Capacity STM

1
Capacity - STM
www.psychlotron.org.uk

• Span-measure studies of STM
• PPs given series of words, digits etc.
• Immediate recall (accuracy and order)
• Lists get progressively longer
• To obtain results, plot length of list against
  correct recall

2
Capacity - STM
www.psychlotron.org.uk
recall
3 4 5 6 7 8 9 10 11
Length of list
3
Capacity - STM
www.psychlotron.org.uk

• Generally it is found that PPs are able to recall
  between 5 and 9 chunks of information (i.e. 72
  chunks)
• Miller (1956) and others suggested that this
  represented the capacity of STM
• A rule can be used to chunk information together,
  allowing STM to hold more (e.g. 4 digits can make
  a date)

4
Capacity - STM
www.psychlotron.org.uk

• Some evidence that chunk is not an appropriate
  capacity measure
• Simon (1974) found that as the size of chunks
  increased (e.g. 1, 2, 4 words) the number of
  chunks recalled decreased
• Findings from speakers of other languages suggest
  STM capacity is time limited not chunk limited
• However, all the evidence points to STM having a
  limited capacity

5
Capacity - LTM
www.psychlotron.org.uk

• STM is used for holding the small amount of
  information we are dealing with at any one moment
• LTM is the store for all our learning, so
  presumably has much larger capacity
• Actual LTM capacity is impossible to test
  experimentally but does not appear to be limited
  (i.e. functionally unlimited