Coding, Capacity, Duration

• Memory can be divided into three main types: sensory, short-term, and long-term.
• Sensory memory refers to our ability to briefly hold onto information from our senses (e.g., seeing something or hearing a sound).
• The hippocampus is the part of the brain that plays an important role in memory formation.
• Short-term memory (STM) holds information briefly while we process it or decide what to do with it.
• Long-term memory (LTM) stores information over longer periods of time, ranging from minutes to decades.
• Coding

  The format in which memory is stored in various memory stores
• Encoding


  The transformation of internal thoughts and external events into short and long term memory
• Encoding

  • Info is processed and categorised for storage and retrieval
  • Types include visual, acoustic, semantic
• Memory network

  Involves the hippocampus and temporal lobe working to store the memory
• Capacity


  How much (the quantity) of information that can be held in the memory store at any one time
• Duration

  How long information stays in the memory store
• Function


  What each store does
• Baddley (1966) Coding method

  • Baddley gave different lists of words to four groups of participants to remember:

  Group 1: Acoustically similar e.g. cat, hat, bat, mat

  Group 2: Acoustically dissimilar e.g. pit, few, cow

  Group 3: Semantically similar e.g. great, large, big, huge

  Group 4: Semantically different e.g. hot, big , good

  • Participants were shown the original words and asked to recall them in the correct order either immediately after hearing the words or after an interval of 20 minutes.
• Baddley (1966) (Coding) found that when participants had to do this recall task immediately after hearing it (STM recall), they tended to do worse with acoustically similar words. This suggests that information is coded acoustically in STM.

  If participants were asked to recall the world list after a time interval or 20 minutes (LTM recall), they did worse with the semantically similar words. This suggests that information is coded semantically in LTM.
• Baddley (1966) (Coding) Supports

  • Separate memory stores 

  identified a clear difference between two memory stores. The idea that STM uses mostly acoustic and the LTM semantic is accurate as shown by later research. 
• Baddley (1966) (Coding) limitations

  • Limited application

  Baddeley used artificial stimuli rather than meaningful material. The word lists had no personal meaning to participants. This means we should be cautious about generalising findings to different kinds of memory tasks. For example, when processing more meaningful information, people may use semantic coding even for STM tasks. Lack of mundane realism.
• Jacobs (1887) - capacity of STM method

  Developed a technique to measure digit span:

  Jacobs et al. gave participants a number of digits, and were required to repeat these out loud.

  If they repeated the amount of digits correctly, one more digit is added. They must do this until failure - This determines the individual’s digit span.
• Jacobs (1887) (Capacity of STM) found that the mean digit span was 9.3.

  This was repeated with letters and the mean span for letters was 7.3.

  This suggests that the capacity of the short term memory is very limited.
• Jacobs (1887) (Capacity of STM) Supports

  • Valid

  it has been replicated. The study was old so lacked adequate control, eg. underestimated digit spans due to distractions (confounding variable). But, when repeated, his findings were confirmed by more controlled studies eg. Bopp et al (2005)
• Jacobs (1887) (Capacity of STM) Limitations

  • Extraneous variables 

  p’s not focused, long time ago, no control
• Miller (1956) - capacity of STM:

  • Observed that many things come in sevens i.e. days of the weeks, notes on the musical scale, 7 deadly sins
  • He argued that the capacity of STM is 7 +/- 2
• Miller (1956) (Capacity of STM) however also noticed that people can recall 5 words as well as they can 5 letters.

  Miller found out that they do this by chunking.
• Miller (1956) (Capacity of STM) Limitations

  •  Overestimation Cowan (2002) reviewed more research and concluded capacity was only about 4, plus or minus 1, chunks. The lower end of Miller’s research (5) was more appropriate.
• Peterson and Peterson (1959) - duration of STM

  They tested 24 undergraduate students, and each participant took part in 8 trials.

  In each trial, participants were given a consonant trigram (CVC or KWN) to remember, but also a 3-digit number, (465).

