STM and LTM

STM and LTM

1. STM

   • Capacity
     • Limited
     • Miller
       • 7 +/- 2
       • His findings have not been replicated so may be more limited
         • Cowan (2001)
           • 4 chunks
             • Size of the chunk affects how many you can remember
               • Simon (1974)
     • Individual differences
       • Increases with age
         • 8 year olds remembered 6.6 digits whereas 19 year olds remembered 8.6
         • Could be due to changes in brain capacity or development of strategies eg chunking
   • Duration
     • Short duration
       • Peterson and Peterson (1959)
         • Used 24 students tested over 8 trials
           • Given constant syllable and three digit number (eg THX 512)
             • Then had to recall syllable after interval of 3, 6, 9,12,15 or 18 seconds
               • During the retention interval they had to count backwards from their three digit number
                 • 90% correct over 3 seconds 20% over 9 and 2% over 18
       • Less than 18 seconds
       • Testing was artificial
         • Doesn't reflect everyday activities
           • But sometimes have to memories meaningless things like phone numbers
       • May be due to displacement rather than decay
         • They were counting numbers in their STM which may overwrite the syllables remembered
           • Reitman (1974) used auditory tones instead of numbers as sound doesn't interfere with verbal rehearsal and duration was found to be longer
   • Coding
     • Acoustic and semantic coding
       • Baddeley (1966)
         • Used semantically similar words (eg great large big) and acoustically similar words (eg cat, cab, cad)
           • Participants had difficulty remembering acoustically similar words in STM but not LTM whereas semantically similar led to small problems in the STM but muddled LTMs
     • The way that information is changed so that it can be stored in the memory
     • Coded acoustically
     • STM may not be exclusively acoustic
       • Some experiments have shown that visual codes are also used

2. LTM

   • Capacity
     • Potentially infinite
   • Duration
     • Bahrick et al (1975)
       • Tested 400 people (aged 17-74) on their memory of classmates
         • Photo recognition rest of 50 photos from yearbook where listed names
           • Those tested within 15 years of graduation got 90%, after 48 70%
   • Coding
     • Coded semantically
     • LTM may not be exclusively semantic
       • Found could be acoustic and visual
     • Baddeley may not have tested LTM as only waited 20 minutes before asking to recall
       • Not really testing LTM