Current social and economic conditions, political pressures, and the historians’ own personal values all affect what facts they choose to have remembered by the generations that follow.
MEMORY AND LEARNING
Learning is a relatively permanent change in behaviour that marks
an increase in knowledge, skills, or understanding thanks to recorded
memories. A memory is the fruit of this learning process, the concrete
trace of it that is left in your neural networks.
Human memory is fundamentally associative. You can remember
a new piece of information better if you can associate it with
previously acquired knowledge that is already firmly anchored in
your memory. And the more meaningful the association is to you
personally, the more effectively it will help you to remember.
So taking the time to choose a meaningful association can pay off
in the long run.
Also, contrary to the image that many people have of memory as
a vast collection of archived data, most of our memories are actually reconstructions.
They are not stored in our brains like books on library shelves.
Whenever we want to remember something, we have to reconstruct
it from elements scattered throughout various areas of our brains.
Thus, scientists today view remembering not
as a simple retrieval of fixed records, but rather as an ongoing
process of reclassification resulting from continous
changes in our neural pathways and parallel processing of information
in our brains.
To illustrate these two
fundamental properties of memory, suppose that a school class
has visited a museum of Egyptian art on a rainy day. Ten years
later, the teacher, now retired, reads a history book that
mentions the name of a mummy that was on display in that museum.
The mummy’s name reminds the teacher of that class trip
ten years ago. Then, by association, the teacher remembers
some students from that class whom he had not even thought
about since then. He can even remember how fascinated they
were with the mummy, and some of the questions they asked him
about it. In short, he has formed associative memories:
one thing reminds him of another, which reminds him of yet
another, and so on.
Now imagine
that one of the students had had a very bad time on that trip,
because she was interested in a boy in that class, and he was
ignoring her. Ten years later, as she is taking off her wet
raincoat, she too remembers that day. Except that now she remembers
herself as holding that boy’s hand while they listened,
enraptured, to the teacher’s explanations. Why the change?
Because she ended up marrying that boy, and they are very happy
together, so her present happiness has embellished her memory
of the past. Thus, memories are not like snapshots that are
always the same every time you take them out to look at them. They
are also something that you reconstruct.
A person’s
short-term memory capacity is generally measured by the number
of items they can retain when each is presented to them only
once. On average, people have a short-term memory capacity
of 7 items, plus or minus 2.
An item can be defined as a “piece” of information.
Consequently, one way to increase the storage capacity of
short-term memory might be to increase the size of these
pieces of information through a more effective encoding strategy,
such as grouping.
Here are two phenomena suggesting
that there are in fact two distinct systems for short-term
and long-term memory.
First of all, our abilities to
retain items at the start and end of a list are not equally
affected by distractions. If a distraction occurs, we
tend to forget the items at the end of the list (i.e.,
those stored in short-term memory) while remembering
the ones at the start of it. In technical terms, the
recency effect is attributable to short-term memory,
while the primacy effect is attributable to long-term
memory.
Second, people with anterograde amnesia
cannot form new long-term memories, but their short-term
memory remains intact.
SENSORY, SHORT-TERM AND LONG-TERM
MEMORY
In the
1960s, the distinction among various types of memory according
to their duration was the subject of passionate debates.
Some scientists thought that the most elegant way to account
for the data available at the time was to conceptualize memory
as a single system of variable duration. But bit by bit,
evidence accumulated that suggested the existence of at least
three distinct memory systems.
Though the mechanisms of these three systems differ, they
do flow naturally from one into the other and can be regarded
as three necessary steps in forming a lasting memory.
According to this now generally accepted model, the stimuli
detected by our senses can be either ignored, in which
case they disappear almost instantaneously, or perceived,
in which case they enter our sensory memory. Sensory
memory does not require any conscious attention; as information
is perceived, it is stored in sensory memory automatically.
