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This article throws light upon the three main stages of memory. The stages are: 1. Sensory Stage 2. Short-Term Memory Stage (STM) 3. Long-Term Memory (LTM).
1. Sensory Stage:
The term ‘sensory memory’ is used to describe the state when the sensory registers receive incoming information and hold them for enough time to be processed. This type of memory is the most basic or primitive form of memory.
It is very brief. Many of the elements entering our sensory memory get eliminated while others are processed further to enter the stages of short-term memory or long-term memory.
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When we look at an object our eyes get fixated at any one point for about one fourth of a second and keep moving in jumps and not continuously. Such jumping movements are known as Saccadic movements and there is also a limit to the amount of information people can get and store in one act of fixation, which in general ranges between 4 and 5.
This limit is referred to as a span of apprehension. Some other properties of sensory memory have also been reported by experiments. Firstly, the sensory register retains the mental representation only for a very brief time. These are known as icons and the sensory register for retaining them is called iconic memory.
Mostly icons do not last for more than a second but under certain conditions this duration gets extended. For example, if the stimulus intensity is high, then the duration of the iconic memory can be longer. It is because of this iconic memory which lasts for some time, we experience continuity in our perception and the jumping experiences resulting from the saccadic movements are not felt.
Another important fact about this memory is that one image can be laid on top of another which results in a summing up of information. Similarly, psychologists refer to what is known as echoic memory referring to auditory memory. While iconic memory and echoic memory are very similar in their properties in general, echoic impressions last longer. Both Icons and echoic are faithful representations of the corresponding stimuli and are not results of any encoding. They are in a way exact representations or photocopies of the sensory impressions that are registered.
2. Short-Term Memory Stage (STM):
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This is the second stage of processing where the information or stimuli received is held for a short time. Though active and conscious, this is less permanent, brief and less organised. We often wonder how we can forget the material or information learnt a few moments ago. For instance, you are trying to add a long list of numbers or counting money and your friend comes and distracts you.
When you return to your work you will realise that you have forgotten what your last count was, and you will have to start right from the beginning, perhaps, muttering a curse. Thus, it can be seen that, at times, material is stored only for a short while and then it is forgotten.
A number of experiments have attempted to study the capacity for retention under conditions of short-term memory. The experiments have taken the form of exposing different kinds of material, numbers, simple digits, words, etc. for a brief time and asking the subject to recall.
Most of these studies have shown that in general, the number of terms or units which people can recall after one presentation varies between 6 or 7, irrespective of the nature of the material, whether they are short numbers or long numbers, short words or long words.
This shows that short term memory involves, grouping of numbers, letters, or digits and that some kind of relating of individual elements into economical and meaningful units takes place, to enable better short-term remembering. Such meaningful grouping of units is called chunking. Each organised unit is known as a chunk. Thus, if 8, 7, 6 represents, one chunk each, 172, 196, 208 also constitute one unit each. The chunking in the former case involves, one digit each, while in the latter, each chunk involves three digits. But, from the point of view of the subject remembering, both kinds of units are equivalent.
It has been found that when chunking is adopted, the ‘immediate memory span or the maximum number of chunks that people are able to recall immediately after one presentation ranges between 5 and 9. Chunking is a strategy that can be adopted and developed to increase the amount of material that can be recalled as part of short-term memory.
One can learn to organise the individual elements into larger chunks as one grows. Chunking can play a unique role when we have to hear and remember, urgent and immediate, and coded messages. One can here see a link between short-term memory and long-term memory. Chunking involves some form of relating the material in the short-term memory to long-term memory.
The ability to develop and use larger and larger chunks, thus helps one to improve one’s memory. The ability to improve chunking involves two processes. On the one hand, as one grows, there is an increase in the number of chunks, one can organise and remember. More important is the ability to make each individual chunk large enough.
A number of studies have shown that people can be trained to organise elements in short-term memory into the longer and longer chunks. Very often when we visit a hotel or a restaurant, we find that waiters taking orders from a number of customers, listen to a number of customers, just once, and remember all of them.
Here, most probably, the waiters have evolved some effective strategy of grouping the orders that bring about an overall increase in the amount of material remembered. While evolving better and longer strategies chunking can contribute to an increase in the overall amount of material.
It should be mentioned that the path of improving memory is a long one which calls for considerable amount of planned effort and learning. In addition, it also involves encoding and decoding of material already stored in one’s short-term memory.
Thus the strategies of chunking should be related to strategies of relating elements in short-term memory to elements in the long-term memory. In fact, where information flows freely between short-term memory and long-term memory, the overall power to remember is generally higher.
3. Long-Term Memory (LTM):
Short-term memory is only one stage of information processing, because we often remember certain events, people, things or experiences for several years. In other words, we never forget about them even if we want to.
For instance, it is quite fascinating to see an eighty-year old grandfather who learnt geography when he was twelve years (with no exposure later in life) teaching about winds and soil to a seven-year-old great-grandson. The fact that some information remains and some gets discarded poses a more challenging problem to the scientist rather than what is stored and where it is stored.
Scientists working in this area have identified various factors which are responsible for short and long-term storages. One assumption is that when the material is in the short-term stage and has to be retained for a longer duration, then rehearsing or repeating the material either silently or aloud is necessary. Going back to the illustration of counting a long list of numbers, supposing you had repeated a couple of times the last number you had counted before attending to your friend, perhaps you might not have forgotten it.
Apart from repetition, other means which facilitate the transformation from STM to LTM are simplification and elaboration. When learnt verbal material is reduced to simple figures and symbols or compressed to abbreviated forms, it could be retained for a longer time. Take the counting example again. Suppose the last number was 144 and this can be reduced to 12.
In the same way, names of the organisations, projects, etc. are reduced to abbreviations. If the whole name has to be recalled, one spends some time splitting the abbreviation and organising the whole name. Yet another way to transfer STM to LTM is by elaborating, which means that the material has to be elaborated by associating it with other material.
Perhaps, you may elaborate 144 by associating it with the telephone number of friends or your own bank account number. You may also convert it into alphabets which correspond to the number like ADD or words like Anand is a dirty dog, or Akshit is a dance director and so on.
Thus, transformation of material into long-term memory is done in order to retain it for a longer time and make it relatively permanent. Information stored in this stage is highly organised because it has been rehearsed, simplified or elaborated and categorized under the label of permanently remembered experiences and may be readily available when the need arises.