Coding, capacity, and duration of memory

• What is coding and what are the 3 types of coding?

  • The format in which we store information in our brains
  • Acoustic coding: storing the sounds of something
  • Visual coding: storing the images/visuals of something
  • Semantic coding: storing meanings/definitions of something
• What research is there on how the LTM and STM are coded?

  • Baddeley (1966): gave lists of words to 4 groups - words were either acoustically similar, acoustically dissimilar, semantically similar, or semantically dissimilar
  • Participants were asked to recall immediately and after 20 minutes
  • When asked to recall immediately, recall was worse with acoustically similar words - when asked after 20 minutes, recall was worse with semantically similar words
  • Findings suggest that information is coded acoustically in our short-term memory and coded semantically in our long-term memory
• What is a strength of Baddeley's research on coding?

  • Separate memory stores: identified a clear difference between short-term and long-term memory - idea that STM uses mostly acoustic coding and LTM mostly semantic has stood the test of the time
  • Important step in our understanding of the memory system, which led to the multi-store model
• What is a weakness of Baddeley's research on coding?

  • Artificial stimuli: word lists had no personal meaning to participants, Baddeley's findings may not tell us much about coding in different kinds of memory tasks
  • People may use semantic coding even for STM tasks when processing meaningful information, suggesting findings have limited application
• What is capacity? What is digit span?

  • The amount of information that can be held in a memory store
  • How much information the STM can hold at one time
• What research is there on capacity? What is chunking?

  • Jacobs (1887) - researcher read out 4 digits for the participant to recall these out loud in the correct order, the number of digits increases until the participant cannot recall the order correctly
  • Mean digit span = 9.3 Mean letter span = 7.3
  • Miller (1956) - noted that in everyday practice things come in sevens (days of the week, musical notes) so the STM's capacity is 7+/- 2 items
  • Chunking: grouping sets of letters/digits into chunks to remember them easier
• What is one strength of research on capacity?

  • Validity - Jacobs (1887)'s study on capacity was old and lacked adequate controls e.g. some participants may have been distracted during testing so findings aren't accurate
  • But findings have been confirmed by better controlled studies such as Bopp and Verhaeghen (2005), suggesting his study is a valid test of digit span in STM
• What is one weakness of research on capacity?

  • Miller (1956) may have overestimated the capacity of the STM
  • Cowan (2001) reviewed other research and concluded that the STM's capacity is only 4+/1 chunks, suggesting that Miller's idea of chunking is more appropriate than 7 items
• What is duration?

  • The length of time information can be held in a memory store
• What research is there on the duration of the STM?

  • Petersen & Petersen (1959): gave trigrams ('ACG') to 24 students with a random 3-digit number to count down from (876,875,874..) until told to stop after varying periods like 3 or 18 seconds - to prevent any mental rehearsal
  • After 3 seconds, recall was 80% accurate
  • After 18 seconds, this dropped to 3%, suggesting that the duration of our short-term memory is around 18 seconds
• What research is there on the duration of the LTM?

  • Bahrick et al. (1975): 392 American participants between 17 and 74 had their recall tested with photo-recognition and free-recall tests of their high-school classmates names
  • Those tested within 15 years of graduation were 90% accurate in photo recognition, dropped to 70% after 48 years
  • Those tested within 15 years of graduation were 60% accurate in free-recall, dropped to 30% after 48 years
  • Shows that LTM may last up to a lifetime
• What is a strength of research into duration?

  • High external validity: Bahrick et al's study used meaningful memories that were personal to participants e.g. their old friends' names and faces
  • LTM studies that used meaningless stimuli like Shepard (1967) had lower recall rates, suggesting Bahrick's findings reflect a realistic estimate of the LTM's duration
• What is a weakness of research into duration?

  • Meaningless stimuli: Petersen & Petersen (1959) used artificial material such as trigrams that have no personal meaning to the participants as they have no incentive to remember it
  • Recalling consonant syllables does not reflect most everyday memory activities, meaning the study lacks external validity