The Nature of Memory: STM, LTM and Duration (Page 20)

The Nature of Memory: STM, LTM and Duration (Page 20)

1. Duration

   • LTM
     • Duration
       • LTM refers to memories that last anywhere from 2 hours to 100 years+
         • i.e. anything that isn't short-term
       • Example: Shepard 1967 - tested LTM duration
         • Participants were shown 612 memorable pics, 1 at a time
           • 1 hour later - shown some of the pics among a set of new 1s
             • Showed perfect regonition
             • 4 months later - still able to recognise 50% of the pics
       • More 'real life' example: Bahrick et al 1975
         • More 'real life' as the material to be remembered was more meaningful to the participants
         • Participants (of various ages) were asked to put names to faces from their high school year book
           • 48 years on about 70% of people were accurate
   • STM
     • Key Study - Peterson & Peterson 1959 (Landmark study)
       • What did they do?
         • Enlisted 24 students from their uni
         • The experimenter said a 3 constant syllable (with no meaning) to the participant followed by a 3 digit number
           • After hearing the syllable the participant had to count back from the number in 3s or 4s until told to stop + then asked to recall syllable
             • Each participant was given 2 practice trials + 8 real trials
               • On each trial the retention interval (time spent counting backwards) was different: 3,6,9,12,15,18 secs
           • The reason for the counting was to prevent rehearsal
       • What did they find?
         • Participants remembered around 90% with 3 sec interval
         • About 2% with 18 sec interval
         • Results suggest - when rehearsal is prevented STM lasts about 20 secs at most
     • Duration
       • ST memories don't last long
       • The info doesn't last very long + STM can't hold much info at a time
         • Rehearsal is needed to keep the info in the STM (re-presenting the info to the STM)
           • The result of the verbal rehearsal - the ST memories are held in the STM store + eventually become LT
   • How long a memory lasts

2. Evaluation

   • The duration of STM may be even shorter
     • Peterson & Peterson findings have been challenged
       • We may argue - the participants may have been relying on more than STM as they knew they knew they were going to be asked to recall the items after a distracting interval
       • Marsh et al 1997
         • Suggests - when participants do not expect to be tested after this interval, forgetting may occur after just 2 secs
           • This suggests - our understanding of STM duration may not be as clear-cut as first thought
   • Not quite so short-term memory
     • More recent research suggests that STM duration is not as short as Peterson & Peterson's study would suggest
       • Nairne et al 1999
         • Found - items could be recalled after as long as 96 secs
           • In this study - participants were asked to recall the same items across trials - earlier studies items differed
         • Suggests - info remains in STM for quite awhile unless it is replaced or overwritten
   • Peterson & Peterson validity
     • 1 criticism of the study - only studying 1 type of memory - memory for syllables + digits, whereas much of the time our memories are concerned with other things, e.g what we did last night
     • A 2nd criticism - Peterson & Peterson weren't actually testing duration. When the participants were counting backwards, the syllables could well have been displaced in STM by the digits - wiping out the memory for the syllables