Forgetting is when learnt information can't be retreieved. 

Forgetting information from STM is tought to be down to an availability problem - the information is no longer available because of the limited capacity or the limited duration of STM. The information may have been pushed out (displaced) or decayed. 

In LTM forgetting can be caused by decay, but it can also be because:

  • The info was stored, but it is hard to retrieve 
  • The info is confused - interference problem 
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A theory about forgetting is that your ability to remember a particular thing you've learnt can be affected by having learnt something similar before or since. This is known as interference. There are two types of interference - retroactive and proactive.

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Retroactive interference

Where new information interferes with the ability to recall older information. 

Research to support retroactive interference:

Underwood and Postman (1960)

  • Lab experiment, participants spilt into two groups.
  • Both groups given a list of paired words to learn. 
  • Experimental group was then given a second list of words to learn, where the first words in each pair was the same as in the first list.
  • Control group wasn't given a second list.
  • Both groups were then tested on their recall of the first word list, by being given te first word from each pair.
  • Recall was better better in the control group, suggesting that retroactive interference of the second word list had affected recall for the experimental group. 
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Proactive interference

Is where older information interferes with the ability to recall new information.

Underwood (1957) provides research for proactive interference:

  • He found that if people had previously leant 15 or more word lists during the same experiment, a day later their recall of the last word list was around 20%.
  • If they hadn't learnt any earlier lists, recall a day later was around 80%.
  • Underwood concluded that proactive interference from the earlier lists had affected the participants' ability to remember later ones.
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Interference theory evaluation

Proactive and retroactive interference are supported by studies, many of which were highly contolled lab experiments.

As well as in lab experiments, there is evidence for interference existing in real-world settings too. E.g. you might forget French vocab if you study German later.

Interference effects seem much greater in artificil lab settings than they do in real life, so it may not be as strong a theory as once thought.

The theory gives us an explanation for why we forget, but it doesn't go into the cognitive or biological processes involved - it doens't fully explain why or how interference happens.

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Cue dependent forgetting

In this theory forgetting is treated as a retrieval failure - the info still exists in memory but it isn't accessible.

We have more chance of retrieving a memory is the cue is appropriate. Cues can be internal or external. We remember more if we are n the same context/mood  as we were in when we coded the information originally. This is cue-dependent learning.

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Tulving and Psotka (1971) - LTM forgetting


  • Compared the theories of interference and cue-dependent forgetting.
  • Each participant was iven 1-6 lists of 24 words. 
  • Each list was divided into 6 catagories. Words were presented in category order.
  • After the lists were presented, in one condition, partiipants had to simply recall all the words - total free recall.
  • In another condition, participants were given all th category names and had to try to recall words from the lists - free cued recall.


  • Total free recall - seemes to be evidence of retroactive interference. Participants with 1 or 2 lists had a higher recall than those with mre lists to remember. 
  • Cued recall test - the effects of retroactive interference disappeared. It didn't matter how many lists a participant had - recall for each list was around 70%.
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Tulving and Psotka (1971) - LTM forgetting


  • Results suggest that interference had not caused forgetting. Because the memories became accessable if a cue was used, it showed that they were available, but just inaccessable. 
  • Therefore, the forgetting shown in the total free recall condition was cue-dependent forgetting.


  • Lab experiment - highly controlled but lacks ecological validity.
  • Results cam't be reliably be generalised to info of other types - only tested memory.
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Cue-dependent evaluation

Cue-dependent foretting is thought to be the best explaation of forgetting inLTM, as it has the strongest evidence. Most forgetting is seen to be caused by retrieval failure. This means that virtually all memory we have is available in LTM  we just need the right cue to be able to access it .

The evidence is artificial, lacking meaning in the world. Also, it would be difficult, if not impossible, to test wheter all information in LTM is accessable and available, and just waiting fot the right cue.

The theory might not explain all memory types. For example, it doesn't explain procedural memory.

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