L1: Coding, Capacity and Duration

• Baddeley (1966) conducted a study on coding in short and long-term memory.

  • ppts given word lists to remember (acoustically similar/dissimilar; semantically similar/dissimilar)
  • STM recall worst on acoustically similar
  • LTM recall worst on semantically similar.

  Suggests STM coding is acoustic; LTM coding is semantic.
• Jacobs (1887) conducted a study on the capacity of STM with digit span.

  • ppts given list of digits; had to recall aloud correctly -> repeated until no longer correct

  Mean = 9.3 (digits) and 7.3 (letters)
• Miller (1956) conducted a study into the capacity of STM using the magic number.

  • noticed things came in sevens (e.g., days of the week)

  Suggests the span of STM is 7+/-2

  • also noticed people can recall 5 numbers as well as they can 5 letters.
  • done by chunking
• Chunking is grouping digits or letters into meaningful units or chunks.
• Peterson and Peterson (1950) conducted the trigram study on the duration of short-term memory.

  • each student given a trigram (e.g YCG) and a 3-digit no.
  • had to count back from no. until told to stop - prevents mental rehearsal of trigram.
  • after each they stopped after diff. amounts of time (3, 6, 9, 12, 15, 18 seconds) - known as retention interval.

  Findings showed the duration of STM is limited (30 secs) unless we repeat it over and over - verbal rehearsal.
• Bahrick et al. (1975) conducted the yearbook study to investigate the duration of LTM.

  • ppts asked to recall names of classmates (free recall)
  • then asked to recall names with either prompt of photo OR given list of names and had to match them to photos.

  Participant accuracy compared:

  • those who grad. 15 yrs before: 90% accurate on photos
  • 48 yrs: 70% photo recognition.
  • 15 yrs free recall: 60% accurate
  • 48 yrs free recall: 30% accurate

  Suggests the duration of LTM can be up to a lifetime.
• One weakness of Baddeley's study into coding is its use of artificial stimuli.

  • evidence: materials used (word lists) had no meaning to ppts. It would make sense to use a meaningful word list (e.g., shopping list)
  • explain: weakness b/c it's hard to generalise these findings to other tasks.
  • link: weakness - artificial stimuli b/c limited application.
• One weakness of Jacobs' study is it lacks validity.

  • evidence: since the study was conducted a long time ago, there may not have been adequate control (e.g., ppts. were distracted)
  • explain: weakness b/c confounding variables may have affected results due to lack of control.
  • link: weakness - lack of control b/c low internal validity.
• One weakness of Peterson and Peterson's study into the duration of STM is that it used meaningless stimuli.

  • evidence: memorising trigrams doesn't reflect IRL memory tasks
  • explain: weakness b/c it means we may not be able to apply these findings beyond research.
  • ink: weakness - artificial stimuli b/c study lacks external validity
• One strength of Bahrick et al.'s study into the duration of LTM is that it has high external validity.

  • evidence: real-life memories were studied (i.e., yearbook photos) with meaningfulness to ppts.
  • explain: strength b/c the recall rates would be higher as the stimuli are more controlled. HOWEVER, it means confounding variables aren't controlled.
  • link: strength - meaningful stimuli b/c high external validity.