Psych: Coding, Capacity, Duration

• Coding


  • Baddeley 1966 a 1966 b
  • Group with different word lists
  • Acoustically similar
  • Acoustically dissimilar
  • Semantically similar
  • Semantically dissimilar
  • Recall immediately after 20 mins
• Short-term memory (STM)


  • Coded acoustically
  • Long-term memory (LTM) coded semantically
• Limitations of Baddeley's study

  • Low ecological validity because it's not using meaningful material
• Capacity


  • Jacobs 1887 Digit Span
  • 4 digit number - participants recall longer till they are unable to recall
  • Extraneous variables
• Miller's Magic Number


  The span of immediate memory is 7 ± 2
• Chunking


  Increases the capacity of the STM
• Limitations of Miller's Magic Number

  • May have overestimated - Cowan 2001
• Duration in STM


  1. Peterson and Peterson 1959

  2. 24 undergraduates, given a program to remember - meaningless

  3. Shown a 3-digit number and asked to count backwards in 3s (avoid rehearsal)

  4. Recall continuously got worse, the longer they had to count

  5. After 3 seconds, 80% recalled correctly

  6. After 18 seconds, 10% recalled correctly
• Limitations of Peterson and Persson's study

  • Artificial stimuli (limitation)
• Duration in LTM


  1. Bahrick et al. 1975

  2. 592 participants, aged between 17 and 74, shown photos from high school yearbook

  3. Recall boosted by photo recognition (50 photos), free-recall (names from class)

  4. Photo recognition within 15 years, 90% accurate, and within 48 years, 70% accurate
• Pos/Neg of Bahrick et al.'s study

  • Good ecological validity
  • Poor internal validity (extraneous variables)
• Coding


  The format or 'type' of information which is stored in each memory store
• Coding in short-term memory

  • Acoustic
• Coding in long-term memory

  • Semantic
• Baddeley (1966) found that more mistakes are 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 volume of information/data which can be kept in any memory store at any one time
• Capacity of short-term memory

  • 7 +/- 2 items (Miller)
• Capacity of long-term memory

  • Unlimited
• Miller's idea that things come in groups of 7 suggests that we are predisposed to remembering this quantity and that such a 'chunking' method can help us recall information
• Jacobs demonstrated that the mean letter span was 7.3 and the mean digit span was 9.3 (i.e. the number of letters or digits we can recall after increasing intervals)
• Duration


  The amount of time that information can be stored in each memory store
• Duration of short-term memory

  • 18-30 seconds (Petersen et al, 1959)
• Duration of long-term memory

  • Unlimited (Bahrick et al, 1975)
• Petersen et al (1959) found that increasing retention intervals decreased the accuracy of recall of consonant syllables in 24 undergraduates, when counting down from a 3 digit number (preventing mental rehearsal)
• Bahrick et al (1975) found that photo recognition of graduating classmates of the 396 participants decreased from 90% to 70% between 15 years and 46 years of graduating
• A key issue with historical psychological research, particularly concerning Jacobs, is the lack of standardisation and appreciation of scientific methods
• Confounding variables such as a noisy room or difficult word lists, may have had a greater influence on accuracy of recall, leading to unreliable results in Jacobs' research
• Strength of Bahrick et al's 1975 study


  • Use of meaningful stimuli
  • Methodology high in mundane realism
• The findings of Bahrick et al have high ecological validity because they can be easily generalised to real-life, due to the stimuli reflecting those which we would often try to learn and recall in our day to day lives: information with personal and meaningful value
• The key issues with the Petersen et al and Miller et al studies is that they feature methodologies with low mundane realism, thus producing findings with little ecological validity
• The use of artificial stimuli which has little personal meaning to the participants, and so does not accurately reflect everyday learning experiences, limits the generalisability of such findings
• More recent research has suggested that Miller may have over-exaggerated the capacity of STM, and that the capacity is more similar to 4 chunks as opposed to the original 5-9 limit