Short and long-term memory

Can be assessed using digit span. Jacobs (1887) used digit span technique to assess STM capacity. Found average span for digits 9.3 items + 7.3 for letters. Suggests may be easier to recall digits as only 9 digits, but 26 letters.

Miller (1956) - article. Reviewed psych research, concluded span of immediate memory about 7 items - sometimes more, sometimes less. Noted people can count seven dots flashed on screen, but not many more. Same true if asked to recall musical notes, letters + words. 

M also found people can recall five words as well sa can recall 5 letters - chunk things together + can then remember more.

Peterson + peterson (1959) - studied duration of STM, 24 students. Each tested over 8 trials - on each trial, given consonant syllable + 3 digit number (eg THX 512). Asked to recall consonant syllable after retention interval of 3, 6, 9, 12, 15 or 18 seconds. During interval, had to count backwards from 3 diit number. 

On average, 90% correct ober 3 seconds, 20% after 9 secs, 2% after 18. Suggests STM v short duration - <18 seconds - as long as verbal rehearsal prevented.

Bahrick et al (1975) - tested 400 people, various ages (17-74) on memory of classmates. Photo-recognition test - 50 photos, some from their high school yearbook. In free-recall test, participants asked to list names could remember from graduating class. 

Those tested w/in 15 years of graduation about 90% correct identifying faces. After 48 years, declined to about 70% photo recognition. Fre recall about 60% accurate after 15 years, 30% after 48 years.

Baddeley (166a + 1966b) used word lists to test effects of acousting + semantic similarity on STM + LTM. Found participants had difficulty remembering acoustically similar words in STM but not LTM, whereas semantically similar words posed little problem for STMs, but muddled LTMs. Suggests STM largely encoded acoustically - LTM semantically.

Word lists: acoustically similar, semantically diff: cat, cab, can, cad, cap, mad, max, mat, man, map.
Semantically similar, acoustically diff: great, large, big, huge, broad, long, tall, fat, wide, high

Capacity of STM may be even more limited - Cowan (2001) - reviewed variety of studies on capacity of STM - found likely to be limited to about 4 chunks. Suggests STM not as extensive as 1st thought. Research on capacity of STM for visual info also found 4 items about limit (Vogel et al, 2001). means lower end of Miller's range more appropriate (7-2=5).

Simon (1974) found people had shorter memory span for larger chunks eg 8 word phrases, than smaller chunks eg one syllable words.

Not same for everyone - individual diffs. Jacobs found recall increaed steadily w/ age - 8 y/os could remember average 6.6 digits, 19 y/os 8.6. Age increase might be due to gradual increase in brain capaoty, or people develop strategies to improve digit spas as get older, eg chunking.

Testing STM artificial - trying to memorise consonant syllables not reflective of everyday memory activies where what trying to remember meaningful. However, do sometimes try to remember meaningless things eg phone numbers or post codes - could have some relevance.

STM results maybe due to displacement - Petersons' study, counting numbers in STM - may displace syllables to be remembered. Reitman (1974) - auditory tones instead of numbers so displacement couldn't occur (sounds don't interfere w/ verbal rehearsal), found duration STM longer. Suggests forgetting in Petersons' study due to displacement rather than decay - not measuring of duration of STM. Nairne et al (1999) found items could be recalled after as long as 96 secs.

Baddeley's study - STM tested by asking to recall word list immediately after hearing it. LTM tested by waiting 20 mins- questionable whether really testing LTM.

STM appears to rely on acoustic coding - however, some shown visual codes also used. Brandimote et al (1992) - participants used visual coding in STM if given visual task + prevented verbal rehearsal in retention interval before performing visual task. 'Translate' visual images into verbal codes in STM, but as verbal rehearsal prevented, used visual codes. Not exclusively acoustic.

LTM not exclusively semantic - Frost (1972) showed LT recall related to visual as well as semantic categories - Nelson + Rothbart (1972) found evidence of acousing coding in LTM.