The nature of memory

What is memory?

How is memory encoded, stored and retrieved?

What different types of memory are there?
Memory at its most basic consists of 3 important stores (sensory memory, short term memory and long term memory) and 3 important processes (encoding, storage and retrieval)

For information to be stored in memory it first has to be converted in to a format that memory can use. Each memory store uses its own type of encoding. An example of this is a red rose which could be encoded in (1) the way it stimulates our senses, e.g. its smell or colour; (2) the sound of the word “rose”; or (3) the things the rose actually means to us. We will return to this example later on the page.

Once the information has been converted to a suitable format for the type of memory store, it has to be placed in the store. Each store has a certain capacity and duration.

This refers to the process of accessing the information that has been stored in memory. Each store differs in the way this is achieved and the effect it has on the information itself. Retrieving information from long term memory can actually alter the information and is a key factor that explains how memories for events may be very inaccurate (this will be discussed further in the section on eyewitness testimony).

Sensory memory
This is the first stage of memory. Information from our senses (sight, sound, taste, tough, smell, and others) is stored in a buffer for anything between a few milliseconds and up to 2 seconds, which allows time for the information to be attended to and used before it fades away. Without sensory memory we would be unable to cope with the massive bombardment of information from the environment that continually assaults our senses. There is a buffer for each sense: visual sensory memory is stored in an iconic buffer and auditory sensory memory is stored in an echoic buffer.

Research into sensory memory has focussed primarily on its capacity. Sperling (1960) researched the capacity of visual sensory memory and concluded that it was essentially very large and that any part of it could be attended to. He presented participants with a grid consisting of 3 rows of 4 letters (12 in total) for 20 milliseconds. When participants were asked to recall all 12 letters they could only manage 3 or 4, but when they were told to recall just one row (indicated by the pitch of a tone - high, medium, or low - immediately after the grid had been presented to them) then they could recall all 4 letters from that row even though they did not know in advance which row to remember.

Short term memory
Short term memory (STM) is also referred to as working memory as it contains everything we are aware of at the moment.

Early research into the capacity of short term memory (Miller, 1956) found it can store about 7 plus or minus 2 items (i.e. between 5 and 9 items or chunks) - this is often referred to as Miller’s magic number. Test your own STM capacity on our games and tests page.

The duration of short term memory (STM) was researched by Peterson & Peterson (1959). They presented participants with trigrams (groups of 3 letters that do not make a word) and asked them to recall them after intervals of 0, 3, 6, 9, 12, 15, and 18 seconds. To stop participants simply repeating the trigrams in their heads (rehearsal) they asked them to count out loud backwards in threes from a certain number (an interference task). The findings were that the accuracy of recall steadily declined until less than 10% of trigrams were recalled after 18 seconds. From this and similar research we can conclude that the duration of short term memory is around 12-30 seconds.
Peterson & Peterson duration of short term memory

Encoding is short term memory (STM) is primarily phonological (by sound). Conrad (1964) asked participants to remember lists of letters that sounded similar (e.g. E, G, B, C) or ones that had dissimilar sounds (e.g. R, K, L, O), with the finding that participants had most difficulty recalling those that were phonologically similar. As letters with similar sounds were confused with one another and ones with different sounds were not, Conrad concluded that short term memory must be encoded by sound (phonologically).

Long term memory
Long term memory (LTM) is our memory of everything that has happened to us, al we know about the world, and the things we can do. It has a capacity that is best described as limitless, although it could never actually be tested as it would be impossible and unethical to completely fill a memory store designed to last a life time.

Baddeley (1966) provided good evidence that encoding in long term memory (LTM) is primarily semantic, that is that it is based on the meaning of the information being stored. Participants were given one of four lists of words: acoustically similar (similar sound), acoustically dissimilar, semantically similar (similar meanings), or semantically dissimilar. After being shown the list of words participants performed a different task for 20 minutes and were then asked to recall the words. Baddeley found that recall was far worse for the semantically similar words than in the other three conditions, and concluded that as the meaning of the words had caused confusion between the individual words on the list then encoding in LTM must be semantically based.

Duration of long term memory (LTM) was researched by Bahrick et al (1975). The participants were 392 graduates from an American high school over a 50 year period who were shown pictures from their yearbooks. Participants were divided into 2 groups: in the recognition group they were asked to select the correct name from a list of names for each photo; and the recognition group they were asked to remember the names of the people in the photos without being given a list of possible names. The recognition group were 90% accurate 14 years after graduation, dropping to 60% accuracy 47 years after graduation. The recall group were 60% accurate 7 years after graduation and less than 20% after 47 years. The conclusion from this is that people evan remember creation types of information for almost an entire lifetime (47 years after graduation is almost a lifetime), and that recognition memory tasks based on recognition seem to be better than ones based on recall.

A Level exam tips
How to answer exam questions on the nature of memory (PSYA1 AQA A specification)
Exam questions on the nature of memory tend to involve completing lists or tables using a list of possible answers. E.g. for a 3 mark question you may be given 6 options and asked to identify which ones describe duration of STM, capacity of LTM, and encoding in STM. The key to doing well is to read the question and then try to answer it without looking at the options so that you are relying on your knowledge and avoid being confused by the incorrect options.