"The purpose of memory is not to let us recall the past,
but to let us anticipate the future. Memory is a tool
for prediction."
- Alain Berthoz
If you show a chess grand master a chessboard on which a game is in progress, he can memorize the exact positions of all the pieces in just a few seconds. But if you take the same number of pieces, distribute them at random positions on the chessboard, then ask him to memorize them, he will do no better than you or I. Why? Because in the first case, he uses his excellent knowledge of the rules of the game to quickly eliminate any positions that are impossible, and his numerous memories of past games to draw analogies with the current situation on the board.
MEMORY AND LEARNING
Learning is a process that lets us retain acquired information,
affective states, and impressions that can influence our behaviour.
Learning is the main activity of the brain, in which this organ
continuously modifies its own structure to better reflect the experiences
that we have had.
But memory is not entirely faithful. When you perceive an object,
groups of neurons in different parts of your brain process the
information about its shape, colour, smell, sound, and so on. Your
brain then draws connections
among these different groups of neurons, and these relationships
constitute your perception of the object. Subsequently, whenever
you want to remember the object, you must reconstruct these relationships.
The parallel processing that your cortex does for this purpose,
however, can alter your memory of the object.
Also, in your brain's memory systems, isolated pieces of information
are memorized less effectively than those associated with existing
knowledge. The more associations between the new information and
things that you already know, the better you will learn it. For
example, you will have an easier time remembering that the entorhinal
cortex is connected to the hippocampus via the dentate gyrus if
you already have some basic knowledge of brain anatomy.
Psychologists have identified a number of factors that can influence
how effectively memory functions.
1)
Degree of vigilance, alertness, attentiveness, and concentration
Attentiveness is often said
to be the tool that engraves information into memory. Thus,
attention deficits can radically reduce memory performance.
You can improve your memory capacity by making a conscious
effort to repeat and integrate information.
2)
Interest, strength of motivation, and need or necessity
It is easier to learn when the subject fascinates you.
Thus, motivation is a factor that enhances memory.
Some young people who do not always do very well at the
subjects they are forced to take in school often have a
phenomenal memory for statistics about their favourite
sports.
3) Affective values
associated with the material to be memorized, and the individual’s
mood and intensity of emotion
Your emotional state when an event occurs can greatly
influence your memory of it. Thus, if
an event is very upsetting, you will form an especially
vivid memory of it. For example, many people remember where
they were when they learned about President Kennedy’s
assassination, or about the attacks of September 11, 2001.
The processing of emotionally-charged events in memory
involves norepinephrine, a neurotransmitter that is released
in larger amounts when we are excited or tense. As Voltaire
put it, that which touches the heart is engraved in the
memory.
4) Location,
light, sounds, smells...in short, the entire context in
which the memorizing takes place is recorded along with
the information being memorizes.
Our memory systems are thus contextual. Consequently,
when you have trouble remembering a particular fact, you
may be able to retrieve it by recollecting where you learned
it or the book from which you learned it. Was there a picture
on that page? Was the information toward the top of the
page, or the bottom? Such items are called “recall
indexes”. And because you always memorize
the context along with the information that you are learning,
by recalling this context you can very often, by a series
of associations, recall the information itself.
Forgetting is another important aspect of
memorization phenomena. Forgetting lets you get rid of the tremendous
amount of information that you process every day but that your
brain decides it will not need in future.
Alan
Baddeley, a specialist in working memory, proposes a model
of working memory with several components: a control system,
a central processor, and a certain number of auxiliary “slave”
systems. One of these slave systems, the phonological or articulatory
loop, specializes in processing linguistic information, while
another specializes in processing visuo-spatial information.
The phonological or articulatory
loop plays an important role in everyday life. For example,
when you repeat a phone number to yourself in your head, you
are activating this loop. This loop is also heavily involved
in reading and writing. The presence in working memory of
another slave system that can manipulate mental images of
visual objects is suggested by tests where subjects are asked
to rotate such images. Perhaps the most important but least
understood component in Baddeley’s model of working
memory is the central processor, whose job would be to select,
initiate, and halt the routines performed by its slave systems.
SENSORY, SHORT-TERM
AND LONG-TERM MEMORY
Sensory memory is the memory that results from our perceptions
automatically and generally disappears in less than a second.
It includes two sub-systems: iconic memory of visual perceptions
and echoic memory of auditory perceptions.
Short-term memory depends
on the attention paid to the elements of sensory memory.
Short-term memory lets you retain a piece of information
for less than a minute and retrieve it during this time.
One typical example of its use is the task of repeating a
list of items that has just been read to you, in their original
order. In general, you can retain 5 to 9 items (or, as it
is often put, 7±2 items) in short-term
memory.
Working memory is a more recent extension of the concept
of short-term memory. As techniques for studying memory have
become more refined, it has become increasingly apparent that
the original conception of short-term memory as a mere temporary
receptacle for long-term memory is too simplistic. In fact,
it is becoming increasingly clear that there is no strict line
of demarcation between memories and thoughts. In order to test
some hypotheses that may provide a better understanding of
this complex phenomenon, the concept of working memory has
therefore been advanced.
Working
memory is used to perform cognitive processes on the
items that are temporarily stored in it. It would therefore
be heavily involved in processes that require reasoning,
such as reading, or writing, or performing computations.
