STM

• Capacity:

  Jacobs investigated capacity by measuring digit span.
• This was measured by reading out a sequence of letters/ numbers, increasing in length and having the participant recall the sequence in the correct order.
• In 1887, Jacobs assessed the capacity of STM using digit span technique.
• This technique involves giving the ppts a list of numbers, starting with 4 digits and then saying them out loud back to the researcher in the correct order. They are then given a list of 5 digits, then 6 and so on.
• He found that the MEAN span for digits was 9.3, but was 7.3 for letters.
• Miller(1956) reviewed psychological research from 1930s-50s and concluded that STM has a capacity of....

  'The Magic Number: 7 +/-2'
• He also suggested that we can 'chunk' pieces of information together, and therefore remember more e.g. words, digits, musical notes.
• Think about phone numbers being read in chunks:

  07959 123 758. This means we're remembering 3 chunks instead of 11 individual digits.
• Strength:

  P- It can help us understand how to improve our memory.

  B- For example, when we are trying to learn information such as phone numbers , we can increase approach used in advertising.

  S- This means the research has practical applications and can be used in real life.
• Weakness:

  P- Miller wasn't particularly precise about chunking.

  B- He didn't describe or investigate exactly how large the chunks should be, meaning we cannot be entirely clear on exactly how large STM is.

  S This suggests that further research into the capacity of STM is needed, especially as the findings may be different nowadays.
• Peterson and Peterson conducted an experiment into the duration of STM.
• Aim- Investigate how different short intervals containing an interference task affects the recall of items presented verbally, and to infer the duration of STM.
• Method:

  -Ppts were 24 male and female university students.

  -The verbal items tested for recall were 48 three consonant nonsense syllables (such as JBW or PDX) spelled out letter by letter.

  -These have since been named 'trigrams'.

  -There were also cards containing three-digit numbers (such as 360 or 294).

  -The researcher spelled the syllable out and then immediately said a three digit number.

  -The ppt had to count down back wards in either 3s or 4s (as instructed) from that number.
• -This was to present repetition of the trigram by the participant.

  -At the end of a pre-set interval of between 3 and 18 seconds a red light went on and the participant had to recall the trigram.
• Result:

  -Peterson and Peterson found that the longer the interval the less accurate the recall.

  -At three seconds, around 80% of the trigrams were correctly recalled, whereas at 18 seconds only 10% were correctly recalled.
• Conclusions:

  -STM has a limited duration of approximately 18 seconds.

  -Furthermore, if we are unable to rehearse information it will not be passed to LTM, providing further support for the MSM and the idea of discrete components.
• Strength:

  P&P's study was highly controlled and took place in a laboratory of Indiana University.

  As a result, Peterson and Peterson had a high degree of control for extraneous variables, which makes their procedure easy to replicate to test reliability.
• Weakness 1:

  P&P used a sample of 24 psychology students, which is an issue for two reasons.

  Firstly, the psychology students may have encountered the MSM of memory previously ad therefore may have demonstrated demand characteristics by changing their behaviour to assist the experimenter.

  Secondly, the memory of psychology students may be different from that of other people, especially if they had previously studied strategies for memory improvement.

  As a result we are unable to generalise the results of this study to non-psychology students.
• Weakness 2:

  -Furthermore, it could be argued that P&P's study has low levels of ecological validity.

  -In this study ppts were asked to recall three-letter trigrams, which is unlike anything people would want to memorise in their everyday lives.

  -As a result we are unable to apply these results to everyday examples of memory and are unable to conclude if the duration of STM may be longer for more important information, such as a vital phone number.