Human memory is a complex phenomenon which psychologists have been studying for years. Atkinson and Shiffrinâs (1968) multi store model shows how memory divides into three different stores, sensory-, short- and long-term memory, which pass information from one to another using various methods. Baddeley and Hitch (1974) criticised the model for oversimplifying short term and long-term memory. Through the development of the working memory model, they claimed that short term memory is composed of three stores: central executive, phonological loop and visuo-spatial sketchpad. In 2000 Baddeley added an episodic buffer which communicates between long term memory and the working memory model. This essay investigates the differences between short- and long-term memory, looking at evidence for aspects of their capacity, duration and coding.
Short and long-term memory have different capacities. Long term memories are thought to have an unlimited capacity whereas short term memories have a limited capacity of seven plus or minus two items according to Miller (1956). It is believed that the number of items the short-term memory can hold can be increased via chunking. Vaughan and Green (1984) studied pigeons to investigate the capacity of long-term memory. The pigeons were studied and appeared to have large long term memory capacity which is barely subject to decay. This study however is an animal study therefore is not ethical as animals cannot consent and cannot be generalised to humans, as a pigeon does not have the same brain as a human. However, this study is scientific and has contributed to our knowledge of memory capacity. A recent study using human participants was conducted by Brady et al. (2008) Participants were given five and a half hours to view 2,500 objects. They were then shown pairs of images and asked to state which they had previously seen. Results showed that participants had remembered thousands of images indicating that the capacity of long-term memory is very high. This study is ethical because participants all gave informed consent before participating . However, an issue with the study is that it does not reflect a real-life situation as it is not an everyday task to view 2,500 objects. Therefore, when generalising to everyday situations the study needs to be viewed with caution. Through these studies we can distinguish the difference between the capacity of both long- and short-term memory.
A difference between long and short-term memory is that both have different time frames in which memories are held. Long term memories are thought to be held for up to a lifetime whereas short term memories are thought to be held for around 18 seconds according to Peterson and Peterson (1959). Within Peterson and Petersons (1959) study 24 psychology students were given the task to recall three letter trigrams after different intervals of time. Students were told to count backwards in threes until they were asked to recall preventing any rehearsal of the trigrams. After three seconds around 80% of the recall was accurate however after eighteen seconds it had decreased to 10%. They concluded that short term memory has a limited duration of around eighteen seconds. This study uses artificial memories therefore lacks ecological validity and the results cannot be applied to everyday memory. However due to the highly controlled laboratories the results have been easy to replicate for example by Murdock (1961). This therefore increases the reliability of Petersons and Petersons findings as the results are consistent. Furthermore, Bahrick et al. (1975) investigated long term memory using 392 students. Participants were given photographs from their high school yearbook along with a selection of names and were asked to match the name with the photograph. It was found that after 14 years 90% of participants were able to match the names to the faces and after 47 years after graduation 60% of participants could correctly match the name to the photo. This led to Bahrick et al. (1975) concluding that people can remember information such as names and faces for almost a lifetime. This provides evidence and support for the idea that long term memory has a duration of up to a lifetime. However, the sample Bahrick used was university graduates therefore this cannot be generalised to the general population as it lacks population validity. Although the sample lacks population validity the study has high levels of ecological validity, as it uses real life memories and does not rely on artificial memories therefore can be used to look at everyday memory. These studies therefore show how short- and long-term memories have different durations in which the memories are held.
Both short term and long-term memories are subject to forgetting. Short term memory forgetting is explained via the trace decay theory, where automatic decay and fading of a memory traces leads to forgetting, investigated by Brown (1958). Forgetting in short term memory is also explained via displacement which is due to it having a limited capacity therefore old information is replaced by new information. Evidence for this is provided by Murdockâs (1962) experiments. It can be argued that short term memory forgetting could be due to decay not only displacement and it is hard to distinguish between the two. Long term memory is explained via retrieval failure which is where memories cannot be accessed because the retrieval cues are not there. An example of this was shown through Baddeley (1975) who showed the importance of the retrieval cue context. Two groups deep-sea divers were asked to memorise a list of words, one in water and one on the beach. When asked to recall, half of the beach group had to recall on the beach and the other in the sea. The sea group were also split with one half recalling in the sea the other on the beach. Results stated that participants who recalled in the same context in which they learnt recalled 40% more words than the groups in a different setting. Indicating that retrieval cues are a cause of forgetting. The study lacks ecological validity due to the artificial nature of the study as it does not reflect a real-life situation. However, retrieval cues are useful as they are used during eyewitness cognitive interviews to encourage the recall of more information. These studies show how the process for forgetting for short- and long-term memory is different.
Long- and short-term memories are processed in different ways. According to Baddeley (1966) short term memories are phonologically coded whereas long term memories are coded semantically. Participants were split into four groups and each group was given either a list of semantically similar, semantically different, acoustically similar or acoustically different words. The words were shown to participants who were then asked to recall them in the original order. Short term recall was better with acoustically different words whereas after a twenty-minute break long-term memory recall was better for semantically different words. Suggesting how there are two distinct stores of memory short and long term, as each codeâs different types of memories. This has led to further research, as Baddeley and Hitch (1974) used this research to develop the working memory model, therefore this study has great application . The study was a laboratory experiment as it uses an artificial setting therefore lacks ecological validity because the task is unrealistic and does not reflect everyday life. However, although this is an issue the study uses highly controlled variables and is highly scientific, meaning it can determine a cause and effect. This study is highly regarded and influential in the scientific world and therefore can be used to show a difference between coding within the two memory stores.
Patients such as Clive Wearing (Baddeley, A. (2014)) who suffers from both anterograde and retrograde amnesia can be used to show the two separate memory stores. Antegrade amnesia is loss of the ability to form new memories. It is believed that the duration of his short-term memory is between seven and thirty seconds long. Whereas retrograde amnesia is loss of long-term memories, which means he has lost certain memories such as life events. Although he does not remember key career moments, he is still able to read and play music pieces. This indicates long- and short-term memory must be different, as Clive has not lost his full long-term memory however, he has lost all off his short term. Whereas if they were the same store, he would not have any memory. Case studies like this have allowed us to see a distinct difference between the two types of memory, which we would not have otherwise seen. However, they are unique studies so we cannot rely on them and generalise these findings to the wider population.
To conclude although there are some similarities between short- and long-term memories there are multiple differences with their duration, capacity and coding which provide evidence for them being two individual stores. The differences mean that we do not remember every sensation forever however, the items we need to remember in order to function (such as family and friendsâ names) are stored for when we need them.