Coding, capacity, duration

• STM is acoustically coded, has a limited capacity of 7+/-2 items and has a duration of 18-30 seconds
• LTM is semantically coded, has an unlimited capacity and a duration of a lifetime
• coding


  format in which info is transformed into and stored in memory
• Baddeley (1966)- Acoustic+semantic


  • gave different word lists to 4 groups: 1) Acoustically Similar (cat/can) , 2) Acoustically Dissimilar (pit/few) , 3) Semantically Similar (great/large) , 4) Semantically Dissimilar (good/hot)
  • pps asked to recall their list in correct order either immediately (test STM coding) or after 20 mins (test LTM coding)
• Baddeley 1966 findings


  • immediate recall worse with acoustically similar words- STM acoustic (sound)
  • recall after 20 mins worse with semantically similar words- LTM semantic (meaning)
• capacity


  amount of info stored in memory
• Jacobs (1887)- testing digit span


  • developed digit span technique
  • pp has to immediately recall sequence of letters/numbers increasing by 1 character/figure with each trial
• Jacobs 1887 findings


  • on average pps could repeat back 9.3 numbers and 7.3 letters in correct order immediately after presented
• Miller (1956) 7+/- 2


  • observed everyday practice + noted things come in 7s e.g days of week, deadly sins etc
  • concluded STP capacity is 7+/- 2 items
  • can be increased by chunking
• duration


  length of time info stored in memory before decays
• Peterson + Peterson (1959)- STM duration


  • 24 undergraduate students given nonsense trigram of 3 syllables e.g YCG to recall
  • prevent maintenance rehearsal, pps given 3 digit number to count backwards from
  • told to stop after 3, 6, 9, 12, 15, 18 second intervals + recall trigram
• P+P 1959 findings


  • after 3 seconds, 80% trigrams correctly recalled
  • after 18 seconds, 10%
  • concluded stm duration without rehearsal is 18-30 seconds
• Bahrick et al (1974)- LTM duration

  • 392 pps aged 17-74
  • given photo recognition test- 50 photos from high school yearbook
  • told to do a free recall test- list names of graduating class
• bahrick 1975 findings


  • recognition test- 90% accurate after 15 years of graduating and 70% accurate after 48 years
  • free recall test- 60% recall after 15 years and 30% after 48 years
• limitation- Baddeley 1966 uses artificial stimuli


  • tasks involved recalling word lists e.g pit, can, cat, have no personal meaning to pps so tells us little about coding for real everyday memory tasks
  • e.g. when processing meaningful info we sometimes use semantic coding even for STM
  • limited application
• limitation- P+P 1959 uses artificial stimuli


  • we sometimes try to recall meaningless things e.g out of curiosity so the study isnt completely irrelevant
  • but the use of artificial tasks like recalling nonsense trigrams lacks mundane realism as it it meaningless to the pps and doesnt reflect relevant everyday memory tasks
  • lacks external validity
• limitation- jacobs (1887) may lack temporal validity


  • study conducted long ago so may not be done to scientifically rigourous standards expected today
  • possible findings affected by CVs e.g. pps being distracted
  • may not apply to todays society
• strength/CA- Bahrick et al 1975 has high external validity

  • procedure used pps high school year book to recall names of graduating class, which is considered meaningful stimuli
  • more likely to reflect everyday situations than fake tasks like word lists
  • however, hard to control EVs as it was unknown if pps kept in contact with their classmates or if anyone looked at their yearbook in previous years
  • this would distort the data produced and lead to unreliable findings