Coding, capacity and duration of memory

• There are three main types of memory: sensory memory, short term memory, and long term memory.
• Sensory memory is where the information goes when it is immediately collected from the senses, such as what we have seen, heard, tasted, touched, or smelled.
• Iconic memory refers to visual stimuli, and echoic memory refers to auditory stimuli.
• Short term memory is our memory for immediate events.
• Long term memory is our memory for events that have happened in the past.
• Capacity in memory refers to how much can be held in the memory store.
• Duration in memory refers to how long the information can be held in the memory store.
• Peterson & Peterson (1959) studied the duration of Short Term Memory (STM) and found that it is less than 18 seconds.
• Baddely used word lists of acoustically similar words and semantically similar words to test how acoustic and semantic coding effects the STM and LTM.
• Coding in memory is the way the information is processed in order for it to be stored.
• Information enters the brain via the senses and can then be stored in three different ways: visual (such as a picture), acoustic (such as sound), or semantic (meaning of experience).
• Jacob’s assessed the capacity of STM using the digit span test where participants had to recall a string of digits/letters in the same order and the number of digits/letters was gradually increased, until the participants could no longer recall the sequence. Jacobs (1887) found that the average capacity span is 9.3 for numbers and 7.3 for letters. 
• Miller investigated the capacity of STM. In a study, he observed that participants could count seven dots but struggled to recall any more than that. Miller argued that the capacity of STM is roughly around 7 2+/2- items.
• Two types of sensory memory is iconic and echoic memory.
• Peterson & Peterson study included 24 student participants. Participants were given a consonant syllable along with a 3 digit number (FDW 829). They were asked to recall their consonant syllable after a set period of time (counting down from either 3,6,9,12,15,18). 90% were correct over 3 seconds and only 2% correct after 18 seconds.
• The duration of LTM is said to be unlimited.
• Bahrick et al (1975) investigated the duration of LTM. A sample of 400 people, all of various ages were asked to recall the names of their classmates from their yearbooks. With photos to aid individuals, 70% of these individuals were able to recall names after 48 years.  For those who were not given photos as aids, the recall after 48 years was roughly 30 %. 
• Baddely found that participants had difficulty in remembering acoustically similar words in STM because they got confused as STM uses acoustic coding, and that recalling semantically similar words after 20 minutes was difficult as LTM uses semantic coding. 
• Strengths of Peterson and Peterson’s study into the duration of STM?

  • Use of scientific method: good control and standardised methods to complete their research and therefore can be easily replicated by other researchers. 
• Weaknesses of Peterson and Peterson’s study into the duration of STM?

  • The simuli used in Peterson and Peterson are artificial. Act of memorising meaningless consonant syllables does not reflect how we memorise things in our everyday life as this would be more meaningful. So, this study may have low ecological validity and lack mundane realism.
  • Small sample size makes it difficult to generalise the findings to the wider population as only students were used.
  • Lab studies often have the problem of demand characteristics.
• Strengths of Bahrick’s study into the duration of LTM?

  • High ecological validity as real-life meaningful memories were used as stimuli, rather than artificial ones. This means that the findings of the study are easier to generalise to how memory operates in everyday life and can be applied to the real world.
• Weaknesses of Bahrick’s study into the duration of LTM?

  • Use of only American participants in sample limits the generalisability of the findings of the study to other non-American populations.
  • Field experiment means that there was a lack of control over confounding variables. Participants could have been in contact with some peers more than other participants or looked at their yearbook photos to rehearse their memory. This makes the findings less reliable.
• Strengths of Baddeley’s study into the coding of memory?

  • Lab study so it can be easily replicated due to standardised methods.
  • Real-life application as it was used to develop the new memory model (Working Memory Model) and can be applied to revision etc.
• Weaknesses of Baddeley’s study into the coding of memory?

  • Low ecological validity as it involved participants remembering meaningless word lists (artificial stimuli). This makes it harder to generalise the findings to everyday memory tasks that does involve meaningful material. This means that the findings have limited application.
  • Small sample size and use of only British students. This limits the generalisability of the findings to the wider population and makes it less representative.
• Strength of Jacob’s study into the capacity of STM?

  • Jacob’s study has been replicated and confirmed by other better controlled studies. This supports its validity.
• Weakness of Jacob‘s study into the capacity of STM?

  • Lacked control because participants could have been distracted by other sensory information. This means that the findings may not be valid as confounding variables were not controlled.
• Sensory memory

  • duration: 0.25-0.5 seconds
  • capacity: very large
  • encoding: modality (sense) specific.
• Short-term memory

  • capacity: 5-9 items
  • duration: 18-30 seconds
  • coding: acoustic
• Long-term memory

  • capacity: unlimited
  • duration: lifetime
  • coding: semantic