May 18 2005
""William James, the great 19th century philosopher, once
commented that memory was simply the other half of the self. And in
a sense, that's very true. If you don't have memory, then you don't
have a self.''
""It's critical for cultures because it's all about transfer of
information across individuals and it's fundamental to you managing
to evolve in a way which allows you to change to your environment,
as well as passing that information on down through our culture.''
""The function is not simply to have them and reflect back on
past experiences when you're 70 or 80 years' old. The function of
memory is to guide behaviour in the future.''
""There's something about memory of plans and goals and the self
which when it's all brought together, it gives us this really quite
complicated dynamic cognitive system that allows us to be who we are
and operate effectively on the world.''
Pam Rutherford: It's hard to imagine a life without memory. From
birth through to death, our brains will file away huge amounts of
information … facts, names, faces, sounds, smells and events and the
emotions that are tied to them. Every second of our waking lives, we
rely on our ability to plunder the memory vaults of our mind … from
knowing how to ride a bike, remembering a birthday or even your
first kiss.
Over the next four weeks in Discovery here on the BBC, I'll be
exploring the science of memory, it's extraordinary capabilities,
how and why it can go wrong, from the vivid intrusions of memory in
post-traumatic stress disorder to our uncanny ability to adopt
memories that aren't even our own.
I'll be finding out how and why memory fails and what we can do
to improve it.
In this programme, I'll be trying to find out what are some of
the brain processes that make up a memory. Do we know about what
memory might be and when and where does it start?
Andrew Mays(??) is a cognitive neuroscientist at the University
of Manchester in the UK. He's trying to understand how what happens
in the brain ends up as memory.
Andrew Mays: The human brain contains something like a million
million or a trillion nerve cells or neurons and in the part of the
brain, the neurocortex, which you can see when you see pictures of
the human brain … that's what's on the top.
Pam Rutherford: The wrinkly stuff.
Andrew Mays: The wrinkly stuff on the top, that's right. The neurons
or nerve cells in there can have up to 10,000 connections with other
neurons. It might be several thousand other neurons that each neuron
connects with. And memory seems to involve either strengthening some
of these connections or weakening or forming new connections … all
those things seem to go on with memory. And that depends on when we
experience new information. It triggers a cascade of chemical
processes within the nerve cells which eventually result … usually
after some hours, that's what's generally believed … in the
formation of these strengthened or weakened or new connections.
Pam Rutherford: But our memory isn't like a video recorder,
capturing everything we experience. It has to be selective. So how
do collections of nerve cells communicating with their neighbours
turn into memory? Which ones will end up having the conversation
back and forth, creating the dialogue of memory, while others spark
into activity briefly, only then to remain silent? In other words,
why do we remember what we do?
Psychologist and memory researcher, Martin Conway.
Martin Conway: One of the interesting things about memory is that we
have very little choice about what we remember. This is one of the
great mysteries; first of all, what we generate in online
experience.
Pam Rutherford: And when you say online, you mean just day to day
living, what we're doing?
Martin Conway: Yes. Well, let's take the event of this interview for
the World Service. We both have mental models of what's going on
here and those mental models have different layers to them. You have
questions you want to ask and answers you'll be quite interested in
finding and I'm trying to give you some impression of memory
research which portrays us in a good light and also say something
interesting to listeners and all these different levels and goals
and plans which are guiding our ongoing experience and they're going
to somehow feed into the memories we retain of this experience.
And that's the bit we don't know. We don't know how that happens.
We know how some parts of it might happen. There is I think a
guarantee that I will remember something of this interview but what
will it be I can't predict now. So what decides what it is I will
remember?
Pam Rutherford: What's the answer to that question?
Martin Conway: We don't know. (laughs)
But there's got to be some exciting things left in research
otherwise it wouldn't be worth doing.
Pam Rutherford: Science might not have a definitive answer about why
some memories take their journey from short-term to long-term memory
while others don't.
But Martin Conway does have a picture of how these initial sparks
of brain activity, the precursors to memory, might orchestrate
themselves to create a more lasting imprint.
Martin Conway: If you imagine, memory is a bit like a roomful of
tuning forks. If we strike one of the tuning forks, it's like a
memory becoming active and entering consciousness. But as it does
that, the vibrations from that tuning fork cause vibrations in
tuning forks that are on its frequency which might be temporarily
close to it in the room. And these, like associated memories and
associated knowledge, become more active and more available for
recall but not necessarily entering consciousness. Technically, it's
called priming.
So if we take our analogy and think about all the knowledge we
have about our lives, about the people we know, the places we've
been, the jobs we've done and also all the memories you have
associated with those things and think of it as being some rather
complicated store … which wouldn't be a store that's like a room but
we can pretend for this analogy it is … then as you take one piece
of information out, you activate lots of other pieces of
information.
Pam Rutherford: Kim Graham is one of the programme leaders at the
UK's Medical Research Council Brain Sciences Unit in Cambridge.
Kim Graham: If you think about last night, what you had for dinner,
if now I talk about that and I tell you about what I have for dinner
and so on, I'm reactivating that trace and that may cause the kind
of links in the brain between the different elements that comprise
that memory to become stronger and to consolidate them. So the idea
would be that what we do is kind of by how important that memory is,
we may reactivate that either by consciously telling people about
something that happened or alternatively, it's thought that sleep
might play a role in this type of reactivation. And the more we
reactivate it, the more we strengthen it and the more likely it is
that it will become permanent.
And that process … going from a kind of very short term initial
trace to something that's more permanent in the brain and that we
can retrieve many many years later … is termed consolidation.
Obviously we can't fill memory with absolutely everything we
experience but how do we know when we experience it whether it's
going to be important or not? So what we do is code everything in a
fast, very rapidly changing system that can hold onto information in
a one-trial experience and then later on what we do is basically
work out how likely it is that we might need that information. Then
what we can do is consolidate it and make it stronger, make it more
likely we keep that piece of information.
So if you think about it, what you want to be able to do when
you're younger and you're learning about new things is to know what
are regularities in an environment and what are not so that you know
cats and dogs are both pets and that you have them at home while
lions and tigers you will see in the zoo. So those types of
regularities and you might want to respond differently, you know, to
cats and dogs versus lions and tigers.
Pam Rutherford: So our memories get reactivated by some kind of
repetition. But how do you test to see how memories behave in the
laboratory?
I asked Mike Page, psychologist at the University of
Hertfordshire in the UK how you test and what he could find out
about my short-term memory.
Mike Page: Well, the sort of things that we would do in the
laboratory is to ask people to recall lists of digits or lists of
letters. So if I say to you, I'm going to give you a list of six
letters, could you please recall it back to me as soon as I finish,
so I say, R, X, Y, H, Q, Z.
