The concept of memory refers to the process by which information is encoded, stored, and retrieved.  Cognitive psychologists have suggested ways to conceptualize the architecture and processes of the memory system by making models of memory. In psychology, a model of memory is a hypothesized representation of memory.  It is more like an outline of the different stores and processes indicating how memory might work according to available evidence. Obviously, models change over time as new evidence becomes available. In order to understand more about the possible structure and function of memory, researchers within the cognitive approach have suggested models of memory that can be tested to determine their validity.

The Multi-store Model

Atkinson and Shiffrin (1968) were among the first to suggest a basic structure of memory with their Multi-store Model [MSM] of memory. Although this model seems rather simplistic today, it sparked much research based on the idea that humans are information processors.

The Multi-store model was suggested in the 1960s and is clearly inspired by computer science. The model is based on a number of assumptions. First, the model argues that memory consists of a number of separate locations in which information is stored.  Second, those memory processes are sequential. Third, each memory store operates in a single, uniform way. In this model, short-term memory (STM) serves as a gateway by which information can gain access to long-term memory. The various memory stores are seen as components that operate in conjunction with the permanent memory store (LTM) through processes such as attention, coding, and rehearsal. You need to pay attention to something in order to remember information. According to this model, rehearsal is vital to keeping material active in STM by repeating it until it can be stored in LTM.

The model suggests that sensory information from the world enters sensory memory, which is modality specific - that is, related to different senses, such as hearing and vision. The most important stores in the model are the visual store (iconic memory) and the auditory store (echoic memory). Information in the sensory store stays here for a few seconds and only a very small amount of the information will continue into the short-term memory (STM) store.

The capacity of STM has traditionally been assumed to be limited to around seven items (7+/-2) and its duration is normally about 6–18 seconds. With rehearsal, information may stay in STM for up to 30 seconds. Information in STM is quickly lost if not rehearsed. Information may also be displaced from STM by new information. For example, when you are rehearsing that phone number for ordering the pizza and then someone calls out your name.  When your attention is taken away from the information in your STM, it is then displaced and no longer available. The rehearsal of material in STM  plays a key role in determining what is stored in long-term memory in the multi-store model of memory.

The long-term memory (LTM) store is conceptualized as a vast storehouse of information. This storehouse is believed to be of indefinite duration and potentially unlimited capacity, although psychologists do not know exactly how much information can be stored there. The material is not an exact replica of events or facts but is stored in some outline form. Memories may be distorted when they are retrieved because we fill in the gaps to create a meaningful memory. This is exactly what is predicted by schema theory.

Evidence in support of the model

In the biological chapter, we looked at the case study of HM (Milner,1966). This is just one example of biological evidence that STM and LTM are located in different stores in the brain. In Milner's study, HM had anterograde amnesia - that is, he could not transfer new information to long-term memory; however, he still had access to many of his memories prior to his surgery. However, the fact that he could create new procedural memories shows that memory may be more complex than the MSM predicts.

Glanzer and Cunitz (1966) used free recall of lists of 15 items combined with an interference task to show that there are two processes involved in retrieving information. The researchers showed fifteen lists of 15 words one at a time. The researchers used a repeated measures design in which the participants were asked to recall the words either with no delay, with a 10-second delay, or with a 30-second delay.  With no delay, the first five and last three words were recalled best but with a 10 or 30-second delay during which the participant counted backward, there was little effect on the words at the beginning of the list but poor recall of later items. This suggests that the later words were held in short-term storage and were lost due to interference whereas the earlier words had been passed to long-term storage. The ability to recall words at the beginning of the list because they had already been transferred to long-term memory is called the primacy effect. The ability to recall words that have just been spoken because they are still in short-term memory is called the recency effect.

Evaluation of the multi-store model

Today the multi-store model is considered to be too simplistic. It reflects the knowledge available in the 1960s but it is an important model all the same because it has influenced our understanding of memory.  First of all, it presents a good account of the basic mechanisms in memory processes (encoding, storage, and retrieval). Secondly, several experiments support the assumption of multiple memory stores. There is also supporting evidence from case studies of patients with brain damage, such as HM suffering from amnesia, who have impaired long-term memory but intact short-term memory. This clearly points toward multiple memory stores. 

The assumption that STM is simply a gateway to LTM has been challenged by Logie (1999). He argues that information in STM is not simply passed into LTM through rehearsal. Instead, there must be an interaction between STM and LTM  in which the information is interpreted with regard to previously stored knowledge and past experience. Short-term memory is therefore not part of a sequential system but rather a 'workstation' that handles and computes information coming from the sensory store together with knowledge already stored in LTM. This also is what schema theory would predict.