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Loss or modification of information encoded in an individual's memory

Forgetting or disremembering is the apparent loss or modification of information already encoded and stored in an individual's short or long term memory. It is a spontaneous or gradual process in which old memories are unable to be recalled from memory storage. Problems with remembering, learning and retaining new information are a few of the most common complaints of older adults. Studies show that retention improves with increased rehearsal. This improvement occurs because rehearsal helps to transfer information into long term memory. Forgetting curves (amount remembered as a function of time since an event was first experienced) have been extensively analyzed. The most recent evidence suggests that a power function provides the closest mathematical fit to the forgetting function.

Failing to retrieve an event does not mean that this specific event has been forever forgotten. Research has shown that there are a few health behaviors that to some extent can prevent forgetting from happening so often. One of the simplest ways to keep the brain healthy and prevent forgetting is to stay active and exercise. Staying active is important because overall it keeps the body healthy. When the body is healthy the brain is healthy and less inflamed as well. Although his methods were primitive, his basic premises have held true today and have been reaffirmed by more methodologically sound methods. The Ebbinghaus forgetting curve is the name of his results which he plotted out and made 2 conclusions. The first being that much of what we forget is lost soon after it is originally learned. The second being that the amount of forgetting eventually levels off. Around the same time Ebbinghaus developed the forgetting curve, psychologist Sigmund Freud theorized that people intentionally forgot things in order to push bad thoughts and feelings deep into their unconscious, a process he called "repression". There is debate as to whether (or how often) memory repression really occurs and mainstream psychology holds that true memory repression occurs only very rarely. One process model for memory was proposed by Richard Atkinson and Richard Shiffrin in the 1960s as a way to explain the operation of memory. This modal model of memory, also known as the Atkinson Shiffrin model of memory, suggests there are three types of memory: sensory memory, short term memory, and long term memory. Each type of memory is separate in its capacity and duration. In the modal model, how quickly information is forgotten is related to the type of memory where that information is stored. Information in the first stage, sensory memory, is forgotten after only a few seconds. In the second stage, short term memory, information is forgotten after about 20 years. While information in long term memory can be remembered for minutes or even decades, it may be forgotten when the retrieval processes for that information fail.

Prompted recall is a slight variation of free recall that consists of presenting hints or prompts to increase the likelihood that the behavior will be produced. Usually these prompts are stimuli that were not there during the training period. Thus in order to measure the degree of forgetting, one can see how many prompts the subject misses or the number of prompts required to produce the behavior.

This method measures forgetting by the amount of training required to reach the previous level of performance. German psychologist Hermann Ebbinghaus (1885) used this method on himself. He memorized lists of nonsensical syllables until he could repeat the list two times without error. After a certain interval, he relearned the list and saw how long it would take him to do this task. If it took fewer times, then there had been less forgetting. His experiment was one of the first to study forgetting.

Cue dependent forgetting (also, context dependent forgetting) or retrieval failure, is the failure to recall a memory due to missing stimuli or cues that were present at the time the memory was encoded. Encoding is the first step in creating and remembering a memory. How well something has been encoded in the memory can be measured by completing specific tests of retrieval. Examples of these tests would be explicit ones like cued recall or implicit tests like word fragment completion. Cue dependent forgetting is one of five cognitive psychology theories of forgetting. This theory states that a memory is sometimes temporarily forgotten purely because it cannot be retrieved, but the proper cue can bring it to mind. A good metaphor for this is searching for a book in a library without the reference number, title, author or even subject. The information still exists, but without these cues retrieval is unlikely. Furthermore, a good retrieval cue must be consistent with the original encoding of the information. If the sound of the word is emphasized during the encoding process, the cue that should be used should also put emphasis on the phonetic quality of the word. Information is available however, just not readily available without these cues. Depending on the age of a person, retrieval cues and skills may not work as well. This is usually common in older adults but that is not always the case. When information is encoded into the memory and retrieved with a technique called spaced retrieval, this helps older adults retrieve the events stored in the memory better. This is sometimes thought to occur especially when memories are similar. Output Interference occurs when the initial act of recalling specific information interferes with the retrieval of the original information. Another reason why retrieval failure occurs is due to encoding failure. The information never made it to long term memory storage. According to the level of processing theory, how well information is encoded depends on the level of processing a piece of information receives. Certain parts of information are better encoded than others; for example, information this visual imagery or that has a survival value is more easily transferred to the long term memory storage. This theory shows a contradiction: an extremely intelligent individual is expected to forget more hastily than one who has a slow mentality. For this reason, an intelligent individual has stored up more memory in his mind which will cause interferences and impair their ability to recall specific information. Based on current research, testing interference has only been carried out by recalling from a list of words rather than using situation from daily lives, thus it is hard to generalize the findings for this theory. People are also less likely to recall items when intervening stimuli are presented within the first ten minutes after learning. Recall performance is better without interference.