Pam Rutherford: R, X, Y, H, Q, Z.
Mike Page: Very good. So that is called the immediate serial recall
task and it's an absolute staple task used in cognitive psychology
and it's been used even before the term cognitive psychology was
termed in the late 1950s.
There are various factors which make that immediate serial recall
task more difficult. Funnily enough, if I were to utter, or you were
forced to utter, a couple of things before you start recalling, that
can actually make the list very much more difficult to recall.
There are various theories as to why this is. Either the extra
items interfere or they simply delay your recall of the list.
So maybe I can try you again on an earlier list, then ask you to
count backwards three, two, one before you respond with the letters.
Okay?
Pam Rutherford: Okay.
Mike Page: So the list is, R, X, Y, H, Q, Z.
Pam Rutherford: Okay, three, two, one, R, H, Y, and I was going to
say, three, Q, Z but I know it's not three, it's a letter so...
Mike Page: Yes.
Pam Rutherford: Something's gone wrong.
Andrew Mays: Actually, even the letters that you got, you made
another transposition error, that is a swop of two items that were
next to each other in the list.
Pam Rutherford: Oh, dear, I'm not doing very well.
Mike Page: Actually that was the same list that you got perfectly
right just a moment ago when you weren't required to say three, two,
one before you started.
And this has practical consequences. A short delay or a little
bit of interference … depending on whose theory you believe … before
you start recalling a list can have really catastrophic effects, as
it did then on your recall ability.
And when in the 1960s, I believe, a zero prefix was introduced to
phone numbers in the UK, there was a greater incidence of
miss-dialings, wrong numbers that was noticed simply because the
time or the extra interference introduced by having to put a quite
redundant zero … that was zero in every case and you didn't have to
remember it … in front of the number that you had to dial caused
people to forget the number that they were dialing.
So short-term memory really is short-term because it can be
disrupted by as little as one or two extra items preceding your
recall.
Pam Rutherford: There's just a brief window to create a memory, to
turn something you've just learnt into something more permanent so
it's kept if not forever long enough to remember it days, weeks,
months or even years later. But it is fragile. If you're distracted,
it could disappear for good.
But it's not just distraction and interference that can cause
problems for our memory. There's increasing evidence that the genes
we're born with play a role in determining our ability to remember.
About one in 10 people are born with a rare form of a gene which
makes it harder for their nerve cells in the brain to receive and
consolidate information.
Mike Page: People with the rare form have a less efficient receptor
and these people, when compared with the vast majority, about 90 per
cent of people, when they learn new information like for instance a
list of words or a list of pictures and you test them immediately,
do just as well as the majority, the 90 per cent, but when you test
them after a delay of either five minutes or a day, their
performance can be on average about 20 per cent worse. They can
recall about 20 per cent less of the information that they learnt
before. So what it strongly suggests is that what's different about
these people is that they don't consolidate, make the memory changes
that result in really good storage, as well as the majority of
people. And this is entirely due to their having a slightly
different genetic makeup.
Pam Rutherford: That's quite staggering really. That's one in 10
people. Do you think there'll be other genetic variants that might
give a kind of difference in memory capability as well?
Mike Page: Yes, I think there will be a lot of these found and I
think it's one of the things that's been neglected, partly because
it has been so difficult to investigate.
Pam Rutherford: There are ways of getting around what we might be
born with. According to Andrew Mays, it's all about how you put
information into memory which determines what will stay there.
Andrew Mays: The best way to learn it is to space your learning. So
you don't say I've got to learn this new lot of chemistry and so sit
down and spend about 10 hours trying to put it into your head in a
sort of mass practice fashion. What you do is you process certain
parts of it on one day and then you come back to it the following
day or a few days later and learn it again. And then you do that
again and again and this is much more efficient with much less time
spent on the learning. You can get up to very high levels of memory
performance and furthermore it survives over long periods of time
much better than if you learn it all in one go.
Pam Rutherford: Why are those spaces so important?
Andrew Mays: The latest idea is that that actually also relates to
consolidation because there are two types of chemical that are
involved with controlling the chemical cascades which produce
consolidation. There are kinases which are protein molecules which
add phosphate groups to proteins and make them active and that
boosts consolidation. But there are also phosphatase proteins which
remove the phosphate groups and that inhibits consolidation. And if
you like, it's a sort of battle or an interplay between these two
types of protein molecule.
Now if you learn stuff in a mass practice fashion, the
phosphatase becomes dominant so it inhibits consolidation whereas if
you spread your learning with big gaps, the phosphatase doesn't
build up very much and the kinase is dominant and the consolidation
process is much more efficient.
Pam Rutherford: So it really is down to the chemicals and they're
competing. So you have to give them the best chance to sort of give
you the best chance.
Andrew Mays: Yes, we're at the very early stages of understanding
this and I'll just give you one more example. If you learn something
last thing at night and then go to sleep and compare that with
learning something during the day and you then have eight active
hours after that in which you're learning new things, what you find
after a few days is that you remember the information that you
learnt the last thing at night immediately before you went to sleep.
You remember that best.
If you learnt something during the day and then carry on learning
other things for about eight hours or so, you remember that stuff
much less efficiently. And the evidence is growing that that's
because if we learn new things, the parts of the brain that store
this new information are busy storing these new memories and that
interrupts the memories that went in immediately before. It prevents
them being consolidated very efficiently.
Pam Rutherford: And I always thought my student days of late night
studying were a bad thing.
When does memory start, the process of allowing us to recall
things we've learnt? When do we first remember anything?
One of my first memories is counting to 20 in the kitchen with my
mother when I was probably about three or four. But I wonder what
was my memory up to before then? When did it start, at six months,
one year or perhaps even two?
Carolyn Rovee-Collier is professor of psychology at Rutgers
University in North America.
Carolyn Rovee-Collier: There is evidence that babies probably form
some kind of memories even prenatally. That is to say, if your
mother reads a passage from Doctor Seuss every day for the last six
weeks of gestation, for six weeks, 20 minutes a day, that baby after
it's born given an opportunity to suck to hear a passage that she
read or a passage that she's reading from a very similar story like
Yertle the Turtle, that baby will suck preferentially to hear the
familiar passage that she had read over that long period of time and
the babies are almost two days' old at this point. So clearly, in
order for them to have a preference for a familiarity, they must
have remembered what had happened before they were born.
What's interesting is that the baby does not seem to process
information that other people in the room are producing. Baby
doesn't respond so actively to the father, to the grandmother or
other people who may be around; only to the mother. And the thought
is that maybe something akin to bone conduction or something like
that is responsible for the effect.
