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This article throws light upon the three main types of memory. The types are: 1. Episodic Memory 2. Semantic Memory 3. Procedural Memory.
Type # 1. Episodic Memory:
William James’ concepts of primary and secondary memory were transfigured by Endel Tulving to episodic memory and semantic memory. Episodic memory is said to be the store of the autobiographical events in the life of the individual and is organised according to the time, space and other qualities of the specific event or events.
What is happening to you now, that of which you are conscious is the reflection of what is being stored in primary and also the current content of the episodic memory. For example, if you come back and narrate about an accident you have witnessed, it is episodic memory. What one can infer from this narration is the underlying process – the episodic memory.
Type # 2. Semantic Memory:
Semantic memory on the other hand, stores a collection of relationships between events which may or may not have passed through episodic memory but stores the collection of relationships between events. In other words, semantic memory includes the organised knowledge we have about language, i.e. words and other verbal symbols, their memory and the relations between them, rules, formulae and the manipulation of these symbols, concepts and relations.
For example, One has to make use of specific words to describe which vehicles collided, (whether it is a Lorry, Fiat, Ambassador or some other vehicles), with what speed they were travelling, (usually in terms of kilometers per hour), who broke the rules, whether the lorry-driver wanted to overtake the car or vice versa and so on.
Episodic memory is autobiographical and more personal and, therefore differs from one individual to another because their experiences are different. However, the semantic memory system is such that it has to make use of language or manipulate words on the basis of accepted rules.
Semantic memory is more or less public and the memory of one person contains roughly the same sort of information as the other, though the pattern of organisation may differ. For instance, if two individuals have visited Kanyakumari, their episodic memories may differ because of their experience. But both will know what the speciality of the place is i.e. how far a away the rock-cut temple is built, why it was built, what is the significance of sand, sea, sunset, sunrise, etc. According to Tulving’s model, input to semantic memory is through episodic memory and each instance of the use of semantic memory constitutes an entry into episodic memory.
Type # 3. Procedural Memory:
Sometimes, the term procedural memory is also used in addition to the terms of episodic memory and semantic memory. This is also known as skill memory. Skill memory mainly involves how to do things in a complex operation.
For example, when one is driving a car or a scooter, this involves many activities to be carried out in a sequence. In fact, there are many activities which involve a retrieval of learnt and stored up information and this happens in an automatic and unconscious manner.
Apart from three types of memory, episodic, semantic, and procedural, there are many activities involved in all these. For example, if we are playing a chess game, this involves semantic memory, in the form of what the situation now is in terms of scores – semantic memory, perhaps, remembering the kinds of moods one may have had in the past-episodic memory and of course, knowing the rules of the game and other procedures which constitute procedural memory. In view of this, many of our actions involve more than one type of memory. Such a situation has led some psychologists to question whether one should make a distinction at all among the three categories of memory.
Psychologists working in this area felt the need to explore further, especially semantic memory due to its richness and relevance to human memory.
Comparison of Sensory Memory, Short-Term Memory and Long-Term Memory:
Our comparison of the three types of memory we may attempt a summary of the differences among them in a tabular form:
The above table attempts a comparison of the salient features of the three categories of memory and shows how they differ.
Serial Position Effects:
A number of studies which required subjects to learn lists of words or syllables or numbers have pointed out to what is often described as a “serial position effect”. One such kind of effect is called the primacy effect. This refers to the phenomenon where subjects have been found to show better performance in recalling those units or chunks, numbers or words that occupy the first positions in the list. Thus, digits, numbers or words which occur as the first, second or third in order in the list have a primacy effect and are found to be remembered better.
Similarly, items which occurred towards the end have also been found to be remembered better. This effect is known as recency effect. Thus, the first few elements and the last few elements tend to be remembered better. Psychologists explain this on the basis that first few units are rehearsed more frequently, thus enjoying an advantage, while the last few items had the advantage of being fresh in the short-term memory.
Even when a person holds information in short-term memory very often the retrieval is not instantaneous and it takes some time. One psychologist, Sternberg on the basis of his research, describes that under these conditions of short-term memory people engage in two types of search.
