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[Memory is a very complex topic, much researched and at the
heart of the “cognitive revolution”: what follows is therefore
even less reliable than usual, but it has been filtered and
distilled with the needs of teachers in mind: please go
elsewhere for a synoptic view, such as
Memory is of course central to learning, which could not happen
without it: indeed “memorising” is a synonym for the lowest
levels of rote learning.
The diagram to the right illustrates
schematically the current view of memory, based on the model of
Atkinson and Shiffrin (1968). Input of sensory information
starts at the top, goes through “sensory memory” or a “sensory
buffer” into short-term memory (STM), and hence to long-term
Two points are worth mentioning for our purposes:
- the process is selective and “lossy”. At each stage
information is filtered, selected and even altered
(represented by the grey arrows which stand for
- Progression to long-term memory (if it is reached)
may well take less than a minute. It is drastically
simplistic, but still salutary, to consider that from
presenting something you have one minute to get it into
a student's mind (LTM)!
sensory buffer is only technically a part of memory: it
might make more sense to regard it as part of the perceptual
system. Information may stay there for about 1/15 of a
second, while the brain assembles it to “make sense”. We are
familiar with the illusion by which a succession of still
pictures presented rapidly enough appear to be moving: it is
the basis of all cinematography. Once the frame rate drops
below about 16 frames per second, however, we may well
become conscious of the flicker or jumps from one still
image to another. Similarly, we do not hear a succession of
phonemes (or speech sounds), but complete words or phrases:
it is as if the brain waits to assemble a meaningful sound
before passing it on to the next stage.
Which is Short-term Memory (if the
information makes it that far). The research suggests that
STM deals best with sounds rather than visual stimuli, but
that may perhaps be a reflection of the problem of devising
experiments which do justice to the fact that visual stimuli
are taken in all at once, whereas sounds are processed in a
linear fashion—over time. In any event, the STM:
- holds material for about 15-30 seconds, although
this can be expanded by practice. This is much
shorter than most of us think—a lot of people seem
to think that it lasts for ten minutes or so. You
can see, however, how disabling damage to the STM
is, as in the case of dementia.
- has a capacity of
seven items (plus or minus two). However,
“items” are defined by meaning rather than size, so
it may be difficult to remember telephone numbers of
more than seven digits, but if “01234” is remembered
as “Bedford STD code” it becomes just one item, and
remembering “7,9,3,1,5,6” after it becomes simpler.
If that too is “chunked” as “my work 'phone number”
it is even easier.
The feedback arrow on the exit from STM represents what
Atkinson and Schiffrin called “rehearsal”: the process of
continually recalling material into the STM in order to work
on it—memories it or digest it. I do violence to the
technicalities if I say [STM + rehearsal + retrieved LTM] =
“Working memory”, but it makes good pragmatic sense. The
process of digestion must (IMO) be important: it is where
processes such as Piaget's
assimilation and accommodation come into play, as part
of the process of “coding” material for long-term storage.
It is another stage at which detail may be lost.
And so to
Long-term Memory. Theoretically, LTM has infinite capacity
and lasts for the rest of your life.
has suggested the useful distinction between three
components of LTM:
- Semantic memory stores concepts and ideas
- Episodic (sometimes referred to as
“autobiographical”) memory contains memories of events.
- Procedural memory concerns skills and
“know-how” rather than “know-that” knowledge.
A few moments' thought will make it clear that these are
fundamentally different. People with amnesia, for example,
typically lose episodic memory, but other memories may be
relatively intact. Episodic and semantic memory are more
prone to distortion than procedural memory, which is more
robust: a skill lost through lack of practice typically
comes back rapidly when called upon, and without significant
degradation. However, semantic and episodic memories are
more amenable to linguistic description and communication.
I have depicted the three forms as overlapping. Apart
from the fact that they are of course simply constructs
imposed on the blooming buzzing confusion of reality, the
relations between them raise interesting issues for
facilitators of learning:
- The relationship between knowing that
and knowing how
from experience” as the creation of semantic memory
from episodic memory, and conversely
- challenging semantic memories (prejudices, for
example) which are based solely on episodic memory.
It is a common-place that LTM “plays tricks” and of course
that we forget things. That is too complex a matter to
go into here, but it is worth mentioning that the “tricks”
are principally in the direction of simplification and
minimizing discrepancies within the memory store (see
cognitive dissonance), and forgetting (apart from the
kind associated with neurological damage) was described—in a
specific context—very well a couple of thousand years ago:
For an excellent
“A sower went forth to sow, bearing
Some fell by the wayside,
Some memories never even make it to LTM.
Some fell upon stony ground.
Some are not consolidated, perhaps
of conflict with existing “knowledge”
Some fell among thorns,
Known as “interference”, competing in context with other
more pressing concerns, or emotional factors leading to
But other fell upon good ground.
A sower went forth to sow, bearing
A sower went forth to sow—let all who hear
Silk, 1962: based on Mark
The only things not mentioned in the parable are “trace
decay” from non-use, and “cue-dependence” where memories are
so tied in to a setting—an episodic memory, probably—that
they cannot be recalled without it.
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