Andrew Mays: Memories from childhood often tend to be rather
enigmatic. People's earliest memories are often fragmentary. There
might be a garden or the layout of a room, a particular toy or a
bench or some objects and they seem to bring with them quite a lot
of meaning but we don't know what that meaning is. Probably these
were objects or places or locations or activities which were highly
relevant to the very young child's plans and goals, plans and goals
the adult no longer has and perhaps can't get back to but you retain
the relics of those plans and goals in the form of visual memories
often of early childhood. That's one illustration of how emotions
might act to determine what gets in there. But we don't really know
how or what processes rather are operating to determine what it is
we will retain at any given time. And my personal view is that we
don't remember them because the goals and plans of the young child
is so radically different from those of even the older child, that
we can't use the current goals and plans to access old memories,
recall it with other goals and plans. So it's a mismatch between the
sort of emotions and knowledge which we can now use to access
memories which is so disjunct from those of the three, four,
five-year-old that we can't access the memories that were created at
that time.
I mean, there are some interesting cross-cultural differences in
childhood memory. I've done some of this work with my colleague Qi
Wang at Cornell University, a leading cross-cultural memory
researcher. It turns out that in Asian cultures, particularly
Chinese cultures, their earliest memories are older than those in
western societies, particularly the USA, and also their earliest
memories tend to be less detailed than those in western cultures.
Pam Rutherford: Why is that?
Andrew Mays: Well, one view is that in western cultures, there's a
massive emphasis on individualism and if you're going to be an
individual, one thing you need is a detailed memory to single you
out as an individual. And so there's a strong emphasis in
remembering, perhaps in child-rearing practices in western culture,
a strong emphasis rather in child-rearing practices on remembering.
It's known that mother and child talk more about the past in western
cultures than they do in Asian cultures.
In Asian cultures, the focus tends to be more on the group and
society and therefore their memories tend to be ones which don't
contain events which are events of striking individuality. They tend
to be events which relate to group activities and family activities
whereas the earliest memories of western adults tend to be ones that
really are striking individuality.
Pam Rutherford: Our memory start before we're born, allowing us to
remember the sound of our mother's voice and as we go through
childhood, the memories we collect will depend on what we experience
and in some cases, where we live. These memories will, if we're
lucky, stay with us for decades despite the constant changes in our
brain. How those memories persist however, according to Andrew Mays,
is still a mystery.
Andrew Mays: The actual ability to reproduce that remembered
experience is somehow maintained so it's not necessarily, certainly
not maintained by the same chemicals because they break down fairly
rapidly over a period of weeks at most or even to take it further,
by the same neurons, the same nerve cells. So these can all change
to a considerable degree. We don't know to what degree but all that
really matters is that we have the ability to reactivate the
representation which corresponds to that experience so that there's
a sort of dynamic process that maintains memories over decades. And
that's my suggestion, and it's not really much more than an informed
guess, but no one can give you at the moment more than an informed
guess.
Pam Rutherford: Next week on Discovery here on the BBC, I'll explore
what happens when our memories fail and look at the strange feeling
of deja vu.
End
BBC WORLD SERVICE: DISCOVERY (1 JUNE 2005)
Transcribed by Gavin Chua
(??): word unsure
Harry Stever: I was in reconnaissance unit in Vietnam for the most
part of the reconnaissance battalion. So I was a reconnaissance
platoon leader. And I was starting to have what they call
flashbacks, which is really a very vivid daydream to me, where
you're just sitting there and all of a sudden things start going
around 24 hours a day. But in the back of my mind, even as I'm
talking to you now, I'm still seeing scenes from my combat
experience rolling through my head. It makes you worry you just
can't function.
Pam Rutherford: We're used to the idea of being in control of our
memories. Mostly we can rely on them to do their job from helping us
remember what to do today, where we were yesterday to the more
unconscious ways it helps us remember how to ride a bike or drive a
car.
But as that account you just heard of ex-US marine Captain Harry
Stever shows, there are times when memory can get out of control.
His experience of post-traumatic stress disorder (PTSD) is one
example of how the memories of traumatic events can become extremely
powerful, intruding unexpectedly into the present as flashbacks,
forcing the emotions, feelings and trauma of the past into an
overwhelming experience of the present.
In this week's programme about memory here on the BBC, I'll be
finding out what happens to memory in conditions like PTSD and
depression, and why emotions play such an important role in how our
experience of the world is stored.
Martin Conway is a psychologist and memory researcher at The
Leeds Memory Group in the UK.
Martin Conway: What happens in PTSD is a person experiences a
traumatic experience, maybe a road traffic accident, maybe a
physical assault. They then enter a period of very very severe
anxiety in which they can't effectively function in the world. That
period of anxiety, one of the major symptoms in that period is the
return intrusively uncontrollably of flashbacks, very vivid memories
of aspects of the trauma. These flashbacks when they occur are like
moments of reliving and you can imagine that they are both
emotionally destabilising but also cognitively destabilising. They
overwhelm the individual.
Let me give you a case example. A man was in a very serious
accident in which he nearly died. At the point he was about to die,
he suddenly had a sadness that he would never see his children
again. He survived physically unharmed but with PTSD. And one of the
flashbacks he had was when he was with his children, he had a
flashback to this moment just before he thought he's going to die
when he'd feel very sad that he'd never see his children again. And
this would occur even though the children were present, even though
he had survived. So these are powerful psychological disturbances.
Pam Rutherford: Chris Brewin is Professor of Clinical Psychology at
University College London. He researches and treats post-traumatic
stress disorder. He thinks there's a particular kind of memory
involved.
Chris Brewin: They also describe a very vivid experience which is
often accompanied by very powerful emotions and sometimes feelings
of hot or cold or pain which were present at the time of the
traumatic event. So people often walk round feeling that they're in
danger even though they know consciously that this event is past.
They nevertheless feel as though, for example, people are following
them down the street as though they're in danger any moment, unless
they take constant guard over themselves. And it's not something
like an ordinary memory which seems to belong in the past.
We think this is not a simple form of autobiographical memory.
It's not like our ordinary memories for things that have happened to
us in the past. But it's a rather different kind of memory which can
only be triggered automatically by reminders that people come across
or things that they choose to think about. And when they do that,
they often see things in a level of detail which is not experienced
in our ordinary memories of the past.
Pam Rutherford: Our brains have evolved to maximise our chances of
survival during a traumatic event. This involves the release of
stress hormones to help ensure we get out of a situation alive. But
it's also this response that's part of the problem.
