Coding, capacity and duration of memory

What is coding?

The format in which information is stored in the various memory stores.

What did Alan Baddeley investigate for coding?

Baddeley gave different lists of words to four groups of participants to remember:

• Group 1 (acoustically similar) - words sounded similar

  e.g. cat,cab,can

• Group 2 (acoustically dissimilar)- words sounded different e.g. pit, few, car

• Group 3 (semantically similar)- words with similar meanings (e.g. great, big, large)

• Group 4 (semantically dissimilar) - words with different meanings (e.g. good, huge, hot)

Participants were shown the original words and asked to recall them in the correct order.

What were Alan Baddeley’s findings for coding?

When they recalled immediately (from STM), they did worse with acoustically similar words.

When they recalled after 20 minutes (from LTM), they did worse with semantically similar words.

These findings suggest that information is coded acoustically in STM and semantically in LTM.

What is capacity?

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

What did Jacobs investigate for capacity?

Jacobs investigated into how much information the STM can hold at one time. He did this by measuring digit span.

For example, the researcher read out four digits and the participant recalls these out loud in the correct order. If this is correct the researcher reads out five digits and so on until the participant cannot recall the order correctly. This indicates the individuals digit span.

What were Jacobs’ findings for capacity?

Mean span for digits across all participants was 9.3 items

Mean span for letters was 7.3

What did Miller investigate for capacity?

Miller made observations of everyday practice.

For example, he noted that things come in sevens. Seven days of the week, seven musical notes, seven deadly sins

What were Miller’s findings for capacity?

The capacity of the STM is about 7 items plus or minus 2.

People can recall 5 words as easily as 5 letters through chunking (grouping sets of words or letters into chunks)

What is duration?

The length of time information can be held in the various memory stores.

What did Peterson and Peterson investigate for duration of STM?

Peterson and Peterson tested 24 students in eight trials each. On each trial the student was given a consonant syllable (such as YCG) to remember. They were also given a 3 digit number. The student counted backwards from this number until told to stop. The counting backwards was to prevent any mental rehearsal of the consonant syllable. On each trial they were told to stop after varying periods of time: 3,6,9,12,15 or 18 seconds (the retention interval).

What were Peterson and Peterson’s findings on duration of STM?

After 3 seconds, average recall was about 80%

After 18 seconds, it was about 3%

Their findings suggest that STM duration may be about 18 seconds.

What did Bahrick et al investigate for duration of LTM?

Bahrick et al studied 392 American participants aged between 17 and 74. High school yearbooks were obtained from the participants or from schools. Recall was tested in various ways:

• Photo recognition test- consisting of 50 photos, some from the participants high school yearbooks

• Free recall test- participants recalled all the names of their graduating class

What were Bahrick et al’s findings for duration of LTM?

Participants tested within 15 years of graduation were about 90% accurate in photo recognition.

After 48 years, recall declined to about 70% for photo recognition.

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

This shows that LTM may last up to a lifetime

What is a strength of Baddeley’s study on coding?

It identified a clear difference between two memory stores

The idea that STM uses mostly acoustic coding and LTM mostly semantic has stood the test of time. This was an important step in our understanding of the memory system which led to the multi-store model.

What is a limitation of Baddeley’s research on coding?

It used quite artificial stimuli rather than meaningful material.

E.g. the word lists had no personal meaning to participants. So Baddeley’s findings may not tell us much about coding in different kinds of memory tasks, especially in everyday life. When processing more meaningful information, people may use semantic coding even for STM tasks.

This suggests that the findings have limited application.

What is a strength of Jacob’s research on capacity?

It has been replicated

Early research in psychology often lacked adequate controls. For example, some participants digit spans might have been underestimated because they were distracted during testing. However, Jacobs’ findings have been confirmed by other, better controlled studies such as Bopp and Verhaeghen 2005

This suggests that it is a valid test of digit span in STM.

What is a limitation of Miller’s research on capacity

He may have overestimated STM capacity

Nelson Cowan reviewed other research and concluded that the capacity of STM is only about 4 plus or minus 1 chunks.

This suggests that the lower end of Miller’s estimate (five items) is more appropriate than seven items.

What is a limitation of Peterson and Peterson’s study on duration of STM?

Stimulus material was artificial

Recalling consonant syllables does not reflect most everyday memory activities where what we are trying to remember is meaningful.

This means the study lacked external validity.

What is a strength of Bahrick et al’s research on duration of LTM?

It has high external validity.

This is because the researchers investigated meaningful memories (e.g. peoples names and faces). When studies on LTM were conducted with meaningless pictures to be remembered, recall rates were lower (e.g. Shepard 1967)

This suggests that Bahrick et al’s findings reflect a more ‘real’ estimate of the duration of LTM.