Coding, Capacity and Duration

Long Term Memory (LTM)

• It is the permanent memory store.

• It has an unlimited capacity.

• It has unlimited duration → it can store memories for up to a lifetime.

Short Term Memory (STM)

• It is the temporary memory store.

• It has a limited capacity of 7 ± 2 items.

• It has a duration of about 18 seconds.

Coding

The process of converting information from one form into another so it can be stored by the memory (acoustically, visually, semantically)

Who researched coding?

• Baddeley

• The aim of his study was to test whether the STM and LTM code differently.

Baddeley: procedure

• 4 groups of participants were used.

• Each group received a different word list.

• Group 1: acoustically similar

• Group 2: acoustically dissmilar

• Group 3: semantically similar

• Group 4: semantically dissimilar

• Participants were asked to recall the lists immediately (to test STM) and then after 20 minutes (to test LTM)

Baddeley: results

• When participants recalled the words immediately, group 1 (acoustically similar words) did worse.

• STM codes information acoustically → similar sounding words are mixed up during the coding process.

• When participants recalled the words after 20 minutes, group 3 (semantically similar words) did worse.

• LTM coded information semantically → similar meaning words are mixed up during the coding process.

Baddeley: evaluation

Strength

• Separate memory stores → this finding is supported by other research such as the multi-store model and it helped shape our understanding of memory.

Limitation

• Artificial task → the world lists had no meaning which is not realistic to situations that we encounter in everyday life.

Capacity

The amount of information that can be held in a memory store.

Who researched capacity?

• Jacobs

• The aim of his study was to see how much information can be held in the STM at a time.

Jacobs: procedure

• A researcher read out a series of digits and the participants then had to recall the them out loud in order.

• For example, the researcher would read out 4 digits. If the participant recalled them correctly he would read out 5 digits and so on.

• This went on until the participant could not repeat the digits back in the correct order.

• The maximum number that the participant could recall in the correct order was their digit span.

Jacobs: results

• He found that the average digit span was 7 items.

• This lead to the conclusion that STM has a limited capacity of 7±2 items.

Jacobs: evaluation

Strength

• High replicability → Jacob’s study is relatively old, and in the past researchers did not know how to control experiments to the extent we do now. However, it has been replicated several times (2005) and has yielded the same results.

Limitation

• Artificial task → the digits used had no meaning which is not realistic to situations that we encounter in everyday life.

Chunking

• Following Jacob’s study, Miller proposed that information is grouped into chunks so there are less items for the STM to remember.

• He noticed that we organise things into groups of 7, supporting the idea that the STM has a capacity of around 7.

• However, later evidence suggests that he may have overestimated the amount of chunks that the STM can hold.

• It has been found that the STM can hold a maximum of 4 chunks.

Duration

The length of time than information can be held in a memory store.

Who researched the duration of the STM?

• Peterson & Peterson

• They aim of their study was to see how long the STM can hold information without rehearsal.

Peterson & Peterson: procedure

• They tested a group of 24 students across eight different trials.

• Participants where given a trigram to remember (XCJ) and a three-digit number (213)

• In order to stop the participants from rehearsing the trigram as it would lead to the transfer of the trigram from the STM to the LTM, they had to count backwards from their number as a distraction.

• They were told to stop counting after a different amount of time across several trials.

Peterson & Peterson: results

• After 3 seconds of counting, recall was 80%.

• After 18 seconds of counting, recall was 3%.

• This suggests that the duration of the STM (the amount of time information can be held without rehearsal) is 18 seconds.

Peterson & Peterson: evaluation

Strength

• Standardised procedure → the study was highly controlled and everyone did the same task, meaning it is easily replicable.

Limitation

• Decay vs interference → They concluded that forgetting in the STM is due to decay, however it has been argued that the participants could have forgotten the trigrams due to interference caused by the number task. This means that the conclusions made about STM duration may not be valid.

Who researched the duration of the LTM?

• Bahrick et al

• They wanted to see how long memories could be stored for in the LTM.

Bahrick et al: procedure

• Participants were american high-school graduates (between the ages of 17-74)

• They were tested on their memory of classmates’ names and faces from their high-school yearbooks.

• They were asked to recall or recognise classmates after different time gaps.

Bahrick et al: results

• Participants tested 15 years after graduating were 90% accurate in photo recognition.

• Participants tested 48 years after graduating were 70% accurate in photo recognition.

• Free recall (asked to recall classmates names without any cues) was generally much lower than recognition but still showed long-term retention.

• This shows that the STM can hold information for up to a lifetime.

Bahrick et al: evaluation

Strength

• High external validity → the study used meaningful memories, making the study more accurate to real-life situations. Other studies of the LTM that used meaningless pictures had lower recall rates. This suggests that Bahrick’s study shows a more accurate representation of the LTM duration.

Limitation

• Memories may have been strengthened by rehearsal over the years (e.g. seeing yearbooks or talking about school), so it may not reflect long-term memory ability completely.