Coding, capacity and duration

• coding

  the format in which information is stored.

  STM is coded acoustically

  LTM is coded semantically
• Research on coding

  Alan Baddeley

  Gave different lists of words to four groups of participants

  • group 1 had words that were acoustically similar e.g. cat, cab, can
  • group 2 had words that were acoustically dissimilar e.g. pit, few, cow
  • group 3 had words that were semantically similar e.g. great, large, big
  • group 4 had words that were semantically dissimilar e.g. good, huge, hot.

  Participants were asked to recall them in the correct order.

  STM tended to do worse with acoustically similar words.

  LTM tended to do worse with sematically similar words.
• Strength of coding - separate memory stores

  Baddeley's study identified a clear difference between the two memory stores.

  Important step in understanding memory, led to the multi-store model.
• Limitation of coding - artificial stimuli

  Used artificial stimuli rather than meaningful material

  Word lists in Baddeley's study had no personal meaning to participants so may not tell us about everyday life.

  Limited application
• capacity

  amount of information that can be held in a memory store
• Research on capacity - digit span

  Joseph Jacobs

  Read out digits to a participant and they had to recall them out loud in the correct order.

  Increased number of digits until the participant failed.

  Found the mean digit span was 9.3 items

  Mean span for letters was 7.3
• Research on capacity - span of memory + chunking

  George Miller

  Made observations of everyday practice

  Noted things come in sevens e.g. 7 days of the week, 7 deadly sins.

  Miller thought that the capacity of STM was about 7 items +/- 2

  Noted people can recall 5 words as easily as they can recall 5 letters. This is an example of chunking
• Strength of capacity - valid study

  Jacobs' study has been replicated

  His research lacked adequate controls + confounding variables

  But, findings have been confirmed since with better controlled studies.
• Limitation - not as many chunks

  Miller may have overestimated STM capacity.

  When other research was reviewed, a researcher concluded the capacity of STM is only about 4 +/- 1 chunks.

  Suggests Miller wasn't accurate
• duration

  length of time information can be held in memory
• Research on duration of STM

  Peterson + Peterson

  Tested 24 students in 8 trials

  Each student was given a consonant syllable (e.g. YCG) to remember

  They were also given a 3 digit number. They had to count backwards from this number to prevent any mental rehearsal.

  On each trial, they stopped after different periods of time in intervals of 3 - 3, 6, 9, 12, 15, 18 seconds.

  After 3 seconds, average recall was 80%, after 18 seconds average recall was 3%.

  Suggests STM duration is about 18 seconds.
• Research on duration of LTM

  Bahrick et al.

  Studied 392 US participants aged between 17 and 74

  Recall was tested using a their high school yearbooks.

  Participants within 15 years of graduating were 90% accurate in photo recognition. 48 years decreased to 70%

  For free recall, it was 60% accurate after 15 years and 30% after 48 years.

  Shows LTM may last up to a lifetime.
• Limitation of duration for STM - artificial stimuli

  Peterson + Peterson's stimulus was artificial

  Study isn't completely irrelevant as we sometimes have to recall meaningless material.

  But, recalling consonant syllables doesn't reflect everyday life.

  Lacked external validity.
• Strength of duration for LTM - external validity

  Bahrick et al.'s study had high external validity

  This is because it used meaningful memories of high school.

  When studies on LTM duration used meaningless pictures, recall rates were lower.

  Suggests they are a strong estimate.