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Memory is a process in which information is
retained about the past...
Memories are thought to have a physical basis or
"trace". Most psychologists agree that there are
three types of memory ­ sensory memory (SM),
short term memory (STM) and long term memory
SM is visual and auditory information that passes
through our senses briefly. SM disappears quickly
through spontaneous decay ­ the trace just fades.
SM isn't around for very long, so most studies are on
STM and LTM.…read more

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STM and LTM differ in terms of:
1. Duration ­ How long a memory lasts
2. Capacity ­ How much can be held in the memory.
3. Encoding ­ Transferring information into code, creating a "trace".
STM has a limited capacity and a limited duration (i.e. we can remember
information for a short time).
LTM has a pretty much unlimited capacity and is theoretically permanent (i.e. lots
of information for a long time).…read more

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Research has been carried out
into the nature of STM and LTM...
Peterson and Peterson (1959) investigated STM using trigrams...
Method: Participants were shown nonsense trigrams (3 random consonants
CVM), 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 "inference 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 ­ it's a laboratory experiment
where the variables can be tightly controlled. However, nonsense trigrams are
artificial, so the study lacks 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 realistic trial.…read more

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Bahrick et al (1975) investigated
LTM in a natural setting...
Method: 392 people were asked to list the names of their ex-classmates. (This is called
"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").
Results: Within 15 years of leaving school, participants could recognise about 90% of
names and faces. They were about 60% accurate on free-recall. After 30 years, free recall
had declined to about 30% accuracy. After 48 years, name recognition was about 80%
accurate, and photo-recognition about 40% accurate.
Conclusion: The study shows evidence of VLTM's in a "real life" setting. Recognition is
better than recall, so there may be a huge store of information, but it's not always easy to
access all of it ­ you just need help to get to it.
Evaluation: This was a field experiment and so had high ecological validity. However in a
"real life" study like this, it's hard to control all the variables, making these findings less
reliable ­ there's 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 information is
stored better. This type of information could be rehearsed (if they were still in touch or talk to
friends about memories), increasing the rate of recall. This means that the results can't be
generalised to other types of information held in LTM.…read more

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STM and LTM have very
different capacities...
Jacobs (1887) studied the capacity of STM
Method: Participants were presented with a string of letters or digits. They had to
repeat them back in the same order. The number of digits or letters increased each
time until the participant failed to recall the sequence correctly.
Results: The majority of the time, participants recalled about 9 digits and about 7
letters. This capacity increased with age during childhood.
Conclusion: Based on the range of results Jacobs concluded that STM has a
limited storage capacity of 5-9 items. Individual differences were found, such as
STM increasing with age, possibly due to increased brain capacity or use of
memory techniques, such as chunking. Digits may have been easier to recall as
there were only 10 different digits to remember, compared to 26 letters.
Evaluation: Jacobs' research is artificial and lacks ecological validity ­ it's not
something you'd do in real life. More meaningful information may be recalled
better, perhaps showing STM to have an even greater capacity. Also, the previous
sequences recalled by the participants might have confused them on future trials.…read more

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