Theories of Forgetting: Interference Theory, Proactive Interference and Retroactive Interference

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  • Forgetting in Long term Memory can be explained by Interference Theory.
  • This theory assumes that memory can be disrupted or interfered either due to newly acquired information or it is inhibited by the old information.
  • During encoding of information in LTM, the information can be interfered either proactively or retroactively.
  • In STM, interference occurs in the form of distractions.

For e. g. – drilling machine outside the classroom interferes with the classroom environment by distracting the students.


For example, A student learnt two languages. He first learnt French and then Spanish. During the exam of each, he showed problems while recalling in each case. In this, interference could occur in two directions. When he went for the exam of the French, his learning of Spanish language may retroactively interfere with the recall of the French language. And during the exam of the second learnt language, the condition would be vice versa. The language French which was learnt earlier might proactively inhibit the recall of the second language i.e.. , Spanish.

Proactive and Retroactive Interference

What is Proactive Interference?

  • Proactive interference or inhibition is the tendency for the older or previously learnt material to interfere with the learning of the new/subsequent material.
  • For example, We all familiar with proactive inhibition. When people get new mobile numbers, they find it difficult to learn it. It is because they remember their old phone number or some of its digits which often leads to confusion and inhibition.
What is Proactive Interference

What is Retroactive Interference?

  • Retroactive interference or inhibition occurs when newer information interferes with the retrieval of the older information.
  • For example, if learning a new computer programming language causes you to forget the previously learnt computer language, then the effects of retroactive interference is experienced.


  • In 1960, Postman did a lab experiment to investigate how retroactive interference affects learning. He divided his participants in experimental group and controlled group. Both groups were given a list of paired words (cat-tree) . The experimental group was made to learn another list of paired words but here the second pair was different (cat-glass) .
  • Results of the recall of list of controlled groups was more accurate than the experimental group.
  • Postman concluded his experiment by stating that in the of experimental group the new items in the second list interfered with participant՚s ability to recall the previous list more accurately.


  • Interference Theory in one form or the other comes out as one of the best explanations of forgetting, especially in case of LTM.
  • Interference, though plays a role in forgetting, but how much forgetting can be attributed to interference is still a question.
  • Also, Interference Theory explains very less about cognitive processes involved in forgetting.
  • Majority of researches to explain this theory are carried out in labs which declares its less external and ecological validity.


1. Which type of interference explain the forgetting of new information due to the previous one?


Proactive Interference

In case of Short-term memory, interference can be explained as:

Distractions: Shreyas got a new cell phone contact number recently. While giving his new contact number to his friend, he got confused with the digits of his previous contact number. What type of interference do you think it is?

Retroactive Interference

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