Memory and Forgetting

models of memory forgetting

Memory plays a very important role in our learning and psychological growth. Through memory of our past experiences, we handle new situation it helps us in our relearning, problem solving and thinking. Since memory is central to almost all cognitive processes such as perception, thinking and problem solving, psychologists have attempted to understand the manner in which any information is committed to memory, the mechanisms through which it is retained over a period of time, the reasons why it is lost from memory, and the techniques which can lead to memory improvement.

The first systematic exploration of memory is credited to Hermann Ebbinghaus, a German psychologist of late nineteenth century (1885). He carried out many experiments on himself and found that we do not forget the learned material at an even pace or completely. Initially the rate of forgetting is faster but eventually it stabilises.

Another view on memory was suggested by Frederick Bartlett (1932) who contended that memory is not passive but an active process. With the help of meaningful verbal materials such as stories and texts, he demonstrated that memory is a constructive process. That is, what we memorise and store undergoes many changes and modifications over time. So there is a qualitative difference in what was initially memorised by us and what we retrieve or recall later.

Memory Process

Memory refers to retaining and recalling information over a period of time. It is conceptualised as a process consisting of three independent, though interrelated stages. These are:

  • Encoding,
  • Storage, and
  • Retrieval.

Any information received by us necessarily goes through these stages.

Models of Memory

Stage Model

Initially, it was thought that memory is the capacity to store all information that we acquire through learning and experience. But with the advent of the computer, human memory came to be seen as a system that processes information in the same way as a computer does. Both register, store, and manipulate large amount of information and act on the basis of the outcome of such manipulations. This led to development of the first model of memory, which was proposed by Atkinson and Shiffrin in 1968 and known as Stage Model of Memory.

According to the Stage Model, there are three memory systems :

  • The Sensory Memory,
  • The Short-term Memory and
  • The Long-term Memory.

Models Stages of Memory

Sensory Memory

  • The incoming information first enters the sensory memory. Sensory memory has a large capacity. However, it is of very short duration, i.e. less than a second.
  • It is a memory system that registers information from each of the senses with reasonable accuracy.
  • Often this system is referred to as sensory memories or sensory registers because information from all the senses are registered here as exact replica of the stimulus.
  • Example: When you just switch of the light bulb, while looking at it, there is a trail of trail of light that stays after the bulb is switched off.

Short-Term Memory

  • Short-term memory (STM), holds small amount of information for a brief period of time (usually for 30 seconds or less).
  • Unless rehearsed continuously, information from STM may get lost in less than 30 seconds. Hence, Atkinson and Shiffrin proposed that information in STM is primarily encoded acoustically, i.e. in terms of sound.

Long-Term Memory

  • Materials that survive the capacity and duration limitations of the STM finally enter the long-term memory (LTM) which has a vast capacity.
  • Once any information enters the long-term memory store it is never forgotten because it gets encoded semantically, i.e. in terms of the meaning that any information carries.
  • What one experiences as forgetting is in fact retrieval failure; for various reasons one cannot retrieve the stored information.

Now, the question arises, how does information travel from Sensory to STM to LTM ?

As an answer, Atkinson and Shiffrin propose the notion of control processes which function to monitor the flow of information through various memory stores. Our senses do not register all the information they receive but through selective attention, only that information which is attended to, enters the STM from sensory registers. Sense impressions, which do not receive attention, fade away quickly.

The STM then sets into motion another control process of maintenance rehearsal to retain the information for as much time as required. This is done through repetition and when such repetitions discontinue the information is lost. Sometimes, there is need to hold information which exceeds normal capacity. In such scenario, another control process operates in STM to expand its capacity called as Chunking. For example, if you are told to remember a string of digits such as 194719492004 (note that the number exceeds the capacity of STM), you may create the chunks as 1947, 1949, and 2004 and remember them as the year when India became independent, the year when the Indian Constitution was adopted, and the year when the tsunami hit.

From the STM, information enters the longterm memory through elaborative rehearsals. This rehearsal attempts to connect the ‘to be retained information’ to the already existing information in long-term memory. The number of associations one can create around the new information determines its permanence.

Levels of Processing Model

The levels of processing view was proposed by Craik and Lockhart in 1972. They proposed that the processing of any new information relates to the manner in which it is perceived, analysed, and understood. This in turn determines the extent to which it will eventually be retained.

They proposed that it is possible to analyse the incoming information at more than one level. One may analyse information through a shallower processing in terms of of its structural and phonetic features. This information which goes through shallower processing tends to forget easily.  However, Encoding information in terms of the meaning it carries (the semantic encoding) is the deepest processing level and it leads to memory that resists forgetting considerably.

