STM - very limited duration. - an example would be trying to remember a seven digit phone number you have just been given. the information would be maintained in your STM by repetition until the number is dialled and then fades when a conversation starts. - rehearsal is saying something over and over and is one way of keeping memory active. the result of verbal rehearsal is that short term memories will eventually become long term. - memories disappear unless they are rehearsed

LTM - potentially unlimited duration. - long term memory store has potentially unlimited duration and capacity. - lasts anywhere from 2 minutes to 100 years

method - opportunity sample of 24 university students. the experimenter said a consonant syllable to the participant flowed by a three digit number (e.g WRT303). immediately after hearing this the participant had to count backwards from the number in 3s or 4s until told to stop. counting backwards was used to stop the participant rehearsing the syllable because rehearsal would aid recall. the participants were then asked to recall the nonsense syllable. each participant was given two practice trials followed by eight trials. on each trial the retention interval (time spent by counting back) was different: 3,6,9,12,15 or 18 seconds.

results - participants remembered about 90% when there was only a 3 second interval and about 2% when there was an 18 second interval. this suggests that when rehearsal is prevented, STM lasts about 20 seconds at most.

method - 392 participants from Ohio aged between 17 and 74. high school yearbooks were obtained from the participants or directly from some schools. recall was tested in various ways including photo-recognition consisting of 50 photos, free recall tests where participants recalled all the names of their graduating class.

findings - participants who were 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 good than photo recognition - after 15 years it was 60% and after 48 it was 40%. this shows that LTM can last a very long time.

a limitation of Peterson and Petersons study is that the stimulus material was artificial. trying to memorise consonant syllables does not reflect most real life memory activities where what we are trying to remember is meaningful. this means that the findings lack external validity as they cannot be easily generalised to everyday life.

one strength of Bahrick et al's study is that it has high external validity. real meaningful memories were studied meaning that the results can be generalised to everyday life.

Jacobs found that the mean span for digits across all participants was 9.3 items. the mean span for letters was 7.3. the recall for digits would be higher because there are 26 letters in the alphabet and there were only 10 digits to remember

Miller (Magic number seven plus or minus two - reviewed psychological research and made observations of everyday practice. he concluded that the span of immediate memory is 7. Miller also found that people can recall 5 words as well as they can recall 5 letters and that we chunk things together to remember them more. chunking is grouping sets of digits or letters into meaningful units to enhance capacity of STM.

limitation - Jacobs study was conducted a long time ago. early research often lacked adequate control. this would mean that the results are not valid because there might have been confounding variables that had not been controlled.

limitation - miller may have overestimated the capacity of STM. for example Cowan reviewed other research and concluded the capacity of STM was only 4 chunks. this suggests that the lower end of Miller's estimate (5) was more appropriate than the seven.