Memory storage is achieved through the encoding process, through either short term or long term memory. Memories are not stored as exact replicas but are modified and reconstructed during recall. In the process of memory encoding, information is filtered and modified for storage in short-term memory. Information in short-term memory is constantly deteriorating; however if the information is deemed important or useful, it is then transferred to long-term memory for extended storage. Because long-term memories must be held for indefinite periods of time, they are stored, or consolidated, in a way that optimizes space for other memories. As a result, long-term memory can hold much more information than short-term memory, but may not be immediately accessible.
The way long-term memories are stored is similar to a digital compression. This means that information is efficiently filed away in a way that takes up the least amount of space, but in the process, details of the memory may be lost and not easily recovered. Because of this consolidation process, memories are more accurate the quicker they are retrieved. As the retention interval between encoding and retrieval of the memory lengthens, the accuracy of the memory decreases.
Memory gaps and errors refer to the incorrect recall or complete loss of a memory. Because memories are reconstructed, they are susceptible to being manipulated with false information. In a 1932 study, Frederic Bartlett demonstrated how serial reproduction of a story distorted accuracy in recalling information. He told participants a complicated Native American story and had them repeat it over a series of intervals. With each repetition, the stories were altered. Even when participants recalled accurate information, they filled in gaps with false information. His work showed long term memory to be adaptable.
Bartlett attributed this tendency to the use of schemas. A schema is a generalization formed in the mind based on experience. People tend to place past events into existing representations of the world to make the memory more coherent. Instead of remembering precise details about commonplace occurrences, a schema is developed. The common use of schemas suggests that memory is not an identical reproduction of experience, but a combination of actual events paired with already existing schemas. Memory is also closely related to imagination. Likewise, the brain has the tendency to fill any blanks and inconsistencies in a memory by making use of the imagination and similarities with any other memories.
Much research has shown that the phrasing of questions can also alter memories. A leading question is a question that suggests the answer or contains the information the examiner is looking for. For instance, one study showed that simply changing one word in a question could alter participants' answers. After viewing video footage of a car accident, participants who were asked how "slow" the car was going gave lower speed estimations that those asked how "fast" it was going. Children are particularly suggestible to such leading questions and misinformation.
Mood and Memory
When we store a memory, we not only record all sensory data, we also store our mood and emotional state. Our current mood thus will affect the memories that are most effortlessly available to us, such that when we are in a good mood, we recollect good memories, and when we are in a bad mood, we recollect bad ones.
The Mood Congruence effect
The mood congruence effect refers to the tendency of individuals to retrieve information more easily when it has the same emotional content as their current emotional state. For instance, being in a depressed mood increases the tendency to remember negative events.
Mood-state dependent retrieval
Another documented phenomenon is the mood-state dependent retrieval, which is a type of context-dependent memory. The retrieval of information is more effective when the emotional state at the time of retrieval is similar to the emotional state at the time of encoding. Thus, the probability of remembering an event can be enhanced by evoking the emotional state experienced during its initial processing.