Forgetting

1
Forgetting

• The inability to recall or recognise something
  that was previously learned
• In short-term memory
• Decay
• Displacement
• In long-term memory
• Interference
• Cue dependent forgetting

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2
Trace Decay (STM)
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3
Trace Decay

• Trace decay
• Based on the idea that information is physically
  represented as a memory trace (i.e. arrangement
  of neurones)
• The trace is fragile and disintegrates if not
  constantly refreshed
• After about 20s, the trace has decayed completely
  recall is no longer possible

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4
Trace Decay

• Peterson Peterson (1959)
• Recall of trigrams after varying intervals
• Interference task to prevent rehearsal
• Found less that 10 recall after 18s
• Claimed evidence for decay in STM
• However, interference task might have caused
  displacement of trigrams

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5
Trace Decay

• Reitman (1974)
• Attempt to avoid the confounding effects of
  displacement
• Used a tone detection task instead of a verbal
  interference task
• Found recall declined by 24 over 15s
• Claimed evidence for decay
• Seems to occur more slowly than Peterson
  Peterson suggested

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6
Displacement (STM)
Short Term Memory
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7
Displacement

• Displacement
• Based on the idea that STM has a strictly limited
  capacity for information
• If STM is full and new information is registered,
  then some existing info is pushed out or
  overwritten

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8
Displacement

• Waugh Norman (1965)
• PPs heard a list of 16 digits
• They were then told one of the digits and had to
  repeat the one that came after it
• Recall was better when the PPs were recalling
  from the end of the list
• Consistent with earlier digits being displaced by
  later ones
• Agrees with other findings (recency effects)

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9
Displacement

• Shallice (1967)
• Repeated Waugh Normans study but varied the
  rate of presentation of the digits
• Found better recall when digits were presented
  faster
• Challenges displacement, as number of bits of
  info was the same
• Supports decay as faster-presented digits had
  less time to decay

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10
Forgetting in STM

• Forgetting in STM is affected by
• Amount of information presented
• Rate of presentation
• Interval between presentation recall
• Task demands between presentation recall
• Very difficult to say whether decay or
  displacement is the most important process
• Other factors also important e.g. acoustic
  similarity in the info (Baddeley, 1966)

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