explanations of forgetting

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Trace decay

  • Info entering the STM leaves a trace due to excitation in the nerve cells
    • neural activity gradually dies away unless rehearsed
    • Hebb (1949) suggested that when learning, the engram (a permanent change in neural tissue representing learnt information) which will be eventually formed is very delicate and liable to disruption as it is an active trace
    • with learning, it grows stronger until permanently formed (structural trace)
  • It is argued that knowledge and skills in LTM will decay if not rehearsed
    • According to Hebb, a trace can only decay in the STM
      • believed that when material is rehearsed the corresponding neural activity causes structural changes in the brain (no longer a trace)
    • Solso (1995) concluded that there is no evidence that major cause of forgetting LTM is neurological decay

Waugh and Norman (1965)

  • Aim: investigate STM using probe technique and support trace decay as theory of forgetting
  • Method: repeated measures design conducted where pps presented with 16 digits at a rate of 1-4 p/s. Last digit, known as probe, occured once before in the list and pps asked to recall what digit followed it. Predicted that pps would recall 1st digit more accurately if presented rapidly as there would be less time for trace decay than in slowly presented digits
  • Result: No relationship between speed and recall, suggesting that trace decay was not a major source of forgetting
  • Conclusion: Forgetting can most likely be explained by interferance rather than trace decay
  • Eval: Keppel and Underwood (1962) supported interferance over trace decay 
    • Both studies lack ecological validity as the tasks were artificial and may not be applied to every day life

Evaluation of trace decay

  • Difficult to test trace decay because pps are tested after different time periods they could be rehearsing and thus strengthening the trace; but if rehearsal is prevented, forgetting could be due to interferance from the task rather than decay of the memory trace
  • It is difficult to apply this to situations where items which cannot be remembered at one time can be remembered at a future time, even though no additional presentations have been made. If the trace has been decayed it should never be available
  • Peterson and Peterson's experiment (1959) is used as evidence for the role of decay in the STM,  as their findings show the memory trace almost completely decays after just 18 seconds when rehearsal is prevented
  • Waugh and Norman, colcluded that interference is the most likely cause of forgetting STM 

Displacement theory

  • Forgetting from STM is due to limitited capacity of storage
    • There are limited number of slots for infromation- aprox.7 (Miller 1956)
    • When the system is full, it pushes out oldest material or is displaced by incoming material
  • Waugh and Norman's study supports the displacement theory for forgetting

Evaluation of discplacement theory

  • Adequate account of forgetting from STM when applied to multi-store memory model
    • Empirical evidence, such as Murdock primary/recency experimental findings, supports displacement theory
    • Although, more recent models, such as WMM, suggest the STM is much more


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