Coding, Capacity, Duration

• What is the definition of memory?

  -Memory refers to the processes that are used to acquire, store, retain and later retrieve information
• What is the definition of coding?

  The way in which information is represented in the memory store, e.g by sound, meaning or image
• What is the definition of capacity?

  The amount of information that can be held in memory at any one time
• What is the definition of duration?

  The length of time that memories can be held
• Sensory register-

  Coding - Sensory

  Capacity- Unlimited

  Duration- Less than 1/2 a second
• STM-

  Coding- Acoustic

  Capacity- 5-9

  Duration- 18-30 secs
• LTM-

  Coding- Semantic

  Capacity- Unlimited

  Duration- Unlimited
• Baddeley (1966) investigated coding of words. He gave 4 different groups 4 different groups of words. Participants had to recall words immediately afterwards in correct order(STM) and again 20 mins later (LTM)
• In Baddeleys research what words were each group given?

  Group 1- Acoustically similar words

  Group 2- Acoustically dissimilar words

  Group 3- Semantically similar words

  Group 4- Semantically dissimilar words
• Findings of Baddeleys research-

  -STM recall task, participants performed worse of acoustically similar words. STM is therefore coded acoustically

  -LTM recall task, participants performed worse on semantically similar words. LTM coded semantically
• Limitation of Baddeleys study- Artificial

  -Stimuli are artificial

  -The task doesn't replicate real life situations so cannot be generalised

  -Lacks mundane realism and ecological validity
• Criticism - Brandimote

  -Brandimote (1992) found that participants encode visually if given a visual task and verbal rehearsal

  -Therefore, Baddeleys research is too simplistic as it doesn’t take into account other types of coding
• Limitation- Limited applications

  -People may encode semantically in STM if stimuli have meaning to them (Wickens 1976)

  -Therefore, study has limited applications
• Limitation - LTM not always semantic

  -LTM not always semantic. Frost(1972) showed how long term recall related to visual as well as semantic

  -Nelson & Rothbart (1972) found evidence of acoustic coding in LTM

  -Coding can vary according to circumstances
• Joseph Jacob’s (1887) (Capacity)

  -Investigated digit span

  -He would give ppts 4 digits to remember and then 5 and so on until person cannot recall order correctly
• Joseph Jacob’s findings -

  -Mean span for digits to be 9.3 items and for letters 7.3

  -Also found capacity changes with age, mean =6.6 for 8 year olds and mean = 8.6 for 19 year olds
• Disadvantage of Jacob’s - Time

  -Research was conducted a long time ago, therefore may not have been adequately controlled

  -Results could be affected by confounding variables
• George Miller (Capacity) (1956) -

  -Made observations and concluded that capacity for STM is 7+ or -2.

  -Also noted that you recall 5 words as well as 5 letters. This is by chunking

  -Known as Millers Magic Number 7
• Limitation of Miller - Overestimated

  -Miller may have overestimated capacity of STM

  -Cowan (2001) reviewed other research and concluded capacity was only about 4 chunks

  -Vogel (2001) found that 4 items were limit for visual items

  -Size of chunks matters. Simon (1974) found people have shorter span for larger chunks
• Conclusion of Peterson

  Concluded that STM has a limited duration of 18-30 secs
• Limitation of Peterson- Artificial

  -Stimuli are meaningless and task is artificial

  -Task to complete and remember trigrams is not an everyday task so lacks mundane realism and ecological validity
• Limitation of Peterson- Lacks internal validity

  -One could ask has the memory trace spontaneously disappeared without rehearsal

  -It may have been displaced by counting backwards

  -Therefore, study may lack internal validity

  -More recents studies Nairne (1999) found items could be recalled after 96 seconds
• Bahrick (1975) (Duration) -

  -Used 392 participants ages between 17-74

  -High school yearbooks were obtained

  -Recall was tested in various ways :

  1)photo recognition

  2)free recall
• Bahrick findings -

  -Participants tested within 15 years of graduation 90% accurate for photo recognition

  -After 48 years recall declined to 70%

  -Free recall 60% after 15 years and 30% after 38 years
• Disadvantage of Bahrick-

  -Confounding variables

  -Had no control over how often participants looked at year book or had come in contact with school friends