Jacobs (1887)

AIM: To examine the capacity of the short-term memory store.

METHOD: Jacobs used a digit span test, where participants were read a series of numbers/letters which gradually increased in length; the participants had to recall the items in the same order. Jacobs noted that in his first experiments, the participants had to orally recall the items, whereas in the later experiments, they produced their answers in written form. Jacobs reported the findings of numerous groups, one of which included 443 female students (aged 8-19) from the North London Collegiate School, and another which included 174 male students (aged 11-13) and 127 female students (aged 13-20).

RESULTS: Jacobs found that the average digit span (across all of the experiments) was 7.3 for letters and 9.3 for numbers. Jacobs also reported the average number of items (numbers/letters) recalled across the age range (8-19) in one of his larger experiments (see Graph 2). He found that the average number of items recalled increased with age.

CONCLUSION:These results support the idea that the STM store has a limited capacity of, on average, 7+/-2 items of information. The results also suggest that the capacity of the STM store slightly increases with age and is not fixed.