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Memory: Key ideas

Look at the key ideas surrounding memory, from long-term memory to memory improvement. Learn more about these, and other ideas with our dedicated analysis.

Capacity, duration, encoding of STM and LTM

There are three main concepts that are core to understanding memory processes; capacity, duration and encoding. The short term memory (STM) and long term memory (LTM) differ quite dramatically in these 3 concepts.

Capacity refers to the amount of information that can be stored at one time in a person’s memory. Research into the STM has shown it has a limited capacity of 7+/- 2 items (Miller, 1956), sometimes referred to as Miller’s magic number seven. This applies to remembering digits, letters, words or larger “chunks” of information. Chunking is when we combine a number of digits or letters together to form 1 item e.g. 1 9 8 7 could be seen as the date 1987 rather than 4 individual numbers, thus leaving a greater capacity to remember further chunked items. The capacity of LTM would be argued by most psychologists to be unlimited. It is very difficult to measure and quantify what the exact capacity is and it seems that we can continue to learn and store information throughout our whole lives.

Duration refers to the length of time stored information can be held for and again differs significantly between STM and LTM. STM has been shown to have a limited and temporary duration of approximately 18 seconds (Peterson and Peterson, 1959) compared to LTM, which is argued to hold information for a very long period of time (Bahrick et al., 1975), almost a whole lifetime.

Encoding refers to the format in which information is stored in memory. Research has shown that the STM predominantly encodes information acoustically, relying on the sound of the item to be remembered (Conrad, 1964). However, STM can also code information visually if it is prevented from using acoustic coding (Brandimonte et al., 1992). On the other hand, LTM predominately uses sematic encoding, using the meaning of the word/item to help code the item for future recall.

Multi-store model of memory

The Multi-store model of memory (MSM) was proposed by Atkinson and Shiffrin (1968) as a structural theory to explain the complexities of how our memory works. They believed the memory system is divided into 3 separate stores; sensory memory, short-term memory and long-term memory and information travels between these stores in a linear way. At each stage of the model there are differences in the capacity, duration and encoding of information. The sensory memory retrieves information from incoming stimuli in the environment and holds this information for a very short period of time before this information is passed on to STM (if attended to) or the information is lost through decay. Information that reaches the STM is normally stored in an acoustic or visual form for a limited duration of time (upto 30 seconds). This information can be lost through decay or displacement if it is not rehearsed sufficiently to transfer into LTM. Information that is transferred to LTM, via rehearsal, will generally be recoded into a semantic form and can be held for an unlimited period of time. However, this information can also be lost through decay, retrieval failure or interference at this stage.

Working memory model

The working memory model (WMM) was proposed by Baddeley and Hitch (1974) in response to the criticisms made of the MSM and its simplicity in describing how STM works. This model suggests a flexible, multi-component system involved in active processing rather than a system of unitary (single, separate and complete) passive stores. It consists of four key components that each serves a different role in the process and storage of information. The central executive is considered to be the most important component of this model as it is in control of all other subsystems and works to combine information from these and the LTM. It has a limited capacity and is only capable of processing a restricted amount of information at once. However, it is a flexible component and can process information from any modality as well as controlling attention, decision-making and problem-solving. The visuo-spatial scratch pad, also referred to as the ‘inner eye’, stores visual and spatial information and is in charge of processing mental images. The phonological loop is divided into two components that both help to store speech-based sounds. The phonological store (inner ear) holds acoustic based information and the articulatory control system’s (inner voice) role is to enable repetition of this stored information to from a stronger trace. Both of these subsidiary systems have a limited capacity and store information for only brief periods of time. The most recent addition to the model is the episodic buffer, added in 2000. The episodic buffer plays an important role in manipulating information we already have stored in our LTM and making it accessible to our working memory when needed. It can also incorporate information from a number of different sources into episodes or chunks. Similar to the other components of this model, it has a limited capacity that relies largely on executive functioning.

Eye-witness testimony

Eye witness testimony (EWT) can be defined as evidence given by a witness to an event such as a crime or accident. It has become a significant area of interest for cognitive psychologists because it relies solely on the memory of the individual witness to recall information about the scene of the crime or details of the perpetrators. This area of study has important implications for police questioning and court hearings as eye witness testimonies are often regarded as vital evidence and seen as a reliable source of information. However, a large body of research has identified that there are often inaccuracies with these accounts. The problems with EWT can occur at any stage in the memory process, for example, they may occur when the memory is being encoded, during the storage process of during retrieval, when the witness is trying to access their memory of the event. The accuracy of EWT is also be affected by the role of anxiety, the age of the witness and the use of misleading questions.

Cognitive interview technique

Geisleman et al. (1985) designed the cognitive interview technique, to be used by police investigators, in an attempt to improve the accuracy of eye-witness testimony. This technique differs quite considerably from traditional police interview technique that simply requires witnesses to recall the events freely, usually following a chronological order, and focusing solely on that witness’ point of view and what they saw directly. The standard police interviews will also involve the witness answering specific questions about the event.

Whereas, the cognitive interview technique is based on four key instructions. The first part of the interview involves the witness recreating the context of the original incident by picturing an image of the environment in their mind, including the weather, the way they were feeling, and other people in the area etc. They will then be required to report every detail of the event even if the detail seems irrelevant or inconsequential. The witness will also be asked to recall the event in a different order. This may involve starting at the end and recalling the event backwards or starting from a significantly memorable point and working forwards or backwards from this point. Finally they will be asked to recall the event from a different perspective e.g. the view of another witness to the incident. The notion behind the use of a cognitive interview is that witnesses will be able to remember more information because they are engaging with their memory on a different level and recounting every piece of information, as opposed to simply recalling what they believed to be important.

Strategies for memory improvement

One of the important applications that memory theory and research provides us with is the ability to improve our memory recall. There are a vast number of techniques, some of which are described below, that have been suggested by psychologists as effective ways to improve our memories. However, they are dependent on the type of information requiring recall and some will work better than others, dependant on the material.

Elaborative rehearsal requires the individual to create a meaningful (semantic) link with the information. This is often done by associating the new information with something already stored in the LTM and thus allowing the individual to access this information through a number of different routes. It is more effective than simple maintenance rehearsal, which simply stores information in the STM for a brief period of time and does not transfer this information successfully into the LTM for future retrieval. Another technique to improve memory is to organise information effectively and works on the principle of elaborative rehearsal. This can be done by “chunking” to increase the capacity of STM or by creating semantic links between words in a list. For example, a list of animals could be put in a hierarchy by listing all mammals, fish, birds and amphibians together under their respective titles.

The use of mnemonics can also be used to code information more meaningfully and create a stronger memory trace for that information. It also provides the person with a retrieval cue which aids recall. For example, the Method of Loci can be used to help remember a shopping list by identifying a number of familiar locations in your house and imagining one item from your shopping list in each of these locations e.g. milk on the doorstep, eggs on the stairs etc. When the individual needs to recall these items they will imagine walking around their house and picturing each of the items in the specific location. The association between a place that the person knows well will act as a retrieval cue to help the person to remember each item on the list.