Peterson and Peterson (1959) - duration of STM
Method: Ppts shown nonsense trigrams (CVM). Asked to recall after either 3, 6, 9, 12, 15, 18 secs. During pause, asked to count backwards in 3s from given number (interference task)
Results: After 3 secs : 80% correct recall
After 18 secs 10% correct recall
Conclusion: When rehearsal prevented, little stays in STM longer than 18 secs
Evaluation: Reliable. Lab experiment, variables controlled.
Nonsense trigrams artificial. Lacks ecological validity.
Meaningful / real life memories may last longer. Duration depends on stimulus
Bahrick et al (1975) - very long term memories
Method: 329 people asked to list names of ex-classmates. Then either shown photos and asked to recall names of people or given names and asked to match to photo.
Results: 15 years of leaving school, recognise 90% of people. 60% on free recall.
30 years free recall 30%
48 years name recognition 80%, photo 40%
Conclusion: VLTM's in real life. Recognition better than recall, may be huge store of info but no easy access.
Evaluation: Field, high eco. validity
hard to control variables, less reliable
Jacobs (1887) - Capacity of STM
Method: Ppts presented with string of letter / digits
Asked to repeat back in same order
Amount of digits / letters increased till ppt failed
Results: Ppts recalled 9 digits / 7 letters
Capacity increased with age during childhood
Conclusion: STM has limited capacity (5-9 items)
Increased with age due to increased brain capacity? or use of memory techniques
Digits easier as only 10 different whereas 26 letters
Evaluation: Artificial. Lacks ecological validity
Meaningful Information recalled better. Maybe STM has greater capacity?