Chris Brewin: The parts of the brain that are involved in memory are
also the parts of the brain that are strongly involved in the stress
response. And we think it's quite likely that why memory behaves
rather differently in PTSD is because of the effects of various
kinds of stress hormones that are released during this very
stressful event. And it may well be that the parts of the brain that
are more rational and reflective simply don't operate so well during
these events. The brain, if you like, is switched into a different
mode in which the emphasis is on taking extreme action, fight or
flight or perhaps freezing, and where the ability to think and
reflect is less important and it might in fact even interfere with
survival.
Pam Rutherford: And it's that stress-driven flight or fight response
which means the brain will focus its attention on certain kinds of
information at the expense of others. And it's this partial memory
which then has the power to become so intrusive later.
Jennifer Wild is a psychologist at the Institute of Psychiatry in
London.
Jennifer Wild: The trauma memory tends to be quite fragmented, and
there are a number of reasons for that. When someone goes through
trauma and it's a very frightening, a very scary experience and they
actually have the perception that they're dying, the brain goes into
data-driven processing. So it processes all the sensory elements.
Whereas normally when you're processing an event, you're processing
more the narrative of what's actually happening because you don't
have that fear-flight response going on. But in trauma you do have
that going on. So you have less the narrative. So because the memory
is fragmented, you have a memory problem. And that's going to lead
to PTSD.
Chris Brewin: It's almost like you're not able to take a slight step
back from the situation. It sounds like and knowing a situation,
it's just pure in the moment.
Jennifer Wild: Totally, that's exactly right. There is too much fear
and perception that I'm dying, this is the end to be able to have
that perceptive and to take a step back.
Pam Rutherford: The brain needs to be able to take this step back
from itself to ensure experiences can be represented in a way that
allows us to distinguish between something being a memory, so
belonging in the past and something more in limbo to having the
power to intrude on the present.
There are different types of memory needed to do this
effectively. Chris Brewin.
Chris Brewin: Our idea is that people have two memory systems. One
is a more verbal system, in which the memory is represented in the
form of words, and also another form which is represented in the
form of pictures. But this second memory system has been described
by a lot of autobiographical memory researchers, and they think that
people have sort of almost like pictures of the events which can be
spontaneously triggered by reminders. And we think that in PTSD
this memory system becomes particularly powerful and particularly
active. The memories are very long-lasting.
Pam Rutherford: And this is a kind of memory that is quite immediate
sort of visual memory. Is this sort of lower down in the system or a
different stage than perhaps the verbal that you're talking about?
Chris Brewin: Yes, it does seem to be a more primitive sort of
memory and almost certainly the memory is not accompanied by any
context. So this may explain why people with PTSD say that they
relive the experience in the present because the memory is not
accompanied by the context that tells the brain that this is
something that happened in the past.
Pam Rutherford: Is that because other memory things aren't
triggered, like the verbal system isn't triggered which would
provide that context and provide a kind of framework almost to know
that this is a memory rather than an experience or an event?
Chris Brewin: Yes, we think that this is very likely to happen when
the circumstances are so overwhelming that that part of the brain
that would normally provide the context and the thought and the
reflection about what's happening is simply not working very
effectively. People may describe being almost paralysed by fright
and simply unable to think or act. And it's likely that this sort of
paralysis or freezing could be related to the inability to form a
more conscious or verbal memory of the experience.
Pam Rutherford: And it's the parts of the brain that are critical
for memory and contextualising normal experience that seem to play a
crucial role in why some people develop PTSD.
Jennifer Wild.
Jennifer Wild: The hippocampus is involved in contextualising
memories and fear responses. And the thinking for quite some time
has been that PTSD causes problems of the hippocampus and then that
maintains the trauma reaction.
But we've also thought, well, possibly there could be problems
with the hippocampus which may predipose somebody to developing
PTSD. And Mark Gilbertson and his team at Harvard have looked at
this in-depth and they looked at 26 pairs of twins, one of whom had
gone to Vietnam, been exposed to combat and developed PTSD. The
other one had stayed in the States and not been exposed to trauma
and not developed PTSD.
And what they found, interestingly, was that their hippocampi
were the same, they're comparable, exactly the same. So the twin who
had PTSD didn't have a smaller hippocampus than the twin who didn't.
So then they wanted to know, okay, well, are these hippocampi any
smaller than other people who had been to Vietnam. So they did
another twin study and they looked at 46 who had gone to Vietnam,
been exposed to trauma, didn't develop PTSD, and their twin brothers
didn't develop PTSD either.
And they compared the first set with the second set, and they
found that the brothers who had gone to Vietnam, developed PTSD, and
their twins who hadn't been to Vietnam both had smaller hippocampi
than this other group who had gone to Vietnam and hadn't developed
PTSD but been exposed to trauma. And the only conclusion they could
come to based on their very strong correlations was that having a
smaller hippocampus is a predisposing factor to developing PTSD.
Pam Rutherford: Looking at groups of twins, some who've gone on to
develop PTSD isn't the easiest way for scientists to investigate it.
Those people's memories are already changed by the condition. But
understanding the memory processes in healthy volunteers might be
one way of understanding who might get PTSD and how to treat it.
Chris Brewin and his colleague Emily Holmes have come up with a
way to do this. They showed healthy volunteers films of traumatic
scenes involving car accidents while at the same time asking them to
perform different kinds of memory tasks.
Chris Brewin: And what we found is that when people do certain kinds
of tasks that we think interfere with the representation of images,
interfere with laying down images into memories, say, for example,
we ask them to tap out various complicated patterns, when they do
that while they're watching the film, they have fewer spontaneous
memories of the film coming back to them in the next week.
But if we ask them to do a verbal task like counting backwards in
threes while they're watching the film, we found that they have more
intrusive memories of the film coming back to them in the next week.
And that supports the idea that these intrusive images could be
supported by a different type of memory which is an image-based form
of memory which is separate from a verbal memory.
Pam Rutherford: So if you disrupt that image memory or effectively
if you're using that image-based memory while you're seeing the
event, it makes it less strong when you recall it afterwards?
Chris Brewin: Yes, if your image-based memory, its resources are
being used by some other tasks while you're watching the film, we
think that it's less efficient in recalling the details as a trauma
film.
Pam Rutherford: And similarly if your verbal memory is used, then
that's less able to form a narrative and therefore help kind of
consolidate this as this is memory, not experience.
