The forgetting curve hypothesizes the decline of memory retention in time. A related concept is the strength of memory that refers to the durability that memory

Memory

In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....

 traces in the brain

Human brain

The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

. The stronger the memory, the longer period of time that a person is able to recall it. A typical graph

Graph of a function

In mathematics, the graph of a function f is the collection of all ordered pairs . In particular, if x is a real number, graph means the graphical representation of this collection, in the form of a curve on a Cartesian plane, together with Cartesian axes, etc. Graphing on a Cartesian plane is...

 of the forgetting

Forgetting

Forgetting refers to apparent loss of information already encoded and stored in an individual's long term memory. It is a spontaneous or gradual process in which old memories are unable to be recalled from memory storage. It is subject to delicately balanced optimization that ensures that...

 curve purports to show that humans tend to halve their memory of newly learned knowledge in a matter of days or weeks unless they consciously review the learned material. This conclusion is not currently supported by evidence since the only studies done by Ebbinghaus are on himself. This does not meet the standards for scientific research.

History

In 1885, Hermann Ebbinghaus

Hermann Ebbinghaus

Hermann Ebbinghaus was a German psychologist who pioneered the experimental study of memory, and is known for his discovery of the forgetting curve and the spacing effect. He was also the first person to describe the learning curve...

 extrapolated the hypothesis of the exponential nature of forgetting

Forgetting

Forgetting refers to apparent loss of information already encoded and stored in an individual's long term memory. It is a spontaneous or gradual process in which old memories are unable to be recalled from memory storage. It is subject to delicately balanced optimization that ensures that...

. The following formula can roughly describe it:

where is memory retention, is the relative strength of memory, and is time.

Hermann Ebbinghaus ran a limited, incomplete study on himself and published his hypothesis in 1885 as Über das Gedächtnis (later translated into English as Memory: A Contribution to Experimental Psychology). Ebbinghaus studied the memorisation of nonsense syllables, such as "WID" and "ZOF". By repeatedly testing himself after various time periods and recording the results.

Description

Ebbinghaus hypothesized that the speed of forgetting depends on a number of factors such as the difficulty of the learned material (e.g. how meaningful it is), its representation and physiological factors such as stress and sleep

Sleep

Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

. He further hypothesized that the basal forgetting rate differs little between individuals. He concluded that the difference in performance (e.g. at school) can be explained by mnemonic representation skills.

He went on to hypothesize that basic training in mnemonic techniques can help overcome those differences in part. He asserted that the best methods for increasing the strength of memory are:

1. better memory representation (e.g. with mnemonic
   Mnemonic
   A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...
   
    techniques)
2. repetition based on active recall
   Active recall
   Active recall is a principle of efficient learning, which claims the need to actively stimulate memory during the learning process. It contrasts with passive review, in which the learning material is processed passively . For example, reading a text about George Washington, with no further action,...
   
    (esp. spaced repetition
   Spaced repetition
   Spaced repetition is a learning technique that incorporates increasing intervals of time between subsequent review of previously learned material; this exploits the psychological spacing effect...
   
   )

His premise was that each repetition in learning increases the optimum interval before the next repetition is needed (for near-perfect retention, initially repetitions may need to be made within days, but later they can be made after years).

There is debate among believers in the hypothesis about the shape of the curve for events and facts that are more significant to the subject. Some believers, for example, suggest that memories for shocking events such as the Kennedy Assassination

John F. Kennedy assassination

John Fitzgerald Kennedy, the thirty-fifth President of the United States, was assassinated at 12:30 p.m. Central Standard Time on Friday, November 22, 1963, in Dealey Plaza, Dallas, Texas...

 or 9/11 are vividly imprinted in memory. Other believers have compared contemporaneous written recollections with recollections recorded years later, and found considerable variations as the subject's memory incorporates after-acquired information. There is considerable research in this area as it relates to eyewitness identification

Eyewitness identification

Eyewitness identification, in criminal law, is evidence received from a witness "who has actually seen an event and can so testify in court"....

testimony. It should be noted that eye witness accounts are demonstrably unreliable.

It is purported that in a typical schoolbook application (e.g. learning word pairs), most students remember only 10% after 3–6 days (depending on the material). Therefore, 90% of what was learned is forgotten.

Research on the relationship between original learning and forgetting shows that higher degree of original learning means lowering forgetting.