Case Studies for the MSM

Jacobs (1887)

Capacity of STM

Jacob’s method

Developed the digit span technique. Researcher reads 4 digits to participants, they have to say the digits out loud. If correct the researcher will read out 5 digits and so on until they can’t recall the order correctly. Determines the digit span of the individual

Jacob’s results

Mean span for digits was 9.3, letters was 7.3

Jacob’s conclusion

STM had a limited capacity of 5-9 items (7+/- 2 items). He suggests that it is easier to recall digits than numbers since there are 9 digits and 26 letters

Peterson and Peterson (1959)

Duration of STM

Peterson and Peterson’s method

Used 24 participants and shown nonsense trigrams. They had to recall the trigrams after 3,6,9,12 or 18 secs. During the time, they had to count backwards in 3s from a large number

Peterson and Peterson’s results

Suggests that our STM memory fades in under a half of a minute if we aren’t rehearsing it. After only 3 secs, 80% recalled correctly. Recall got progressively worse. After 18 secs, fewer than 10% recalled correctly

Why were participants asked to count backwards?

The counting acted as prevention to rehearsal. If participants could have rehearsed the letters, it would be a test for LTM

Peterson and Peterson’s conclusion

When rehearsal is prevented, very little can stay in the STM for longer than 18 secs

Baddley (1996)

Coding in the STM and LTM

Baddeley’s method

Gave different lists of words to 4 groups of participants to remember. Acoustically similar words, acoustically dissimilar words, semantically similar words and semantically dissimilar words

Baddeley’s results

When recalling immediately after hearing it (STM recall), did worse with acoustically similar words. When recalling after a 20 mins time interval (LTM), did worse with semantically similar words

Baddeley’s conclusion

Information in STM is coded acoustically, information in LTM is coded semantically

Bahrick (1975)

Duration of LTM

Bahrick’s method

American high school graduates were tested for memory of their classmates from yearbooks. Were showed high school photos, some included faces of former classmates and some were strangers. The participants were divided into 9 groups, according to the time elapsed since graduation

Bahrick’s results

Those who had left high school in the last 15 years identified 90% of the photos. Those who graduated 48 years ago, recall had declined to 70%

Bahrick’s conclusion

Suggests that memories in the LTM can last up to a lifetime