capacity refers to how much can be held
in a particular place
Capacity of STM
digit span technique - Jacobs 1887
used the technitque to assess capacity of STM - found that ave span for digits =
9.3 items and 7.3 for letters - suggests this is because there's only 9 letters and
26 letters
Baddeley et al 1975
if people could remember more short words than long words in a recall
test and so demonstrate that pronounciation time, rather than the
number of items to be recalled, determines the capacity of STM
reading speed was measuresd - participants given 5 words on screen
words taken from one-syllable and polysyllablic words - participants asked to write down
5 words in order immediately after - recalled long and short words
could recall more short than long words
Increasing capacity of STM
Miller 1956 - the magic number 7 plus or minus 2
he reviewed psychological research and concluded that the span of immediate memory is 7; people can cope well with
counting 7 dots flashed onto a screen but not many more than this
He also found that people can recall 5 words as well as they can recall 5 letters - we chunk things together and then can remember more
Evaluation
Jacob
individual differences: the digit span not the same for everyone - increased with age - 8
year olds could remember an average of 6.6 digits whereas the mean for a 19 year old = 8.6
digits
Capacity of STM may be more limited
Cowan 2001 - reviewed a variety of studies on the capacity of STM and
concluded that STM is likely to be limited to about 4 chunks. Suggests
that STM may not be as extensive as first though
some researchers looked at capacity of STM for visual
information and found that 4 items was about the limit
(VOGEL ET AL 2001)