Aim: To investigate if there are separate memory stores (STM and LTM).
Method: A lab experiment was conducted. Participants were presented with a list of words at the rate of one per second. Immediately after, partipcants were asked to recall them in any order (free recall).
Results: Murdock found that words presented either early in the list or at the end were more often recalled, but the ones in the middle were more often forgotten.
Conclusions: Murdock suggested that words early in the list were put into LTM (primacy effect) because the person has time to rehearse the word, and words from the end went into STM (recency effect). Words in the middle of the list had been there too long to be held in STM (due to displacement) and not long enough to be put into LTM.
Aim: To research the capacity of STM.
Procedures: Participants were presented with strings of letters or digits and were asked to repeat them back in the same order. The length of the string was increased, from three to four, five, six etc., until the participant was unable to repeat the sequence accurately.
Results: On average, participants recalled nine digits and seven letters. The average recall increased with age.
Conclusions: STM has a limited storage capacity of between five and nine items, but learned memory techniques (e.g. chunking) may increase capacity as people get older.
Since there are 26 letters in the alphabet but only ten digits (0–9), letters may be harder to recall.
Criticisms: The research is artificial. In real-life settings people do not usually need to remember strings of meaningless numbers or letters, and the research therefore has low ecological validity. If the information to be remembered has more meaning, it might be remembered better.