Coding, capacity, and duration

• AO1 - Baddeley’s research

  Baddeley gave different lists of words to 4 groups to remember:

  • Group 1: acoustically similar words
  • Group 2: acoustically dissimilar words
  • Group 3: semantically similar words
  • Group 4: semantically dissimilar words
• AO1 - Baddeley’s findings

  • When recalling from STM, participants tend to do worse with acoustically similar words, therefore information is coded acoustically in STM.
  • When recalling from the LTM, participants tend to do worse with semantically similar words, therefore information is coded semantically in LTM.
• AO1 - Jacobs‘ research

  • Found out how much information STM can hold at one time by measuring the digit span.
  • Researcher reads out 4 digits and increases the number of digits until the participant can’t recall the order correctly.
• AO1 - Jacobs’ findings

  Found that the mean span was 9.3 numbers and 7.3 letters in the correct order, immediately after they were presented.
• AO1 - Miller’s research

  • Observed everyday practice.
  • Noted that most things come in sevens - notes of musical scale, days of the week, deadly sins.
• AO1 - Miller’s findings

  • Miller thought the span of STM is about 7 items, plus or minus 2.
  • Can be increased by chucking, which is grouping sets of digits or letters into meaningful units.
• AO1 - Peterson and Peterson’s research

  • Tested 24 students in 8 trials each.
  • In each trial, they were given a consonant syllable to recall and a 3-digit number to count backwards from to prevent any mental rehearsal of the consonant syllable.
  • The retention interval was varied at 3,6,9,12,15 or 18 seconds.
• AO1 - Peterson and Peterson’s findings

  • They found that after 3 seconds, average recall was about 80% and after 18 seconds it was about 3%.
  • Findings suggested that STM duration may be about 18 seconds without rehearsal.
• AO1 - Bahrick et al’s research

  • Studied 392 American participants ages 17-74.
  • Recall was tested by photo-recognition test and the free recall test.
  • Photo-recognition test: consisting of 50 photos from the participants’ high school year books.
  • Free recall test: participants recalled names from their graduating class.
• AO1 - Bahrick et al’s findings

  • In the recognition test, 90% were accurate after 15 years and 70% were accurate after 48 years.
  • In the free recall test, 60% could recall after 18 years, dropping down to 30% after 48 years.
  • LTM may last up to a lifetime.
• AO3 - ✔️Baddeley’s study is that it identified 2 memory stores


  • Later research shows that there are exceptions to Baddeley’s findings.
  • The idea that STM uses mostly acoustic coding an LTM mostly uses semantic coding.
  • This was an important step in our understanding of the memory system, which led to the multi-store model.
• AO3 - ✖️Baddeley’s study is that it used artificial stimuli


  • The words used has no personal meaning to the participants so it tells us little about coding for everyday memory tasks.
  • When processing more meaningful information, people use semantic coding even for STM.
  • Suggests that the findings from this study have limited application.
• AO3 - ✔️Jacobs’ study is that it has been replicated


  • The study is very old and may have lacked adequate controls.
  • E.g. confounding variables - participants being distracted.
  • Despite this, Jacobs’ findings have been confirmed in later controlled studies.
  • Shows that Jacobs’ study is a valid measure of STM digit span.
• AO3 - ✖️Miller’s study is it may overestimate STM capacity.


  • Cowan reviewed other research and concluded that the capacity of STM was only about 4 (plus or minus 1) chunks.
  • Suggests that the lower end of Miller’s estimate (5 items) is more appropriate than 7 items.
• AO3 - ✖️Peterson and Peterson’s study is the meaningless stimuli


  • The study isn’t completely irrelevant as we do sometimes try to remember fairly meaningless material.
  • But recall of consonant syllables doesn‘t reflect meaningful everyday memory tasks.
  • Therefore, the study lacked external validity.
• AO3 - ✔️Bahrick et al’s study is it has high external validity


  • Researchers investigated meaningful memories.
  • When lab studies were done with meaningless pictures to be remembered, recall rates were lower.
  • Suggests that Bahrick et al’s findings reflect a more ‘real’ estimate of the duration of LTM.