Jacobs’ (1887)

• Jacobs’ (1887) study of the capacity of short-term memory - AIM:

  To investigate how much information can be held in short-term memory (STM).

  To do this he needed an accurate measure of STM capacity and so he devised a technique called the ‘serial digit span. His research was the first systematic study of STM capacity.
• Jacobs’ (1887) PROCEDURE:

  A laboratory experiment using the digit-span technique.

  They were required to serial recall (repeat back to the experimenter in the same order in which they were presented.

  The pace of the item presentation was controlled to half-second intervals through a metronome.

  The sequence length that was recalled correctly on at least 50% of the trials was taken to be the participant’s STM span (or digit span).
• Jacobs‘ (1887) FINDINGS:

  Jacobs found that the average STM span (number of items recalled) was between 5 and 9 items. Digits were recalled better (9.3 items) than letters (7.3 items). Individual differences were found, hence the range 5—9. Furthermore, STM span increased with age as in one sample he found a 6.6 average for 8-year-old children compared to 8.6 for 19-year-olds.
• Jacobs’ (1887) CONCLUSIONS:

  The findings show that STM has a limited storage capacity of between 5 and 9 items. The capacity of STM is not determined by the nature of the information to be learned but by the size of the STM span, which is fairly constant across individuals. Individual differences were found as STM span increased with age, which may be due to increasing brain capacity or improved memory techniques, such as chunking.
• Jacobs’ (1887) GRAVES: Mundane Realism

  lacks mundane realism as the digit-span task is not representative of everyday memory demands and the artificiality of the task may have biased the results. Letters or digits are not meaningful information and so may be remembered less well than more meaningful information. Thus, the capacity of STM may be greater for more everyday memory Jacobs’ findings cannot be generalised to real-life memory and so ecological validity must be questioned.
• Jacobs’ (1887) GRAVES: Real-life application

  The findings have been usefully applied to improve memory For example, telephone numbers, post codes, and car registrations are based on this idea of total digit span. Moreover, memory-improvement techniques are based on the findings that digit span cannot be increased; but the size of the bits of information can be.
• Jacobs’ (1887) GRAVES: Studies to Support

  Miller (1957) did an earlier study into “the Magic Number 7, plus or minus 2”. He found that STM has a capacity of 7 items (or “bits”) of information comfortably, but struggles to hold more than 9. Miller found that “bits” of information can be grouped together into “chunks”.