.
Can
episodic memory be a (narrow) cognitive ability? It has to fulfill a number of conditions for
that. In the first post of this series
we've seen that episodic memory develops through the lifetime. In the second post we've began to look into individual
differences in episodic memory. We've
discussed people with especially high episodic memory.
In
this post we'll discuss a group of people with an especially poor episodic
memory.
First,
a quick reminder of concepts (you can skip to the green color below):
Episodic
memory is memory for
life events that we'd experienced in a specific place at a specific time.
The hallmark
of episodic memory is the experience of mentally "being there".
Autobiographical memory is composed of episodic memory and
semantic knowledge about ourselves and about things that took place in the
world during our lifetimes. Semantic knowledge about the self is, for example, knowledge about our
character and hobbies and about places we've been to, in a way that is not
necessarily tied with specific episodic memories (I know I'd visited a specific
place and know what it looks like, but don't remember the experience itself).
Semantic memory is the fund of knowledge we've accumulated over the years
(facts, ideas, word and concept meanings, knowledge about our culture).
In
2004 a woman named Susan McKinnon read
a paper about psychologist Endel
Tulving, that drew the distinction between semantic and episodic
memory. The paper presented a case of a
man whose episodic memory was negatively affected as a result of brain damage following a car accident.
McKinnon realized that that man's symptoms resemble her experiences (minus the
brain damage).
Tulving
expressed his belief that there are intelligent and completely healthy people
with no ability to remember personal experiences. These people have poor episodic memory. Tulving thought that soon these people will
be discovered. McKinnon realized Tulving
is referring
to people like her.
McKinnon
is healthy, she is married and has a family.
She is now retired and in the past has worked as a professional. She doesn't remember any events of her
life. She doesn't remember good and
exciting events, arguments or traumatic events.
She knows about the existence of these events but has no experience of
them. She doesn't remember books she'd
read or movies or TV series she'd watched.
Her ability to form mental images is not very good.
In
2006 McKinnon decided to approached Dr. Brian Levine who worked with Tulving. Levine tested her and she became the first
person to be diagnosed with SDAM
– severely deficient autobiographical memory. Later Levine found two more people with a
similar autobiographical memory, and in 2015 published with his colleagues Palombo, Alain, Söderlund & Khuu a paper about
SDAM. Since the paper's publication,
hundreds of people approached Dr Levine thinking they too have SDAM. Levin's group now tests these people. Levine assumes he'll find less than 15 people
with SDAM in this group.
The three
people with SDAM are intelligent people (their IQs are above 110), they are all
well educated (one of them has a Phd.) and they all work. Their poor
autobiographical memory does not affect their everyday functioning. These people are healthy, they do not suffer
head injuries, neurological diseases or psychological trauma. Two of them have had a single episode of
depression many years ago, when they were adolescents. Two out of three are in long term
relationships and one is single.
All of them
realized they have poor autobiographical memory during late adolescence or
early adulthood.
The researchers
compared them with 15 people similar in age (47 on average) and education (16.5
years of education on average).
Of the
cognitive tests, the only measure all three were poor at was recall of the RCFT
figure.
The
authors think that visual recall is inherent to autobiographical
remembering. That is, when we recall a
past event we create a visual image of it.
They cite another study in which two
healthy people with a total inability to form visual imagery throughout their
lives had poor ability to relive episodic events. One of them, who by chance had
neuropsychological testing in the past, had poor visual memory, and poor RCFT
performance.
How
was autobiographical memory assessed in this study?
Each person of
the SDAM and the control group chose two events from each of six life periods: a week ago, a month ago, a year ago, ten
years ago, during adolescence and in childhood. Each of these events had to have
happened at a specific time and place. The people could look at almanacs or ask
people close to them to name such events (for instance, "on July 2016
you've visited Seorak Park in South Korea"). The consulted people were asked not to add
any details about the event.
Each person of
the SDAM and the control group elaborated about these events to the best of his
ability. The researchers analyzed the
stories and classified the details to be episodic (directly related to the main
event, specific to time and space, creates a feeling of re-experience) or
semantic/"external" (for example, facts about Korea of about other
places in Korea which are not necessarily related to the same visit).
The researchers found that the people with SDAM
produced much less episodic details relative to the control group – but only
for events that happened during youth and adolescence.
The number of
episodic details that the three people with SDAM could tell about events in
later lifetimes was not significantly different than that of the control
group. This was so despite the fact that
SDAM people said they don't have an experience of these events. How could this be?
The researchers
assume that SDAM people could provide episodic-like details as a result of
activating non episodic processes (semantic processes). SDAM people are used to make up for the lack
of personal experience by becoming familiar with the story of the event. The story of the event is retold each time
the event is mentioned, and people who were present when the event took place have
a chance to add details to the retelling.
Pictures from the event also enrich the story. I'll also hypothesize that events from the
remote past are less often spontaneously mentioned, and are mentioned less in
the company of people who took part in them and can enrich the story.
Apparently it's hard to distinguish between episodic
details and episodic-like details. Often
"rememberer" himself has difficulty distinguishing between them. Each time we tell an episodic event we combine
episodic details and episodic-like details.
I'm not sure that we can distinguish between small details that we
remember directly from an event that occurred many years ago, and small details
that someone else who was present in the event added to the event's story. During remembering we are also assisted,
without being aware of it, by a "script" or a "schema"
according to which such an event is supposed to happen.
This emphasizes the extent to which autobiographical
memory is a phenomenon that is in between the personal and the interpersonal/social. Autobiographical memory is to some extent a
story with a number of authors, a story that is influenced by values and norms
of the culture we live in.
In order to
overcome such issues the authors let judges who were blind to the person's
group affiliation have a qualitative impression
of the memory. The judges did get the
impression that the memory quality of the three SDAM people for events that
occurred not only during childhood and adolescence, but also ten years or one
year or one week before was poorer (in terms of the richness of the memory and
the extent of reference to events that happened before and after the main
event) than the memory quality of the control group.
Neurologically, the three SDAM people had smaller right
hippocampuses than the control group.
During recall of episodic events under fMRI, SDAM people had less
activity in brain areas related to autobiographical memory and visual memory.
To sum up, we've
seen evidence for the possible existence of a group of people who can't
remember events from their lives, who have no episodic memory. These are healthy, educated working people that
are highly functioning cognitively and interpersonally. Due to the small size of the group it's hard
to tell whether their poor visual memory characterizes other people with
SDAM. Generally, it's hard to come to
any conclusions on the basis of a group of three people. A larger study is being currently conducted.
These findings are thought provoking. We are used to think about our life story as
an essential part of our selves, and of autobiographical memory as an essential
part of our selves. But these people
definitely have a self concept, personality, hobbies, values, beliefs, opinions
and friends. They know who they are.
Furthermore: the ability of these people to function so
well in everyday life in all respects – professionally, personally – raise the
question: to what extent is episodic memory essential? And if it's not
essential – why did it develop?
Palombo,
D. J., Alain, C., Söderlund, H., Khuu, W., & Levine, B. (2015). Severely deficient autobiographical memory
(SDAM) in healthy adults: A new mnemonic syndrome. Neuropsychologia, 72, 105-118. http://www.sciencedirect.com/science/article/pii/S002839321500158X
The
strange case of the woman who couldn't remember her past – and can't imagine
her future. Erika
Hayasaki. WIRED.
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