Salvador Dali's the Persistence of Memory



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Long term memory (LTM)

Capacity is vast.  As far as we know capacity has never been reached, but don’t worry the term is still young!  However, it’s unlikely that you’ve ever heard anyone complain that they need to delete a few memories before they can store anything new!  As far as I’m aware nobody has tried to estimate capacity, but Solso (1991) compares it favourably with the largest computers. 

A Stunning factoid for you to contemplate.  In 1973 Petr Anokhin of Moscow University wrote:

“We can show that each of the 10 billion neurons in the human brain has the possibility of connections to 1 with 28 noughts after it; that’s 10,000,000,000,000,000,000,000,000,000 connections!  It means that the total combinations in the brain, if written out, would be 1 followed by 10.5 kilometres of noughts!

One way psychologists have studied memory is to experiment on themselves.  The beautifully named Marigold Linton kept a detailed diary recording daily events and facts about flowers etc on cue cards over many years.  Each day was represented by a single word.  When given the cue word she was able to recall with 70% accuracy all the events and information recorded for that day even 7 years later.



Bahrick et al Year Book study (1975)      


374 participants aged between 17 and 74 were tested on their memory of school friends.  A number of different tests were carried out including a free recall of all the names of classmates they could remember, recognition of classmates from a selection of 50 photographs, a name recognition test and a photo matching test.

In order to check accuracy of recall the researchers used year books for the relevant year groups of the participants. 


For participants that had left school up to 34 years previously, accuracy of recall on the face and name recognition tasks was still an amazing 90%.  Even for participants who had left school 48 years previously it was 80%. 


Recall can be accurate over a very long period of time, leading to the term vLTM (very long term memory) to describe this phenomenon. 


The procedure used is a field experiment so is much higher in ecological validity since this is far more similar to the purpose we generally use our memories for.

However, the study was poorly controlled.  The researchers assumed that last contact with their classmates would have been when they left school.  Little consideration seems to have been made of participants seeing classmates in the intervening years or even of them having looked through yearbooks themselves! 

Only one type of recall (visual) was tested.  It could even be argued that recognition of this sort is not recall as such anyway!


Evidence for two memory stores (STM and LTM)

This is a favourite on examination papers.  Clearly you could talk about research into the two main memory stores mentioned above.  In addition to this it would be essential to mention some, if not all, of the following:

Multistore model of memory

Discussed in the next section, this would be a good start to the essay since it suggests how the two main stores work in conjunction with one another.

Primacy and recency effect.

Murdock (1962) gave 103 psychology students lists of words to free recall (in any order) in 90 seconds.  Typically words at the start of the list and especially those at the end tended to be recalled most often.  This was explained by words at the start being rehearsed from STM into LTM creating a stronger trace and those at the end still being present in STM when recall begins.  Evidence for two separate stores. 


Amnesiac case studies

Most people with memory problems have either impairment of their STM or LTM, not usually both.  This suggests that they are different systems. 

HM (or Henry M)

The classic case is that of H.M who at the age of 27 underwent surgery in an attempt to cure his epilepsy apparently triggered by a cycling accident when he was nine.  A surgeon, William Scoville removed both his temporal lobes including a structure known as the hippocampus (Latin for sea horse) and an area known to be crucial to memory. 

Following the procedure HM was unable to create new long term memories (anterograde amnesia) and lost some of his existing LTM retrograde amnesia).  However his STM remained intact with a normal capacity and duration, limited only by his inability to rehearse. 

HM is still alive today, now in his early eighties and being cared for in a residential home in Connecticut (Wikipedia) he is still being studied by cognitive psychologists!   HM’s pattern of memory loss is not unusual.  Clive Wearing suffered a similar form of amnesia following a herpes simplex (cold sore) infection that spread to areas of his temporal lobes. 

Interestingly in both cases and in most cases of amnesia affecting LTM it is mainly episodic memory that is lost, the ability to recall memories of events and certain factual information such as faces, dates etc.  So called semantic memory is largely unaffected so patients can still use language, walk, cycle etc. and still retain an understanding of ‘how things work.’ 

HM therefore could be taught new skills, which over time would improve with practice.  However, he would have no recollection of ever having performed them before!  

