Capacity

• Capacity

  • capacity refers to the amount of information that can be held at any one time in memory
  • how to investigate capacity - experiments that investigate capacity traditionally use the serial digit span method in which numbers/letters etc have to be recalled in the correct order
  • e.g. of a digit span test

  
• Digi Span Test

  • rows increase by 1
  • sequence/string of numbers/letters
  • avoid 7 + w as they are 2/3 syllables - 2 items to store in memory
  • avoid memorable/significant patterns e.g cat/123
  • avoid repettition e.g 999/ccc
  • avoid rhymes e.g P,C,D,E
• Miller's Research

  • Miller (1956) published famous article - ‘The Magical Number Seven, Plus or Minus Two’ in which he reviewed existing research into STM
  • he said that we can hold 7 'items' in STM plus or minus 2
  • conclusion - most adults can store between 5 and 9 items in their short-term memory - magic number is 7 - thought this because STM only has a certain number of “slots” in which items could be stored
• Miller - Chunking

  • Miller believed that our short-term memory stores ‘chunks’ of information rather than individual numbers or letters - if we can “chunk” info together we can store a lot more info in our STM - method of increasing capacity of STM
  • chunking can explain why we are able recall items e.g mobile phone numbers, which contain more than 7 digits - phone numbers have 11 digits so we chunk info into groups e.g 07306 …19…02…08, so we only need to remember 4 chunks of information, not 11 individual digits
• Jacob's Research Support

  • Jacobs (1887) conducted experiment using a digit span test, to examine capacity of STM for numbers and letters
  • pps were presented with lists of words/numbers that they had to recall immediately after presentation
  • used a sample of 443 female students (8-19) from NLCS
  • pps had to repeat back string of numbers/letters in same order and number of digits/letters was gradually increased, until pps could no longer recall sequence
  • gradually increased length of these digits etc. until pp could only accurately recall information, in correct order, on 50% of occasions
• Jacob's Research - Findings

  • Jacobs found a difference between capacity for numbers and for letters
  • found out people find it easier to recall numbers > letters
  • average span for letters was 7.3 and for numbers it was 9.3. So on average participants could recall 9 numbers but only 7 letters
  • also noticed that recall seemed to increase with age - 8 y/o being able to recall an average of 7 digits whereas by 19 recall had increased to 9 digits
  • supports Miller's research (5-9)