Chris Brewin: Yes, that's exactly right. Well, this is very
interesting because what treatment for PTSD often involves is
getting people to produce a very detailed narrative about the
events. And some people are very surprised by this and they say,
well, if you ask people to focus on these horrible things that have
happened, this is just going to make them worse. But the experience
of everybody who treats PTSD is the complete opposite … that if you
get them to focus on describing what they saw, what happened in
detail, in words, this seems to have a very therapeutic effect. And
according to our theory this is because the verbal memory that
they're elaborating and creating in much more detail into fears with
the image-based memory, which they have been constantly retrieving
as part of the PTSD.
Pam Rutherford: So subsequently that verbal memory which you're
encouraging people to use will be kind of embedded within the
imagery, therefore not making it this powerful flashback but making
more the memory.
Chris Brewin: It may be embedded with the imagery or it may be
separate from the imagery and it may be that some kinds of
competition goes on. So when you hear the ambulance siren if you
retrieve a new narrative memory then you're less likely to respond
with fear and panic because that memory contains the idea that your
trauma is something that belongs in the past. Whereas if you
retrieve the image, which can't distinguish between the past and the
present, then you begin to feel panic all over again.
Pam Rutherford: And Jennifer Wild believes that an important result
of this kind of descriptive treatment for PTSD is actually making a
new memory of the original traumatic event.
Jennifer Wild: So often people have been through a car accident, for
example, and they have a feeling at the time that they were going to
die and they're still left with that feeling I'm going to die and
it's a very present fear. But they've survived and it hasn't quite
been linked up yet. So effective treatments link up the two. I now
know that I had this accident but I survived, I'm alive, I still see
my family, I still see my friends, I'm okay. So it's linking up the
two pieces of information and creating a new memory.
Pam Rutherford: It's not just in the relatively rare condition of
post-traumatic stress disorder that memories can be altered by
powerful emotions. Depression affects more than 120 million people
worldwide. And according to the World Health Organisation it's one
of the leading causes of disability.
In depression memory also plays an important role. Martin Conway.
Martin Conway: One feature of memory in depression is that it
becomes more over general and less specific. If you ask a depressive
patient, for example, to recall an experience with his father, let's
say, then a typical sort of response might be, well, we used to go
for walks in the park together. And if you push them, that's all
they'll say. They won't get any further. They will never get to a
specific experience.
Pam Rutherford: Tim Dalgleish is a clinical psychologist at the UK
Medical Research Council's Cognition and Brain Sciences Unit in
Cambridge. He points out that this bias doesn't apply to everybody.
Tim Dalgleish: People with depression often have a relatively
even-handed or non-prejudiced memory about other things. But when it
comes to remembering things about their selves, it's very much
focused on the negative. For example, they might be able to look at
what a friend is doing and be able to say to that friend: ""But,
remember, you did this, which was really good,'' or ""Well, that
happened which was really good.'' In other words, they've kind of
got double standards. They are able to turn their mental spotlight
on somebody else's life and perhaps even draw out quite positive
things. But when it comes to their own life they just can't see
anything positive even though somebody else might well be able to.
And so I think a useful way to think about this is like it's a form
of prejudice against yourself. In that way it just self-perpetuates
just like any form of prejudice. Anyone who is prejudiced isn't
going to take things on face value. They're always going to see the
world in a way that feeds their prejudice. And it's the same in
depression.
Pam Rutherford: And it's this kind of negative memory bias for the
self that Tim Dalgleish has been investigating to see how it might
play a role in perpetuating depression.
Tim Dalgleish: What we did is say to people who are either feeling
very depressed or a group of other people who are feeling fine as a
sort of controlled group, pick an event from your childhood or early
adulthood which you find extremely distressing and which was very
distressing at the time. So they will choose this event. And then
for half of them we say: ""Well, what we want you to try and do now
is try not to think about that event for 10 minutes.'' And for the
other half of the people we don't tell them anything so they can
think about whatever they like.
And what we find is that if we measure the number of times these
people think about this event in the 10 minutes, we find that the
depressed people who were trying not to think about the distressing
childhood event actually think about it more often than the other
people who we didn't give those instructions to. So in other words,
trying to suppress thoughts of this event ironically makes it happen
more often.
Pam Rutherford: And do you know why that happens?
Tim Dalgleish: I think the best answer we've got is that the people
who are depressed are trying not to think about this one event by
forcing themselves to think about other things that have happened to
them.
However, unfortunately when they do that, the other things they
think about are also very distressing and actually remind them of
the thing that they're not trying to think about. So, ironically
they end up thinking about it more often by trying to get away from
it.
Whereas in the other group who aren't deliberately trying not to
think about something, they don't seem to have this difficulty.
What it tells us is that trying to suppress or distract negative
thoughts and negative memories isn't going to be a particularly
productive strategy. And what we try and encourage people to do in
therapy is to actually rather than try and go round their thoughts,
go through the middle, if you like, and actually deal with the
content, think about what the implications are and try and change
the way they think about themselves in the world.
Pam Rutherford: So, trying to suppress or ignore memories in both
depression and PTSD doesn't seem to work in treating either
condition. In some way the memory needs to be addressed or it will
continue to intrude. In PTSD, the process of describing the memory
seems to change it enough to help prevent it resurfacing.
And according to Chris Brewin, there are similar ways of changing
memories in depression which might seem an unconventional treatment
but are in fact very successful.
Chris Brewin: Fairly recently we've discovered that people who are
depressed often have frequent intrusive memories that are not
dissimilar to the memories experienced by people with PTSD. Often
they don't relive the event in the present to the same degree but
they're often very vivid and they're often accompanied by a great
deal of emotion.
But what's interesting is that if you're depressed and you're
having a lot of these intrusive memories, your depression is likely
to last longer than if you're not having them.
So at the moment we're beginning to see is it possible to improve
levels of depression by helping people to change these pictures in
their mind. So we're using a technique called Rescripting, which
involves asking people to focus on the images that are coming into
their mind and to actually try changing them in various ways and
make them less distressing.
Pam Rutherford: How do you do that?
Chris Brewin: Well, you might ask people just to change the way
something looks or to imagine it was further away or to turn
something upside down or to make it look perhaps rather funny or
ridiculous.
Pam Rutherford: Can you give an example of the sort of thing you
might do?
Chris Brewin: Well, for example, if somebody had a distressing image
involving a large black rectangle suddenly coming into their mind,
we might ask them to imagine that this rectangle was struck by
lightning or beginning to crumble into lots of tiny pieces, so that
every time the image comes to mind, we ask them to practise changing
this into the alternative image which would be less distressing for
them.
Another method that we're also trying out is to see whether
people can imagine some kind of supernatural being perhaps or a
guardian angel going back into the memories themselves at a younger
age and providing support and comfort and reassurance to themselves
in the earlier memory.
