Retrieval failure is one of the most common causes of forgetting and one possible explanation of this is known as the decay theory. This theory gives an explanation of forgetting as a problem of availability – that is, information is lost completely from the memory system through disuse and passing of time which as examined by Hebb in 1949. It is biological processes in the brain which cause the trace decay until eventually the message it carried is lost. This theory has led to further research by scientists to look at how neural circuits change when long-term memory forms and furthermore, how changes such as this could decay over time (Villarreal et al., 2002). However it has been also been criticised in the sense that we do still recall things we haven’t thought about for a long time such as riding a bike: although we’ve not been renewing the physical memories in the meantime the memory is still there. Also, some professional actors are able to recite lines from productions they were in two years earlier despite having learnt other scripts since (Noice and Noice, 2002b).
The interference theory proposes that we forget information due to other items in long-term memory impairing our ability to retrieve it (Postman and Underwood 1973), two types of this are known as proactive and retroactive interference. Proactive interference happens when