Transcript trace decay ppt

Trace Decay
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The theory suggests that learning causes a
physical change in the neural network of the
memory system, creating a memory trace or
“engram”
Hebb (1949) looked at the brain and showed
that a memory occurs when a group of nerve
cells excite (stimulate) one another
www.psychlotron.org.uk
Trace decay
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Engram = biochemical change (presumably in neural tissue) that
represents a memory
Once this memory trace has been created,
it must be reinforced through repetition to
strengthen it
If the trace is not reinforced by practice it
will simply weaken and decay, causing
forgetting to occur. We need to use it or
lose it!
www.psychlotron.org.uk
Trace Decay (STM)
So, trace decay explains forgetting as a
problem of availability – that is, the
information is lost completely from the
memory system through disuse and
passage of time
Biological processes in the brain cause the
trace to decay until eventually the message
it carried, is lost
Evaluating the trace decay theory
of forgetting – AO2 points
- The problem is that we do recall things we
have not thought about for a long time. For
example we can ride a bike after a long
period. We have not been renewing the
physical memories in the meantime, but
the memory is still there.
- Sometimes, after being presented the right
cues, memories are triggered and longforgotten memories remembered
- Many elderly people can recall incidents from their youth
in great detail. Unless they have recalled the instance
many times throughout their lives, the trace should have
decayed
- If the trace decay theory is correct, and you hadn’t
played the guitar for 20 years then not only would you be
unable to recall the chord sequence for a particular song,
but it would also take you as long to learn the song the
second time as it did the first. This simply isn’t true.
- People under hypnosis can often recall things that they
haven’t thought about for years, so their traces may still
be there
- Trace decay cannot explain why some people seem to
have poor recall of even recent events, while others
have incredible memories going back for decades. Why
are there these huge individual differences?
Trace Decay
+ Peterson & Peterson (1959)
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Had participants recall trigrams after varying intervals
During rehearsal an Interference task was given (counting
backwards in threes) to prevent rehearsal
They found less that 10% of information was recalled after 18
seconds
This is evidence for trace decay in STM. Participants weren’t
able to practice/repeat the information/memory, and so the
memory traces decayed
- However, this was a laboratory experiment, so the study
involved artificial tasks and an unnatural setting, and
therefore lacked ecological validity. So the results may
not be valid for the “real world”, and therefore this study
cannot support the trace decay theory of forgetting
www.psychlotron.org.uk
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