But it sounds a really strange thing to do. And in some says it
is a bit unusual. But we're very struck by how easy people find it
to do this and how what a powerful technique this can be.
A lot of therapy has focused on making people think more
logically and more rationally. And that's certainly been very
effective. Of course what we're trying to do in some ways is the
opposite because the new things that we're trying to introduce are
often not logical or rational at all. In fact, they're completely
impossible.
But that doesn't seem to matter. So what we're thinking now is
that it's not being more logical or more rational is important; it's
having an alternative that is more positive.
Pam Rutherford: For people with post-traumatic stress disorder, the
memories might never go away but understanding them can help.
Harry Stever.
Harry Stever: The more you learn about anything that's wrong with
you from a common cold to foot lice, the more you know about it, I
think the easier it is to handle it. When I first started to
experience PTSD, I had no idea what was going on. I didn't know how
to react, I didn't know what to expect, what is happening to me. But
this is what happens, this is what you can expect in a certain
situation. And this is normal, you're not unique in this, you're not
alone. And the more you learn about it, the easier it is to handle I
think.
Pam Rutherford: Next week in the last programme of this BBC series
about memory, I'll be going to two memory clinics to find out about
the kinds of techniques which can help improve failing memory.
Ends
BBC WORLD SERVICE: DISCOVERY (25 MAY 05) [QL]
[QL]
[QL]
Transcribed by Serene Ng [QL]
[QL]
[QL]
(??) …… word/s unsure [QL]
[QL]
[PARA]
""A literal memory would be no use at all because it would take
as long to remember as it did to live it.'' [QL]
[PARA]
""A significant proportion of the population will in response to
fairly innocuous suggestions develop a memory of an event that
didn't occur. [PARA]
We questioned people several times about whether they were
subject to a vicious animal attack when they were young. A
significant portion of people eventually will say if you ask them
about it enough, they will say, ya, you know, now I do remember,
that did happen to me, it was terrible.'' [QL]
[QL]
Pam Rutherford: Memories allow us to think about our past, live in
the present and plan for the future. Without them, life would be
nearly impossible. During our waking lives, our brains will be
highly selective about choosing which bits of information it
encounters to put into memory. Given the size of the job, can we
always expect our memories to be completely reliable? [PARA]
In this edition of Discovery about memory on the BBC, I'll be
looking at how and why our memories fail, from the everyday glitch
of struggling to find a word you know is just on the tip of your
tongue to its uncanny ability to deceive us into adopting memories
that aren't even our own. I'll be finding out why these lapses
reveal what an efficiently organised, creative and dynamic system
our memory really is. [PARA]
First, something you might have come across before. [QL]
[PARA]
""It feels really weird because it feels like a flash of memory's
come back to you and you feel like something happened to you and you
can't quite realise what it is.'' [QL]
[PARA]
""Almost seems as if you're suddenly living through something
that you've seen immediately before, you can't really recall when or
how but you know that you've been there before. You know that you've
seen that before, you just don't know how.'' [QL]
[PARA]
Deja vu. [PARA]
Most of us will have had the strange sensation where the
unfamiliar suddenly feels all too familiar … I've been here before
except I haven't. [PARA]
Surprisingly some people with memory disorders can experience
this sensation for everything they do all the time. [QL]
[QL]
Mrs Kaveski: From the very moment he wakes up, the first thing he
would say, well, what day is it. It's Thursday. Any letters? I go
downstairs, bring the mail and he looks at the envelopes and say, we
already had it, it came yesterday. No, it couldn't. This is from
Cousin So-and-So and she writes only once a year. [PARA]
And then we'd go shopping and the first thing when we go out into
the street, and the woman with the pram passes by and he would say,
oh, she's here again. She must be very very regular in her customs. [PARA]
This car is trying to run us over again … this is jokingly when
we are crossing the road. [PARA]
Everything, everything happening, he would say, oh, it's already
happened. [QL]
[QL]
Pam Rutherford: Mrs Kaveski(??) is the wife of one of the patients
who feels permanent deja vu. His condition inspired researchers at
the Leeds Memory Group in the UK to try and understand how these
sensations shed light on the distinction between memory and
consciousness. [PARA]
Chris Moulin was one of the first to meet him. [QL]
[QL]
Chris Moulin: The man came to the memory clinic where I was working
with a very peculiar memory disorder in that it wasn't that he was
forgetting things, it was that he felt like he'd encountered
everything before. So he had what his wife described as a persistent
sensation of deja vu. [PARA]
When he was presented to the memory clinic, he said there was no
point going because he'd already been referred there before and he'd
already been before. In due course we checked our records; it wasn't
the case at all. [PARA]
He and similar people like him constantly report thinking that
they've done things before, so they won't watch the television
because they say they've seen the programmes before. Even news
events and striking news events like the Bali bombing, these people
will say that they knew how many people were going to die, they knew
that it was going to happen and all those kinds of things. He was
saying he wouldn't watch the television because he'd watched all
these programmes before and his wife said to him, well, you know, if
you've seen this programme before, what happens next and he'd say,
well, how should I know what happens next. I've got a memory
problem. [PARA]
So these people are quite aware of their problems and are
insightful but they're not consciously aware that they've got this
funny memory glitch. [QL]
[QL]
Pam Rutherford: And it's the strange peculiarities of this memory
glitch that's providing Chris with clues to understanding how our
sensation of memory might be separate from the memory itself.
