The nature of short term memory

What is the capacity of STM?

• limited

• Can hold about 7 items

Supporting research into the capacity of STM

Jacobs

What was Jacobs’ procedure?

• P’s presented with a sequence of digits/letters and required to repeat them back in the same order

• The pace was controlled at half second intervals using a metronome

• Procedure was repeated a number of times and the longest list of sequences that was correct 50% of the time was taken as the p’s digit span

What were Jacobs’ findings?

• p’s recalled more digits than letters

• The average span for digits was 9.3 and 7.3 for letters

• The capacity increased steadily with age - in one sample of school girls he found that 8 year olds had an average of 6.6 digits whereas 19 year olds has 8.6

• Capacity is usually phrased as 7+/-2

What is the duration of STM?

• Ranges from a few seconds up to a minute

• Somewhere between 15-30 seconds

Supporting research into duration of STM

Peterson and Peterson

• investigated how long simple information stays in STM without repetition

What was Peterson and Peterson’s procedure?

• on each trial the p’s saw a trigram, which consisted of three consonants

• A different trigram was used for each trial

• P’s asked to recall each trigram after a delay of seconds: 3,6,9,12,15,18

• Once they were shown a trigram they had to perform an interference task which prevented the repition of the trigram

• They were shown a random three digit number and had to count backwards from it in 3’s

• After the appropriate time delay the trigram had to be recalled

What were Peterson and Peterson’s findings?

• the longer the time delay, the more forgetting

• After 3 seconds - 90% of the trigram was recalled

• After 18 seconds - 5% of the trigrams were recalled

• It was concluded that information is lost rapidly from STM when there is no opportunity for repetition

What i the coding in STM?

• mainly acoustic (verbally)

• Rehearsal is a verbal process regardless of whether the listener of items is presented acoustically or visually

• Visual coding does occur as does semantic coding

Supporting research for coding in the STM

Baddeley

What was Baddeley’s procedure?

• divided p’s into groups (independent groups design) and gave them different word lists to learn

• In the STM condition they had to recall the words in the correct order immediately after hearing them