Memory STM and LTM

Memory STM and LTM

1. STM

   • capacity- 7 chunks +/- 2
     • Jacobs
   • duration- 18-30seconds
   • encoding- Acoustic or visual
     • Baddley found that STM has trouble recalling acoustically similar words, little difficulty with semantically similar
       • Baddeley (1966) tested the effects of acoustic and semantically similarity on short and long term re-call
         • He gave ppts a lists of words which were acoustically similar or dissimilar and wordsd that were semantically similar and dissimilar
           • He found that ppts had difficulty remembering acoustically similar words in STM but not in LTM. Semantically similar words posed little problem for short-term recall but lead to muddled long- term memories

2. LTM

   • Capacity- potentially unlimited
   • Duration- hours to a life time
     • Bahrick
   • Encoding is Semantic (meaning)
     • LTM has trouble recalling semantically similar words, little trouble with acoustically similar words
       • (Baddeley 1966)

3. Peterson and Peterson 1959

   • conducted a study on STM with the help of 24 students from theur uni
     • the experimenter said a consonant syllable to the pp followed by a three digit number (eg WRT 749) the consonant sylable was selected to have no meaning
       • immediately after hearing the syllable and number, the pp had to count backwards from this number in 3s or 4s until told to stop.
         • The pp was then asked to recall the nonsense syllable. (the reason for counting backwards was to stop the pp rehearsing the syllable because rehearsal would aid recall.)
           • each pp was given two practice trails followed by eight trials. on each trial the retention interval (time soent counting backwards) went up by 3 seconds.
             • findings- the ppts remembered about 90% when there was only a 3-second interval and about 2% when there was an 18 second interval.
               • This suggests that, when rehearsal is prevented; STM lasts about 20 seconds at most.
                 • The findings of this study have been challenged
                   • it could be argued that the PPTs of this study were relying on more than STM alone because they knew that they were going to be asked to recall the items after an interval filled with a distracting activity
                     • other research such as Marsh et al 1997 has suggested that when PPTs do not expect to be tested after this interval, forgetting may occur after just 2 seconds, suggesting that our understanding of the STM may not be as clear-cut as we first thought.
                   • more recent research suggests that the duration of STM is longer than found in Peterson and Peterson's study.
                     • Nairne et al (1999) found that items could be recalled after as long as 96 seconds.
                       • in Nairne's study, PPTs were asked to recall the SAME items across trials, whereas in the earlier study different items were used on each trial, which would have led to interface between items, decreasing recall.
                         • it seems, therefore, that information remains in STM for quite a while unless other material overwrites it.
                   • one criticism made of Peterson and Peterson's research is that psychologists are only studying one kind of memory-memory for syllables and words-whereas much of the time our memories are concerned with other things, such as what you did last night or what your children look like.
                   • Peterson and Peterson were not actually testing duration. When the PPTs were counting backwards, the nonsense syllable could well have been displaced in STM by the numbers, thus wiping out the memory for the syllables.