Coding, Capacity and Duration of Memory

BADDELEY (1966)

Method:

• Gave lists of words to four groups of participants to remember:
• Group 1 (acoustically similar): words sounded similar (e.g. cat, can, cab)
• Group 2 (acoustically dissimliar): words sounded different (e.g. pit, few, cow)
• Group 3 (semantically similar): words with similar meaning (e.g. great, large, big)
• Group 4 (semantically dissimilar): words that all had different meanings (e.g. good, huge, hot)
• Ppts shown original words and asked to recall them in the correct order

Results:

• When immediately asked recall after hearing (STM recall) they tended to do worse with acoustically similar words
• When asked to recall after 20 minutes (LTM recall) they tended to do worse with semantically similar words.
• This suggests that information is coded semantically in LTM

P: One limitation of Baddeley's study is that it used artificial stimuli

E: For example the words lists had no personal meaning to the participants

E:This is a limitation because when processing more meaningful information, people may use semantic coding even for STM tasks. Which means we should be cautious about generalising the findings as the study may lack ecological validity as well as internal validity, suggesting the findings from the study have limited application

D: However, the study used a laboratory experiment which has high control of extraneous variables and therefore objectivity which would suggest it has high internal validity and is therefore generalisable.

Jacobs (1887)

Method:

• Developed a technique to measure digit span
• The researcher gives, for example 4 digits and then the ppt is asked to recall them in the correct order out loud. If their answer is correct the researcher reads out 5 digits and so on until the ppt cannot recall the order correctly. 
• This determines an individual's digit span

Results:

• He found the mean digit span across all ppts was 9.3 items
• The mean span for letters was 7.3

P: One limitation of Jacobs' study is that it was conducted a long time ago

E: Early research in psychology often lacked adequate control. For example, ppts may have been distracted while they were being tested so they didn't perform as well as they might.

E: This would mean the results may lack internal validity because there were confounding variables that were not controlled, it way also lack temporal validity as the results may not be consistent as it was conducted such a long time ago.

D: However, the results of the study have been confirmed in other research, which means the study does have internal and temporal validity

Miller (1956)

Method:

• He made observations of everyday practice
• He noted that things come in 7's, e.g. 7 notes on a musical scale, 7 days of the week, 7 deadly sins etc.

Results:

• This suggests that the capacity of STM is about 7 items (plus or minus 2)
• However, Miller also noted that people can recall 5 words as well as they can recall 5 letters.
• They do this by chunking- grouping sets of digits or letters into units or chunks

P: One limitation of Miller's research is that he may have overestimated the capacity of STM.

E: For example, Cowan (2001) reviewed other research and concluded the capacity of STM was only about 4 chunks.

E: This suggests that the lower end of Miller's estimate (5 items) is more appropriate than 7 items

D: An implication of this is that we may not be able to generalise Miller's findings.

Peterson and Peterson (1959)

Methods:

• 24 undergraduate students
• Each student took part in 8 trials
• On each trial the student was given a consonant syllable (also known as a trigram e.g. YCG) to remember and was also given a 3 digit number
• The student was then asked to count backwards from that 3 digit number until told to stop
• This counting backwards was to prevent any mental rehearsal of the consonant syllable (which would increase the student's memory for the consonant syllable (which would increase the student's memory for the consonant syllable)
• On each trial they were told to stop after a different amount of time- 3, 6, 9, 12, 15, 18 seconds. This is called the retention interval
• Results:
• The percentage of correct reponses decreased as the retention interval increased. This suggests that STM may have a very short duration, unless we repeat something over and over again (verbal rehearsal)

P: One limitation of the study is that it uses artificial stimuli

E: Trying to memorise consonant syllables does not reflect most real-life memory activities where what we are trying to remember is meaningful

E: This suggests that the study may lack external and ecological validity

D: However, sometimes we do try to remember fairly meaningless things, such as phone numbers so it may not lack external and ecological validity

Bahrick et al (1975)

Method:

• 392 ppts from Ohio aged 17-74. Used high school yearbooks.
• Recall tested using 1) photo-recognition test consisting of 50 photos, some from yearbook 2) free recall test where ppts recalled all the names of their graduate class

Results:

• Ppts who were tested within 15 years of graduation were about 90% accurate in photo recognition, free recall was 60%. After 48 years, recall declined to about 70% for photo recognition, free recall dropped to 30%.
• This shows that LTM has a very long duration 

P: One strength of Bahrick et al (1975) is that it has higher external validity

E: The study used real-life meaningful memories to study

E: When studies on LTM have been conducted with meaningless pictures to be remembered, recall rates were lower e.g. Shepard (1967). This suggests that the study is more valid and therefore can be generalised

D: However, the issue with real-life research is that confounding variables are not controlled, for example the fact that the ppts may have looked at their yearbook photos and rehearsed their memory over the years, this would lower the internal validity of the study