Why do we forget? To understand the reasons (theories) behind forgetfulness which is a normal memory problem, it is necessary to give forgetfulness or memory lapses a scientific definition as well as to obtain an understanding of the basic memorization process (memory processes). Memory process basically consist of three stages or steps -the transmission of perceived information (stimuli) from sensory memory to short-term memory via working memory to the long-term memory. See post “Classification of Memory – Types of Memory” for difference between sensory, short-term and long-term memory and the distinction between short-term versus working memory. This three stages process of memory formation (memorization) are separated as 1) memory acquisition, encoding 2) memory consolidation (via working memory) 3) long-term memory storage. A fourth step involves the retrieval of these stored memory and this is equivalent to what we say “remember” “recall the memory” and “recollection of the memory”.  (see post “How Do We Remember: Memory Acquisition, Consolidation And Retrieval” for more detail and in depth discussion).

Forgetfulness (memory lapses) is the term used to define normal memory retention loss (the apparent loss of information already encoded and stored in an individual’s long term memory) that could occur at any age. As we age, forgetfulness may become more frequent, but this is still a normal part of aging process as long as the memory lapses issue or problems not severe or frustrating enough to interfere daily life. (see post “Age-Related Memory Loss Diseases – Amnesia With Age” for abnormal memory failure problems). Broadly speaking, forgetfulness (the memory loss issue termed as memory lapses) can refer to any disruption on the chain of the three stages of memory process described above. But strictly or narrowly speaking, forgetfulness is the problem on the linkage between “long-term memory storage” and memory recollection (memory retrieval). Either the stored information is lost from long-term memory storage (known as decay theory) over time, especially there is no memory rehearsal or repetition; or the ability to retrieve and recall memory is impaired at the fourth step. Either disruption will cause people to “forget”. Broadly, any loss of information at the sensory memory or short-term memory stage can be thought of “forgetfulness” too. Because the information never gets encoded or consolidated and to be processed for further long-term storage, there is nothing to retrieve. The information lost at the sensory memory stage is normal if no attention or focus is exerted when stimuli was perceived. The impairment or disruption on memory encoding or memory consolidation will prevent information from being transferred from short-term memory to long-term memory.

There are minor differences in the manifestation of forgetfulness. The symptoms of forgetfulness can be categorized into several major types such as transience, blocking, absent-mindedness, misattribution, suggestibility, bias, scrambling, multi-task inefficiency (see post “types of forgetfulness).  Next presented is 4 basic theories (mechanisms) of forgetfulness to explain why do we forget:

Decay theory of forgetfulness

Decay theory of forgetfulness states that memory fades (retention loss) occurs over time. The Theory appears to apply to both short-term and long-term memory storage. Over time, if without rehearsal or recollection, stored information may lost and no longer available for later retrieval. Memory strength could wear away. Actively rehearsing information is believed to be a major factor counteracting this temporal decline. It is known that neurons die off gradually as we age although new brain cell can be created at any age. This partially explains why aged people are more easier to forget things. One observation is that some long-term memory are more resistant to time decay. People sometimes remember events or experiences long time ago with accuracy. This fact suggests that time decay is not the only factor that contribute to memory fades.

Interference theory of forgetfulness

Interference theory implies that memory information can be competing and interfering with each other if the stored information is very similar to the new information. Proactive interference is the case that a similar past memory make the new information difficult to remember. Retroactive interference is the case that a new information make it difficult to remember a similar past experience or learned information.  The basic assumption is that the stored memory is intact but during the process of retrieval, information could be distorted by the newly acquired (learned) material due to similarity and competition. Interference theory explains the observation of multi-task inefficiency, especially in elder people. This is termed as Dual Task Interference. The efficiency for people to do multiple tasks decreases if they try to complete them at the same time.

Fail to retrieve (memory recall problem)

Fail to retrieve (memory retrieval and recollection problem) explains the problem associated with the memory recollection and retrieval step. There are three main types of memory recall used in studies: free memory recall, cued memory recall and serial recall. Serial recall measure and individual’s ability to recall items or events in the order in which they occurred. This mechanism of forgetfulness is less associated with normal people. Aging people or people with amnesia are easily found with impairment of memory retrieval due to disease, injury.

Failure to Store (encoding failure )

Encoding failure (fail to store) is associated with the impairment of memorization process when short-term memory failed to enter into long-term memory storage. Sometimes information is not encoded simply because attention and focus is not exerted, and was ignored by the brain. This is normal and with common sense, if one does not pay attention and concentrate, many details of the perception simply slipped away. Amnesia patients or aging people may have encoding failure due to the changes in their brain structure that are involved in the biochemical process of memory encoding and consolidation. An impaired working memory function will reduce an individual’s ability to process and synthesize perceived information including properly store them in the appropriate areas of brain (not all memory are stored in one area of the brain).

Motivated forgetting

This is to cope with the persistence in remembering traumatic events or experiences; Motivated forgetting describes the practice to forget those traumatic or disturbing events or experience. Suppression and repression are the two basic forms of motivated forgetting.