Transcript trace decay ppt

Trace Decay
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
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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!
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
Trace Decay Experiment
Ethics
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This experiment aims to investigate one
aspect of memory.
You do not have to participate.
You may withdraw at any time.
Trace decay
You will see a trigram card
After this you will be asked to count backwards
from 50 in 3’s
Ready…..
FHT
Count
Recall
KLB
Count
Recall
MCF
Count
Recall
HYC
Count
Recall
DJR
Count
Recall
MCG
Count
Recall
PDC
Count
Recall
PSF
Count
KCB
Count
Recall
HSJ
Count
Recall
Supporting Evidence for Trace
Decay Theory
Peterson & Peterson (1959)
 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
Evaluation
However, a weakness of this research is
that it was conducted in a laboratory.
Consequently, the experiment involved
artificial tasks (lacked --------------------------)
and an unnatural setting, and therefore
(lacked________________)
So the results may not be valid in the “real
world”, and therefore this study cannot
easily be generalised to how we use
memory in the real world.
Evaluating the trace decay theory
of forgetting – AO2
- One problem is the theory is limited.
There are things that it cannot explain.
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
appropriate cues, memories are triggered
and long-forgotten memories remembered
This suggests the engram did not decay
- 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 according to trace decay theory.
- 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 intact.
- 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.