KF who suffered damage to his STM following a motorcycling accident still retained a near normal LTM.  However, yet again the situation wasn’t quite that simple since KF could still recall visual information using his STM but struggled with auditory and verbal information, making conversation difficult. 

What amnesiacs tell us about memory

We therefore have a situation were cases of amnesia can both support the idea of two memory stores whilst at the same time question the idea.  This is particularly good stuff to include in a discussion of the existence of two memory stores. 

    Two memory stores

Amnesiacs tend to lose only one store (either STM or LTM) supporting the idea of two separate stores presumably located in different brain areas or structures. 

More than two stores

However, HM and Clive Wearing both provide us with evidence that LTM is more complex and seems to comprise at least two components (semantic and episodic LTM).  More on this when we look at types of LTM.  Similarly KF suggests that STM is also more complicated having separate stores for both auditory and visual information.  See later section on working memory.


Working memory model

This is explained in later sections and argues that STM may not be just one store but a collection of components each with a different task.  This would be evidence for there being more than two stores.

Brain areas

Modern scanning techniques have found that different areas of the brain operate when different stores are being used providing best evidence for different memory types.  The prefrontal cortex is active when STM (now more correctly referred to as working memory) is being used whereas the hippocampus in the temporal lobes is active for LTM.

Brain areas known to be involved in LTM


Types of Long term memory

First a note of caution.  ‘Types of long term memory’ is not specifically mentioned in the specification, nor do some of the texts, e.g. Cardwell for AS cover the topic.  However, some texts, including ours, do and the wording in the specification is sufficiently woolly to allow a question on it.  To date no questions have been set on the topic, however, information contained in this section and covered in class will at the very least be useful in part c questions that deal with STM and LTM.

We saw in the videos on amnesia that many patients suffering memory loss still have vital aspects of their LTM intact.  It is very rare for amnesiacs to lose their memory for skills such as language (reading and writing) and for walking, swimming etc.  As we saw in the case of Clive Wearing his ability to play the piano and conduct choirs was still intact despite most other memories having been lost.  In the video his long suffering wife says that his episodic memory is severely impaired whilst his semantic memory is largely intact.  This is one way of distinguishing types of LTM, however, there are others:  What follows is a brief summary of these, with examples and similarities drawn between them.

Episodic and Semantic (Tulving 1972)

  • Episodic memory contains the details of your life.  When Victoria Beckham gets someone to write her autobiography for her she would first sit down and tell them, presumably in words of not more than two syllables, all the interesting events that have happened to her.  For example the chive she had for dinner each day in August and the counselling she received on discovering she had a split end! 
  • Semantic memory contains our memories of the World and how it works.  Continuing the theme, hubbie Dave would store here his vast knowledge of the English language, capital cities of the World (presumably so they can name their next son Ulan Bator), and most importantly his footballing skills, specifically how to bend it like… well Beckham! 

Research evidence: Tulving (1989) using radioactive gold, found different areas of the brain are active when the two memory types are being used.  Episodic engages the frontal lobes, semantic the posterior lobes.


Declarative and Procedural (Cohen and squire 1980)

  • Declarative (knowing that).  For example knowing capital cities and other factual information and knowing about personal events in our life.  This is different to Tulving who believed that these two types of information were stored in different aspects of LTM.
  • Procedural (knowing how).  This covers our knowledge or memory for skills such as walking, talking, driving, playing football etc.

Research evidence: Squire et al (1992) used PET scans to show that different areas of the brain were active during each memory type. 

Implicit and Explicit (Graf and Schacter 1985)

  • Explicit: similar to declarative and being used for memories that we have to consciously recall, for example we need to think about personal memories and memories for trivia.
  • Implicit: similar to procedural and being used for memories that we don’t have to consciously think about.  These are mostly skills such as walking and talking.  If we do consciously think about such activities e.g. driving, they can become more difficult.

Evaluation: Implicit/explicit is particularly useful in explaining amnesia in brain-damaged patients, typically these having damage to their explicit memory but retaining an intact implicit memory. (E.g. H.M. and Clive Wearing).

Clive Wearing and wife Deborah


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