Coding, capacity & duration

• Research on coding


  Baddeley (1966) gave acoustically similar, acoustically dissimilar, semantically similar and semantically dissimilar lists to participants.

  Recalling acoustically similar words from STM they struggled with, When they recalled from LTM they did worse with the semantically similar words.

  This suggests that information is coded acoustically in the STM and semantically in the LTM.
• Research on capacity

  Jacobs (1887) read numerous digits at a time and the participant recalls these digits. this continues until the participant can no longer recall the digits in order.

  He found the mean digit span was 9.3 items. The mean letter span was 7.3.
• Span of memory and chunking

  Miller (1956) thought the capacity of STM is about 7+/-2. he also found that people recall 5 words by chunking.
• Research on duration.

  STM

  Peterson & Peterson (1959) tested 24 students in 8 trials. After 3 seconds average recall was 80%, after 18 seconds it was 3%. This suggests that the STM duration is 18 seconds.

  LTM

  Bahrick et al (1975) studied 392 American participants (17 - 74). Recall tested in various ways. 1. Photo-recognition from high school yearbooks, 2. Name recall of their graduating class.

  Participants tested within 15 years of graduation were 90% accurate in photo recall, after 48 years this declined to 70%.

  Free recall was less accurate (<15 yrs 60%, >48 yrs 30%)
• Strengths of Baddeley's 1966 study.

  His theory identified a clear difference between the two memory stores, the idea that the STM uses mostly acoustic coding and LTM uses mostly semantic coding.
• Limitations of Baddeley's 1966 study.

  Used artificial stimuli. The word lists had no meaning to the participants so this suggests the findings have limited application as people may code semantically in the STM when processing more meaningful information.
• Strengths of Jacobs' study (1887)

  His study has been replicated and confirmed by other, more controlled studies since. (Bopp & Verhaeghen 2005)
• Limitations of Miller's research

  He may have overestimated STM capacity.

  Cowan (2001) Reviewed other research to conclude that the STM is only about 4+/-1 chunks.
• Limitation of Peterson & Peterson's (1959) study.

  Stimulus material was artificial.

  This does not reflect everyday activity and therefore lacks external validity.
• Strength of Bahrick et al's (1975) study

  High external validity. The researchers investigated meaningful memories rather than artificial values.