Coding, Capacity and Duration

• Coding definition:

  The format in which information is stored in the various memory stores.
• Capacity definition:

  The amount of information that can be held in memory.
• Duration definition:

  The length of time information can be held in memory.
• Short-term memory (STM):

  The limited-capacity memory store.

  Coding is mainly acoustic (Baddeley).

  Capacity is between 5 and 9 items on average (Jacobs/Miller).

  Duration is between 18 and 30 seconds (Peterson and Peterson).
• Long-term memory (LTM):

  The permanent memory store.

  Coding is mainly semantic (Baddeley).

  It has unlimited capacity.

  Can store memories for up to a lifetime (Bahrick et al.).
• 𝙍𝙀𝙎𝙀𝘼𝙍𝘾𝙃 𝙊𝙉 𝘾𝙊𝘿𝙄𝙉𝙂:

  Baddeley (1966) gave different lists of words to four groups of participants. Participants were shown the original words and asked to recall them in the correct order.

  When they had to do this recall task immediately after hearing it, they tended to do worse with acoustically similar words.

  If participants were asked to recall the word list after a time interval of 20 minutes, they did worse with the semantically similar words.

  
  

  This suggests that information is coded acoustically in the STM and semantically in the LTM (separate stores).
• 𝙍𝙀𝙎𝙀𝘼𝙍𝘾𝙃 𝙊𝙉 𝘾𝘼𝙋𝘼𝘾𝙄𝙏𝙔: 𝘿𝙄𝙂𝙄𝙏 𝙎𝙋𝘼𝙉

  Jacobs (1887) developed a technique to measure digit span in the STM. The researcher gives 4 digits and then the participant is asked to recall these in the correct order out loud.

  If this is correct the researcher reads out 5 digits and so on until the participant cannot recall the order correctly. This determines the individual's digit span.

  
  

  Jacobs found that the mean span for digits across all participants was 9.3 items. The mean span for letters was 7.3.
• 𝙍𝙀𝙎𝙀𝘼𝙍𝘾𝙃 𝙊𝙉 𝘾𝘼𝙋𝘼𝘾𝙄𝙏𝙔: 𝙈𝙀𝙈𝙊𝙍𝙔 𝘼𝙉𝘿 𝘾𝙃𝙐𝙉𝙆𝙄𝙉𝙂

  Miller made observations of everyday practice. He noted that things come in sevens: there are 7 notes on the music scale, 7 days of the week, 7 deadly sins and so on. This suggests that the span (or capacity) of STM is about 7±2 items.

  
  

  Miller also noted that people can recall 5 words as well as they can recall 5 letters or digits, through a process called chunking.
• 𝙍𝙀𝙎𝙀𝘼𝙍𝘾𝙃 𝙊𝙉 𝘿𝙐𝙍𝘼𝙏𝙄𝙊𝙉: 𝙎𝙏𝙈

  Peterson and Peterson tested 24 undergraduate students. Each student took part in 8 trials. On each trial the student was given a trigram (e.g. YGC) to remember. They were also shown a 3 digit number and asked to count backwards from this number until told to stop (to prevent rehearsal of the trigram).

  
  

  On each trial they were told to stop after a certain amount of time; 3, 6, 9, 12, 15 or 18 seconds. Their findings found that STM has a duration of up to 18 seconds.
• 𝙍𝙀𝙎𝙀𝘼𝙍𝘾𝙃 𝙊𝙉 𝘿𝙐𝙍𝘼𝙏𝙄𝙊𝙉: 𝙇𝙏𝙈

  Bahrick et al. (1975) studied 392 participants from the Amercian state of Ohio aged between 17 and 74. High school yearbooks were obtained from the participants or directly from some schools. Recall was tested in various ways such as a photo recognition test or a free recall test (names).

  
  

  Participants who were tested within 15 years of graduation were about 90% accurate in photo recognition. After 48 years, recall declined to about 70% for photo recognition.

  This shows that LTM can last a very long time.
• 𝙀𝙑𝘼𝙇𝙐𝘼𝙏𝙄𝙊𝙉𝙎:

  1. separate memory stores (Baddeley)
  2. artificial stimuli (Baddeley)
  3. valid study (Jacobs)
  4. not so many chunks (Miller)
  5. meaningless stimuli (Peterson and Peterson)
  6. high external validity (Bahrick)
• 𝟭. 𝗦𝗘𝗣𝗔𝗥𝗔𝗧𝗘 𝗠𝗘𝗠𝗢𝗥𝗬 𝗦𝗧𝗢𝗥𝗘𝗦:

  One strength of Baddeley's study is that it identified a clear difference between two memory stores.

  Later research showed that there are some exceptions to Baddeley's findings. But the idea that the STM uses mainly acoustic coding and the LTM uses semantic coding has stood the test of time.

  
  

  This was an important step in our understanding of the memory system, which led to the Multi-Store Model.
• 𝟮. 𝗔𝗥𝗧𝗜𝗙𝗜𝗖𝗜𝗔𝗟 𝗦𝗧𝗜𝗠𝗨𝗟𝗜:

  One limitation of Baddeley's study was that it used quite artificial stimuli rather than meaningful material.

  The word lists had no personal meaning to participants. This means we should be cautious about generalising the findings to different kinds of memory tasks. For example, when processing more meaningful information, people may use semantic coding even for STM tasks.

  
  

  This suggests that the findings from this study have limited application.
• 𝟯. 𝗩𝗔𝗟𝗜𝗗 𝗦𝗧𝗨𝗗𝗬:

  One strength of Jacob's study is that has been replicated.

  The study is old and early research in psychology often lacked adequate control. For example, some participants may have been distracted while they were being tested so they didn't perform as well as they might. This would mean that the results might not be valid because there were confounding variables that were not controlled.

  
  

  However, the results of this study have been confirmed in other, more controlled, research studies, suggesting that Jacobs' study is a valid test of STM digit span.
• 𝟰. 𝗡𝗢𝗧 𝗦𝗢 𝗠𝗔𝗡𝗬 𝗖𝗛𝗨𝗡𝗞𝗦:

  One limitation of Miller's research is that he may have overestimated the capacity of STM.

  For example, Cowan (2001) reviewed other research and concluded that the capacity of STM was only about four chunks (plus or minus 1).

  
  

  This suggests that the lower end of Miller's estimate (five items) is more appropriate than seven items.
• 𝟱. 𝗠𝗘𝗔𝗡𝗜𝗡𝗚𝗟𝗘𝗦𝗦 𝗦𝗧𝗜𝗠𝗨𝗟𝗜:

  A limitation of Peterson and Peterson's study is that the stimulus material was artificial.

  Trying to memorise consonant syllables does not reflect most real-life memory activities where what we are trying to remember is meaningful - we could say that the study lacked external validity.

  
  

  However, we do sometimes try to remember fairly meaningless things, such as phone numbers, so the study is not totally irrelevant.
• 𝟲. 𝗛𝗜𝗚𝗛 𝗘𝗫𝗧𝗘𝗥𝗡𝗔𝗟 𝗩𝗔𝗟𝗜𝗗𝗜𝗧𝗬:

  One strength of Bahrick et al.'s study is that it has high external validity.

  Real life meaningful memories were studied. When studies of LTM have been conducted with meaningless pictures, recall rates were lower (Shepard, 1967). The downside of real-life research is that confounding variables are not controlled, e.g. participants may have looked at their yearbook photos and rehearsed their memory over the years.

  
  

  However, this ultimately suggests that Bahrick et al.'s findings reflect a more 'real' estimate of the duration of the LTM.