Models of Memory

Imagine, for a moment, that your brain saved information much just as a computer does.  Would you have one big folder entitled, "Memories", in which everything would be saved?  Or would there be separate sub-folders for different types of memories?  Moreover, how does your brain "save" information in the first place?

A number of models have been developed to help explain different types of memory, and how your brain creates a new memory.  Try the exercise below to explore different types of memory.
Try it Out

Imagine you were at a friend's birthday party, and met a very attractive person through a mutual friend.  You start chatting to this person and find out you have lots of thing in common.  As the party wears down, you ask this person for their phone number.  The person tells you their number, but your phone has run out of battery, and there isn't a pen and paper handy.  You need to memorize the number, and keep it in memory long enough to write it down later.

Are you read to give this a try?  

1.  Scroll to the bottom of the page, where you will see a phone number.  You are only allowed to look at the number for 10 seconds.  Then scroll back up.

2.  Play the video below to distract you.  Can you remember the number?

3.  When the video ends, you may now write down the phone number. Check to see if you were able to remember correctly!
Multi-Store Model of Memory

Were you able to remember the phone number accurately?  If so, well done!  The phone number was 10 digits long, which is more than most people can remember.  Research has shown that the average person can remember about 7 new "items", such as numbers or words.  But even if you remembered the number, chances are that you will probably forget it very soon - within minutes or hours at the most.  Some memories, however, never seem to fade.  You can easily remember your own phone number, can't you?  And, by the way - did you notice (and remember) a string of 5 letters underneath the phone number?  Yes, it was really there - scroll down again to check!

This activity suggests there are at least three different types of memory.  There is your sensory memory, the things that enter your senses briefly, but which you fail to really notice or pay much attention to.  This might include all of the billboards that you walk past when riding the subway, or the faces of the people you pass by while walking to school.  If you really pay attention to something around you, however, this information enters your short-term memory, which can hold a few items of information for a limited time.  You need to constantly "rehearse" this information, perhaps by repeating it silently to yourself, to prevent you from forgetting it.  Finally, once you have rehearsed the information for long enough, it may enter your long-term memory.  These are your long-lasting, nearly permanent memories of everything you have learned in your life, until now.  This model of memory, known as the multi-store model, can be summarized by the diagram:
  • Sensory memory: All of your sensory experiences - from the magazine covers that you scan while browsing a bookstore, to the song lyrics that you hear on the radio - are held in memory for the shortest of periods, less than a second.  Unless you consciously pay attention, these memories will quickly vanish. (In the phone number activity, the string of letters underneath the phone number was an example of sensory memory.  Because you didn't pay much attention, you quickly forgot them).

  • Short-term memory: If you do pay attention to something in your surroundings, this information will enter short-term memory.  Most people can only hold around 5-9 "items" in their short-term memory at any given time (the average is 7).  Moreover, short-term memories are only held for around 6-12 seconds.  You must constantly "rehearse" the memory (for instance, by silently repeating the items) to prevent the information from being lost.  (In the phone number activity, the number you tried to memorize was an example of short-term memory)

  • Long-term memory: With enough rehearsal, information may eventually enter your long-term memory.  Your long-term memory store can hold vast amounts of information for a potentially unlimited time.  Everything that you know well - such as all of the vocabulary that you have learned in your Native language, the names of your family members, and so on - is kept in your long-term memory.  Although the journey to get information into your long-term memory is a long and arduous one, once the information gets there, it is kept relatively permanent.

Evaluating Multi-Store model

  • The multi-store model was the first model of memory to distinguish between short-term and long-term memory.  It is historically important, and served as the foundation for later, more detailed theories

  • The multi-store model is supported by many research studies that demonstrate the limited capacity of short-term memory, the importance of rehearsal, and the difference between short-term and long-term memory.  For an example of one such study, see below

  • However, the multi-store model is now considered too simplistic.  It does not explain many important aspects of memory:  for instance, how memories can become distorted, or why traumatic experiences (such as those experienced by victims of violence or war) can result in extremely vivid memories with no rehearsal
Think Critically

Imagine you were trying to memorize a list of 15 words - perhaps a list of grocery items you need to buy.  You read each word, one at a time, repeating the words silently to yourself.  Immediately after reading the list, you try to remember as many of the words as you can.  Which words do you think you will remember the most - those at the beginning, the middle, or the end of the list?

