AO3 - short and long term memory

• The capacity of STM can be assessed using digit span. In one of the earliest studies in psychology, Joseph Jacobs (1887) used this technique to assess STM capacity. He found that the average span for digits was 9.3 items and 7.3 for letters.
• Peterson and Peterson (1959) studied the duration of STM. Each participant was tested over 8 trials. On each trial a participant was given a consonant syllable and a 3 digit number. They were asked to recall the consonant syllable after a retention interval of 3, 6, 9 or 18 seconds. During the retention interval they had to count backwards from their 3 digit number. Participants, on average, were 90% correct over 3 seconds, 20% correct after 9 seconds and only 2% correct after 18 seconds. This suggests that STM has a duration - less than 18 seconds - as long as verbal rehearsal is prevented.
• LTM Duration- Bahrick (1975) showed old photographs and names (including those of old school friends) to participants aged 17-74, recall was 90% after 15 years, and still 80% for names after 48 years. This suggests that the duration of the LTM is very large, potentially limitless.
• The capacity of STM may be even more limited. One criticism of the research investigating STM is that Miller's original findings have not been replicated. Cowan (2001) reviewed a variety of studies on the capacity of STM and concluded that STM is likely to be limited to about four chunks. Research on the capacity of STM for visual information (rather than verbal stimuli) also found that four items was about the limit. This means that the lower end of Miller's range is more appropriate (i.e. 7 - 2 which is 5). This suggests that STM may not be as extensive as was thought.
• Another criticism of research investigating STM is that it is artificial. Trying to memorise consonant syllables does not truly reflect most everyday memory activities where what we are trying to remember is meaningful. However, we do sometimes try to remember fairly meaningless things, such as groups of numbers (phone numbers) or letters (postcodes). This means that, although the task was artificial, the study does have some relevance to everyday life.
• Baddeley used word lists to test the effects of acoustic and semantic similarity on STM and LTM. He found that participants had difficulty remembering acoustically similar words in STM but not in LTM, whereas semantically similar words posed little problem for STMs but led to muddled LTMs. This suggests that STM is largely encoded acoustically whereas LTM is largely encoded semantically.
• LTM may not be exclusively semantic In general LTM appears to be semantic but not always. Frost (1972) showed that long-term recall was related to visual as well as semantic categories, and Nelson and Rothbart (1972) found evidence of acoustic coding in LTM. Therefore it seems that coding in LTM is not simply semantic but can vary according to circumstances
• • Capacity LTM- Wagnaar (1986) kept a diary over the course of six years which recorded over 2,400 events. He tested himself on the events and found a 75% recall after 1 year and a 45% recall after 5 years, suggesting that the capacity of the long term memory is very large, potentially limitless.