One typical example of the use of working memory is the
task of repeating a list of items that has just been
read to you, but in the reverse of their original order.
Another good example is the task of simultaneous interpretation,
where the interpreter must store information in one language
while orally translating it into another.
Working memory appears to be
composed of several independent systems, which would
imply that we are not aware of all the information
that is stored in it at any given time. For example,
when you drive a car, you are performing several complex
tasks simultaneously. It is unlikely that all of the
various types of information involved are being handled
by a single short-term memory system.
Long-term memory includes both our memory of recent
facts, which is often quite fragile, as well as our memory
of older facts, which has become more consolidated. Long-term
memory consists of three main processes that take place consecutively:
encoding, storage, and retrieval (recall) of information.
The purpose of encoding is to assign
a meaning to the information to be memorized. For example,
you might encode the word "lemon"
as “fruit, roundish, yellow”. If you could not
recall the word “lemon” spontaneously, then invoking
one of the indexes that you used to encode it (such as “fruit”)
should help you to retrieve it. How effectively you can retrieve
information depends on how deeply you have encoded it, and
hence on how well you have organized it in your memory. The
process of encoding refers not only to the information being
memorized, but also to its environmental, cognitive, and emotional
context. Also, using mnemonic
devices to associate ideas and images helps us to create
links that facilitate encoding. (One classic example is the
acrostic Every Good Boy Deserves Favour, for the musical notes
on the lines of the treble clef.) But even when information
has been well encoded, it can still be forgotten.
Storage can be regarded as the active process of consolidation
that makes memories less vulnerable to being forgotten. It
is this consolidation that differentiates memories of recent
facts from memories of older ones. The latter have been associated
with a larger amount of pre-existing knowledge. Sleep, and
in particular the rapid-eye-movement (REM) phase of sleep,
along with reviewing (such as studying for exams) play a large
role in consolidation.
Lastly, retrieval (recall) of memories, whether voluntary
or not, involves active mechanisms that make use of encoding
indexes. In this process, information is temporarily copied
from long-term memory into working memory, so that it can be
used there. The more a memory has been encoded, elaborated,
organized, and structured, the easier it will be to retrieve.
Thus, we see that forgetting can be caused by failures at any
of these stages: poor encoding, insufficient consolidation,
or difficulties in retrieval.
Retrieval of information encoded in long-term memory is traditionally
divided into two categories: recall and recognition. Recall
involves actively reconstructing the information, whereas recognition
only requires a decision as to whether one thing among others
has been encountered before. Recall is more difficult, because
it requires the activation of all the neurons involved in the
memory in question. In contrast, in recognition, even if a
part of an object initially activates only a part of the neural
network concerned, that may then suffice to activate the entire
network.
Semantic memory can
be regarded as the residue of experiences stored in episodic
memory. Semantic memory homes in on common features of
various episodes and extracts them from their context.
A gradual transition takes place from episodic to semantic
memory. In this process, episodic memory reduces its sensitivity
to particular events so that the information about them
can be generalized.
Conversely, our understanding of
our personal experiences is necessarily due to the concepts
and knowledge stored in our semantic memory. Thus, we
see that these two types of memory are not isolated entities,
but rather interact with each other constantly.
In Alzheimer’s disease, patients
quickly develop difficulty in retrieving individual words
and general knowledge. Studies have shown that in tasks such
as describing and naming items, these patients display a
loss of knowledge of the specific characteristics of semantic
categories. Initially, they lose the ability to distinguish
fine categories, such as species of animals or types of objects.
But over time, this lack of discrimination extends to broader,
more general categories. At first, if you show such patients
a spaniel, they may say, “that is a dog”. Later,
they may just say “that is an animal”.
DIFFERENT TYPES OF LONG-TERM
MEMORY
As the diagram below
shows, long-term memory can be divided into explicit
and implicit memory, and implicit memory can in turn
be divided into various
subtypes. But always bear in mind that in the actual
workings of human memory, these various subsystems are
interacting all the time. The interactions between episodic
and semantic memory-two distinct forms of explicit memory-may
offer the best example (see sidebar).
Episodic memory (sometimes called autobiographical memory)
lets you remember events that you personally experienced at a specific
time and place. It includes memories such as the meal you ate last
night, or the name of an old classmate, or the date of some important
public event.
The most distinctive feature of episodic memory is that you see
yourself as an actor in the events you remember. You therefore
memorize not only the events themselves, but also the entire context
surrounding them.
Episodic memory is the kind most often affected by various forms
of amnesia. Also, the emotional charge that you experience at the
time of the events conditions the quality of your memorization
of the episode.
Semantic memory is the system
that you use to store your knowledge of the world. It is a knowledge
base that we all have and much of which we can access quickly
and effortlessly. It includes our memory of the meanings of words–the kind of memory that
lets us recall not only the names of the world’s great capitals,
but also social customs, the functions of things, and their colour
and odour.
Semantic memory also includes our memory of the rules and concepts
that let us construct a mental representation of the world without
any immediate perceptions. Its content is thus abstract and relational
and is associated with the meaning of verbal symbols.
Semantic memory is independent of the spatial/temporal
context in which it was acquired. Since it is a form of reference
memory that contains information accumulated repeatedly throughout
our lifetimes, semantic memory is usually spared when people suffer
from amnesia, but it can be affected by some forms of dementia
(see sidebar).
