"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).
