Info that enters the STM leaves a trace in the brain due to the excitation of nerve cells.
This neural activity gradually fades away unless the material is rehearsed.
Hebb argued that whilst learning the engram (permanent change in neural tissue) which will eventually be formed is very delicate and liable to disruption because it is an active trace. Whilst learning it grows stronger until a permanent engram is formed.
Some researchers argue that if knowledge and skills in the LTM are not used and practised the engram will decay. Hebb argued that it can only apply to the STM as he believes when we rehearse material the corresponding neural activity causes a structural change in the brain (no longer a trace).
Solso also concluded that the major evidence for forgetting from the LTM is neurological decay.
Waugh and Norman Study
EVALUATION OF TRACE DECAY:
- Difficult to test the trace decay theory, if participants are tested after different time periods they could be rehearsing and strengthening the trace, but if rehearsal is prevented by a distractor task forgetting could be due to interference from the task rather than decay of the memory trace.
- It has difficulty dealing with situations where items which cannot be remembered at one time can be remembered at another, even though no additional preservations have been made. If it has decayed it should never be available.
- Experiment by Peterson and Peterson used as evidence for the role of decay in STM, as findings show after 18 seconds the trace has almost completely decayed when rehearsal is prevented.
- Waugh and Norman concluded that interference is the most likely cause of forgetting.
Explains forgetting from the STM in terms of the limited capacity of this store. Suggests there are a limited number of slots for infor in STM approximately 7 as found by Miller, and when the system is full the oldest material is pushed out/displaced by incoming information.
Waugh and Norman study offers support to this theory.
- Gives an adequate account of forgetting in the STM when applied to the MSM.
- Empirical evidence such as the primacy/recency experimental findings, offers support for the theory. However more recent models such as WMM have indicated that STM is much more complex than the unitary limited capacity short term store proposed by Atkinson and Shiffrin.
Concerned with what happens before, during and after learning.
At the beginning of storage process, interference can prevent new info from passing from STM to LTM. In LTM as the store of info grows there will be increasing interference between competing memories.
2 types of interference:
- Proactive interference - where earlier learning interferes with what you are presently trying to learn. e.g you learnt spanish and are now finding it hard to learn french.
- Retroactive interference - where more recent learning interferes with the recall of earlier material e.g you know your present phone number but can't remember your old one.
Study by Keppel and Underwood…