research on duration & capacity

• Jacobs measuring digit span


  1. Researcher reads out digits

  2. Participant recalls digits in correct order

  3. Researcher increases number of digits until participant cannot recall correctly

  4. This indicates the individual's digit span
• Jacobs found the mean span for digits across all participants was 9.3 items
• Jacobs found the mean span for letters was 7.3
• Miller - Chunking


  Grouping sets of digits or letters into units or chunks
• Miller thought the span (capacity) of STM is about 7 items, plus or minus 2
• Jacobs (1887) found out capacity of STM by measuring digit span
• Miller (1956) made observations of everyday practice
• Miller noted things come in sevens: e.g. seven notes on music scale, seven deadly sins
• Duration of STM was investigated by Peterson and Peterson (1959)
• Peterson and Peterson - duration

  • tested 24 students in eight trials each
  • on each trial the student was given a consonant syllable (such as YCG) to remember
• Peterson and Peterson - duration

  • they were also given a 3-digit number
  • the student counted backwards from this number until told to stop
  • the counting backwards was to prevent any mental rehearsal of the consonant syllable (which would increase the duration of STM for the syllable)
• Peterson and Peterson - duration

  On each trial they were told to stop after varying periods of time: 3, 6, 9, 12, 15 or 18 seconds (the retention interval)
• Peterson and Peterson (1959) findings:

  • after 3 seconds, average recall was about 80%
  • after 18 seconds it was about 3%
  • suggested that STM duration may be about 18 seconds
  • unless we repeat the information over and over (i.e. verbal rehearsal)