Capacity, Duration and Encoding

Capacity, Duration and Encoding

1. Duration

   • Definition; How long the memory lasts before it is no longer available
   • Peterson and Peterson (1959)
     • - Participants are shown 3 Nonsense Trigrams - Asked to recall after 2,6,9,12,15,18 seconds - Given an interference task of counting backwards in 3's - this stopped rehearsal - After 3 seconds could recall 80% and after 18 seconds could only recall 10%
       • Evaluation:
         • X = Lacks Ecological validity because it is a laboratory experiment and people would likely remember more meaningful information then something that lacks depth
         • X = Nairne (1999) - Found that items could be recalled after 96 seconds, Same itemes rather than different items so no ther material replaces it, can remain in the STM for longer
           • X = Each Participant saw many trigrams and this could have lead to confusion meaning that the first trigram was the only realistic trial
         • v/ = The results are more likely to be reliable because the variables are tightly controlled and can also be replicated
   • Bahrick (1975)
     • - Done a free recall test on 392 for their classmates - Given a photo - Recognition test or a name recognition test - within 15 years they could recognise about 90% of names and faces and 60% accurate on free recall - 48 years name recognition was 80% accurate and Photo Recognition was 40%. Recognition is better than recall so a huge store of energy but need help accessing it
       • Evaluation
         • A field experiment so it has high ecological validity
           • However it is difficult to control all the variables making the results less reliable and no way of knowing if the information is recalled for
         • Shows that meaningful information is stored better
           • However the recall could have been rehearsed due to contact with old school friends so the results could not be generalised to other types of information held in the LTM

2. Capacity

   • Definition; The measure how much the memory can hold and is measured in terms of bits such as number of digits
   • Jacobs (1887)
     • Presented a string of letters and told to repeat back in the same order and only stop when failed - recalled 9 digits and 7 letters - Limited capacity can hold around 5-9 items - More can be held with increased age or chunking - easier to remember 10 digits than 26 letters
       • Miller (1956)
         • Argued that it is 7 plus/minus two, use chunking to combine individual numbers or letters into larger more meaningful information
       • It is artificial and lacks ecological validity
       • More meaningful information may be recalled better perhaps showing STM having a greater capacity
       • Previous sequences may have confused them on future trials