Research has shown that people tend to remember the words in the beginning and end of the list, but tend to forget the words in the middle.  The enhanced memory for the words in the beginning of the list is called the primacy effect, and the enhanced memory for the words at the end of the list is called the recency effect.  This is illustrated by the graph below.

  • How would you explain the primacy and recency effects?

  • According to the multi-store model of memory, there are three types of memory: sensory store, short-term, and long-term.  In which store are the words from the beginning of the list kept?  What about the words at the end of the list?
Research: Murdoch

Aim: Investigate how the position of words in a list affects memory 

Procedure

  • Participants were shown a list of words, one at a time, for 1-2 seconds each

  • Immediately after all the words were shown, participants tried to recall as many of the words as they could

Results

  • Participants tended to remember more of the words at the beginning of the list (known as the primacy effect) and at the end of the list (known as the recency effect)

  • Participants had the worst recall for the words in the middle of the list

Conclusion

  • The primacy and recency effects can both be explained by the multi-store model of memory

  • The words in the beginning of the list tend to be rehearsed the most, as participants tend to silently repeat these words to themselves over and over again, from the very beginning of the task.  Thus, the earliest words tend to be stored in long-term memory

  • The words at the end of the list are the most recent, as participants have seen them just a few seconds before the recall task.  Thus, these words are still retained in short-term memory

Evaluation

  • This study provides support for the multi-store model of memory.  The primacy and recency effects can be explained by two separate stores of memory, short and long term

  • It is debatable whether the words in the beginning of the list are really in long-term memory.  For instance, most participants probably won't remember the words for much longer after the experiment is over

  • Trying to remember a list of random words is quite an artificial task - if real life, we tend to remember things that have some sort of meaning or importance, rather than just a random sequence of words.  This study may therefore lack in ecological validity




Working memory model

The multi-store model raises further questions about memory.  For instance, how does rehearsal take place in short-term memory?  Is there only one kind of short-term memory, or are there several?

The working memory model is a more developed version of the multi-store model, updated to reflect the latest research on the workings of short-term memory.  Short-term memory is renamed as working memory, because it functions as a sort of "mental workspace", allowing your mind to temporarily hold information as some cognitive task is being performed.

For instance, try to multiply the numbers 22 x 11 in your head.  Can you do it?  You might realize that 11 can be written as 10 + 1, and so 22 x 11 is the same as 22 x (10 + 1) or 22 x 10 + 22 x 1, which is 220 + 22 = 242.  In order to solve this mentally, you must be able to temporarily store and manipulate these numbers in your head - which is possible because of working memory.

Furthermore, the working memory model also distinguishes between different short-term memory stores, which explains why certain memory tasks (but not others) interfere with one another.  For instance, in the beginning of this lesson, you probably found it very difficult to keep the phone number in your mind while listening to "Call me maybe".  This is because listening to the lyrics of the song interferes with your ability to mentally repeat the digits to yourself.  But if you just watched the video, with the sound on mute, there would be less interference.

Based on these findings, the working memory model has proposed the following memory structure:


  • Central executive: This is the "CEO" of the memory system, which directs the other systems (called "slave systems").  For instance, when trying to multiply 22 x 11 in your head, the central executive directed the other systems to manipulate the numbers and carry out the calculations.  The most important function of the central executive is attention control - directing your memory subsystems to focus on the task at hand, or switching from one task to the next.  For example, when sitting in class, your central executive must ensure that attention is given to the teacher (rather than daydreaming about your weekend) for any memory of the lesson to be stored

  • Phonological loop: This is the verbal component of short-term memory.  The phonological store is your "inner ear", and stores auditory information for a brief period of time - just 1.5 - 2 seconds.  The articulatory control system is your "inner voice", used when mentally repeating information to yourself, like a telephone number.  If your "inner voice" repeats information, your "inner ear" hears that information and briefly remembers it, and the cycle repeats itself until it is embedded in long-term memory.

  • Visuo-spatial sketchpad: This is the visual & spatial component of short-term memory.  It is like an "inner eye" that can visualize a mental picture, from either your sensory memory or your long-term recollection.  For instance, if you visualize the route you travel to school each day, you are using your visuo-spatial sketchpad to "see" a mental picture of your journey to school.

  • Episodic buffer: This is a sort of mental "TV screen" where all the information from your senses, short-term and long-term memory is projected, ready for you to make use of.  The episodic buffer explains how we can integrate and make use of information from different memory stores, and some researchers believe the episodic buffer is the source of consciousness.