Types of Memory

Long-Term Memory types:

  • Declarative vs Procedural – All information pertaining to facts, names, dates. Whereas, Procedural memory, refers to memories relating to procedures for accomplishing various tasks and skills such as how to ride a bicycle etc. Facts retained in the declarative memory are amenable to verbal descriptions while contents of procedural memory cannot be described easily.
  • Episodic vs Semantic – This was proposed by Tulving.
    • Episodic: Episodic Memory contains biographical details of one’s personal life experiences. Consequently, its contents are generally emotional in nature
    • Semantic: Contains meaning of words and concepts, rules of using these in language. Semantic memory is not easily forgotten as the information is stored in highly organized way in logical hierarchies, from general to specific ones. Example: 2+6=8 or the fact that New Delhi is the capital of India.


Forgetting is failure to retrieve information from long term memory store.

Hermann Ebbinghaus

Curve of forgettingThe first systematic attempt to understand the nature of forgetting was made by Hermann Ebbinghaus, who memorised lists of nonsense syllables and then measured the number of trials he took to relearn the same list at varying time intervals. He observed that the course of forgetting follows a certain pattern.

Observations:  The rate of forgetting is maximum in the first nine hours, particularly during the first hour. After that the rate slows down and not much is forgotten even after many days.

Although Ebbinghaus’s experiments constituted initial explorations and were not very sophisticated yet they have influenced memory research in many important ways. It is now upheld, almost unanimously, that there is always a sharp drop in memory and thereafter the decline is very gradual.

Causes of Forgetting

Forgetting due to Trace Decay

Trace decay (also called disuse theory) is the earliest theory of forgetting. This theory propounds that it is due to gradual fading of memory traces or decay that happens with lapse of time. This does not explain why certain memories fade forever while others seem to be well preserved. Passing of time cannot, therefore, be considered as the main cause of forgetting.

Forgetting due to Interference

Interference theory suggests that forgetting is due to interference between various information that the memory store contains. Interference can be proactive (forward moving) which means what you have learnt earlier interferes with the recall of your subsequent learning or retroactive (backward moving) which refers to difficulty in recalling what you have learnt earlier because of learning a new material.

Forgetting due to Retrieval Failure

Forgetting can also occur because at the time of recall, either the retrieval cues are absent or they are inappropriate. This view was advanced by Tulving and his associates who carried out several experiments to show that contents of memory may become inaccessible either due to absence or inappropriateness of retrieval cues.


Enhancing Memory


There are a number of strategies for improving memory called mnemonics (pronounced ni-mo-nicks).

Mnemonics using Images

Mnemonics using images require that one creates vivid and interacting images of and around the material one wishes to remember. The two prominent mnemonic devices, which make interesting use of images, are:

  • The keyword method
    • In this method already remembered word is used as the keyword and then images of keyword and the target word are evoked and imagined as interacting.
  • The method of loci
    • In this method items that one wants to remember are placed as objects arranged in a physical space in the form of visual images.

Mnemonics using Organisation

Organisation refers to imposing certain order on the material one wants to remember. The framework one creates while organisation eases the task of retrieval.

  • Chunking – In chunking, several smaller units are combined to form large chunks.
  • First Letter Technique – In this, the first letter of each word one wants to remember is picked up and then arranged to form another word or a sentence. For example, way to remember colours of a rainbow – VIBGYOR- that stands for Violet, Indigo, Blue, Green, Yellow, Orange and Red).

Applying Memory

In place of mnemonics, a more comprehensive approach to memory improvement has been suggested by many psychologists. In such an approach, emphasis is laid on applying knowledge about memory processes to the task of memory improvement. This includes:

  • Engage in Deep Level Processing:  Deep processing would involve asking as many questions related to the information as possible, considering its meaning and examining its relationships to the facts you already know.
  • Minimise Interference : Interference is a major cause of forgetting.  Maximum interference is caused when very similar materials are learned in a sequence and hence should be avoided.
  • Give Yourself enough Retrieval Cues : While you learn something, think of retrieval cues inherent in your study material. Identify them and link parts of the study material to these cues.


Thomas and Robinson developed the PQRST model for remembering more. PQRST stands for five steps that need to be followed to enhance memory. These are –  Preview, Question, Read, Self-recite and Test (PQRST)PQRST Technique to enhance Memory

  • Preview refers to giving a cursory look at the chapter and familiarising oneself with its contents.
  • Question means raising questions and seeking answers from the lesson.
  • Read – Start reading and look for answers of questions you had raised. Also, think about the meaning and relate this to other things you know about this and similar topics.
  • Self-Recite – Once you have finished reading, think back about what were the main ideas you learnt. Try and recite some of this information.
  • Test – In the end, test how much you have been able to understand.


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