Because a memory can
be deliberately recalled or consciously evoked, the psychological
concept of remembering has come to be regarded as a special
function of the brain. But there is another way to look at
it: all of our behaviours can be regarded as involving an
act of remembering. The voluntary recollection of an abstract
concept would then be only a particular case of this very
general process, a phenomenon related to what we call consciousness.
HOW EXERCISING YOUR
MEMORY STRENGTHENS IT
The more we think about a piece of information
that we want to remember and its relations to other concepts that
we already know, the less chance there is that we will forget it.
This may be why forgetting is associated more with episodic
memory than with semantic memory. It is probably easier to draw
connections between the meaning of a new word and our network of
existing knowledge than to draw such connections for any particular
episode in our lives.
More generally, the less any given fact is
integrated with our overall personality and activities, the faster
we will forget it. We quickly forget anything that is not supported
by a motivation and does not lead to an action.
Various theories have been developed with
regard to forgetting. They deal with the process of memorization
or the processing of information.
Decline
Theory
Like any biological process, memory deteriorates and becomes
more fragmented over time.
According to the decline theory, forgetting occurs when
the memory is not exercised or the information in question
is not retrieved often enough.
This is confirmed by statistics on the words that people
forget in a language. Proper nouns, which are used less often,
disappear first. Next come common nouns, then adjectives
(which are used more often, because they can modify many
nouns), then verbs, and then, lastly, exclamations and interjections.
Defective-Recall
Theory
Forgetting is a disturbance in the retrieval of information,
not in its storage.
According to the defective-recall theory, if you are momentarily
unable to access a piece of information in your memory, the
reason is insufficient encoding, or a lack of relationship
to your existing semantic knowledge, or inappropriate retrieval
indexes.
But the stored information still exists somewhere in your
memory, because at some other time, you might suddenly be
able to access it.
Motivated-Forgetting
Theory
According to this theory, there are unconscious mechanisms
that make us forget unpleasant or painful facts.
Indeed, psychoanalysts have shown that forgetting is often
associated with events that have disagreeable or stressful
connotations.
Freud postulated a selective process by which people reject,
or suppress in their unconscious, certain memories associated
with past traumas that would be unbearable to remember. Psychoanalysis
is based on the idea that such suppressed memories have not
really been forgotten and can be brought back to patients’ conscious
awareness.
Interference
Theory
According to interference theory, a piece of information
is forgotten because some other piece of information prevents
it from being retrieved.
In retroactive interference, new memories tend to erase
older ones. Conversely, in proactive interference, older
memories prevent new facts from being committed to memory
effectively.
Thus, together, retroactive and proactive interference enable
us to update our knowledge of the world. New information
can overwrite some of the older information in our memories,
through retroaction, but not all of it, because proaction
prevents it.
Some forms of amnesia
are highly specialized and affect only a limited aspect of
memory. One very curious example is the condition known as
prosopagnosia. This rare form of amnesia prevents its victims
from recognizing people’s faces. Whether they see these
faces live or in photos, and even if the faces are those
of co-workers or family members (or even, in the most severe
cases, their own faces!), they do not know whom they are
looking at. But this can change if a person whom they are
looking at speaks. Often, people with prosopagnosia can recognize
someone’s voice and silhouette, and the rest of their
memory functions normally.
This deficit piqued certain researchers’
curiosity. They investigated, and learned that certain neurons
in the human brain react only when we see faces, and not
when we see other objects. The researchers explained this
very high degree of specialization as follows. 1) The ability
to recognize individuals is very important in social species
such as humans, and humans recognize other humans mainly
by their faces. 2) All faces are constructed according
to the same pattern. They differ only in very slight details,
which is why specialized neurons have developed to recognize
such details.
TYPES OF AMNESIA
Amnesias can be divided into two
categories: neurological amnesias (originating from organic
lesions) and psychogenic amnesias (arising from psychic traumas).
In both categories, a number of different syndromes have been
clearly identified. Here are some examples.
