periods with clear beginning
and end points (for example, being in high school, military service, the time
when I lived in Tel Aviv etc.).
The middle level has general event
descriptions: event that repeat themselves (for example,
driving to work each morning) or singular events (for example, my vacation in
South Korea). The events are represented
at this level as conceptualized and abstract summaries of experiences.
The lowest level has specific event
knowledge. In
this level concrete, sensory and perceptual aspects of events are represented. They can take the form of visual, auditory, tactile or other images of the event – what the surrounding
looked like, who was present at the event, how I felt during the event etc.
When people receive a key word and are asked
to recall a specific event related to this word, they create associations for the word that become
the basis for memory search. For
example, for the word "calm" I can think about "my dog
Jane". Now people access the level
of representation of life periods ("when I lived in Tel Aviv") or the
level of general events ("I used to take her for walks") and from
here they go on to the specific event level ("one day we went on a walk to
"Ben Shemen" forest and she was frightened by a wild boar that suddenly appeared on the path").
For post traumatic people, this kind of memory
search may lead to emotionally difficult places. Consider
the following protocol from a patient in response to the cue summer. She was
thinking back of summer holidays and found “hot summer evenings” coming to
mind. Further specifying on this theme, she began to retrieve a specific summer
evening when, although already after 10:00 p.m., the temperature was still
agreeable, and she was sitting outside with friends talking about the new puppy
she had bought. Subsequently, however, this triggered another memory from that
same summer when she was assaulted when walking the dog in the neighborhood
park.
As a result of these kinds of experiences
people with PTSD and people with depression tend to avoid memories which are
too specific, Conway and Pleydell – Pearce
argue that these people stop their search in memory at the level
of general event description and tend to avoid reaching the level of specific
events.
Capture
Individuals suffering from depression and people
with a tendency for rumination may get "caught at the middle level (the
general event level). When such people receive,
for example, the key word "happy", they may ruminate: "why can't I be more happy?" These thoughts "capture" them and
prevent them from retrieving specific events from
autobiographical memory. These people move
across the middle level of autobiographical memory instead of moving downward
towards the more specific level.
Executive functions
Searching in memory according to a cue requires effort,
strategy, control and monitoring – that is, executive functions. During the search a person has to inhibit
irrelevant autobiographical knowledge (and also ruminative thoughts that
disturb the search for a specific event).
People with depression and post trauma have depleted
attention resources and executive control.
Their difficulties are especially salient in the aspects of initiating
and managing the search and inhibiting irrelevant information during the search.
Thus, functional
avoidance, "capture"
at the middle level of autobiographical memory and poor executive functions
cause the overgeneral memory phenomenon.
These factors also work together and interact and thus exacerbate the
problem.
Overgeneral autobiographical memory may lead
to slow recovery from depression or traumatic events. OGM may also lead to difficulties in problem
solving, because OGM makes it harder for us to lean on past experience when we
deal with new situations.
Fortunately, training
people with depression or PTSD to retrieve specific memories can lead to
improved emotional state and can prevent the development of another episode of
depression. This can be done, for example, by creating a
list of specific memories that the patient wants to remember. Each item on the list is linked via visual
imagery to a specific location on a "mental trail". The person takes a mental hike and retrieves
the memories along the trail. This technique
prevents the development of depression.
Another way is to train depressed people to
focus on concrete images which are not self centered and have aspects of
perceptual processing/mental imagery (“Think
about the face of the Mona Lisa,” “a raindrop falling down a window pane”). This leads
to retrieval of much more specific autobiographical memories. Retrieval of specific memories alleviates
depression.
One of the authors of this paper, Dalgleish,
elaborates on this subject in this interview:
Clinical depression and memory: Professor Tim Dalgleish
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