Coding, Capacity and Duration of Memory

• coding 


  the format information is stored
• duration 


  the length of time information is held for
• capacity 


  the amount of information that can be stored
• the coding, capacity and duration of STM 


  coding: acoustic

  capacity: 5-9 items

  duration : 18 seconds
• coding, capacity and duration of LTM 


  coding: semantic

  capacity: unlimited

  duration: a lifetime
• a research study which shows evidence for the coding in STM and LTM 


  Baddeley (1966)
• a research study which shows evidence for the capacity of STM 


  Jacobs (1987)
• a research study which shows evidence for the duration of STM


  Peterson and Peterson (1959)
• evidence for coding in STM and LTM: Baddeley (1966)

  • gave different lists of words to 4 groups of participants to remember:

  group 1- words acoustically similar (e.g. cat, cab, can)

  group 2- words acoustically different (e.g. pit, few, cow)

  group 3- words with similar semantic meanings (e.g. great, large, big)

  group 3- words with different meanings (e.g. good, huge, hot)

  • ppts. were shown original words and asked to recall them in correct order
  • when recalled immediately (recall from STM), they did worse with acoustically similar words
  • when recalled list after 20 minutes (recall from LTM), they did worse with semantically similar words
  • info coded acoustically in STM and semantically in LTM
• evidence for capacity of STM: Jacobs (1987)

  • 4 digits read out and ppt recalls these out loud in correct order
  • if correct researcher reads out 5 digits and so on until pts cannot recall order correctly= individual’s digit span
  • mean span for digits across all ppts= 9.3 items
  • mean span for letters= 7.3 items
• evidence for STM: Peterson and Peterson (1959)

  • nonsense triagrams (e.g. ZFB) given to pptss
  • had to count backwards in threes from a large three-digit number (prevent mental rehearsal) for varying periods of times (after 3, 6, 9, 12, 15 or 18 seconds)
  • found 80% of triagrams were recalled correctly after 3 seconds
  • only 3% after 18 seconds
  • suggests STM duration= about 18 seconds
• evidence for duration of LTM: Bahrick et al. (1975)

  • 400 pts aged between 17 and 74 years- shown a set of photos and list of names (some random and some from old yearbook)
  • asked to identify ex-school friends
  • those who left high school in last 15 years identified 90% of faces and names
  • those who‘d left 48 years previously identified 80% of names and 70% of faces
  • suggests memory for faces= long lasting