coding, capacity, duration

• Short-Term Memory is the limited capacity memory store
• Long-Term Memory is the permanent memory store
• Coding - format in which information/memory is stored in
• Capacity – the amount of information that can be held in a memory store
• Duration - the length of time information can be held in memory
• STM coded acoustically (by sound)

  LTM coded semantically (by meaning)
• Baddeley found participants did worse with acoustically similar words in the STM, suggesting that information is coded acoustically because similar-sounding information conflicted with each other
• Baddeley found participants did worse with semantically similar words in LTM, suggesting that information is coded semantically because information with similar meanings conflicted with each other
• Baddeley’s study used artificial stimuli rather than meaningful material. The word lists had no personal meaning to participants. We should be cautious about generalising the findings to different kinds of memory tasks
• Miller (1956) concluded that the capacity of STM is 7 + or - 2 bits of information
• Miller also noted that in order to increase this capacity, people chunk information together. E.g remembering a phone number as one chunk
• Cowan (2001) reviewed other research and concluded that the capacity of STM was only about four chunks. This suggests that the lower end of Miller’s estimate (5 items) is more appropriate than 7 items
• The capacity of the LTM is potentially unlimited
• The duration of the STM is 18-30 seconds
• Peterson and Peterson gave pps a nonsense trigram of three syllables and three digits. To prevent rehearsal, they had to count backwards in threes from the number until told to stop. Then they had to recall the trigram.

  Recall was generally accurate after 3 seconds but by 18 seconds, it declined from 80% to 10%
• The duration of the LTM is potentially lifelong
• Peterson and Peterson’s study used artificial stimulus material
• LTM research was investigated by Bahrick et al (1975). 

  • Participants aged between 17 and 74 were required to identify schoolmates from their high school yearbook. 
  • People who left school within 15 years were very accurate with photo recognition (90%) but even those who’d left decades earlier were still 70% accurate
• Bahrick et al’s study has higher external validity because real life meaningful memories were studied
• When studies on LTM have been conducted with meaningless pictures to be remembered, recall rates were lower (shepard 1967).
• Bahrick et al used real life research so confounding variables were not controlled. Participants may have looked at their yearbook photos recently, rehearsing their memory