Short Term Memory

Short Term Memory

1. Three Characteristics:

   • 1. Limited Capacity
   • 2. Limited Duration
   • 3. Encoding

2. Miller's Magic Number

   • The capacity of short term memory is limited to 7+/-2 items
     • You can recode smaller bits of info into larger bits by chunking
     • Digit span tests support Miller's magic number
     • People find it easier to recall numbers than letters

3. STM can be improved with training, after 230hrs of training a student's digit span increased to 79

   • Semantic chunking strategy e.g., 3492 was chunked into 3min, 49.2sec, almost a world record for 1 mile.

4. Serial Recall

   • Recall words in the order presented
     • The proportion of the words recalled is plotted as a function of the order in which they were presented, producing a serial position curve
   • Primacy Effect
     • Better recall at the beginning, occurs because items early in the list are sufficiently rehearsed before other items are presented to get into LTM
   • Recency Effect
     • Better recall at the end, occurs because the later items in the list are still in STM
   • Items in the middle aren't rehearsed long enough to get into LTM, and were not presented recently enough to remain in STM

5. STM Recall

   • Testing STM, participants are given a word list to memorise, and then required to perform a distractor task to prevent rehearsal
   • After a variable interval participants are asked to recall as many items from the memorised list as possible
   • Evidence indicated that we begin to lose material from STM within 3sec, and within 15-30sec, all material is lost

6. Rehearsal

   • Maintenance Rehearsal
     • Repeating items silently
     • Can increase the duration for retention of info in STM
     • As soon as rehearsal stop, info is lost
     • Unrehearsed material disappears rapidly from STM via process of decay
   • Factors Affecting Rehearsal
     • Pronunciation time has a significant effect on the number of items we can store in STM

7. Encoding

   • Process of manipulating and transforming info to mentally label it, forming a memory code
   • When asked to remember word lists participants tend to use maintenance rehearsal to memorise the material
     • Misremembered words might be related in terms of meaning (moose→elk) suggesting semantic encoding (this doesn't happen often)
     • Misremembered words might rhyme with real stimulus (moose→goose) suggesting phonemic encoding