Long-Term Memory Systems

There are several ways the organization of long-term memory Opens in new window can be modeled and understood. For example, there is certainly a memory store associated with each of the five senses: visual, auditory, tactile, olfactory, and taste.

Although most assessment instruments have simply divided long-term memory into visual and auditory components, research and applied psychologists have developed a more elaborate organization of long-term memory structures that is now widely accepted and seems consistent with actual brain structures and functions.

Long-term Memory Types

The primary division of long-term memory is into declarative (explicit) Opens in new window and nondeclarative (implicit) memory Opens in new window.

A.    Declarative Memory

Declarative memory defines the capacity to learn, store, and recall information explicitly; it is memory for facts and events. It is demonstrated by speaking, and arises with conscious recall.

Declarative memory is divided into an episodic Opens in new window and semantic Opens in new window components.

1. Episodic Memory

Episodic memory stores information about events together with their spatio-temporal context. It contains episodes, or personal experiences and the specific objects, people, and events that have been encountered at a particular time and place.

For example, the people you met and the hands you shook at your last birthday party makes up episodic memory. Although episodic memory Opens in new window seems primarily visuospatial and contextual, it also includes verbal content.

2. Semantic Memory

Semantic memory is devoted to storing general knowledge about words, objects, and concepts, of the sort learned in schoo (Tulving 1972). Knowing that Thomas Jefferson wrote the Declaration of Independence is an example of semantic memory Opens in new window.

We are usually consciously aware of declarative information, which is sometimes referred to as explicit memory. This memory form is impaired in amnesia, in particular, the capacity to encode and retrieve new episodic information.

Brain lesions can cause anterograde amnesia Opens in new window, which denotes the difficulty to form new memories. They can also induce retrograde amnesia Opens in new window, i.e. an incapacity to retrieve memories that were formed before the injury injury.

Semantic memory is comparatively less vulnerable, but may be impaired through lesions to distinct anatomical structures.

B.     Nondeclarative Memory

Nondeclarative memory refers to the capacity to learn information implicitly, mainly through repeated exposure to a stimulus or task. There are three major categories of nondeclarative memory Opens in new window:

1. procedural memory,
2. priming and
3. classical conditioning.

1. Procedural Memory

Procedural memory holds procedural knowledge. It is memory for skill, demonstrated by doing, and arises without conscious recall. Knowing how to ride a bicycle at automatic level without conscious effort, is a good example of procedural memory Opens in new window.

A person who knows how to ride a bike can demonstrate that s/he has this ability only by actually doing it. The subconscious nature of procedural memory becomes evident when we learn how to perform some skill—such as playing the piano—forget how, but then show improvement when we attempt to perform the action at a later date.

2. Priming

Priming relates to the fact that seeing a word or image seems to prime (promt) the individual’s ability to come up with the correct response.

During priming Opens in new window, cues prompt accurate recall or performance without the individual’s recollection of the acquired information or that it was previously learned. Priming occurs even when people say that they do not remember any exposure to the stimulus.

3. Classical conditioning

Classical conditioning is a phenomenon in which the individual learns the predictive relationship of one environmental stimulus with another.

Automatic stimulus-response associations can be formed through conditioning. The conditioning begins when an initially neutral stimulus is paired with an unconditioned stimulus that elicits a reflex response.

The conditioning is complete when the neutral stimulus elicits the response in the absence of the unconditioned stimulus. The classic example is Pavlov’s dog learning that a sound reliably predicted the delivery of food.

Nondeclarative memories depend on brain areas that are involved in the sensory and perceptual processing of information, and are relatively preserved in amnesia.