Research into the capacity of STM
Miller (1956) identified that people have a digit span of 7 items +/- 2 items. This means that on average we are able to remember between 5- 9 numbers in our short term memory
Grouping items into chunks of 3 items can enhance the capacity of the Short term memory especially if the chunks are meaningful to the individual.
Grouping items into chunks of 3 items can enhance the capacity of the Short term memory especially if the chunks are meaningful to the individual.
Research into the duration of STM
Peterson & Peterson (1959)
Aim: To test how long STM lasts when rehearsal is prevented.
Procedure:
Findings:
The percentage recall was: After 3 SECONDS = 80% After 18 SECONDS = LESS THAN 10%
Recall decreases steadily between 3 and 18 seconds suggesting that the duration of the STM is not much more than 18 seconds.
Conclusions: The memory trace in the STM has just about disappeared after 18 seconds. Information held in the STM is quickly lost without rehearsal. This supports the hypothesis that the duration of the STM is limited to approximately 20 seconds. They also concluded that this is evidence that the STM is distinct from the LTM as the LTM has a much longer duration.
A02 Criticisms:
1. The trigrams are artificial and they do not reflect everyday memory.
2. I may be that interference for earlier trigrams may cause poor recall, not simply decay.
3. A strength is that the research method employed (laboratory experiment) allows us to see that causal effect of time passing (IV) on recall of the trigrams (DV).
Procedure:
- Participants were presented with sets of trigrams (nonsense syllables in sets of three, eg. BCM, CPW) which they were then asked to recall in order after a delay of 3, 6, 9, 12, 15 and 18 seconds.
- In order to prevent rehearsal, participants were given an interference task of counting backwards in threes from a random three digit number to prevent rehearsal (known as the Brown-Peterson technique).
- Recall had to be 100% accurate and in the correct order in order for it to count as correctly recalled.
Findings:
The percentage recall was: After 3 SECONDS = 80% After 18 SECONDS = LESS THAN 10%
Recall decreases steadily between 3 and 18 seconds suggesting that the duration of the STM is not much more than 18 seconds.
Conclusions: The memory trace in the STM has just about disappeared after 18 seconds. Information held in the STM is quickly lost without rehearsal. This supports the hypothesis that the duration of the STM is limited to approximately 20 seconds. They also concluded that this is evidence that the STM is distinct from the LTM as the LTM has a much longer duration.
A02 Criticisms:
1. The trigrams are artificial and they do not reflect everyday memory.
2. I may be that interference for earlier trigrams may cause poor recall, not simply decay.
3. A strength is that the research method employed (laboratory experiment) allows us to see that causal effect of time passing (IV) on recall of the trigrams (DV).
Research into duration of the LTM
Bahrick et al (1975)
Aim:
Investigation of the duration of very-long-term memory (VLTM).
Tested the duration by testing recall of real-life information.
Procedure:
Participants included 392 American ex-high school students aged 17-74.
Recall was tested in four ways:
1. Free recall of the names of as many of their former classmates as possible.
2. A photo recognition test where they were asked to identify former classmates in a set of 50 photos, only some of which were their classmates.
3. A name recognition test.
4. A name and photo matching test.
Findings:
90% accuracy in FACE AND NAME RECOGNITION after 34 YEARS
80% accuracy for NAME RECOGNITION after 48 YEARS
40% accuracy for FACE RECOGNITION after 48 YEARS
60% accuracy for FREE RECALL after 15 YEARS
30% accuracy for FREE RECALL after 30 YEARS
Name matching condition were 90% accurate after 14 years and 60% accurate after 47 years.
Where as the recognition group were 60% accurate after 7 years and less than 20% accurate after 47 years.
Conclusions:
Classmates are rarely forgotten, but cues are sometimes needed.
Recognition was better then recall.
A02:
Investigation of the duration of very-long-term memory (VLTM).
Tested the duration by testing recall of real-life information.
Procedure:
Participants included 392 American ex-high school students aged 17-74.
Recall was tested in four ways:
1. Free recall of the names of as many of their former classmates as possible.
2. A photo recognition test where they were asked to identify former classmates in a set of 50 photos, only some of which were their classmates.
3. A name recognition test.
4. A name and photo matching test.
Findings:
90% accuracy in FACE AND NAME RECOGNITION after 34 YEARS
80% accuracy for NAME RECOGNITION after 48 YEARS
40% accuracy for FACE RECOGNITION after 48 YEARS
60% accuracy for FREE RECALL after 15 YEARS
30% accuracy for FREE RECALL after 30 YEARS
Name matching condition were 90% accurate after 14 years and 60% accurate after 47 years.
Where as the recognition group were 60% accurate after 7 years and less than 20% accurate after 47 years.
Conclusions:
Classmates are rarely forgotten, but cues are sometimes needed.
Recognition was better then recall.
A02:
- A positive is that this study uses meaningful stimuli to test subjects (high-school year books) and they tested peoples memories from their own lives.
- A weakness is that it is unclear whether the drop off in accuracy at 47 years is due to the limits of duration or a general decline with memory as we become older.
Research into encoding in STM & LTM
Baddeley (1966)
Aim; To explore the effects of acoustic and semantic coding in Short term memory and long term memory Procedures;
-acoustically dissimilar words (eg pen, day few): Words that sound different
-semantically similar words (eg great, big, large): Words that have the same meaning
-semantically dissimilar words (eg hot, old, late): Words that have a different meaning
- In the STM study, participants were asked immediately after presentation, to recall, in serial order, a list of five words taken from a pool of words in the following categories.
-acoustically dissimilar words (eg pen, day few): Words that sound different
-semantically similar words (eg great, big, large): Words that have the same meaning
-semantically dissimilar words (eg hot, old, late): Words that have a different meaning
- In the LTM study, each list of words was extended to ten, and recall was tested after an interval of twenty minutes.
- Words with similar sounds were much harder to recall using STM than words with dissimilar sounds
- Similarity of meaning had only a very slight detrimental effect on STM
- When participants were recalling from LTM, recall was much worse for semantically similar words than for semantically dissimilar words
- Recall from LTM was the same for acoustically similar and acoustically dissimilar words
- STM relies heavily on acoustic coding
- LTM primarily makes use of semantic coding
- The use of the experimental method allows a causal link to be drawn between type of coding used in STM and LTM and the accuracy of recall, since it allows the control of extraneous variables, high in Validity and Reliability.
- It is scientific in it’s approach, which also adds credibility to the research
- The conclusions of this study may not reflect the complexities of encoding. Evidence from other studies shows that, in certain circumstances, both STM and LTM can use other forms of coding.