Coding, Duration, and Capacity of Memory

Clive Wearing

suffered a brain infection

STM duration 7-30 seconds (damage to hippocampus)

unable to store new memories or control his emotions

retrograde amnesia

Jacobs (1887)

investigated capacity of STM

digit span test

7 +- 2 items

suggests capacity of STM limited

Peterson & Peterson (1959)

investigated duration of STM

gave pps a consonant trigram followed by a three-digit number. they were asked to recall the consonant syllable 3 seconds from the number and after a particular interval (3, 6, 9, 12, 15, 18 seconds) recall the number trigram (to prevent verbal rehearsal)

pps were 90% correct after 3 seconds but only 2% correct after 18 seconds

suggests STM has duration of 18 seconds without rehearsal

define memory

the process of retaining information after the original stimulus is no longer present

define capactiy

how much information can be held

define duration

how long a memory can be held before it is no longer available

define coding

how we change information to store it in our memory

one limitation is research findings for the capacity of STM are limited

Cowan (2001) reviewed many studies on STM and found STM is likely to be more limited than 7 chunks (instead, chunks)

research on STM is varied and suggests a more limited capacity of STM than what Jacobs found

research on the capacity of STM lacks reliability

one limitation is the effect of individual differences on the capacity of STM

Jacobs found digit recall increased with age = 8 year olds recalled 6.6 digits on avg whereas 19 year olds recalled 8.6 digits on avg

findings are non-generalisable to whole population

lacks population validity

one limitation is research on the duration of STM lacks mundane realism

Peterson & Peterson (1959) made pps memorise 3 consonants with no meaning = this artificial task does not reflect everyday uses of STM

however, there is some relevance to everyday life such as memorising phone numbers or postcodes

questionable applications to real life

one limitation of research on the duration of STM is the findings may have been due to displacement

Peterson & Peterson (1959), pps were counting the numbers in their STM which may displace the syllables to be remembered

Reitman (1974) used auditory tones instead of numbers so that displacement wouldn’t occur and foun that the duration of STM was longer

suggests that forgetting in the Petersons’ study was due to displacement rather than decay = they did not measure what it set out to measure
lacks validity

Bahrick et al (1075)

A: investigate duration of LTM

P: 400 pps of various ages were tested on their memory of their former classmates using either a photo-recognition test of 50 photos or a free-recall test (listed names)

F: photo-recognition = pps who were tested within 15 years of graduation were 90% accurate in identifying classmates, compared to 70% after 48 years

free-recall = 60% accuracy after 15 years, 30% accuracy after 48 years

C: LTM has a large duration especially if visual images are shown = unlimited duration

Baddeley (1966)

A: investigate coding of STM and LTM

P: showed pps two word lists (one with acoustically similar but semantically different words, and vice-versa) and made them recall each list

F: pps had reduced accurate recall with the acoustically similar words in STM but not LTM, whereas had reduced accurecall

C: