coding, capacity and duration of memory

• Coding


  Baddeley (1966) - Acoustic and semantic
• Acoustically similar words


  • cat, cab, can
• Acoustically dissimilar words


  • pit, few, cow
• Semantically similar words


  • great, large, big
• Semantically dissimilar words


  • good, huge, not
• Immediate recall was worse with acoustically similar words
• Acoustically similar words


  Short-term memory (STM) = acoustic
• Recall after 20 mins was worse with semantically similar words
• Semantically similar words


  Long-term memory (LTM) = semantic
• Jacobs

  1887
• Testing digit span


  1. Researcher reads 4 digits and increases until the participant can't recall the order correctly

  2. The final number = digit span
• Average digit span was 9.3 numbers in the correct order immediately after they were presented
• Average letter span was 7.3 letters in the correct order immediately after they were presented
• What did Jacob’s research

  Capacity - testing digit span
• Miller observed


  1. Everyday practice

  2. Things come in 7‘s e.g. notes of music, days of the week
• The span of STM is 7 items (plus or minus 2)
• Chunking


  • Grouping sets of digits/letters into meaningful units
  • Increases the span of STM
• Short term memory (STM) has a limited capacity of about 7 +/- 2 items
• What did miller research?

  capacity - magic number 7 +/- 2
• miller


  1956
• Duration STM - Peterson and Peterson 1959


  1. Students given nonsense trigram to recall

  2. Students given 3 digit number to count back from

  3. Retention interval varied: 3,6,9,12,15, or 18 seconds
• Findings

  • After 3 seconds average recall was 80%
  • After 18 seconds average recall was 3%
  • STM without rehearsal is up to 18 seconds
• What did perterson and peterson research?

  Duration of STM
• peterson and Peterson

  1959
• Bahrick study


  1975
• Participants

  • 392 Americans aged between 17-74
• Recognition test

  50 photos from high school yearbook
• Free recall test


  Participant listed names of their graduating class
• findings - Recognition test - 90% accurate after 15 years, 70% after 48 years
• Findings - Free recall test - 60% accurate after 15 years, 30% after 48 years
• What did Bahrick research?

  Duration of LTM
• Bahrick 1975


  Yearbook photos
• one strength of Baddeley study is that it identified 2 memory stores


  Later research showed that there are exceptions to Baddeleys findings. But STM is mostly acoustic and LTM is mostly semantic. This led to the development of the MSM
• one limitation of Baddeleys study is that it used artificial stimuli 


  the words used had no personal meaning to the participants so tells us little about coding for everyday memory tasks. when processing more meaningful information, people use semantic coding even for STM. this means the findings of this study have limited application
• one strength of Jacobs study is that its been replicated


  this is an old study and may have lacked adequate controls (confounding variables). despite this, Jacob’s findings have been confirmed in later controlled studies (e.g. Bopp and Berhaeghen 2005). this shows that Jacob’s study is a valid measure of STM digit span
• one limitation of millers research is it may overestimate STM capacity

  For example Cowan (2001) reviewed other research. he concluded that the capacity of STM was only about 4 (+/-1) chunks. this suggests that the lower end of millers estimate (5 items) is more appropriate than 7 items
• one limitation of Peterson and Petersons study is the meaningless stimuli


  we sometimes try to recall meaningless things so the study is not completely irrelevant. but, recall of nonsense trigrams doesn't reflect meaningful everyday memory tasks. therefore the study lacked external validity
• one strength of bahricks study is that it has high external validity


  everyday meaningful memories e.g. peoples names and faces were studies. when lab studies were done with meaningless pictures to be remembered, recall rates were lower (Shepard 1967). this means that bahricks findings reflect a more real estimate of the duration of LTM