4.1.2 Capacity

Question 1

Research - digit span

Answer 1

Joseph Jacobs (1887):
Researcher read out 4 numbers for the participant to recall in the correct order
If the order is correct then the researcher reads out 5 numbers to recall
This continues until the participant gets the number wrong
This then indicates an individual’s digit span
Jacobs found that the mean span for digits across all participants was 9.3 items.
The mean span for letters was 7.3.

Question 2

Research - span of memory + chunking

Answer 2

Span of memory and chunking:
George Miller (1956) made observations of everyday practice – lots of things come in groups of 7.
Miller thought that the span (capacity) of STM is about 7 items, plus or minus 2.
He also claimed that people can recall 5 words as easily as they can recall 5 letters.
This is because we group sets of digits or letters into units or chunks. Known as chunking.

Question 3

Evaluation - strengths

Answer 3

Jacob’s study has been replicated various times (digit span)
Old studies tend to lack controls e.g., some participants’ digit span could have been underestimated because they were distracted taking the test (confounding variable)
However, the study’s findings have been confirmed by better controlled studies (Bopp and Verhaeghan 2005)

Question 4

Evaluation - weaknesses

Answer 4

Nelson Cowan (2001) reviewed other research and found that STM is only about 4 (plus or minus 1) chunks
Cowan said that the lower end of Miller’s estimate (5 items) is more appropriate