Cognitive Psychology

Diagnosis: HM was a patient with severe and frequent epilepsy. His seizures were based in a brain structure called the hippcompus. In 1953, doctors decided to surgically remove part of the brain round this area.

Results: The operation reduced his epilepsy, but led to him suffering memory loss. He could still form short - term memories (STMs) but was unable to form new long term memories (LTMs). For example, he could read something over and over without realising that he has ever read it before. He also moved house and had difficulty recalling the new route to his hoyse. However, he could still talk and show previous skills (procedural memory). From his tests, they found HMs episodic memory (for past events) and semantic memory (for knowledge, e.g. word meanings) was affected more than his procedural memory. 

Method: Participants were shown nonsense trigrams (3 random consonants e.g. CHM) and asked to recall them after either 3, 6, 9, 12 15 or 18 seconds. During the pause, they were asked to count backwards in threes from a given number. This was an interference task - it prevented them from repeating the letters to themselves

Results: After 3 seconds participants could recall about 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: The results are likely to be reliable - its a laboratory experiment where the variable can be tightly controlled. However, nonsense trigrams are artificial, so the study lack ecological validity. Meaningful or real-life memories may last longer in STM. Only one type of stimulus was used - the duration of STM may depend on the type of stimulus. Also, each participant saw many different trigrams. This could have led to confusion, meaning that the first trigram was the only realisitic trial 

Method: 392 people were asked to list the names of their ex-classmates. (This is called a 'free recall test'). They were then shown photos and asked to recall the names of the people shown (photo-recognition test) or given names and asked to match them to a photo of the classmate (name recognition test). Within 15 years of leaving school, participants could recognise 90% of names and faces, They were about 60% accurate on free recall. After 30 years, free recall has declined to about 30% accuracy, After 48 years, name-recognition was about 80% accurate, and the photo-recognition about 40% accurate.The stduy shows evidence of VLTMs in a real life setting, Recognition is better than recall, so there may be a huge store of ingormation, but its not always easy to access all of it - you just need help to get to it.This was a field experiment and so had high ecological validity. However, in a real life study like this, its hard to control all the variables, making these finding less reliable - theres no way of knowing exactly why information was recalled well. It showed better recall than other studies on LTM, but this may be because meaningful informaion is stored better. This type of information could be rehearsed (if youre still in touch with classmates, or if you talk to friends about memories of classmates) increasing the rate of recall. This means that the results cant be generalised to other types of information held in LTM.