Jacobs (1887)

Aim: To investigate the capacity of short-term memory (STM).

Method: Jacobs used a digit span technique. Participants were presented with sequences of numbers or letters that gradually increased in length. They had to recall the items in the correct order. The longest sequence recalled correctly was taken as the participant’s memory span.

In Jacobs’ earlier experiments, participants recalled the sequences aloud. In later experiments, they wrote down their answers. Jacobs reported findings from several samples, including:

• 443 female students aged 8–19 from North London Collegiate School

• 174 male students aged 11–13

• 127 female students aged 13–20

Results: Jacobs found that:

• the average memory span was 9.3 items for numbers

• the average memory span was 7.3 items for letters

• participants could generally recall more numbers than letters

• average memory span increased with age, indicating that older participants recalled more items than younger participants

Conclusion: Jacobs concluded that STM has a limited capacity. His findings are broadly consistent with the later estimate that STM can hold approximately 7 ± 2 items. The results also suggest that STM capacity increases during childhood and adolescence rather than remaining entirely fixed.