Memory is the term used to refer to the brain's information processing system. This system stores, manages, and retrieves information and consists of sensory memory, short term memory, and long term memory. Long term memory is the part of memory used for permanently storing and is often available for the span of an entire lifetime. Information is transferred from the working memory into long term memory with little deletion, also known as decay.
Further, long term memory is comprised of three systems. These systems are procedural, semantic, and episodic memory. Procedural memory is comprised of skills one has, such as riding a bike or tying one's shoes. Semantic memory is a structured set of facts and concepts. Episodic memory stores the events and experiences that occurred in one's life.
Semantic and episodic memories are classified as declarative memories because people consciously recall them and are able to describe, or declare, their memories. On the other hand, procedural memory is classified as nondelcarative because it is expressed through actions and performance without a conscious effort at recalling them. When was the last time you actually thought about how to walk? One does not need to recall how to do it. It is imprinted in the procedural memory from repetition.
Episodic memory, first coined by Endel Tulving in 1972, is a phenomenon in and of itself. This system is sometimes referred to as "autobiographical" memory because the memories themselves are connected to a specific time and place in one's life. It is from this memory that we reconstruct the events that took place in one's life.
Episodic memory is unique from the other memory systems because it is very personal. There is an actual feeling of nostalgia or remembrance when using episodic memory. Other memory systems are purely factual. For example, describing your summer vacation to the beach uses episodic memory and carries with it a sense of emotion. You remember sights, smells, and even how you felt. Further, there is a definite time-line of events. However, knowing that the ocean is comprised of salt water would be factual and part of the semantic memory system. One does not remember when or where one was when this fact was learned. The knowledge transcends the events surrounding this memory and there is no personalized feeling, emotion, or nostalgia connected with the fact.
Tulver maintains that there is a distinction between remembering and knowing. The brain separates remembering into the episodic memory system. Furthermore, the psychologist William James emphasized, "Memory requires more than the mere dating of a fact in the past. It must be dated in my past." To date a memory into one's past, episodic memory is utilized.
Episodic memory is not fully developed in humans until about four years of age. Additionally, it is the most susceptible to being lost. Neurodegenerative disorders, such as Alzheimer's, ravage episodic memory, causing it to be first of the types of memory to be lost.
While episodic memory is distinct from the other memory systems, it is incorrect to assume that humans use only one type of memory system at any given time. Generally, there is a blending of all three types being utilized. Going back to the beach vacation analogy, if you were to learn to swim while on vacation, which utilizes procedural memory, you may also recall the summer when you learned to swim. While the act of swimming itself is part of procedural memory, the memory of learning to swim is episodic. You may even utilize semantic memory by recalling that the stroke you prefer is the breast stroke. Referring to Tulver, the knowledge of how to swim is different than the remembrance of swimming. Remembering events that occurred in ones life is part of this unique and distinct system of storing and retrieving information referred to as episodic memory.
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Tulving, E. (1972). Episodic and semantic memory. http://alicekim.ca/EMSM72.pdf