Decay theory states that when something new is learned, a neurochemical, physical "memory trace" is formed in the brain and over time this trace tends to disintegrate, unless it is occasionally used. Decay theory states the reason we eventually forget something or an event is because the memory of it fades with time. If we do not attempt to look back at an event, the greater the interval time between the time when the event from happening and the time when we try to remember, the memory will start to fade. Time is the greatest impact in remembering an event. Trace decay theory explains memories that are stored in both short term and long term memory system, and assumes that the memories leave a trace in the brain. According to this theory, short term memory (STM) can only retain information for a limited amount of time, around 15 to 30 seconds unless it is rehearsed. If it is not rehearsed, the information will start to gradually fade away and decay. Donald Hebb proposed that incoming information causes a series of neurons to create a neurological memory trace in the brain which would result in change in the morphological and/or chemical changes in the brain and would fade with time. Repeated firing causes a structural change in the synapses. Rehearsal of repeated firing maintains the memory in STM until a structural change is made. Therefore, forgetting happens as a result of automatic decay of the memory trace in brain. This theory states that the events between learning and recall have no effects on recall; the important factor that affects is the duration that the information has been retained. Hence, as longer time passes more of traces are subject to decay and as a result the information is forgotten. One major problem about this theory is that in real life situation, the time between encoding a piece of information and recalling it, is going to be filled with all different kinds of events that might happen to the individual. Therefore, it is difficult to conclude that forgetting is a result of only the time duration. It is also important to consider the effectiveness of this theory. Although it seems very plausible, it is about impossible to test. It is difficult to create a situation where there is a blank period of time between presenting the material and recalling it later.

Forgetting can have very different causes than simply removal of stored content. Forgetting can mean access problems, availability problems, or can have other reasons such as amnesia caused by an accident. An inability to forget can cause distress, as with post traumatic stress disorder and hyperthymesia (in which people have an extremely detailed autobiographical memory).

Psychologists have called attention to "social aspects of forgetting". Though often loosely defined, social amnesia is generally considered to be the opposite of collective memory. "Social amnesia" was first discussed by Russell Jacoby, yet his use of the term was restricted to a narrow approach, which was limited to what he perceived to be a relative neglect of psychoanalytical theory in psychology. The cultural historian Peter Burke suggested that "it may be worth investigating the social organization of forgetting, the rules of exclusion, suppression or repression, and the question of who wants whom to forget what". In an in depth historical study spanning two centuries, Guy Beiner proposed the term "social forgetting", which he distinguished from crude notions of "collective amnesia" and "total oblivion", arguing that "social forgetting is to be found in the interface of public silence and more private remembrance". The philosopher Walter Benjamin sees social forgetting closely linked to the question of present day interests, arguing that "every image of the past that is not recognized by the present as one of its own concerns threatens to disappear irretrievably". Building on this, the sociologist David Leupold argued in the context of competing national narratives that what is suppressed and forgotten in one national narrative "might appear at the core of past narrations by the other" thus often leading to diametrically opposed, mutually exclusive accounts on the past.