Definitions of STM & LTM
Short-term Memory (STM) = Your memory for immediate events
Long-term Memory (LTM) = Your memory for events that have happened in the past
How they Differ:
1. Capacity - the amount of information that can be stored in your memory at any one time
2. Duration - how long the memory lasts
3. Encoding - the way information is stored in memory e.g visually or by sound
Capacity of STM (Key Study, Jacobs) - Aims & Proce
To investigate how much information can be held in STM. Jacobs needed an accurate measure of STM capacity and so he devised a technique called the "serial didgit plan". His research was the first study of STM capacity.
A Lab experiment using the didgit-span technique was conducted. Particepants (p's) were presented with a sequence of letters or didgits followed by a serial recall. The pace of the item presented was controlled to half-second intervals through a metronome. Initially the sequence was 3 Items, which then increased by a single item until the p's consistantly failed to reproduce the sequence correctly. This was repeated over a number of trials to establish the p's didgit span. The longest sequence legth that was correctly recalled on at least 50% of the trials was taken to be the p's STM span.
Capacity of STM (Key Study, Jacobs) - Findings & C
Findings: Jacobs found that the average STM span (numbers of items recalled) was between 5 and 9 items. Digits were recalled better (9.3 items) than letters (7.3 items). STM span increased with age, as in one sample he found a 6.6 average for 8-year old children compared to 8.6 for 19-year old's.
Conclusions: The Findings show that STM has a limited storage capacity of between 5 and 9 items. Individual differences were found as STM span increased with age, which may be due to increasing brain capacity or improved memory techniques.
The IV is the amount of numbers that the p had to remember.
The DV is the amount of numbers remembered correctly.
A lab experiment was used, repeated measures.
One control would be the half-second intervals measured by a metronome.
Capacity of STM (Key Study, Jacobs) - Evaluation
One Strength of using a labratory experiment is the high level of control that is possible to achieve. In this study one example of a control used was the half-second intervals measured by a metronome. A high level of control is good because it improves the reliability of the results.
A weakness of this experiment is that it can be seen to lack ecological validity as it was conducted in a labratory setting which is controlled and highly artificial. This means that you could not generalise it to the real world settings.
In addition, another weakness is, the task that was used (seeing a string of numbers or letters and being asked to recall them in order) cannot be generalised to every day memory tasks, because the numbers would lack significance. This means that the experiment would lack mundane realism.
Increasing Capacity of STM
One way of increasing the capacity of STM is to use a method known as chunking. This is when you take large lists of numbers or letters and break them up into larger chunks and remembering those.
Miller found that it is not just between 5 and 9 single items, but 5 and 9 CHUNKS of information.
Also, he found that chunks of information that have significant meaning are easier to remember.
Encoding in STM
Def: the way information is stored in memory
- STM & LTM differ in the way that information is encoded
- It is suggested that
- STM may encode acoustically (by sound)
- LTM may encode semantically (by meaning)
- much of the evidence about encoding comes from studies into SUBSTITUTION ERRORS
- This occours when people confuse one item with another
- If they confuse letters that sound alike, it indicated ACOUSTIC encoding is used
- If letters are confused that have a similar meaning, then this indicates SEMANTIC encoding
Key Studies for Encoding in STM (Conrad & Baddely)
Conrad (1964) - Visually presented students with letters one at a time.
- Found that letters that are acoustically similar are harder to recall from STM than those that are acoustically dissimilar.
- This suggests that STM mainly encodes things acoustically, even though the items are presented visually.
Baddely (1966) - P's divided into 2 groups and given a list of words which were acoustically similar or acoustically dissimilar (lab experiment)
- IV = type of word list. DV= number of errors made.
- Independent groups design
- FINDINGS: Recall was worse for acoustically similar words (only 55% accurate) compared to words with dissimilar sounds.
- CONCLUSIONS: STM relies more on the sound of words