Coding, capacity and duration of memory - Memory

Coding

Information is stored in different forms - this is referred to as 'coding'. It is almost the minds method of applying labels to information and placing it in the correct cupboard.

Research by Alan Baddeley found that short term memory is coded acoustically and long term memory is coded semantically. 

Baddeley divided lists of words into four groups and asks participants to remember them.

When trying to recall from short term memory participants did worst on acoustically similar words and when recalling from long term they did worst with the semantically similar words. See the video below for  a simple explanation.

It seems counterintuitive to think that because participant did worse on acoustically similar words for short term memory that indicates that short term memory codes acoustically. For your exam please try to remember that short term memory is coded acoustically and long term memory codes semantically. That is a chunk of AO1 that you need to recall if asked in the exam.

Capacity

Capacity refers to how much information short term memory can hold at one time. Jacobs (1887) studied capacity by measuring digit span. 

He did this by calling out a range of number of digits, e.g. four digits and if the participant recalls these in the correct order they go on to 5 digits, 6 digits and so on. The study carries on until the participant cannot recall the numbers in the correct order.

Jacobs found that the mean for all participants was 9.3 - meaning they could get to the point where they could recall 9.3 digits before their short term memory would fail to recall.

George Miller (1956) in his paper The Magic Number Seven (plus or minus two) where he claimed the capacity of short term memory was seven items, plus or minus two. He also noted that remembering words or letters people like to 'chunk', as chunking helps us remember long items such as our phone number in chunks!

The below video gives a good explanation of Miller's study up to around 3 minutes.

Activity Time - Be The Psychologist!

In pairs or in groups, design your own study based on Jacobs study of digits. 

Write out a list of numbers starting with 3, then 4, then 5, and so on all the way to 10. For example

492

5174

90472

284759

9428197

Keep the list out of sight of your partner and ask them to recall the numbers in the order that they were given. 

See how far you can get and how many you can recall.

Duration

Capacity looked into how much information short term memory could hold, now duration looks at how long it can hold information.

Short Term Memory

A study by Peterson and Peterson (1959) found that the duration of short term memory is about 18 seconds unless there is opportunity to repeat information over and over in verbal rehearsal. 

In their study they asked participants to remember letters (consonant syllable or trigram meaning 3 letters that do not form a recognised word, such as KRC, BWY) and numbers followed a number to count back from - this counting backwards was to disrupt and prevent mental rehearsal of the consonant syllable, oh those sneaky Petersons! If rehearsal is prevented, information vanished rapidly from short term memory.

As mentioned above, they found the duration of memory in this study to be 18 seconds.

Long Term Memory

Bahrick et al (1975) tested long term memory in a study that looked at recall of old high school yearbooks to see if the participants could remember the names of their old classmates. There was also free recall to see if participants could recall all the names of their graduating class.

Those tested after 15 years had 90% accuracy in photo recognition.

After 48 years it was 70% for photo recognition.

Free recall was less accurate - 60% after 15 years and 30% after 48 years.

This goes to show that Long Term Memory can last a lifetime!

Let's get thinking!

Can you recall all the names of everyone who was in your P1 or P7 class at the end of primary school? 

If you are into sports, can you recall the starting players on your favourite team from a big game within the last 10 years or more?

Thats the end of the AO1.

Evaluation

1. A strength of Baddeley's study is that it identified a clear difference between two memory stores - short term and long term memory. It has contributed to other important study's in Psychology such as the Working Memory Model and the Multi-Store Model of Memory.

2. A criticism of Baddeley's study is that it used artificial stimuli - the words and activities had no meanings to the participants

3. Jacobs' study on digit span has been replicated and this shows that it is a valid test in studying short term memory.

4. A limitation of Miller's study is that Miller may have overestimated short term memory capacity. A review by Nelson (2001) found that the capacity of short term memory may only be 4 (plus or minus 1) chunks.

5. A strength of Bahrick et al's study is that is has high external validity. The researchers investigated meaningful memories which had a high recall rate. A later study into long term memory by Shepard (1967) showed that long term memory rates were lower when trying to remember meaningless pictures. This suggests that Bahrick et al's study gives a more real view of the capacity of long term memory.