UNSW. Australia: Throughout our lives we have multitudes of experiences that shape how
we then behave in the world. Some of these lessons are learnt rapidly,
such as why we shouldn’t put our hand on a hot pan on the stove. Other,
more autobiographical experiences can be stored and recalled explicitly as our memories.These
memories can be recalled and described, such as what we did for certain
birthdays, or experiences from our holidays. We can also learn to
perform certain actions and behaviours that are totally new to us – for
example, learning to ride a bike and drive a car. These actions can be
thought of as muscle memories, or “non-declarative” memory.
Forgotten - but not gone
However,
it seems we don’t retain all of our memories and experiences. There are
times in your life when you find yourself pondering basic general
knowledge questions and wonder where these gaps in information have
sprung from. Despite all those hours of study at school, many of us
can’t remember how to say “two beers please” in Spanish when we are on
holiday, or how to work out a specific angle of a triangle, despite
being proficient in these skills some years ago.
Why is it that we lose the information that we have learnt? Is it still there but inaccessible, or is it gone forever?
Memory can be thought of as having two components: storage – the process of encodinga memory, and retrieval – the process of recalling the memory. Memories are stored in short-term memory stores and then can be transferred to long-term memory.
Short-term
memory has a limited capacity (about seven items) and duration (15-30
seconds). There are two ways in which capacity is tested, one being
span, the other being recency effect. Miller’s (1956) “magic” number 7 (plus or minus two) provides evidence for the capacity of short-term memory.
Most
adults can store between five and nine items in their short-term
memory. The duration of short-term memory seems to be between 15 and 30
seconds, according to the researchers Atkinson and Shiffrin (1971).
After this time the information decays and fades away unless repeated
verbally (rehearsal), which keeps the information in short-term memory.
Then information that survives in short-term memory can pass into
long-term memory.
So a piece of information can be learnt through
practice, making it easy to be recalled in a test a few days later.
However, the strength of a memory at the time is misleading when it
comes to predicting whether we will remember it in the future.
This
suggests that acquiring new memories interferes with previously stored
information, and indicates that the human brain has a limit to how much
information can be stored. We do not know the capacity of the brain, or
the full capacity of our memory.
Theoretically, the
capacity of long-term memory could be unlimited, the main constraint on
recall being accessibility rather than availability. The brain contains a
vast number of cells that are proposed to work together as a network to
encode memories and store them.
There is a theory of forgetting
in cognitive psychology that suggests the encoding of new memories can
cause interference with recall of memories previously encoded (known as retro-active interference).
This interference is proposed to prevent the recall of a specific
memory by competing for expression. So a new memory blocks the recall of
an older memory.
Retrieval failure theory
Retrieval failure is
where the information is in long-term memory, but cannot be accessed.
When we form a memory we also learn about the situation and environment.
These can form retrieval cues.
These cues prompt the retrieval of
a memory and without them the information may not be accessible. These
cues act as a hint or clue that can assist memory retrieval.
Forgetting
is greatest when the situation where the information needs to be
recalled is very different from when the information was encoded. This
can mean that information that we have learnt in a school environment
may not be as easily retrieved when in the “real world”. So, if you had
learnt the Spanish phrase for “two beers please” in a bar, you would be
able to recall it easily when in the same environment again.
These retrieval cues can be important for people suffering with memory impairments caused by neurodegenerative diseases such as Alzheimer’s disease.
Being
unable to recall information is very upsetting. This can, in turn,
cause a change in the internal (emotional) state of the person, which
makes recalling a memory even more difficult. However, by providing
retrieval cues such as old photographs, or returning to a childhood
home, a flood of lost memories can be triggered.
Amy Reichelt is a Senior Research Fellow in the School of Psychology at UNSW.