Coding, capacity, duration

• Encoding


  The way information changes its format so it can be stored in memory.
• Storage


  Holding information in the memory system
• Retrieval


  Recovering the information from storage
• Capacity


  This is a measure of how much information can be held in memory
• Duration


  The length of time information can be held in memory
• Short term memory


  A limited capacity memory store
• Long term memory


  A permanent memory store
• Sensory memory

  • Immediate information coming in from the environment first registers in the sensory store
  • Holds information for a fraction of a second after the physical stimulus is no longer there
  • Can be visual or auditory
• Short term memory


  A temporary store where small amounts of information can be kept for a brief period of time. Information can be easily lost.
• Long term memory


  A permanent store where limitless amounts of information can be stored for a long period of time.
• Capacity of the STM

  • STM has a limited capacity, it can only hold a small amount of information before it is forgotten.
• How do we test the capacity of STM?


  Serial digit span study
• Capacity of STM- Jacobs

  • Capacity of STM for numbers and letters
  • 443 female students, aged 8-19
  • Task involved participants repeating back a string of numbers or letters in the same order and the number of digits and letters were gradually increased until the participants could no longer recall the sequence.
  • Found that the students on average had an average span of 7.3 letters and 9.3 digits
  • Capacity of STM is very limited
• Capacity of STM- Miller

  • Reviewed existing research into STM
  • Concluded we can hold 7 items in the STM, plus or minus 2 so it can range between 5-9 items
  • Miller believed that our STM stores chunks of informations rather than individual numbers or letters
  • This can explain why we are able to recall items like phone numbers
  • Chunking allows us to group information to help improve the capacity of STM
• Why does Jacob’s study lack validity?

  • Jacob’s study was conducted a long time ago
  • Early research in psychology often lacked adequate control. E.g some participants may have been distracted while they were being tested so they didn’t perform as well as they might.
  • Shows that results may not be an accurate representation of STM capacity due to confounding variables
• Why did Miller overestimate STM capacity?

  • Cowan, reviewed other research and concluded that the capacity of STM is about 4 items
  • This shows that the lower end of Miller’s estimate (5 items) is more appropriate than 7 items.
• Capacity of LTM

  • The actual LTM capacity is impossible to test experimentally but does not appear to be limited.
  • Problems with testing LTM include whether the memory has genuinely decayed or whether we have forgotten the cue.
• Duration of the STM

  • STM does not last very long
  • Rehearsal keeps memory active
  • Verbal rehearsal can allow the memory to be transferred to LTM
• Duration of STM- Peterson and Peterson

  • Participants given a trigram, but were immediately asked to count backwards in 3’s out loud (prevents rehearsal)
  • Participants then asked to recall the letters in the correct order.
  • Found the longer the interval, the less accurate the recall
  • We cannot hold information in the STM store unless we rehearse it.
  • STM has a very short duration of approx 18 seconds
• Why did Peterson and Peterson’s study on the duration of STM lack external validity?

  • Stimulus material was artificial
  • For instance, Peterson and Peterson made their participants memorise consonant syllables
  • This does not reflect real life memory activities, where we try to remember more meaningful information.
  • Lacks external validity
• Duration of LTM- Bahrick et al

  • Studied 392 US high school graduates aged 17-74
  • High school yearbooks obtained from participants
  • Recall tested through: Photo recognition (50 photos from high school yearbook), free recall tested through (participants recalled the names from their graduating class.
  • Participants tested within 15 years of graduation were about 90% accurate in photo-recognition. After 48 years this declined to 70% accuracy
  • Free recall was less good than recognition. After 15 years, recall was 60% accurate and dropped to 30% accurate after 48 years.
• Why does Bahrick et al’s study have high external validity?

  • For example, they studied real-life meaningful memories e.g recalling the people in our high school years
  • Other studies have supported the idea that meaningful memories last longer in our LTM. For instance, Shepard found that studies on LTM conducted with meaningless pictures, recall rates were lower.
  • Suggests findings reflect an accurate duration of LTM
• 3 ways of coding

  • Acoustic coding: The sound of a stimulus
  • Visual coding: Physical appearance of a stimulus
  • Semantic coding: Meaning of a stimulus
• What types of coding do STM and LTM use?

  • STM: Acoustic
  • LTM: Semantic
• Coding in the STM

  • Information arrives in sensory memory in its original form e.g sound or vision
  • This information needs to be encoded in a format that the STM store can deal with
• Baddeley’s coding study

  • Gave participants different lists of words to four groups of participants to remember.
  • Group 1: Acoustically similar
  • Group 2: Acoustically dissimilar
  • Group 3: Semantically similar
  • Group 4: Semantically dissimilar
  • When participants had to do this task after hearing it (STM recall) they performed worse with acoustically similar words.
  • If participants were asked to recall a word list after a time interval of 20 minutes (LTM recall), they performed worse with semantically similar words.
• How is Baddeley’s study useful?

  • Identified a difference between the 2 memory stores
  • His research has identified that STM and LTM codes in different ways
  • His research found that STM codes acoustically and LTM codes semantically.
  • Therefore this shows that there must be separate stores which each have a specific function.
• Why does Baddeley’s coding study lack external validity?

  • Used artificial stimuli
  • For instance, the word list had no personal meaning to participants
  • Baddeley’s research tells us little about coding different memory tasks, especially in day-to- day life
  • Therefore his research has limited application and lacks external validity