The third and final stage of the MSM is the long-term memory (LTM). If information is rehearsed in the STM then it is passed onto the LTM, where it has a potential duration of up to a life time. According to the MSM model the capacity of the LTM is potentially unlimited but as we are constantly adding to our LTM there is no adequate way to measure this. The main type of encoding for the LTM is semantic though, as with the STM, this is not exclusively so and it has been known to use other types of encoding as well. You can lose information from the LTM through either decay or interference
The MSM has fairly high face validity. However, high face validity is only one small strength in the MSM and what is really needed to make a fair judgement is empirical research evidence.
Strong evidence that there are separate short-term and long-term stores is provided a piece of research carried out by Glanzer and Cunitz into the primary and recency effect. Participants were presented with a list of words one at a time, and asked to recall them either immediately or after a delay of 30 seconds - participants in the delayed recall group were prevented from rehearsing the words as they had to count backwards for the 30 seconds delay. The findings were that participants who recalled the list immediately remembered the first and last few words best, participants that recalled the list after a delay only remembered the first few words, and both groups of participants had difficulty recalling words from the middle of the list. The researchers concluded that words from the beginning of the list were remembered because they had entered long term memory (they called this the primacy effect), and words at the end of the list were remembered well in the immediate recall condition because they were still in short term memory (they called this the recency effect). The primacy effect and recency effect can be taken together to provide evidence that human memory has separate short and long term stores, and therefore provides evidence for the validity of the model as it too claims there are separate short term and long term memory stores.
Other piece of evidence for the MSM are the cases of HM and Clive Wearing. Both of these patients had severe damage to the areas of their brain that contain the hippocampi (in HM’s case the Hippocampi were removed altogether) After suffering their brain damage, both HM and Clive Wearing lost the ability to form new long term memories. Both had normally functioning short term memories, but as STM only has a duration of up to 30 seconds anything that happened to them was completely forgotten. They could remember things from their pasts prior to their brain damage. This severely debilitating condition provides strong evidence that short term and long term memory are completely separate entities in the human brain, and again supports the validity of the multi store model of memory.
However, there are cases that the MSM cannot explain all cases such as that of KF. KF suffered brain damage in a motorcycle accident. Unlike HM and Clive Wearing, KF’s long term memory was normal, but his short term memory was damaged to the extent that he could only remember 2 items or chunks instead of the usual 7 +/- 2. This causes a problem for the model as it says that information must be retained and rehearsed in short term memory before it can be passed to long term memory - if KF’s short term capacity was reduced then following the model one would expect his ability to pass information to long term memory to also be reduced, but it was not and so the model must be flawed.
Another case that goes against the MSM is that of HM as the MSM states that each unitary store is a passive warehouse therefore if part of it gets damaged then all of it gets damaged. However, HM did retain some long-term memories from before he suffered his brain damage, he did have retrograde memory loss of up to 11 years before his operation but that was thought to be down to medication he had had to take to prevent his epileptic seizures. Therefore the idea of each unitary store being a passive warehouse can simply not be the case as HM clearly retained some long-term memories when he should have lost all of them. Also HM, though unable to make new long-term memories could learn new skills, one example of this was the pursuit rotor task in which he simply had to use a pencil to follow a wavering line on a rotating disc. Each time he was asked to repeat the task he was unable to remember ever having seen the disc before, but on each occasion he became more accurate through practice. HM had therefore learned a new skill, which must be stored in long term memory, and so the idea that long term memory is a single unitary store as represented by the multi store model must be incorrect; there must be more than one type of long term memory.
Overall a huge criticism of the MSM is that it is too reductionist to explain the complexities and this is supported by the cases I have already gone over.