Evaluating Working model

  • This model explains why it is possible to multi-task on some occasions, but not others.  As long as the two tasks utilize different short-term memory systems (for instance, driving a car, which utilizes the visuo-spatial sketchpad, while talking to a friend, which utilizes the phonological loop), it is possible to perform well on both tasks.  However, if the two tasks involve the same memory system (for instance, talking with a friend while trying to do mental arithmetic, which both utilize the phonological loop), multi-tasking is nearly impossible

  • How the different memory systems interact with each other is not entirely clear.  Although the episodic buffer has been proposed as a bridge between the different memory systems, how the episodic buffer actually works is difficult to fully explain

  • The working model memory explains short-term memory well, but says very little about long-term memory, and does not explain how long-term memories may become lost, distorted, or fabricated


Research: Landry & Bartling

Aim: Investigate the effects of "multi-tasking" when both tasks utilize the same working memory system - in this case, the phonological loop

Procedure

  • Participants were randomly divided into two groups - the "multi-tasking" group and the "single task" group

  • All participants were shown 10 letter strings, each consisting of 7 random letters (eg. GHKALKE).  Participants had to memorize each string of letters, then write their answer down on an answer sheet

  • The participants in the "multi-tasking" group were also told to repeatedly say the numbers "1" and "2" at a rate of two numbers per second, while they were trying to memorize the string of random letters
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Findings

  • The participants in the "multi-tasking" group performed significantly worse, recalling the letters with 45% accuracy compared with 76% in the "single task" group

Conclusion

  • Repeating the numbers "1" and "2" made it more difficult to mentally rehearse the string of letters, resulting in diminished memory

  • This study suggests that multi-tasking leads to impaired working memory, especially when both tasks utilize the same working memory system (in this case, the phonological loop)

Evaluation

  • This was a well-controlled lab experiment, demonstrating a clear causal relationship between the independent variable (single vs. multi-tasking) and the dependent variable (recall of letters)

  • Supports the predictions of the working memory model, in particular the idea that each memory system has limited capacity

  • Since this experiment involved memorizing random strings of letters, a task not normally important for everyday life, this experiment may be low in ecological validity.  However, this study may help understand the risks of multi-tasking in the real world
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Checklist

  • I can explain the multi-store model of memory, including the capacity and duration of the sensory store, short-term memory, and long-term memory.  I can also evaluate the theory

  • I can describe the Aim, Procedure, Findings, and Conclusion of the research study by Murdoch, and evaluate the study

  • I can explain the working memory model, describing the role of the central executive, visuo-spatial sketchpad, phonological store, articulatory control system, and episodic buffer. I can also evaluate the theory

  • I can describe the Aim, Procedure, Findings, and Conclusion of the research study by Landry & Bartling, and evaluate the study
Quiz Yourself!

1.  According to the multi-store model, how long is information kept in the sensory store?

(a) Less than a second

(b) 1-2 seconds

(c) 6-12 seconds

(d) 30-60 seconds


2.  According to the multi-store model, around __________  can be saved in short-term memory, for around ______________ .

(a) 5-9 items, 6-12 seconds

(b) 6-12 items, 5-9 seconds

(c) 7-11 items, 30-60 seconds

(d) 7-11 items, 5-9 seconds


3.  According to Murdoch, what explains the primacy effect?

(a) Words from the beginning of a list are kept in the sensory-store

(b) Words from the beginning of a list are kept in short-term memory

(c) Words from the beginning of a list are kept in long-term memory

(d) Words from the beginning of a list are kept in the episodic buffer


4.  According to the working memory model, what is the main function of the central executive?

(a) Rehearsal

(b) Forming a mental picture of what you are trying to remember

(c) Multi-tasking

(d) Attention control


5.  According to the working memory model, the articulatory control system is the _______

(a) Inner eye

(b) Inner voice

(c) Inner ear

(d) Inner touch


6.  Kate thinks that she can do her Math homework while having a conversation with a friend on the phone.  What prediction would the working memory model make?

(a) Performance will not be impaired, because the episodic buffer can integrate information from different working memory subsystems

(b) Performance will not be impaired, because the tasks utilize different working memory subsystems

(c) Performance will be impaired, because doing Math and talking to a friend both utilize the phonological loop

(d) Performance will be impaired, since the central executive cannot focus on two tasks at once 
Answers

1 - A, 2 - A, 3 - C, 4 - D, 5 - B, 6 - C




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