Coding Capacity and Duration of Memory (1)

Research on coding (1)

Information is stored in memory in different forms, depending on the memory store.

 

The process of converting information between different forms is called coding.

 

Baddeley (1966) = gave different lists of words to four groups of participants to remember

 

Group 1 = (acoustically similar) words sounding similar

Group 2 = (acoustically dissimilar) words sounded different

Group 3 = (semantically similar) words with similar meanings

Group 4 = (semantically dissimilar) words with different meanings

Research on coding (2)

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

 

When they did this task immediately, recalling from short term memory (STM), they tended to do worse with acoustically similar words.

 

When they recalled the word list after a time interval of 20 minutes, recalling from long term memory, they did worse with the semantically similar words.

 

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

A03 - strength for coding

Identified a clear difference between two memory stores

 

Baddeley’s study identified a clear difference between 2 memory stores.

 

Later research showed that there are some exceptions to Baddeley’s findings. But the idea that STM uses mostly acoustic coding and LTM is 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.

A03 - limitation for coding

Used artificial stimuli rather than meaningful material

 

Baddeley’s study used artificial stimuli rather than meaningful material.

 

For example the words list had no personal meaning to participants.

 

So Baddeley’s findings may not tell us much about coding in different kind of memory tasks especially in every day life.

 

When processing more meaningful information, people may use semantic coding even for STM tasks.

 

This suggests that the findings from this study have limited application.

Research on capacity (1)

Digit Span

 

Jacob’s (1887) found out how much information the STM can hold at one time by measuring digit span.

 

For example, a researcher reads out four digits and the participant recalls these out loud in the correct order.

 

Research on capacity (2)

If this is correct the researcher reads our 5 digits and so in until the participant cannot recall the order correctly.

 

This indicated the individuals digit span.

 

Jacob’s found that the mean span for digits across all participants = was 9.3 items, the mean span for letters was 7.3.

Research on capacity (3)

Span of memory and chunking

 

Miller (1956) =

Made observations for everyday practices, he noted that things come in 7’s.

 

7 notes on the musical scale, seven days of the week, 7 deadly sins, and miller thought this was no accident

 

• The span of the STM might be about 7 items plus or minus 2.

• He also noted that people can recall 5 words as easily as they can recall 5 letters.

 

We do this by chunking (grouping sets of digits or letters into units or chunks

A03 - strength for capacity

A valid study as it has been replicated

 

The study is a very old one and early research in psychology often lacked adequate controls.

 

For example some participant's digit spans might have been underestimated because they where distracted during testing (extraneous variables)

 

Despite this Jacob’s findings have been confirmed by other better controlled studies since, (bopp et al 2005)

 

This suggests that Jacob’s study was a valid test of digit span in STM

A03 - limitation for capacity

Overestimated STM capacity

 

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 (5 items) is the more appropriate than 7 items.

Research on duration (STM) (1)

The Petersons (1959) tested 24 students in eight trials.

 

On each trial the student was given a consonant syllable to remember. They where also given a 3 digit number.

 

The student counted backwards from this number until told to stop. The counting back was to prevent any mental rehearsal of the consonant syllable.

 

On each trial they were told to stop after varying periods of time: 3,6,9,12,15,18 seconds (the retention interval)

 

After 3 seconds average recall was about 80%, after 18 seconds it was about 3%. Peterson’s findings suggested that the STM duration may be about 18 seconds, unless we repeated the information over and over.

Research on duration (LTM) (1)

Bahrick (1975) studied 392 American participants aged between 17 and 74.

 

High school year books were obtained from the participants or directly from some schools.

 

1. Photo recognition, the test consisting of 50 photos, some of the participants recalled all the names of their high school year book

2. Free recall test where participant's recalled all the names of their graduating class

 

Participants tested within 15 years of graduation were about 90% accurate in the 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, dropping to 30% after 48 years.

 

This shows that LTM may last up to a lifetime for some material.

 

A03 - STM

Petersons results may be due to interference rather than decay (limitation)

 

Peterson’s concluded that the forgetting in STM was due to the decay of memory traces over time.

 

However, it could also be due to interference from counting backwards (the effects of interference)

 

This suggests that the conclusions about duration of STM may not be valid.

 

A03 - LTM

Bahrick’s study had high external validity

 

This is because the researchers investigated meaningful memories (peoples names and faces).

 

When studies on LTM were conducted with meaningless pictures to be remembered, recall rates where lowered. (Shepard)

 

This suggests that Bahricks findings reflect a more real estimate of the duration of LTM.