Neurological
Amnesias
Alzheimer’s disease strikes later in life
and is characterized by degeneration of certain neurons
in the brain. Memory problems are one of the first warning
signs of this illness. This is what makes Alzheimer’s
so hard to diagnose early. As people get older, many of
them start to experience minor memory losses as a normal
phenomenon associated with aging. But for people with Alzheimer’s,
over a few years, all of the various forms of memory fall
apart. Episodic memory (memory of events in their own lives)
is first to go. Next comes short-term memory, then memory
of the meanings of words, and then procedural (“how-to”)
memory. In the end, all reasoning, attention, and language
abilities are disrupted.
Korsakoff’s
syndrome is caused by chronic alcoholism (possibly
because it induces a vitamin B1 deficiency). The brain
damage caused by this syndrome leads to progressively
worsening anterograde amnesia. It may also be accompanied
by retrograde amnesia, in which the newer memories
disappear first. People with Korsakoff’s are
often totally unaware of it, and answer questions by
confabulating, with a sort of euphoria that also leads
to false memories. But the essential characteristic
is still anterograde amnesia, where immediate memory
is preserved, but permanent new memories cannot be
established.
Amnesic ictuses are short amnesic episodes that
occur suddenly and last just a few hours. Their causes
are poorly understood. In people who are over 50 years
old but in good health otherwise, the average ictus lasts
six to ten hours and is not accompanied by any permanent
brain damage. But during these episodes, people suffer
from major anterograde amnesia, almost instantaneously
forgetting everything that has just happened. In addition,
they may experience retrograde amnesia covering several
decades of their lives.
Psychogenic
Amnesias
The most common form of psychogenic amnesia is that associated
with a violent experience, such as being mugged or
raped.
This form of psychogenic amnesia is often accompanied
by a fugue state arising after an encounter that
involves an emotional shock. The police often pick up people
in such states who cannot even remember their names and
addresses.
These people lose their biographical memories, but preserve
their semantic and procedural memories. Their episodes
of amnesia can last from a few hours to several days, or
sometimes even months. Such cases are rare, however, though
they are often heavily reported in the media.
Multiple personality disorder, in which two or
more personalities give the impression of co-existing in
the same body, also involves a significant memory disturbance.
Each of these personalities seems to have no access to
the memories stored by the others.
This form of amnesia chiefly affects biographical memories,
leaving semantic and procedural memory accessible to all
of the person’s identities. This disorder is believed
to develop as a defence mechanism against childhood deprivation
or abuse.
ANTEROGRADE
AND RETROGRADE AMNESIA
Anterograde amnesia, also known as fixation
amnesia, is the inability to remember or recognize new information
or new events that occurred after the amnesia’s onset. Retrograde
amnesia, also known as evocation amnesia, is the inability to remember
or recognize information or events that occurred prior to onset.
The famous patient H.M., for example (see
sidebar), was found to have severe anterograde amnesia together
with less severe retrograde amnesia covering the two years preceding
his brain surgery.
This inability to store new long-term memories
literally froze his personal history and knowledge at the point
where they were at the time of his operation. For example, after
his operation, H.M. could no longer recall a list of words a
few minutes after hearing it. He also had difficulty with new
words that were entering the language at the time, such as “jacuzzi” and “granola”.
And yet his short-term memory and implicit
memory, as well as his memories of the distant past, were intact.
For example, he could acquire and master new skills, such as
tracking a target or copying an object in a mirror, even though
he could not remember having practiced these skills many times
in order to do so. This separation of his declarative memory
from his other forms of memory contributed greatly to the identification
of the major
categories of memory that are recognized today.
The
Hanoi Towers Problem: one of the tests used to assess H.M.’s
cognitive abilities after the operation that caused his
amnesia.
Source: Center for Research, Teaching
and Learning - National Technical Institute for the Deaf
In both of these tests, H.M. improved
his skills over the course of several days, even though
each time he took these tests, he thought that he was doing
so for the first time. This shows that despite his amnesia,
he could still acquire certain procedural
memories.