  Participants were then told to count backwards from that-3 digit number until they were told to stop either after 3, 6, 9, 12, 15 or 18 seconds - This was to prevent any ‘rehearsal’ of the consonant trigram – to prevent them remembering it.
• Peterson and Peterson (1959) (duration of STM) Findings

  After 3 seconds 80% of the trigrams were recalled correctly.

  After 6 seconds this fell to 50%.

  After 18 seconds less than 10% of the trigrams were recalled correctly

  The longer participants had to count backwards, the less likely they were to recall the trigram accurately.

  Peterson & Peterson concluded that STM has a limited duration of approximately 18 seconds. Furthermore, the results show that if we are unable to rehearse information, it will not be passed into the LTM.
• Peterson and Peterson (1959) (duration of STM) Supports and limitations

  
  

  Lacked external validity. This is because the stimulus material was artificial. Trying to memorise consonant trigrams does not reflect most real-life memory activities where what we are trying to remember is meaningful. BUT - we do sometimes try to remember fairly meaningless things like phone numbers.
• Tulving (1985) Types of LTM:

  1. Episodic memory - Our ability to recall events from our lives.

  • Time stamped
  • include several elements e.g. people, places, objects
  • Require conscious effort to recall.

  1. Semantic memory - Memories that relate to knowledge of the world.

  • A combination of an encyclopaedia and a dictionary.
  • Less personal, more facts
  • Not time stamped
  • Require conscious effort

  1. Procedural memory - Our memory for actions, skills i.e. how we do things.

  • without conscious awareness or much effort.
  • difficult to explain to someone else
• Tulving (1985) (Types of LTM) Support one

  • Clinical evidence

  HM and Clive Wearing. Their episodic memory was impaired due to amnesia - they had difficulty recalling events that had happened in the past. But, their semantic memory was intact (they still understood the meanings of words) and their procedural memory was also intact ( they could tie their shoe laces). 

  This supports Tulving’s view that there are different memory stores in the LTM i.e. one can be damaged but the other can be unaffected showing that these memory stores are separate and located in different areas in the brain.
• Tulving (1985) (Types of LTM) Support two and three

  • Real life application

  The ability to identify different types of LTM has allowed psychologists to target certain kinds of memory in order to better people’s lives.

  • Belleville et al. (2006) demonstrated that episodic memories could be improved in older people who had a mild cognitive impairment. The trained participants performed better on a test of episodic memory after training than a control group.

  Identifying different types of LTM enables specific treatments to be developed.
• Tulving (1985) (Types of LTM) Limitations

  • Case studies 

  Poor control over variables reduces validity of findings. Small samples and very unique cases lack of generalisability to the public.

  • Cohen and Squire (1980) 

  Disagree with Tulving’s divison. They accept procedural memories represent one type of LTM but argue that episodic & semantic memories are stored together in one LTM store - declarative memory (can be consciously recalled). So procedural memories classified as non-declarative.

  Important to get semantic & episodic distinctions right as it influences how memory studies are conducted.
• Bahrick (1975) - duration of LTM method

  • conducted a longitudinal study which followed 392 American participants aged between 17 and 74.
  • Participants were required to identify schoolmates from their high school yearbook either by naming them in a free recall test (no clues), or by matching photos to names.
• Bahrick (1975) (duration of LTM) Findings

  Participants who were tested within 15 years of graduation were about 90% accurate in photo recognition, dropping to 70% after 48 years.

  
  

  Free recall was less good than recognition. After 15 years this was about 60% accurate, dropping to 30% after 48 years.
• Bahrick (1975) (duration of LTM) Support & Limitation

  • High external validity 

  Researchers investigated meaningful memories ie. faces and names. Shepard (1967) tried with meaningless pictures to be remembered and recall rates were lower.

  This suggests a more ‘real’ estimate of LTM duration.

  
  

  Limitations

  • Extraneous V:  They could have went through the year book before - rehearsal
• Total studies in coding, capacity, and duration of STM and LTM

  Coding: Baddley (1966)

  Capacity of STM: Jacobs (1887) & Miller (1956)

  Duration of STM: Peterson & Peterson (1959)

  Duration of LTM: Bahrick (1975)