- Why do we forget at all?
- What do we forget and how?
As important as memory is, also the process of Forgetting is present to everybody.
Therefore one might wonder:
One might come up with something you could call “mental hygiene”. It is not useful to remember every little detail of your life and your surrounding, but rather a disadvantage because you maybe would not be able to remember the important things as quickly or even quick enough but have an overload of facts in your memory. Therefore it is important that unused memories are “cleaned up” so that only relevant information is stored.
There are different theories about how things are forgotten. One theory proposes that the capacity of the Long Term Memory is infinite. This would mean that actually all memories are stored in the LTM but some information cannot be recalled (anymore) due to factors to be mentioned in the following paragraphs:
There are two main theories about the causes of forgetting:
In 1885 Herrmann Ebbinghaus did several self-experiments to research human forgetting. He memorized a list of meaningless syllables, like “WUB” and “ZOF”, and tried to recall as many as possible after certain intervals of time for several weeks. He found out that forgetting can be described with an almost logarithmic curve, the so called forgetting curve which you can see on the left.
These theories about forgetting already make clear that memory is not a reliable recorder but it is a construction based on what actually happened plus additional influences, such as other knowledge, experiences, and expectations. Thus false memories are easily created.
In general there are three types of tendencies towards which people’s memories are changed. These tendencies are called
One distinguishes between three major types:
(For a list of more known memory biases see: List of memory biases)
There are moments in our lives that we are sure we will never forget. It is generally perceived that the memories of events that we are emotionally involved with are remembered for a longer time than others and that we know every little detail of them. These kinds of memories are called Flashbulb Memories.
The accuracy of the memories is an illusion, though. The more time passes, the more these memories have changed while our feeling of certainty and accuracy increases. Examples for Flashbulb Memories are one’s wedding, the birth of one’s child or tragedies like September 11th.
Interesting changes in memory can also occur due to Misleading Postevent Information (MPI). After an event information given another person can so to say intensify your memory in a certain respect. This effect was shown in an experiment by Loftus and Palmer (1974): The subjects watched a film in which there were several car accidents. Afterwards they were divided into three groups that were each questioned differently. While the control group was not asked about the speed of the cars at all, in the other groups questions with a certain key word were posed. One group was asked how fast the cars were going when they hit each other, while in the other question the verb “smashed” was used. One week later all participants were asked whether they saw broken glass in the films. Both the estimation of speed and the amount of people claiming to have seen broken glass increased steadily from the control group to the third group.
Based on this Misinformation Effect the Memory Impairment Hypothesis was proposed.
This hypothesis states that suggestible and more detailed information that one receives after having made the actual memory can replace the old memory.
Keeping the possible misleading information in mind, one can imagine how easily eyewitness testimony can be (purposely or accidentally) manipulated. Depending on which questions the witnesses are asked they might later on remember to see, for example, a weapon or not.
These kinds of changes in memory are present in everyone on a daily basis. But there are other cases: People with a lesion in the brain sometimes suffer from Confabulation. They construct absurd and incomplete memories that can even contradict with other memories or with what they know. Although the people might even be aware of the absurdness of their memories they are still firmly convinced of them. (See Helen Phillips' article Mind fiction: Why your brain tells tall tales)
If one cannot remember an event or detail, it does not mean that the memory is completely lost. Instead one would say that these memories are repressed, which means that they cannot easily be remembered. The process of remembering in these cases is called recovery.
Recovering of a repressed memory usually occurs due to a retrieval cue. This might be an object or a scene that reminds one of something which has happened long ago.
Traumatic events, which happened during childhood for example, can be recovered with the help of a therapist. This way, perpetrators have been brought to trial after decades.
Still, the correctness of the “recovered” memory is not guaranteed: as we know, memory is not reliable and if the occurrence of an event is suggestible one might produce a false memory.
Look at the illustration to the right to be able to relate to these processes.
How did the memory for an event become what it is?
Other than on a daily basis errors in memory and amnesia are due to damages in the brain. The following paragraphs will present the most important brain regions enabling memory and mention effects of damage to them.