CAPACITY
What is capacity?
Capacity is the measure of how much can be held in memory.
STM capacity.
Digit Span.
This is how much information the STM can hold.
Jacobs (1887)
- The researcher was asked to read out four digits an the participant would have to recall these out loud in the correct order.
- Each time the participant got a number sequence right the researcher would add an digit.
- This is how you would measure an individual's digit span.
- Jacob found that the mean span for digits across all participants was 9.3 numbers.
- The mean span for letters was 7.3
This may be because there are only 9 numbers while, their are 26 letters in the alphabet.
Span of memory and chunking.
George Miller in 1956 wrote an article called THE MAGIC NUMBER SEVEN PLUS OR MINUS TWO.
Miller observed everyday practices.
He found that things came in sevens:
- Seven notes on the musical scale.
- Seven days of the week.
- Seven deadly sins.
He believed that the capacity or span of STM was seven items, plus or minus two.
He found that people recalled five numbers better than five letters because of chunking. Chunking was a way of grouping sets of digits or letters into units.
Evaluation.
A valid study.
Jacob's study is replicable.
His study was conducted very early on and older studies often lacked adequate controls.
Despite this, Jacob's findings have been confirmed by Bopp and Vernhaegham 2005.
Limited capacity.
Cowan 2001 concluded that STM is likely to be limited to about four chunks.
This suggests that STM may not be as extensive as originally believed.
Vogel et al 2001 found that Miller's findings were overestimated and 5 should be the limit not seven.
Size of Chunks.
The size of chucks affects how you remember.
Simon 1974 found that people had a shorter memory span for larger chunks.
Individual differences.
The capacity of STM is not the same of everyone. Meaning, we are forced to generalise findings to all age groups.
Jacob found that digit span increased with age. At eight average 6.6 but at 19 it is 8.6.