Capacity, coding & duration

• Encoding - Info is converted into a code that can be stored in memory.

  Storage - As a result of encoding info is stored within the memory system.

  Retrieval - Recovering stored info from the memory system.
• Short Term Memory (STM) - memory for events in the present or immediate past.

  • Has limited capacity
  • Limited duration
• Long Term Memory (STM) - events that happened in the more distant past

  • Has unlimited capacity 
  • Unlimited duration(potentially)
• Baddeley (1966) - Coding in STM & LTM

  Procedure: 

  • Acoustically similar words (eg. cat, car, cab) or dissimilar (eg. pit, few, gold).
  • Semantically similar words (large, big, obese) or dissimilar ( eg. good, hot, watch)

  Findings and conclusions:

  Immediate recall worse with acoustically similar words

  STM is acoustic.

  Recall after 20 minutes worse with Semantically dissimilar words

  LTM is semantic.
• AO3 - Limitation of Baddeley’s research

  (-) He didn’t use meaningful material

  Words used had no personal meaning to pts.

  When processing more meaningful information, people may use semantic coding even for STM tasks.

  = this means that the results of this study has limited application.

  We can’t generalise the findings to different kinds of memory tasks.
• Extending the capacity of STM

  Miller (1956) found that the capacity of STM could be considerably increased by combining/organising separate ‘bits’ of information, e.g. letters or digits, into larger chunks. 

  Chunking involves making the info more meaningful, through organising it in line with existing knowledge from your LTM - in this case, of abbreviation sfor qualifications.
• AO3 - Limitation of Miller’s research

  (-) Miller may have overestimated capacity of STM

  Example: Cowan (2001) reviews other research. He concluded that capacity of STM was only about 4 chunks.

  = this suggests that the lower end of Miller’s estimate ( 5 items) is more appropriate than 7 items
• Further evidence for the capacity of STM

  Jacobs ( 1887)

  Procedure: Digit span: researcher reads 4 digits and increases until the participant cannot recall the order correctly.

  Findings and conclusions: On average, participants could repeat back 9.3 numbers and 7.3 letters in the correct order immediately after they were presented
• AO3 - Limitation of Jacobs’ research

  (-) Conducted a long time ago

  Early research in psychology often lack of control of extraneous variables. Issue with validity. 

  HOWEVER,

  Jacob’s results have been confirmed in other research confirming its validity.
• Duration of STM

  How long can you retain a new phone number before you have to write it down? 

  And iff you didn’t rehearse it?

  • The duration for which STM can retain info is temporary – a very short time
  • Not much research interest of this aspect, but some findings suggest only a few seconds before it fades/decays (unless we rehearse it)
• Peterson & Peterson (1959)

  • Got students to recall combinations of 3 letters (trigrams), after longer and longer intervals (3, 6, 9, 12, 15 or 18 seconds)
  • During the intervals, students were prevented from rehearsing by a counting task!
  • Their findings suggest that our STM fades in under a half a minute if we are not rehearsing it:
  • After 18 secs, fewer than 10% recalled correctly.
  • After only 3 secs, 80% recalled correctly.
  • Recall got progressively worse as the delay grew longer!

  Duration of STM without rehearsal is about 18 to 30 seconds
• AO3 - Limitation of Peterson & Peterson’s research

  (-) the study used artificial stimulus

  Trying to memorise syllables doesn’t reflect every memory activities (meaningful tasks). 

  Therefore this study lacks of external validity. The results can’t be applied to everyday life.

  However, we do sometimes try to remember meaningless things such as phone numbers.

  So the study is not totally irrelevant.
• Bahrick et al. (1975) - LTM

  Procedure: He tested 392 Americans aged between 17 and 74.

  • Recognition test: 50 photos from participants’ high school yearbook
  • Free recall test: pts listed names of their graduating class

  Findings and conclusions:

  • 90% accuracy for remembering faces & names 34yrs after graduation
  • Declined after 48yrs (70%), particularly for faces
• AO3 - A strength of Bahrick’s study

  (+) High external validity

  Real life meaningful memories were studied.

  When lab studies were done with meaningless pictures to be remembered, recall rates were lower ( eg. Shepard, 1967).

  Negative points of such real-life research= confounding variables are not controlled. Bahrick’s pts may have looked at their yearbook photos and rehearsed their memories over the years.