coding capacity and duration

• Coding - Baddeley (acoustic and semantic)


  • Procedure - participants were given acoustically similar words or dissimilar words and were asked to remember them
  • Findings - Immediate recall was worse with acoustically similar words so short term memory is acoustic. Recall after 20 minutes was worse with semantically similar words so long term memory is semantic.
• Capacity - Jacobs (testing digit span)


  • Procedure - researcher reads four digits and increase until the participant cannot recall the order correctly.
  • Findings - on average, participants could repeat back 9.3 numbers and 7.3 letters in the correct order immediately after they were presented
• Capacity - Miller (magic number 7 ± 2)


  • Procedure - Miller observed everday practice, noted that things come in sevens.
  • Findings - the span of short term memory is about 7 items (plus or minus 2) but is increased by chunking.
• Duration STM - Peterson and Peterson (consonant variables)


  • Procedure - 24 students were given a consonant syllable to recall a 3 digit number to count backwards from . The retention interval was varied
  • Findings - after 3 seconds, average recall was about 80%, after 18 seconds it was about 3%. Short term memory duration is up to 18 seconds.
• Duration LTM - Bahrick (yearbook photos)


  • Procedure - participants were 392 americans aged between 17 and 74. There were two conditions : recognition test (50 photos) and free recall test (listed names)
  • Findings - recognition test results was 90% after 15 years and 70% after 48 years. Free recall test results was 60% after 15 years and 30% after 48 years.
• Evaluation of Baddeley's study

  One strength of Baddeley's study is that it identified two memory stores. Later research showed that there are exceptions to Baddeley's findings. But Short term memory is mostly acoustic and long term memory is mostly semantic. This led to the multi-store model being developed.
• Evaluation of Baddeley's study

  One limitation of Baddeley's study is that it used artificial stimuli. The words used had no personal meaning to participants so tells us little about coding for everyday memory tasks. When processing more meaningful information, people use semantic coding even for short term memory. This means the findings of this study have limited application
• Evaluation of Jacobs' study

  One strength of Jacobs' study is that it has been replicated. This is an old study and may have lacked adequate controls. Despite this, Jacobs' findings have been confirmed in later controlled studies. This shows that Jacobs' study is a valid measure of short term memory digit span.
• Evaluation of Miller's study

  One limitation of Miller's study is that it may overestimate short term memory capacity. For example, Cowan reviewed other research. He concluded that the capacity of short term memory was only about 4 chunks. This suggests that the lower end of Miller's estimate is appropriate than 7 items.
• Evaluation of Peterson and Peterson's study

  One limitation of Peterson and Peterson's study is that it used meaningless stimuli. We sometimes try to recall meaningless things so the study is not completely irrelevant. But recall of consonant syllables does not reflect meaningful everyday memory tasks. Therefore, this study lacked external validity.
• Evaluation of Bahrick study

  One strength of Bahrick's study is that it had high external validity. Everyday meaningful memories were studied. When lab studies were done with meaningless pictures to be remembered, recall rates were lower. This means that Bahrick's findings reflect a more real estimate of the duration of long term memory.