coding, capacity and duration of memory Flashcards
summary of short-term memory (STM)
- limited-capacity memory store
- coding is mainly acoustic (sounds)
- capacity is between 5 and 9 items on average
- duration is about 18 seconds
summary of long-term memory (LTM)
- permanent memory store
- coding is mainly semantic (meaning)
- has unlimited capacity
- can store memories for up to a lifetime
what is coding?
the format in which information is stored
what is capacity?
the amount of information that can be held in a memory store
what is duration?
the length of time information can be held in memory
what was the process of baddeley’s (1966a, 1966b) experiment?
participants were shown groups of words and asked to recall them in the correct order
what were the groups in baddeley’s experiment?
- group 1 (acoustically similar): words that sound similar eg. cat, cab, can
- group 2 (acoustically dissimilar): words that sound different eg. pit, few, cow
- group 3 (semantically similar): words with similar meanings eg. great, large, big
- group 4 (semantically dissimilar): words with different meanings eg. good, huge, hot
what did baddeley (1966a, 1966b) find?
- when the participants recalled words immediately, recalling from STM, they tended to do worse with acoustically similar words
- when they recalled the words after a time interval of 20 mins, recalling from LTM, they did worse with the semantically similar words
- this suggests that information is coded acoustically in STM and semantically in LTM
evaluation for research on coding: identification of clear difference between two memory stores
- idea that STM uses mostly acoustic coding and LTM has mostly stood the test of time
- this was an important step in our understanding of the memory system, which led to the multi-store model
- however, later research has shown that there are some exceptions to baddeley’s findings
evaluation for research on coding: use of artificial stimuli, low mundane realism
- baddeley’s study used quite artificial stimuli rather than meaningful material
- for example, the word lists had no personal meaning to participants
- therefore, baddeley’s findings may not tell us much about coding in different kinds of memory tasks, especially in everyday life
- for example, when processing more meaningful information, people may use semantic coding even for STM tasks
- this suggests that the findings from this study have limited application
how did jacobs (1887) investigate the capacity of the STM?
by measuring digit span
describe the procedure for how jacobs (1887) measured digit span
- the researcher read out four digits and the participant recalls these out loud in the correct order
- if this is correct, the researcher read out five digits and so on until the participant cannot recall the order correctly
- this indicates the individual’s digit span
what did jacobs (1887) find out digit span?
- the mean span for digits was 9.3 items
- the mean span for letters was 7.3
- therefore, the capacity of STM was greater for digits than numbers
how did miller (1956) investigate the capacity of the STM?
he made observations of everyday practice
what did miller (1956) note about everyday things?
- they come in sevens
- eg. seven notes on the musical scale, seven days of the week, seven deadly sins etc.
what did miller (1956) conclude about the capacity of the STM?
- the capacity is about 7, plus or minus 2
- he also noted that people can recall five words as easily as they can recall given letters
- we do this by chunking: grouping sets of digits or letters into units or chunks
evaluation for research on capacity: jacobs’ study has been replicated
- old study; early research in psychology often lacked adequate controls
- eg. some ps’ digit spans may be underestimated as they were distracted during testing (CfV)
- jacobs’ findings have been confirmed by other, better controlled studies (eg. bopp and verhaeghen 2005)
- jacobs’ study is a valid test of digit span in STM
evaluation for research on capacity: miller may have overestimated STM capacity (cowan 2001)
- reviewed other research, concluded that capacity of STM is about 4 (±1) chunks
- lower end of miller’s estimate (5) is more appropriate than 7 items
who researched the duration of the STM?
- peterson and peterson (1959)
- they tested 24 students in eight trials (each ‘trial’ being one test)
what was the procedure of peterson and peterson’s (1959) trials?
- the student was given a consonant syllable (eg. YCG) to remember
- they were also given a 3-digit number
- the student counted backwards from this number until they were told to stop
> the counting backwards prevented any mental rehearsal of the consonant syllable, which would increase the duration of STM memory for the syllable - on each trial, they were told to stop after varying periods of time: 3, 6, 9, 12, 15 or 18 seconds (the retention interval)
what did peterson and peterson (1959) find?
- after 3 seconds, the average recall was about 80%
- after 18 seconds it was about 3%
- these findings suggested that STM duration may be about 18 seconds, unless we repeat information over and over (ie. verbal rehearsal)
who did bahrick et al. (1975) study in his research into the duration of the LTM?
392 american participants aged 17-74
how did bahrick et al. (1975) test recall?
- photo-recognition test consisting of 50 photos, some from the participants’ high school yearbooks
- free recall test where participants recalled all the names of their graduating class (high school yearbooks were obtained from ps or directly from some schools)
what did bahrick et al. (1975) find about the duration of the LTM?
- participants tested within 15 years of graduation were about 90% accurate in photo recognition
- after 48 years, recall declined to about 70% for photo recognition
- free recall was less accurate than recognition: about 60% after 15 years, dropping to 30% after 48 years
- this shows that LTM may last up to a lifetime for some material
evaluation for research on duration: meaningless stimuli in STM study
- in peterson and peterson’s study, the stimulus material was artificial
- recalling consonant syllables does not reflect most everyday memory activities where what we are trying to remember is meaningful
- however, the study is not completely irrelevant because we do sometimes try to remember fairly meaningless material (eg. phone numbers)
- however, the study lacked external validity
evaluation for research on duration: bahrick et al.’s study has high external validity
- it has high external validity because the researchers investigated meaningful memories (ie. of people’s names and faces)
- when studies on LTM were conducted with meaningless pictures to be remembered, recall rates were lower (eg. shepard, 1967)
- this suggests that bahrick et al.’s findings reflect a more ‘real’ estimate of the duration of the LTM
