Long-Term Memory in Psychology: Types, Capacity & Duration

Long-term memory (LTM) is the final stage of the multi-store memory model proposed by Atkinson-Shiffrin, providing the lasting retention of information and skills.

Theoretically, the capacity of long-term memory could be unlimited, the main constraint on recall being accessibility rather than availability.

Duration might be a few minutes or a lifetime.  Suggested encoding modes are semantic (meaning) and visual (pictorial) in the main but can be acoustic also.

Using the computer analogy, the information in your LTM would be like the information you have saved on the hard drive. It isn’t there on your desktop (your short-term memory), but you can pull up this information when you want it, at least most of the time.

Types of Long-Term Memory

Long-term memory is not a single store and is divided into two types: explicit (knowing that) and implicit (knowing how).

There are two components of long-term memory: explicit and implicit. Explicit memory includes episodic
 and semantic memory. Implicit memory includes procedural memory and things learned through conditioning.

One of the earliest and most influential distinctions of long-term memory was proposed by Tulving (1972).  He proposed a distinction between episodic, semantic, and procedural memory.

Procedural Memory

Procedural memory is a part of the implicit long-term memory responsible for knowing how to do things, i.e., memory of motor skills.

It does not involve conscious (i.e., it’s unconscious-automatic) thought and is not declarative.  For example, procedural memory would involve knowledge of how to ride a bicycle.

Semantic Memory

Semantic memory is a part of the explicit long-term memory responsible for storing information about the world.  This includes knowledge about the meaning of words, as well as general knowledge.

For example, London is the capital of England. It involves conscious thought and is declarative.

The knowledge that we hold in semantic memory focuses on “knowing that” something is the case (i.e. declarative).  For example, we might have a semantic memory for knowing that Paris is the capital of France.

Episodic Memory

Episodic memory is a part of the explicit long-term memory responsible for storing information about events (i.e. episodes) that we have experienced in our lives.

It involves conscious thought and is declarative.  An example would be a memory of our 1st day at school.

The knowledge that we hold in episodic memory focuses on “knowing that” something is the case (i.e. declarative).  For example, we might have an episodic memory of knowing that we caught the bus to college today.

Cohen and Squire (1980) drew a distinction between declarative knowledge and procedural knowledge.

Procedural knowledge involves “knowing how” to do things. It included skills, such as “knowing how” to playing the piano, ride a bike; tie your shoes, and other motor skills.

It does not involve conscious thought (i.e. it’s unconscious – automatic).  For example, we brush our teeth with little or no awareness of the skills involved.

Declarative knowledge involves “knowing that”, for example London is the capital of England, zebras are animals, your mum’s birthday etc.

Recalling information from declarative memory involves some degree of conscious effort – information is consciously brought to mind and “declared”.

Evidence for the distinction between declarative and procedural memory has come from research on patients with amnesia. Typically, amnesic patients have great difficulty retaining episodic and semantic information following the onset of amnesia.

Their memory for events and knowledge acquired before the onset of the condition tends to remain intact, but they can’t store new episodic or semantic memories. In other words, it appears that their ability to retain declarative information is impaired.

However, their procedural memory appears to be largely unaffected. They can recall skills they have already learned (e.g. riding a bike) and acquire new skills (e.g. learning to drive).

Very Long-Term Memory Experiment

Bahrick, Bahrick, and Wittinger (1975) investigated what they called very long-term memory (VLTM). Nearly 400 participants aged 17 – 74 were tested.

Participants were asked to list the names they could remember of those in their graduating class in a free recall test.

There were various conditions including: a free recall test, where participants tried to remember names of people in a graduate class; a photo recognition test, consisting of 50 pictures; a name recognition test for ex-school friends.

Results of the study showed that participants who were tested within 15 years of graduation were about 90% accurate in identifying names and faces. After 48 years they were accurate 80% for verbal and 70% visual.

Participants were better at photo recognition than free recall. Free recall was worse. After 15 years it was 60% and after 48 years it was 30% accurate.

They concluded that long-term memory has a potentially unlimited duration.

A strength of this study s that it used meaningful stimuli. Bahrick et al. tested people’s memories from their own lives by using high school yearbooks. The study has higher external validity when compared to studies using meaningless pictures (where recall rates tend to be lower).

But the study did not control for confounding variables (they may have rehearsed their memory of the photos over the years), so any real-world application should be applied with caution.


Bahrick, H. P., Bahrick, P. O., & Wittinger, R. P. (1975). Fifty years of memory for names and faces: a cross-sectional approach. Journal of Experimental Psychology: General, 104, 54-75.

Cohen, N. J., & Squire, L. R. (1980). Preserved learning and retention of pattern analyzing skill in amnesia: Dissociation of knowing how and knowing that. Science, 210, 207–209.

Tulving, E. (1972). Episodic and semantic memory. In E. Tulving & W. Donaldson (Eds.), Organization of Memory, (pp. 381–403). New York: Academic Press.

Olivia Guy-Evans

BSc (Hons), Psychology, MSc, Psychology of Education

Associate Editor for Simply Psychology

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Saul Mcleod, PhD

Educator, Researcher

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.