Short-Term and Long-Term Memory

• There are three types of memory: sensory memory (SM), short-term memory (STM) and long-term memory (LTM) 
• SM is visual and auditory information that passes through our senses very briefly. It disappears quickly through spontaneous decay - the trace just fades. 
• STM has a limited capacity and limited duration. 
• LTM has an unlimited capacity and is permanent. 

Peterson and Peterson - STM using trigrams

• Method: Participants were shown nonsense trigrams (3 random consonants) and asked to recal after either 3 second intervals increasing. In the pause they were asked to cound backwards in threes as an interference task.
• Results: After 3 seconds, participants recalled 80% of trigrams correctly. After 18 seconds, only about 10% were recalled correctly.
• Conclusion: When rehearsal is prevented, very little can stay in STM for longer than about 18 seconds. 
• Evaluation: Reliable - lab experiment with highly controlled variables. Lacks ecological validity - as trigrams are not present in everyday life, meaningful memories may last longer in STM. Only one type of stimulus was used so did not compare how different stimuluses may affect STM. Participants could have become confused as they had to see many different trigrams. 

Bahrick et al - studied VLTM's 

• Method: 392 people asked to list the names of their ex-classmates (free recall) They were then shown photos and asked to recall (photo-recognition test) or given names to match to photos (name-recognition test) 
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