Coding, capacity and duration

What is coding?

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

What is capacity?

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

What is duration?

The length of time information can be held in memory for

What is STM?

Limited capacity store

What is the coding of STM?

Acoustic

What is the capacity of STM?

5-9 items

What is the duration of STM?

18 seconds

What is LTM?

Potentially permanent memory store for information that has been rehearsed for a prolonged time

How is LTM coded?

Semantic

What is the capacity of LTM?

Practically unlimited

What is the duration of LTM?

Potentially up to a lifetime

How did Baddeley (1966) research how memory is coded?

• Four groups were given different lists of words to remember - acoustically similar, acoustically dissimilar, semantically similar and semantically dissimilar.

• They were then asked to recall the original words in the correct order.

What did Baddeley (1966) find?

• When they did the task immediately, they tended to do worse when recalling from STM with acoustically similar words

• After 20 minutes, they did worse with semantically similar words recalling from LTM.

• Demonstrates information is coded acoustically in STM and semantically in LTM.

Strength of Baddeley (1966)’s research

• Identifies clear difference between STM and LTM and the way they are coded has not been disproven.

• Important step to understand the memory system, leading to MSM.

Limitation of Baddeley (1966)’s research

• Used artificial stimuli - word lists had no personal meaning to participants

• Findings may not reflect how coding works in everyday life

• When processing meaningful information, people may use semantic coding for STM

• Suggests findings have limited application

What did Jacobs (1887) research on digit span?

Researcher read out an increasing amount of digits until the participant could not recall directly

What did Jacobs (1887) find?

• Mean span for digits was 9.3 items

• Mean span for letters was 7.3 items

Strength of Jacobs (1887)’s research

Jacobs’ study has been replicated - though it is an old study, and early psychology lacked adequate controls, Bopp and Verhaeghen (2005), a more controlled study, suggests that Jacobs’ study is valid.

Limitations of Jacobs (1887)’s research

Some participants’ digit spans might have been underestimated because they were distracted during testing - confounding variable

What research did Miller (1956) do on span of memory?

• He noted things made of 7s

• He thought from this that the capacity of STM is about 7 items (+-2)

What did Miller (1956) define ‘chunking’ as?

Grouping sets of digits/letters into ‘chunks’ to remember them better

Limitations of Miller (1956)’s research

Cowan (2001) reviewed other research and concluded the capacity of STM is only 3-5 chunks - suggests Miller may have overestimated capacity of STM

What did Peterson & Peterson (1959) research on duration of STM?

• 24 students were given a consonant syllable and a 3-digit-number to remember.

• Participants counted back from this number until they were told to stop at a random time (prevents any mental rehearsal of consonant syllables).

What did Peterson and Peterson (1959) find?

• After seconds, average recall was about 80%.

• After 18 seconds, this dropped to 3%.

• Shows STM duration is around 18 seconds, but could be made longer when rehearsing information.

Strength of Peterson & Peterson (1959)’s research

Reflects how memory works when we try to remember fairly meaningless materials like phone numbers.

Limitation of Peterson & Peterson (1959)’s research

Used artificial stimuli. Recalling consonant syllables does not reflect everyday memory activities - suggests findings lack external validity

What did Bahrick et al. (1975) research on duration of LTM?

• 392 Americans aged 17-74 participated in a photo-recognition and a free recall test.

• Photo-recognition: 50 photos from their high-school yearbook.

• Free recall: All the names of their graduating class.

What did Bahrick et al. (1975) find?

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

• After 48 years, this decreased by 20%.

• Free recall was less accurate - after 15 years, 60%. After 48 years, 30%.

• Shows LTM can potentially last for up to a lifetime.

Strength of Bahrick et al. (1975)’s research

• Researchers investigated meaningful memories - Shepard (1967) found that, when studies were conducted on LTM using meaningless materials, recall rates were lower.

• Suggests findings reflect a real estimate of the duration of LTM - high external validity