research

• Jacobs (1887) assessed the capacity of STM using the digit span test where participants had to recall a string of digits or letters in the same order and the number of digits or letters was gradually increased, until the participants could no longer recall the sequence. Jacobs found that the average capacity span is 9.3 for numbers and 7.3 for letters. Digits were recalled better than letters, possibly because there are only 10 digits compared to 26 letters.
• Miller investigated the capacity of STM.

  Procedure:

  • Reviewed research into memory span and everyday observations (e.g. things like how we remember phone numbers).
  • Found people can recall around 7 items (give or take 2) — often written as 7 ± 2.
  • Suggested that we group information into chunks (e.g. digits, letters, or words) to increase STM capacity.
• Peterson & Peterson study included 24 student participants. Participants were given a trigram along with a 3 digit number (FDW 829). They were asked to recall their trigram and 3 digit number after a set period of time (counting down from either 3,6,9,12,15,18) to prevent rehearsal. ~80% were correct over 3 seconds and only ~10% correct after 18 seconds.
• Bahrick et al (1975) investigated the duration of LTM. A sample of 392 American participants, all of various ages were asked to recall the names of their classmates from their yearbooks. In one condition, participants had photos to aid recall, whereas in the other condition the participants recalled freely with no aid.

  
  

  Photo recognition:

  • 90% accuracy within 15 years of graduation.
  • 70% accuracy after 48 years.

  Free recall:

  • 60% accuracy after 15 years.
  • 30% accuracy after 48 years.
• 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. 
• Strength of Peterson and Peterson’s study into the duration of STM?

  • Use of scientific method: good control and standardised methods, increases internal validity of 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 trigrams 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.
  • Sample bias — only psychology students used, may show demand characteristics or have better memory strategies.
• 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 Jacobs study into the capacity of STM?

  • Jacobs study has been replicated and confirmed by other better controlled studies Miller (1956). This supports its validity.
  • Jacobs used a controlled lab environment and a standard digit span procedure, which improves the reliability and replicability of the findings.
  • His methods became the basis for many later STM capacity studies.
• Weaknesses of Jacob‘s study into the capacity of STM?

  • As an early psychological experiment, Jacobs may not have controlled for extraneous variables that could affect memory span (e.g. attention, rehearsal strategies, fatigue) - reduces internal validity, as other factors might explain performance.
  • The study is very old (conducted in 1887) modern participants might perform differently due to changes in education etc. - lacks temporal validity.