There is a general agreement that there is an STM/LTM distinction, and this is well supported by the empirical evidence. For example, some of the evidence in support of the distinction between STM and LTM comes from case studies of people with brain damage which gives rise to memory impairment. Milner (1966) reported on a young man, referred to as HM, who was left with severe memory impairment after brain surgery. He was able to talk normally and to recall accurately events and people from his life before surgery, and his immediate digit span was within normal limits. He was, however, unable to retain any new information and could not lay down new memories in LTM. When told of the death of his favourite uncle, he reacted with considerable distress. Later, he frequently asked about his uncle and, on each occasion, reacted again with the level of grief appropriate to hearing the news for the first time. KF, a motorcycle accident victim investigated by Shallice and Warrington (1970), suffered from the reverse of this memory impairment. He had no difficulty in transferring new items into LTM but had a grossly impaired digit span. Cases such as these lend support to the Atkinson and Shiffrin model, in that they seem to point to a clear distinction between LTM and STM. There does seem to be fairly strong support for a difference between LTM and STM in terms of duration, capacity and effects of brain damage. However, there are problems with the model of Atkinson and Shiffrin. The model is too simple and inflexible and fails to take account of factors such as the strategies people employ to remember things. It also places emphasis on the amount of information that can be processed rather than its nature. Some things are simply easier to remember than others, perhaps because they are more interesting, more distinctive, funnier, or whatever. The multistore model cannot account for this. Furthermore, alternative explanations can account for the empirical findings e.g. the levels of processing model. This model was put forward by Craik and
Lockhart (1972). According to them, processing varies in terms of depth, 'Trace persistence is a function of depth of analysis, with deeper levels of analysis associated with more elaborate, longer lasting, and stronger traces'.
The multistore model has also been criticised for focusing on the structure of the memory system at the expense of adequately explaining the processes involved. For example, visual stimuli registering in sensory memory are thought to be changed to an acoustic code for access to STM. In order to translate the pattern of the letter 'M' into the sound 'em', the individual needs to access knowledge about letter shapes and sounds which is stored in LTM. This means that information from LTM must flow backwards through the system to the recoding stage prior to STM. This suggests that the flow of information through the system is interactive rather than strictly sequential as Atkinson and Shiffrin suggested.
In conclusion, the multistore model may be over-simplified and inaccurate in some areas but it has still been the basis of many later models and is still a useful way to look at memory in general.
