Long-term memory (LTM) is the relatively permanent memory storage system that holds information indefinitely. LTM may be regarded as involving three stages, encoding, storage and retrieval (getting information in, keeping it there and then getting it back out), and appears to contain several different kinds: episodic, semantic, declarative and procedural.
Encoding is the label given to the way in which objects and events in the world come to be represented in memory. Our normal perception of objects and events requires considerable encoding. However, the application of further encoding processes can produce memory representations of objects and events that differ considerably from those arising solely from perceptual processes.
A memory store is where non-active memory representations are held. For example, imagine your favorite item of clothing. When not in use, the memory representation upon which this image depends will be held in a memory store.
Retrieval is the label given to the way in which information held in memory is made available for use. Retrieval involves finding, activating and sometimes further processing pertinent memory representations.
Episodic memory is considered to be a record of a person’s experiences. It stores information about the events and occurrences that make up a person’s life and, crucially, the subjective experiences that accompany the information retrieved from episodic memory. Therefore, the answers to questions such as, ‘What did you do yesterday afternoon?’ and ‘Have you seen this picture before?’ would tax episodic memory.
Semantic memory is considered to be our general knowledge store. In short, it contains all the information underlying our understanding of the world. For example, it provides the information we use to recognize or describe different types of animals, objects, etc., it provides the information for using and understanding language and it stores the sort of information we would employ to choose our ideal summer holiday destination. Questions such as ‘What is the capital of Scotland?’ and ‘Did Plato own a car?’ would tax semantic memory. However, no personal experience accompanies the information retrieved from semantic memory.
Declarative and procedural systems
Squire (1992) proposes two separate LTM systems: a declarative system and a procedural system.
Declarative knowledge corresponds to ‘knowing that’. Responses to semantic and episodic memory tasks typically provide declarative information, such as ‘(I know that) the capital of Scotland is Edinburgh’, or ‘(I know that) I have seen that picture before’. Cohen (1984) describes declarative knowledge as being represented in a system ‘… in which information is … first processed or encoded, then stored in some explicitly accessible form for later use, and then ultimately retrieved upon demand’.
Procedural knowledge, on the other hand, corresponds to ‘knowing how’. For example, the type of information underlying the ability to ride a bicycle is procedural knowledge. Cohen (1984) describes procedural knowledge as being involved when ‘experience serves to influence the organization of processes that guide performance without access to the knowledge that underlies the performance’. One way to access this information is to observe performance of a procedure that employs the information: try riding a bike and observe what you do and when, and consider why you do it.
Cohen, N. J. (1984). Preserved learning capacity in amnesia: Evidence for multiple memory systems. In L. R. Squire and N. Butters (Eds.), Neuropsychology of Memory. New York: Guildford Press.
Rutherford, A. ( 2005). Long-term memory: Encoding to retrieval. In N. Braisby and A. Gellatly (Eds.), Cognitive Psychology. Oxford: Oxford University Press.
Squire, L.R. (1992). Declarative and nondeclarative memory: Multiple brain systems supporting learning and memory. Journal of Cognitive Neuroscience, 4, 232–243.