le or is not accessible. It is in terms of availability and accessibility that the importance of forgetting, with regard to demonstrating separate stages in memory is to be approached. Failures of availability and accessibility include encoding failure occurs when data is not stored in the short or long term memory. Trace decay involves the physical form of memory disappearing with time due to neural decay; it explains sensory memory, short term memory forgetting and the effect of rehearsal. In regard to the long term memory, some kinds of memory do not decay e.g. how to drive or ride a bike whereas others do not decay but become inaccessible e.g. the success of recall under hypnosis, electrical stimulation of the brain or the effectiveness of cues. Displacement is another form of forgetting which applies only to the short term memory. According to research the short term memory is limited in capacity and therefore any excess information would be overwritten (displaced), Shallice (1967) found that the speed of presentation of digits affected recall less than the number of items which suggests that displacement must have caused the effect. This does not happen in the long term memory as it has a potentially unlimited capacity. Other failures of availability include interference - where one set of information competes with another causing it to be overwritten or completely lost e.g. McGeoch and McDonald (1931) with the findings being similar to the studies of trace decay. Studies of the effects of brain damage in terms of memory failure highlight the way memory works at a neurophysiological level. Retrograde amnesia affects the short term memory because events immediately prior to the trauma are permanently forgotten presumably because information is lost from the short term memory at the time of the trauma (lack of consolidation). Whereas anterograde amnesia affects the long term memory structure, permanent memories remain intact but suf...
