Decay theory offers an
explanation for forgetting
in both short-term memory
and long-term memory.
Memories have been shown to
involve structural changes in
the brain and the establishing
of fixed connections between
neurons (Rose 1992).
The decay explanation for forgetting is really
a biological explanation which suggests that,
unless information is rehearsed, the trace
connections between neurons which make a
memory permanent are not sufficiently fixed
and simply fade away (Hebb 1949).
This would explain forgetting in
short-term memory. In long-term
memory, it is proposed that memories
that have been rehearsed and have
become fixed as a structural change in
the brain can nevertheless fade away
over time if they are not used regularly.
Studies by Brown (1958)
and Peterson and Peterson
(1958) offered support for
the decay theory of forgetting
from short-term memory.
technique they used has
become know as the
The task involved displaying sequences of
3 consonants (3 consonant trigrams), such
as 'B T F', to participants for a few seconds.
Immediately after the display, participants
heard a number and were then required to
count backwards from this number in threes.
The task of counting backwards was
designed to prevent rehearsal of the
trigram. It was usually found that
when people were prevented from
rehearsing information, it is very
quickly lost from short-term memory.
by more than 50% in
less than 6 seconds.
The findings of studies
using the Brown-Peterson
technique support the view
that information is lost from
short-term memory through
a process of decay.
Other research has
shown that the passage of
time does not affect recall
from short-term memory.
Waugh and Norman
argued that even
traces decay over time.
In other words, if memories
are not used they gradually
fade away as time passes.
This is sometimes referred
to as the Law of Disuse.
Ebbinghaus investigated this
himself by learning 169
different lists of 13 nonsense
syllables, made up of
sequences (E.g. BEJ, ZUX etc),
and then testing himself after
different intervals of time.
He used nonsense
syllables rather than real
words so it would be a true
test of memory, and not a
test of existing memories for
words he already knew and
could link to other things.
He found that forgetting
followed a particular
pattern, known as the
'forgetting curve', with rapid
forgetting at first and a
gradual levelling off.
Bjork and Bjork (1992)
have recently suggested a
new theory of 'disuse'. They
argue that memory traces
compete with each other for
access to a retrieval path.
Frequent retrieval of one particular
memory trace strengthens its access to
the retrieval route, making it easier to
access in the future. At the same time, this
has the effect of blocking off the retrieval
route to other rival memory traces.
This theory explains why
information that is not
retrieved regularly becomes
less easy to access,
supporting the decay theory.
Most studies of decay
tasks and so have very
low ecological validity.
Decay theory is difficult to investigate in
a real-life way because the time
between learning something and
recalling it will be filled with all kinds of
different events. In studies which involve
a distracter task, such as
Brown-Peterson, it might be the
distracter task which causes forgetting,
and not simply the passage of time. This
would support the interference theory of
forgetting rather than decay theory.
Decay theory cannot explain why
people often remember clearly
events that happened several years
ago, even though they have not
thought about them for a long time.
Solso (1995) points out that there is
no evidence that neurological decay
is responsible for normal forgetting,
although it is obviously responsible
for forgetting in conditions such as
Sperling's research (1960)
does support the idea that
information decays and is
lost from sensory memory.