Coding, Capacity and Duration

• Coding - Type/ format of information in each memory store.

  • Baddeley (1966) - Coding is acoustic in STM and semantic in LTM.

  He found more mistakes made when recalling acoustically-similar words straight after learning them, whilst more mistakes are made when recalling semantically-similar words 20 minutes after learning them (LTM recall).
• Capacity - The amount of information that can be stored in a memory at any time.

  • Miller - Capacity of STM is 7 +/- 2, while for LTM it is unlimited. This is from the idea that we are predisposed to remembering quantities of 7 (like 7 days a week) so such quantities can be remembered by 'chunking'.
  • Jacobs - The mean letter span was 7.3 and the mean digits span was 9.3 (number of letters/digits we recall after increasing intervals).
• Duration - Amount of time information can be stored in each memory store.

  • Petersen et al (1959) - Duration of STM is 18-30 seconds.

  He found increasing retention intervals decreased the accuracy of recall of consonant syllables in 24 undergraduates when preventing mental rehearsal (by counting down from a 3 digit number).

  • Bahrick et al (1975) - Duration of LTM is unlimited.

  He found photo recognition of graduating classmates of 396 participants decreased from 90%-70% between 15 and 46 years of graduating.
• Strengths of coding, capacity and duration:

  • Real life application - Bahrick et al (1975) use of meaningful stimuli with high mundane realism. This suggests his findings have high ecological validity because they can be easily generalised to real-life, due to the stimuli reflecting those we would often try to learn and recall in our daily lives (information with personal and meaningful value).
• Limitations of coding, capacity and duration:

  • Historical issues - Lack of standardisation and scientific methods. For example, current laboratory experiments produces highly reliable and valid data through controlling extraneous / confounding variables. The same can't be said for Jacobs where confounding variables (eg- noisy room or difficult word lists) may have had greater effects on the accuracy of recall, giving unreliable results.
• Limitation of coding, capacity and duration:

  • Lacks mundane realism - Petersen et al and Miller et al studies produced findings with little ecological validity. This is due to use of artificial stimuli which has little personal meaning and so does not accurately reflect everyday learning experiences. This limits generalisability of the study.
• Limitation of coding, capacity and duration:

  • Counter research studies - Recent research suggested that Miller may have over-exaggerated the capacity of STM, and that capacity is more similar to 4 chunks as opposed to the original 5-9. This reflects the lack of control over confounding variables which may have contributed to this inaccurate measurement.