But sensory memory is essential, because it is what gives
us the effect of unity of an object as our eyes jump from
point to point on its surface to examine its details, for
example.
For instance,
if the object in your sensory memory is a red octagon,
you may or may not pay attention to it. If you do pay
attention, you recognize that it is a stop sign. Once
you have paid such attention to a piece of information,
it can pass on to your short-term memory. Your
short-term memory lets you record limited amounts of
information for periods of less than one minute. With
an active effort, you can keep a piece of information
in short-term memory for longer–for example,
by repeating a telephone number until you have finished
dialing it. Otherwise, the memory will disappear in
less than a minute.
Keeping an item in short-term memory for a certain amount
of time lets you eventually transfer it to long-term memory
for more permanent storage. This process is facilitated
by the mental work of repeating the information, which
is why the expression “working memory” is
increasingly used as a synonym for short-term memory. But
such repetition seems to be a less effective strategy for
consolidating a memory than the technique of giving it
a meaning by associating it with previously acquired knowledge.
Once the piece of information has been stored in your long-term
memory, it can remain there for a very long time,
and sometimes even for the rest of your life. There are,
however, several factors that can make these memories
hard to retrieve. These factors include how long it has
been since the event stored in your memory occurred,
how long it has been since the last time you remembered
it, how well you have integrated it with your own knowledge,
whether it is unique, whether it resembles a current
event, and so on.
Implicit memory is the kind of
latent memory that we are not aware of, but that nevertheless
influences our behaviour. All advertising is based on the
principle of implicit memory. We are so bombarded by advertising
messages that we think we no longer even see them and hence
do not remember them. But experiments have shown that when
we go into a store and have to choose among products with
equivalent characteristics, we tend to buy the one that
has been the subject of an advertising campaign, and we
cannot even say why!
The same principle would also explain
what is happening when you have a brilliant idea that seems
to have sprung straight out of your own imagination, then
realize later on that you actually read about it while
browsing through last Saturday’s newspaper.
DIFFERENT
TYPES OF LONG-TERM MEMORY
From a clinical
and physiological standpoint, many observations suggest
that there may be various sub-categories of long-term memory.
For example, certain kinds of amnesia affect certain kinds
of memories, but not others. Similarly, researchers have
found that various brain structures specialize in processing
various kinds of memories.
One of the most fundamental of
these distinctions is between declarative and non-declarative
memory, based on whether the memory’s content can be
expressed verbally.
Traditionally, most memory studies have focused on explicit
memory, which involves the subjects' conscious
recollection of things and facts. For instance, subjects
might be asked to memorize a given set of items (a
list of words, a group of pictures, etc.) and then
recall them verbally.
Also, things that are encoded in implicit memory can
be recalled automatically, without the conscious effort
needed to recall things from explicit memory.
Perhaps the best known of the various types of implicit
memory is procedural memory, which enables people
to acquire motor skills and gradually improve them. Procedural
memory is unconscious, not in the Freudian sense of suppressed
memories, but because it is composed of automatic sensorimotor
behaviours that are so deeply embedded that we are no
longer aware of them. Patients with profound amnesia
often retain their procedural memory, which argues for
a system of separate neural pathways.
Implicit memory is also where many of our conditioned
reflexes and conditioned
emotional responses are stored. The associative
learning that constitutes the basis for these forms of
memory is a very old process, phylogenetically speaking,
and can take place without the intervention of the conscious
mind.
We form implicit memories
without being aware that we are doing so. Hence, scientists
who study such memories must often try to uncover them
by indirect methods, such as "priming". In priming, researchers try to
increase the speed or accuracy with which their subjects
make a decision by first exposing them to information
that relates to the same context, but without the subjects'
having any other particular reason to retrieve the piece
of information concerned. For example, subjects will
take less time to decide that the string of letters "doctor" is
a word if they have first been shown the word "nurse" than
if they have first been shown an irrelevant word, such
as "north", or a nonsense word, such as "nuber".
