Coding, Capacity and Duration of Memory

Coding, Capacity and Duration of Memory

1. Once information gets into the memory system, it is stored in different formats, depending on the memory store.

   • the process of converting information from one form to another is called coding.

2. Baddeley (1966a, 1966b) gave different lists of words to four groups of participants to remember

   • GROUP 1 (acoustically similar)
     • GROUP 2 (acoustically dissimilar)
       • GROUP 3 (semantically similar)
         • GROUP 4 (semantically dissimilar)
   • When asked to recall immediately after hearing the words (STM recall), they tended to do worse with acoustically similar words.
     • This suggests information is encoded acoustically in the short term memory.
   • When asked to recall after 20 minutes (LTM recall), they tended to do worse on semantically similar words.
     • This suggests information is encoded semantically in the long term memory.

3. Capacity is the amount of information that can be held in a memory store.

4. Jacobs (1887) developed a technique to measure digit span.

   • E.g. the researcher gives the participant 4 digits and then asks them to recall it. If correct, the amount of digits increases until they cannot recall it correctly.
     • Jacobs found that the mean span for digits across all participants was 9.3 items and 7.3 for letters.

5. Miller (1956) noted that things came in sevens; there are 7 notes on a musical scale, 7 days of the week, 7 deadly sins etc.

   • This suggests the the capacity of STM is about 7 items (+ or - 2).
   • Miller also noted that people can recall 5 words as well as they can recall 5 letters. This is done by chunking - grouping sets of digits or letters into units.

6. Duration is the length of time information can be held in memory.

7. Peterson and Peterson (1959) tested 24 undergraduate students on the duration of their STM, each taking part in 8 trials.

   • On each trial the student was given a consonant syllable to remember and also given a 3-digit number.
     • They were then asked to count backwards from the 3-digit number until told to stop. This was done to prevent any mental rehearsal of the consonant syllable which would increase the student's memory for it.
       • On each trial they were told to stop after a different amount of time e.g. 3, 6, 9, 12, 15 or 18 seconds. This is called the retention interval.
         • The graph shows the results of the study. It suggests tht STM may have a very short duration, unless we repeat something over and over again (i.e. verbal rehearsal)

8. Bahrick et al. (1975) tested the duration of LTM by studying 392 participants from the American state of Ohio, aged between 17 and 74.

   • High school yearbooks were obtained and recall was tested in several ways: (1) photo-recognition test consisting of 50 photos, some from the participants yearbook; (2) free recall test where participants recalled all the names of their graduating class.
     • Participants who were tested within 15 years of graduation were about 90% accurate in photo recognition. This fell to about 70% after 48 years.
       • After 15 years, free recall was about 60% and this dropped to 30% after 48 years.
         • This shows LTM can last a very long time.

9. EVALUATION

   • Baddeley's study used quite artificial stimuli rather than meaningful material. The word list had no personal meaning to participants so we should be cautious about generalising the findings to different kinds of memory task. E.g. when processing more meaningful information, people may use semantic coding even for STM tasks. This suggests that the findings have limited application.
   • Jacob's study was conducted a long time ago and early research in psychology often lacked adequate control. There may have been confounding variables. However, the results have been confirmed in other research, supporting its validity.
     • One limitation of Miller's research is that he may have overestimated the capacity of the STM. E.g. Cowan (2001) reviewed other research and concluded the capacity of the STM was only about 4 chunks. This suggests that the lower end of Miller's estimate (five items) is more appropriate than seven.
   • The stimulus material in Peterson and Peterson's study was artificial and meaningless. It does not reflect most real life memory activities so it lacks external validity.
     • Bahrick's study has higher external validity because real life meaningful memories were studied. When studies on LTM have been conducted with meaningless pictures to be remembered, recall rates were lower. However, using real life research means confounding variables are not controlled e.g. the participants may have looked at their yearbook photos and rehearsed their memory over the years.

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