Memory: Long- and Short-Term Memory

Welcome to Memory, six days before Paper One.  If you can hear vaguely anxious noises, they’re coming from me.  Although, thankfully, I’m a bit better at Memory than I am at Social Influence, so with any luck, this won’t take too long.

The first things we’re going to talk about are Long- and Short-Term Memory, what they are, and how they work.  I mean, the whole topic is about those things, but this is your starter building block, where we’ll start to implement an understanding of it, and that sort of thing.

The first thing you need to know is that there are three key points to either side of memory: capacity, duration, and coding.  You really need to know these to understand everything else, so try to get the figures to stick in your mind as best you can.

Let’s talk about capacity first.  Capacity refers to how much information the brain can remember.  It can be pretty difficult to remember a lot of stuff at once – I’m sure everyone’s been in a situation where you’ve just woken up or just come home and a parent, roommate, sibling or spouse immediately bombards you with information of chores you need to do, and it’s just noise – you can’t take any of it in.  Capacity is the reason for this.  Your Short-Term Memory can only hold five to nine items at a time (seven is the key number here – we even refer to it in Memory as ‘Miller’s Magic Number’).  Any more than that, and the human brain can’t process the information.  We assess the short-term memory using something called a digit-span test, which I’m sure you’ll be able to find with ease on the internet.  This is, however, in contrast to the Long-Term Memory, which most psychologists believe can store information for an infinite amount of time.

Cowan, contesting Miller’s magic number, reviewed a number of studies on the short-term memory and found that the capacity of the short-term memory may be even more limited.  Cowan’s estimate was that it was more accurate to around four chunks.  A study by Vogel on visual, as opposed to verbal stimuli, found that the number was indeed closer to four chunks.  Simon also found that the size of the chunk matters, as an eight word phrase is much harder to remember than a single number.

I’m going to cease evaluating here, very briefly, to explain what a ‘chunk’ is.  The textbook doesn’t really go into it, but mercifully, I have a very good teacher who recognised this and explained it to us.  A chunk is essentially the same thing as an item; chunking is a technique we use to help us remember things, according to a three hour lecture on Lynda dot com.  This makes a lot of sense – when you have to remember a phone number, do you try and remember the whole 11 numbers, or do you break it down into three or four parts?  Most people would answer that by saying that they break it down into three or four parts.  For example, my chunking method for phone numbers is 5 numbers, then 3, then 3.  That is chunking, put simply.

The other criticism of testing capacity comes from Jacobs, who points out that there are individual differences in the duration of memory.  Eight year olds, for example, had an average capacity of 6.6 items, whereas 19 year olds had a mean average capacity of 8.6 digits.  There are a couple of theories about why this is: one suggests that people’s brain capacity increases with age, whilst another suggests that as we get older, we develop strategies to help us retain information – like chunking, which we’ve covered just above, there.

An infinite long-term memory is really nifty.  It doesn’t quite account for the fact that most of us don’t have any memories preceding our third year of life, but theories surrounding that are still very much foetal, and we don’t cover them in A Level Psychology.  If you’re interested, though, popular opinion amongst researchers is split between the lack of memory being due to trauma and the lack of memory being due to underdevelopment of the brain.

After capacity, we move onto duration.  Duration means how long things can stay in the brain for, and it has been tested in various ways.  For the short-term memory, a pair of researchers called Peterson and Peterson (married, not siblings), gave participants a consonant syllable (e.g. FRB) and a three-digit number to memorise.  They were asked to recall the consonant syllable after a retention interval of 3, 6, 9, 12, 15 or 18 seconds.  The reason for the three-digit number was to prevent participants from rehearsing the information, as this would allow it to pass into the long-term memory, therefore reducing the internal validity of the study.  The end result was that participants were 90% correct after 3 seconds, 20% correct after 9 seconds, and only 2% correct after 18 seconds.  As a result of this, it is generally believed that the duration of the short-term memory is less than 18 seconds, which – to me, at least – makes a lot of sense.  There are criticisms of this, however, which we’ll talk about shortly.

Peterson and Peterson’s study on the Short-Term Memory’s duration has also been criticised.  One popular criticism is that it’s an artificial way of testing Short-Term Memory, as memorising a random string of letters and numbers isn’t true to the things we have to remember in everyday life.  However, the study has been defended by some, who rightly point out that there are situations in which we do have to recall strings of numbers and letters.  Such examples would be car license plates or phone numbers.  More people still point out that these things have some meaning attributed to them – it’s really up to you, as someone studying the subject, to decide which side of the debate you’re on.

Furthermore, whilst the use of numbers prevented rehearsal of the letters, and therefore a transfer into the long-term memory, its effectiveness in improving internal validity has been questioned.  This is because there’s also a phenomenon called displacement in memory.  This means that a short-term memory is replaced with something else that an individual is trying to remember – such as a string of three numbers.  Reitman used auditory tones to test the short-term memory, and found that participants could remember up to 96 seconds worth of information.  This suggests that duration in Peterson and Peterson’s study may be due to displacement, rather than decay, as originally thought.

The duration of the LTM is supposedly unlimited, however, a study by Bahrick – intentionally or otherwise – calls this into question.  Bahrick tested 400 participants between the ages of 17 and 74 on their memory of their classmates under two different conditions.  One condition was photo recall, in which the participant was shown a photo of classmates and asked to name them.  The other condition was free recall, in which the participant was asked to name as many classmates as possible from memory.  Photo recall showed 90% accuracy after 15 years and 70% accuracy after 48 years.  Free recall showed 60% accuracy after 15 years and 30% accuracy after 48 years.  Both conditions suggest some kind of decay occurs during memory.  The other explanation is that cues, rather than the memories themselves, decay – which we’ll come onto in a couple of days’ time.

Finally, we have coding.  Coding is how things are remembered – or encoded, if we’re going to be technical – and we probably should be technical, as this part of psychology is quite scientific.  There are two main types of coding: acoustic and semantic.  Acoustic means sound-based – think acoustic guitar, or the acoustics in a concert hall.  Semantic means meaning-based – there’s nothing in particular that we can link this to, but it might help you to remember that there are three main facets of language, and semantics is one of them, because it refers to what the words mean.

Baddeley found that a list of words that are acoustically similar but semantically different (cat, cap, can, cad, cab, etc.) were easily confused in the short-term memory, but not the long-term memory, suggesting that short-term memories are encoded acoustically.  This makes quite a lot of sense to me, as someone who had to try and remember the words in the short term to transfer them over here (spoiler alert: they’re in a different order to the one they appear in in the textbook – this will not matter in an exam).  On the flipside, he found that semantically similar words (great, large, big, wide, tall, etc.) were confused in the long-term memory, but not the short-term memory, suggesting that the long-term memory codes things semantically.

However, Baddeley also tested LTM by waiting 20 minutes.  I’m sure that you’re already wondering whether 20 minutes can really be considered long-term memory – it isn’t short-term memory, but it’s also not really long-term memory either.  This is the conclusion that most researchers have come to, too.

Although the STM seems to rely on acoustic coding, it is thought that there is also a visual element to coding.  Brandimote showed participants an image and prevented any verbal rehearsal.  The result was that participants found a way to code the image visually, rather than verbally.

The same applies to the LTM.  Frost found evidence of visual coding taking place in the LTM, whilst Nelson and Rothbart found evidence for acoustic coding occurring in the LTM.  This suggests that coding depends on circumstance as well as the type of memory.


And that’s the different types of memory.  Next, we get to talk about the Multi-Store Memory Model, otherwise known as my favourite.