Episodic memory is the memory of autobiographical events that can be explicitly stated or conjured.
It is the collection of past personal experiences that occurred at a particular time and place. For example, if one remembers the party on their 6th birthday, this is an episodic memory.
They allow an individual to figuratively travel back in time to remember the event that took place at that particular time and place.
Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions of memory – the other is implicit memory.
The term “episodic memory” was coined by Endel Tulving in 1972. He was referring to the distinction between knowing and remembering. Knowing is more factual (semantic) whereas remembering is a feeling that is located in the past (episodic).
Tulving has seminally defined three key properties of episodic memory recollection. These are a subjective sense of time (or mental time travel), connection to the self, and autonoetic consciousness.
Autonoetic consciousness refers to a special kind of consciousness that accompanies the act of remembering which enables an individual to be aware of the self in subjective time. Aside from Tulving, others named the important aspects of recollection which include visual imagery, narrative structure, retrieval of semantic information and the feelings of familiarity.
Events that are recorded into episodic memory may trigger episodic learning, i.e. a change in behavior that occurs as a result of an event. For example, a fear of dogs after being bitten by a dog is a result of episodic learning.
One of the main components of episodic memory is the process of recollection. Recollection is a process that elicits the retrieval of contextual information pertaining to a specific event or experience that has occurred.
There are essentially nine properties of episodic memory that collectively distinguish it from other types of memory. Other types of memory may exhibit a few of these properties, but only episodic memory has all nine:
- Contain summary records of sensory-perceptual-conceptual-affective processing.
- Retain patterns of activation/inhibition over long periods.
- Often represented in the form of (visual) images.
- They always have a perspective (field or observer).
- Represent short time slices of experience.
- They are represented on a temporal dimension roughly in order of occurrence.
- They are subject to rapid forgetting.
- They make autobiographical remembering specific.
- They are recollectively experienced when accessed.
Relationship to semantic memory
Endel Tulving originally described episodic memory as a record of a person’s experience that held temporally dated information and Spatio-temporal relations.
A feature of episodic memory that Tulving later elaborates on is that it allows an agent to imagine traveling back in time. A current situation may cue retrieval of a previous episode, so that context that colors the previous episode is experienced at the immediate moment.
The agent is provided with a means of associating previous feelings with current situations. Semantic memory, on the other hand, is a structured record of facts, concepts, and skills that we have acquired. Semantic information is derived from accumulated episodic memory.
Episodic memory can be thought of as a “map” that ties together items in semantic memory. For example, all encounters with how a “dog” looks and sounds will make up the semantic representation of that word.
All episodic memories concerning a dog will then reference this single semantic representation of “dog” and, likewise, all new experiences with the dog will modify the single semantic representation of that dog.
Together, semantic and episodic memory make up our declarative memory. They each represent different parts of context to form a complete picture. As such, something that affects episodic memory can also affect semantic memory.
For example, anterograde amnesia, from the damage to the medial temporal lobe, is an impairment of declarative memory that affects both episodic and semantic memory operations. Originally, Tulving proposed that episodic and semantic memory were separate systems that competed with each other in retrieval.
However, this theory was rejected when Howard and Kahana completed experiments on the latent semantic analysis (LSA) that supported the opposite.
Instead of an increase in semantic similarity when there was a decrease in the strength of temporal associations, the two worked together so semantic cues on retrieval were strongest when episodic cues were strong as well.
Relationship to emotion
The relationship between emotion and memory is complex, but generally, emotion tends to increase the likelihood that an event will be remembered later and that it will be remembered vividly.
Flashbulb memory is one example of this. An example of this would be an experience such as a close family member dying or the Christmas that you got the exact toy you wanted as a kid. The experience holds so much emotional significance that it is encoded as an extremely vivid, almost picture-perfect memory.
However, whether the vividness of the flashbulb memory is due to a virtual “flash” that occurs because of the emotional experience has been hotly contested. Flashbulb memories may occur because of our propensity to rehearse and retell those highly emotional events, which strengthens the memory.