Decay theory
Obviously memories are stored somewhere, and the obvious place is the brain.
Decay theory assumes that memories have a physical or biological basis in the
brain, and that the encoding of memories involves a structural change in the brain.
The physical representation of a memory is called a memory trace or an engram.
This theory sees forgetting as the physical breakdown or decay of the memory
trace.
Assuming that rehearsal does not take place, the mere passage of time will cause
the memory trace to break down. This explains why forgetfulness increases with
time. According to the theory, metabolic processes happen over time which causes
the structural change to break down if it is not maintained through repetition.
Hebb (1949) argues that during learning that the engram which is formed is timid and
fragile. With learning (repetition), it grows stronger until a constant engram is formed
through neurochemical and neuroanatomical changes. According to the theory, short
term forgetfulness happens because the active trace is disturbed.
Peterson & Peterson (1959) provides evidence for this theory. They discovered that if
participants were prevented from rehearsing a list of words, their recall dropped from
80% after 3 seconds, to 20% after 18 seconds. In terms of decay theory, the engram
could not grow stronger and so broke down.
Similarly Watkins et al (1973) asked participants to either listen to and
remember notes, or listen to them, hum and identify them before being asked
to recall them. He found that participants who had been asked to hum and
identify the notes recalled fewer, presumably because this task had
prevented rehearsal, and the memory trace had decayed.
Decay
Lashley (1931) investigated whether by making physical alterations to the brain, he could induce
forgetting. If this was the case, then it would suggest that memory has a physical basis
and that forgetting is a result of the decay of the memory trace. He trained
rats to learn mazes, and then removed sections of their brains. He found a
relationship between the amount of brain removed, and the
amount of forgetting. This supports decay theory. Evaluation:
Issues of ecological validity. Generalisability from rats to
humans. Alternative explanations for results
However, if decay was the only explanation for loss of memories from LTM, we
would expect that all memories would decay at approximately the same rate,
regardless of what happened in the intervening time. However in a study by
Jenkins & Dallenbach (1924) participants who were asked to recall a series of
nonsense syllables after being asleep for eight hours were able to remember
many more than those who had been awake for eight hours. If decay theory was
correct, we would expect the same amount of forgetting from both groups. Decay
therefor cannot be the only explanation. Something else must be affecting
forgetting.
Evaluation: Generally, there is little support for decay theory, as it cannot explain how we
are able to remember things from many years ago. For example, flashbulb memories seem
to be immune to decay, even though the memory has not been rehearsed.
Interference
According to this theory there are two types of interference. Proactive
interference is when previous learning interferes with later learning.
Retroactive interference is when later learning disrupts earlier
learning. For example, if you learned a set of facts about India, and I
then asked you to learn a set of facts about China, you could
experience interference in one of two ways. The facts about India
could disrupt your learning of China (proactive interference) or the
new facts about China could alter what you know about India
(retroactive interference).
A common everyday example of proactive interference is when you rearrange the location of
items in a room. You may keep going back to the place where items used to be instead of where
they are now!
Underwood &Postman (1960) used a paired associate learning task to test the effect of
interference. Participants are asked to learn a series of word pairs, so that they can be presented
with the first word (the stimulus word), and recall its paired word (response word). They are then
given another list of word pairs to learn which have the same stimulus word, but a different
response word. Participants have their recall tested on either the first or second list of words. As
expected, recall of the response words is poorer, and affected by both previous learning
(proactive) and later learning (retroactive). However, this effect is only present when the same
stimulus words are used in both lists.
Evaluation: Like decay theory, interference theory is a very limited explanation of
forgetting. Research suggests that interference only plays a part when the two stimuli are
very similar. How often would this apply to real life?
A study by Tulving & Psotka (1971) initially seemed to provide evidence for interference.
Participants were asked to learn a list of words which were in categories (such as, animals,
furniture etc). When asked to free recall the words, as those who had
only learned a few categories were able to recall a higher percentage
than those who had many. This suggests that retroactive interference of
the later words was causing the unlearning of the early words. However,
when the participants were given the category names, recall for all
participants increased, regardless of how many categories they has to
learn (see textbook photocopy pg 54 for a more detailed description of
this study). This cannot be explained by interference alone. Another
explanation is needed.
Cue dependent forgetting
This theory states that forgetting is not due to the loss of a memory, but rather is due to the
inability to access that memory. This is known as retrieval failure. The memory is still there, but it
is inaccessible. The reason that it is unavailable is because you do not have the right cue. For
example, if I asked you what Freud’s first name was, you might not be able to access that piece
of information. However, if I said it began with “S”, that may be enough of a cue for you to access
the name “Sigmund”.
Cues can either be external (something about the environment or context) or internal (something
about your own state or mood).
Context dependent learning (external) was demonstrated
by Abernethy (1940) who found that students who sat a
test in the same room, by the same instructor as in their
normal lessons got higher marks. Presumably, the
environment acted as a cue to memory.
It’s not just the environment that can act as a cue to
learning. As we looked at in the role of emotion, our
internal mental or emotional state can act as a cue. This
is state dependent learning. Goodwin et al (1969) found that people who had forgetting
things when drunk, could recall those things when drunk again. Miles & Hardman (1998)
similarly found that things learned when exercising were better remembered when
exercising that when at rest.
Cue dependent learning can better explain the results of Tulving & Psotka than
interference.
Some psychologists believe that all forgetting is cue dependent. It is very difficult to test this
hypothesis however, as (similarly to repression) we cannot tell if a memory is simply inaccessible,
or is not there. The probability is that a lot of forgetting can be attributed to cue dependent
learning, but not all.
Emotional explanations of forgetting
We looked at some explanations of forgetting when we examined the role of emotion in
memory. These are recapped below:
Repression is an explanation of forgetting which states that traumatic memories are
repressed into the unconscious.
Suppression – involves being motivated to forget an event or experience by making a
deliberate conscious effort to keep it out of consciousness (p.381-382 Grivas et.al.)
Evaluation:
Needs to be investigated in laboratory – ethics?
Some studies (Baddeley 1990) who exposed subjects to mildly upsetting experience – potential
evidence to support repression
Your Forgetting revision booklet has an extract from HILL which details further evaluations