AS- Level Psychology - Short Term and Long Term Memory Research.

Peterson and Peterson (1959) Investigated Duration of Short term memory.

Method: Participants were shown Nonsense trigrams (e.g CMV) and asked to recalled them after 3,6,9,12,15 or 18 seconds. During the pause they were asked to count backwards from 3 from a given number. This was an 'Interference task'. 

Results: After 3 seconds, participants could recall 80% of trigrams correctly. After 18 seconds only 10% were recalled.

Conclusion: When rehearsal is presented, very little can stay in STM for longer than 18 seconds.

Evaluation: (+) Lab experiment, Therefore the variable can be tightly controlled.  (-) Nonsense trigrams are artificial and therefore lacks ecological validity, which means its artificial and cannot generalise to everyone.

Bahrick et al (1975) - Studied very long term memories (VLTMs) 

Method: 392 people were asked to list the names of their ex classmates. (Free recall test) They were shown photos and asked to recall names of the people shown (Photo recognition test) or given names and asked to matched with photo (name recognition test) 

Results: 15 years after leaving school - participants could recognise 90% of names and faces, 60% accurate on free recall. After 30 years - free recall declined to 30%, After 48 years - name recognition was 80% accurate, and photo regognition 40%.

Conclusion: Evidence of VLTM in a real life setting. May be a huge store of info but just need some help to get to it.

Evaluation: (+) High Ecological Validity (-) real life study means its hard to control variables. (-) no way of knowing why information was recalled well.

Jacobs (1887) Studied the capacity of Short Term Memory.

Method: Presented with a string of letters or digits. They had to repeat them back in same order. The number of lettters or digits increased untill failed to recall correctly.

Results: Majority of the time, 9 digits and 7 letters were recalled. The capacity increased with age.

Conclusion: STM has a limited storage capacity of 5-9 items. Individual differences were found including age & Chunking techniques. Digits may be easier to remember as their is 10 different digits to remember, compared to 26 letters.

Evaluation: (-) Articial, Lacks ecological validity. (-) Previous sequences recalled by participants may have confused them on future trials.

Baddeley (1966) Investigated encoding in STM and LTM.

Method: Participants were given four sets of words. Either acoustically similar (e.g. man mad mat), acoustically dissimilar (e.g. pit cow bar), semantically similar (e.g. Big large huge), semantically dissimilar (e.g. Good hot pig). It was a Independent groups design. Participants were asked to recall after a 20 mins task.

Results: Participants had problems recalling acoustically similar words when recalling immediately. If recalling after interval they had problems with semantically similar words.

Conclusion: LTM relys on semantic encoding, STM relys on acoustic encoding.

Evaluation: (-) Lacks ecological validity (-) Other types of LTM e.g. episodic memory,procedural memory.