When we forget, we can say that one of two things has happened – that either a memory has vanished, or that it cannot be retrieved. Just as there are models that attempt to describe how memories are formed, there are models that attempt to describe how they are lost.
The loss of previously encoded information stored within memory is commonly referred to as ‘forgetting’ or ‘disremembering’ and there are several accounts of the processes involved.
Explanations for these processes depend on memory type – forgetting from long-term memory can be explained referring to interference theory and lack of consolidation, whereas forgetting from short-term memory can be explained referring to trace decay theory or displacement theory.
The Displacement Theory
Displacement Theory attempts to explain how we forget information in short-term memory. Based on Miller’s famous Magical Number Seven, Plus Or Minus Two – his suggestion for the normal capacity of human memory – short-term memory can only hold a limited amount of information.
Displacement Theory proposes that when short-term memory becomes full, new information pushes out, or displaces, old information to incorporate the new.
Evidence for this comes in the form of ‘free-recall.’ Studies using this technique usually require a group of participants to listen to a list of words read aloud at a certain rate, and then asked to recall as many of the words as possible afterwards. As this technique is simple and easily replicated, it is considered a reliable form of evidence.
In the past, this kind of study has produced meaningful patterns. When plotting a graph where y is the average word recall and x is the position of word in list, a pattern in data repeatedly appears:
This pattern indicates two things: items towards the beginning of a list are normally better recalled and items towards the end of a list are normally better recalled. The former is referred to as the ‘primacy effect’, whereas the latter is referred to as the ‘recency effect’.
Displacement Theory can effectively explain the observation of the recency effect: the most recent words in the list will have not yet been displaced from short-term memory and so will be free to recall.
It also works in tandem with the multi-store model of memory, in which information becomes stored in long-term memory due to rehearsal, to be able to explain the primacy effect. As the words in the list are read, each new word will add more competition (and therefore more difficulty) for the limited capacity of the short-term memory. Because of this, words that appear earlier in the list will have a greater chance of being transferred to long-term memory.
The middle section of the graph can also be explained. The primacy effect indicates items available from recall from long-term memory, whereas words from the middle of the list were previously in short-term memory but have now been displaced by the words at the end of the list.
It is important to note that Displacement Theory was used to provide an account of how the process of forgetting could work in the original modal model of memory. This model has since received widely criticised for its simplicity and has been largely superseded by the working memory model.
It is difficult to tell whether or not forgetting can be explained exactly by Displacement Theory. There are competing theories, involving processes such as decay and interference, that also attempt to explain the loss of encoded information in memory, with evidence to support them.