Patients like Mr Kaveski are more likely to experience a feeling of
familiarity for the kinds of things that are least likely to have
happened to him, which is counter-intuitive but very revealing. [QL]
[QL]
Chris Moulin: It turns out that the more bizarre and less
commonplace the event, then the more likely they were to have deja
vu. For example, he was told that one of his friends had died and
there was an invitation to the funeral and he said, you know, I'd
already been to the funeral before. And that's not a very normal
memory. [QL]
[QL]
Pam Rutherford: Does the fact that it's the more vivid, the more
novel, all the things that are less likely to have happened, does
that reveal something about what's going on? [QL]
[QL]
Chris Moulin: Yes, very much so. We think that of course that tells
you that what happens in those cases are those events that really
grab attention and we think what's happening with patients like this
is that when something grabs their attention and they process it
kind of deeply or it makes a lot of sense to them, they mistake that
for actually processing a memory. So they confuse the present with
the past, if you see what I mean. [PARA]
So we're quite used to doing that sort of thing. If you
interrogate yourself and think about the things you can remember,
you look for evidence and you look for things that are striking or,
you know, the context that you can remember or the extra information
and you use that as evidence to know that you're having a memory. [PARA]
Well, what we think is that these people are doing that online,
if you like, so they're doing that as they are seeing things. So
they mistake the present for the past because it kind of triggers
those kinds of recollections. [PARA]
So for instance … I'll try and elucidate … if I'm sat here in
this room now, if I'd like to think about whether I've been in this
room before, I could use say the pictures on the wall, the way the
chairs are arranged and all that as evidence to know if I've been
here before and I would kind of bring to mind, you know, how I was
when I was last in the room. But what these people are doing is
they're seeing the information and that's triggering in them this
sensation that they have been here before because they're kind of
using that information, the novel environment and that sort of
thing, as if it is a memory and processing it as if it's a memory. [QL]
[QL]
Pam Rutherford: So what's happening in deja vu? It sounds like there
is this sort of distinction between the knowledge of a memory and
the memory itself. Can you tell me a bit more about that? [QL]
[QL]
Chris Moulin: Yes, I mean, that's the main thing that these patients
say and it suggests that there's two kinds of processes in the mind
and one is sort of the content of memory of which we can just think
of as maybe the story … just like maybe if you have a computer,
that's where the files are stored … and then on top of that, there
is the process that accesses those memories and that process
involves some kind of conscious awareness. So that might be … the
computer metaphor doesn't really work because we never say that
computers are conscious … but that might be those kinds of
organisational strategies and the feelings that you get once you
kind of remember something. And we know that's what happens and if
you think about how your memories are organised, if you want to
reminisce about something, it gives you very strong sensations and
those sensations are meaningful. So it's a very useful normal thing.[PARA]
But we think with these people, the conscious awareness part is
firing mistakenly so that's becoming activated when there is no real
content there. And of course that's a good analogue of what probably
is happening in deja vu. So when you have a deja vu, there's no
content there but you erroneously get this sensation. [QL]
[QL]
Pam Rutherford: So next time you get that strange feeling of deja
vu, remember, it's just a reflection of your memory's ability to
take a step back from itself. Normally, the sensation of something
being a memory would happen at the same time as having the memory
itself but in deja vu, you just get that sensation. [PARA]
But there are times when our memory deceives us not by eerily
popping up when least expected but by a frustrating reluctance to
reveal parts of its contents. [QL]
[QL]
Debbie Burke: Well, it's almost there. You know what it is.
Sometimes I recall one letter, the first one or not, but you can't
really seem to visualise the word as itself; you imagine the idea
but you can't see what it looks like. [PARA]
You can taste the word. You have that annoying irritating feeling
that you have just before you're going to sneeze where you can
almost get the word out and so this feeling that it's on the tip of
the tongue, that the word is just about to come back to you but you
can't quite get it out so that when we're unable to produce the
words of famous people, for example, or people who are in the news,
it's very embarrassing and we feel that it's communicating to other
people that we're just not very smart. [QL]
[QL]
Pam Rutherford: Debbie Burke is professor of psychology at Pomona
University in California in the United States. She's carried out
extensive research into the maddening phenomena of forgetting words
on the tip of your tongue. She says that by looking at who or what
you have tip-of-the-tongue experiences for, you can find out why
they happen. [QL]
[QL]
Debbie Burke: I have tip-of-the-tongues all the time for names of
people; for famous actors, for example. I was having a
tip-of-the-tongue for Julia Roberts' name the other day. I remember
what she looks like, I can remember the movies that she was in but
what I'm unable to come up with is the sound of the name. [QL]
[QL]
Pam Rutherford: Does it more often happen with proper nouns or
people's names? [QL]
[QL]
Debbie Burke: Oh, absolutely. Proper names are the most frequent
kind of word that we have tip-of-the-tongue experiences for and it's
very troubling to people because with other words, with vocabulary
words, you can usually find a substitute and you can just move
around this problem, this error that you're having but there's no
other substitute for a name, for example, when you got to introduce
somebody so it can be enormously embarrassing and people feel very
stupid when this happens. But it's a very normal process. [QL]
[QL]
Pam Rutherford: So what does this state reveal about how our minds
and memories of words are organised? [QL]
[QL]
Debbie Burke: We tend to think of words as being unitary. They have
a meaning, they have a sound, we know how to spell them and in fact,
something like the tip-of-the-tongue experience tells us that
they're not represented in a unitary way in the mind. If they were
we would always be able to remember all aspects … meaning the sound,
the spelling. The fact that we can remember the meaning and not the
sound tells us that those are separate representations. [PARA]
We think about this as a failure in the connection between the
meaning of the word, the synthetic properties of the word, and the
sound of the word and in fact, in the way we describe this in our
models in terms of the connections weakening between the sounds or
what we call the phonology of the word and the meaning or the
semantics of the word and when those connections become weak because
the word hasn't been used recently or it hasn't been used
frequently, then we're unable to retrieve the sound of the word from
memory. [PARA]
The other thing that has an effect on the strength of
connections, we believe, is the age of the person and as people grow
older, they start to have more of these tip-of-the-tongue
experiences. But it's a completely normal part of ageing and some of
the people who come into our labs say they are coming to be tested
because they're so worried about their memory, they're forgetting
names all the time and they are really worried that this is a sign
of Alzheimer's. [PARA]
Now it is true that an early symptom of Alzheimer's Disease can
be something like a tip-of-the-tongue experience but the difference
is that in Alzheimer's people will forget very common words. So for
example, somebody in a mild early stage of Alzheimer's might forget
what the name of a fork was or a spoon and that simply wouldn't
happen in normal ageing. [PARA]
One of the things we tell older adults is that if you're going to
go to a party or you're going to a meeting and you know who's going
to be there and you're worried about remembering their name, before
you go, just pronounce the names of each of the people. It's not
enough just to read them. You actually have to say them. And that
will increase the probability that you're going to be able to name
them, to know their name when you actually see them. So that
rehearsal of the sounds of the word can really be helpful in
reducing the likelihood of a tip-of-the-tongue. [QL]
[QL]
Pam Rutherford: Why should our brains be organised in this way, to
separate out things we would normally think of as belonging
together, like the sound of a word and its meaning? Debbie Burke
believes it makes sense for our brains to be organised in a way that
would minimise problems caused by damage or injury. [QL]
[QL]
Debbie Burke: And this is what some researchers have called a form
of graceful degradation; that is, you have the representation of
these objects, their meanings, their sounds, their names,
distributed over the brain so that if you damage one part of it, you
don't lose the whole concept and the word and its sound and its
spelling. You just lose some part of it. [QL]
[QL]
Pam Rutherford: If you would like to feel a sensation of deja vu,
find out more about tip-of-the-tongue or just listen again to this
programme about memory on the BBC World Service, then you can via
our webpage. Go to bbcworldservice.com and follow the links to the
Discovery programme. [PARA]
The everyday slips of memory like deja vu and tip-of-the-tongue
provide a window on aspects of how our memories are normally
organised, usually to work efficiently and provide us with an
accurate view of the world. But our memories can fail in ways with
potentially far more damaging consequences. [PARA]
Professor Elizabeth Loftus from University of California in
Irvine has been researching false memories for more than 30 years.