The first one is called parallel search. In this kind of search, the person searches and examines all the elements in short-term memory, at the same time and simultaneously. On the other hand, the other type of search known as serial search involves examination of one piece in one short-term memory at a time.
According to Sternberg whenever parallel search is employed, the number of elements or digits or chunks in the original learning situation has no effect on the time taken to respond. The time taken is the same whether the list is long or short. But, on the other hand, if serial search is employed and one item at a time is examined the time taken depends on the length of the list.
The longer the original list the longer is found to be the response time. Another interesting phenomenon is that if serial search is employed the search process does not stop when the correct recognition occurs but continues till the whole list is exhausted. This is called exhaustive serial search.
Rehearsal:
A very frequently used term in explaining the process of storage and retrieval in remembering is the term rehearsal. Rehearsal is a strategy of repeating whatever one hears or verbally encoding and repeating whatever one sees. The importance of rehearsal in storage and retrieval was highlighted even by Ebbinghaus, the father of memory research.
Psychologists distinguish between two types of rehearsal. The first type of rehearsal known as maintenance rehearsal involves a mere repetition again and again of what one has heard or seen. This kind of rehearsal is helpful in retrieving materials from short-term memory, but is not very helpful in transferring material from short-term memory into long-term memory.
The other kind of rehearsal is known as elaborative rehearsal which goes beyond mere repetition and involves a process by which the individual relates newly learnt material to material already learnt and remembered. Thus, elaborative rehearsal involves a much deeper level of processing and results in imprinting of information.
Studies on the role of rehearsal have by and large tended to emphasise that the role of internal factors and processes is much more important in effectively remembering than external factors like the pattern of presentation, number of repetitions, duration of exposure etc.
Retrieval:
The final stage and the ultimate objective in any act of memorizing or remembering is retrieval of the information stored. The process of retrieval is more particularly relevant to long-term memory where the information stored stays for a long time. No study has been made or perhaps can be made, to determine how long the elements in long-term memory stay.
The trace decay theories which argue that memory traces gradually fade away would suggest that the information stored in short-term memory would stay till the memory traces stay, but cannot say how long it will take for these traces to fade away.
On the other hand other theories like interference theories which postulate that failure in retrieval is due to interference from subsequently learnt new material would argue that if there were no interfering materials, earlier stored materials in long-term memory would stay forever. The fact that certain memories can be recalled after decades of their registration lends some support to such a view.
Notwithstanding the controversy arising from the divergence of approaches it has been shown that retrieval is facilitated by certain clues. In this context, one may refer to what is known as Encoding Specificity Principle. This means that retrieval is likely to be better, the greater the degree to which one is able to reach out for the information that was registered and encoded at the time of original learning.
Yet another principle known as Context Dependence Principle holds that retrieval will be more effective if the situation under which recall is made resembles the situation under which original learning took place. The greater the degree of similarity between the situation and conditions of original learning and that of recall, the more effective will be the memory. Thus very often it has been found that people giving evidence recall evidence if they are taken to the actual sight of an accident or crime. Here, it may be seen that what comes into operation is more of recognition than recall.
As a counterpart of Context Dependence which refers to external conditions, psychologists also speak of State Dependence which refers to the degree of similarity between the condition of the original experience and the condition of recall in terms of the internal psychological conditions of the person.
Thus, when we meet an old friend after a long time and engage in pleasantries we recall similar experiences which we had decades ago. Similarly experiments by Bower have shown that when we are in a negative state, for example, in a state of mourning more negative elements from one’s memory are likely to be retrieved.
A number of studies on people suffering from affective disorders or mood disorders, which were traditionally known as Manic Depressive Disorders have shown that when the patient is in an exalted state more pleasant and successful memories are recalled and while he is in a depressed mood unpleasant memories are remembered. Such findings have been reported by Henry, Weingartner & Murphy.
Another interesting feature of retrieval in long-term memory is what is usually referred to as “feeling of knowing experience”. Hart, Nelson and others refer to such a feeling on the part of subjects and report the findings of certain studies.
In their studies they asked the subjects to guess how many correct answers they will be able to recognise if they are provided with other alternatives, whenever recall failed. The result showed that the subjects guessed the possibility of success correctly to the extent of 70% in predicting their ability to recognise the correct answer.