According to her, there's a flimsy curtain that separates memory
from imagination. [PARA]
Eye-witness accounts of a crime are just one of the areas where
memories can go badly wrong. [QL]
[QL]
Professor Elizabeth Loftus: What we've done in our laboratory
experiments to try to study this process, this phenomenon is we'll
actually show people simulated crimes or accidents. We might show a
film of a crime or an accident, for example, and then we ask people
questions or we expose them to some new information to see whether
or not it will distort or contaminate their memory. [PARA]
And so for example, in one study we showed people an accident
where a car goes through an intersection with a stop sign and later
on, we suggest through a leading question that it was a yield sign
instead of a stop sign and what we find then is that many people,
sometimes as many as 80 per cent of people, will tell us that they
saw the yield sign instead of the stop sign. So they have succumbed
to the suggestion in our leading question and they've adopted it as
their own memory. Now that's just one example of how misinformation
can contaminate somebody's memory. [PARA]
But you can go even further with someone's memories. So our more
recent studies show that we can plant entirely false memories into
the minds of people. We can make people believe, for example, that
when they were six years' old, they were lost in a shopping mall and
they were frightened and crying, they were lost for an extended
time, they were ultimately rescued by an elderly person, reunited
with the family. We told them that we had talked to their parents
and that we'd found out some things that happened to them early in
life. We actually did talk to the parents and we did find some true
memories from the parents and then the parents also helped us
construct the made-up false memory. So we would then tell our
subjects we've talked to your mother, we've found out some things
that happened to you, we want to see if you can remember these
things and we tell them the true memories and then we also tell them
the made-up story. And through several suggestive interviews, we try
to get them to remember this thing that we've completely made up
with the help of their family members. [PARA]
Now after we did the lost-in-the-mall study, people criticised it
by saying oh, getting lost is so common, can't you show this with
events that would be more traumatic or more unusual or more bizarre
and so other scientists picked up on our procedure and planted very
unusual and would-be traumatic experiences if they actually had
happened; so for example, making people believe that they were
victims of a vicious animal attack as a child or making people
believe that they nearly drowned and had to be rescued by a
lifeguard as a child and a significant number of people will come to
pick up the story and adopt it as their own memory. [QL]
[QL]
Pam Rutherford: But if people will easily adopt memories that aren't
even their own, is there any way we can distinguish them from the
real thing? Daniel Schacter is author of The Seven Sins of Memory
and chair of psychology at Harvard University. He's got people to
experience false memories and then monitors their brain activity
while they're in a brain scanner. [QL]
[QL]
Daniel Schacter: Let me give a concrete example from a study we
recently did and published just last year where we created false
memories by showing people pictures of shapes, kind of nonsense
shapes, squiggles of objects that don't exist in the real world. And
they were all based on a prototype shape. They all kind of looked
like the prototype but we never showed people the prototype. And
later on what we found is that during true recognition of shapes
people had seen, there was more activity in certain parts of the
brain that are involved in visual processing than during false
recognition of the prototype that they thought had been on the list
because it's so similar to everything else they did see but it
wasn't really there. So we could tell when true memory was occurring
because there was more activity in certain parts of the visual
cortex. [QL]
[QL]
Pam Rutherford: Does this mean we're going to be able to actually
tell when the people are lying? [QL]
[QL]
Daniel Schacter: Well, it's an interesting question and I think we
have to be very cautious on this point. The work that we and others
have done in the laboratory allows us to tell in general … we're
comparing in a group of, you know, a dozen volunteers who
participated in our experiment. We averaged across all of them and
we get kind of a composite image and we looked at that group image,
we can tell true from false; but it's quite another matter to tell
true from false in individual participants with any degree of
accuracy. That we can't do. We have certainly not done that in our
work. That's not to say it can never be done but as far as I am
concerned, based on work that we've done … and we've done a fair
amount of it in this area … we're nowhere near being able to use
these imaging devices to reliably tell true from false memory. [PARA]
Now remember, this is not the same as wilful lying. In these
experiments, people believe what they're saying, they believe in the
validity of their memories, there's no intentional deception. So
it's really another question as to whether these imaging techniques
can be used to detect intentional deception. Here, everyone believes
they're telling the truth but sometimes they're wrong. [QL]
[QL]
Pam Rutherford: Why do our memories go wrong? Are these failings a
sign of a poorly designed system? Elizabeth Loftus thinks they
actually reveal the qualities of normal memory. [QL]
[QL]
Professor Elizabeth Loftus: These studies and findings are telling
us about the way normal memory works and you can ask well, why would
we have been built with a system, why would we have evolved with a
memory system that's so malleable? And one answer to that question
is that this malleable system means that if we happen to have errors
in memory or errors creep into our memories, automatically or
through inference processes, then we can update them and correct
them with new correct information because correcting a wrong memory
probably involved processes that are very similar to the kind of
distortions of memory that we are studying. [QL]
[QL]
Pam Rutherford: Daniel Schacter believes that our sins of memory are
the result of a creative memory that normally works very well.
Daniel Schacter: These sins can be viewed as kind of adaptive
byproducts of features of memory that work well most of the time.
Our memory for what happened and where it happened and who said what
is not perfect and therefore we can sometimes get part of the event
right but get the context wrong.
Well, let's think for a moment about what memory would be like if
we did remember every aspect of every event we ever experience. It
might well be the case that under those circumstances our minds
would be flooded with all kinds of useless details. This is kind of
a cost we pay for a benefit that results in a memory that does a lot
of good things. Our memory allows us to generalise, to kind of build
up a general picture of the world but because we rely on a memory
system that's not a literal record of what happened, doesn't contain
every fact, every contextual detail, building up a general picture
serves us very well but sometimes can get us into trouble when we
need those exact details.
Pam Rutherford: Next time you're struggling with some of the
everyday glitches in memory, try and consider that they're just
reflections of this built-in natural creativity and flexibility of
the way our brains are organised.
In next week's programme about memory on the BBC, I'll be
exploring the power of intrusive memories in mental illnesses like
post-traumatic stress disorder and depression and I'll be finding
out why our emotions play such an important role in laying down
memories.
End
